// File: contracts/vault/VaultCore.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

/**
 * @title OUSD Vault Contract
 * @notice The Vault contract stores assets. On a deposit, OUSD will be minted
           and sent to the depositor. On a withdrawal, OUSD will be burned and
           assets will be sent to the withdrawer. The Vault accepts deposits of
           interest from yield bearing strategies which will modify the supply
           of OUSD.
 * @author Origin Protocol Inc
 */

import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import { SafeMath } from "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/utils/Strings.sol";

import { StableMath } from "../utils/StableMath.sol";
import { IOracle } from "../interfaces/IOracle.sol";
import { IVault } from "../interfaces/IVault.sol";
import { IBuyback } from "../interfaces/IBuyback.sol";
import "./VaultStorage.sol";

contract VaultCore is VaultStorage {
    using SafeERC20 for IERC20;
    using StableMath for uint256;
    using SafeMath for uint256;
    // max signed int
    uint256 constant MAX_INT = 2**255 - 1;
    // max un-signed int
    uint256 constant MAX_UINT =
        0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff;

    /**
     * @dev Verifies that the rebasing is not paused.
     */
    modifier whenNotRebasePaused() {
        require(!rebasePaused, "Rebasing paused");
        _;
    }

    /**
     * @dev Verifies that the deposits are not paused.
     */
    modifier whenNotCapitalPaused() {
        require(!capitalPaused, "Capital paused");
        _;
    }

    modifier onlyOusdMetaStrategy() {
        require(
            msg.sender == ousdMetaStrategy,
            "Caller is not the OUSD meta strategy"
        );
        _;
    }

    /**
     * @dev Deposit a supported asset and mint OUSD.
     * @param _asset Address of the asset being deposited
     * @param _amount Amount of the asset being deposited
     * @param _minimumOusdAmount Minimum OUSD to mint
     */
    function mint(
        address _asset,
        uint256 _amount,
        uint256 _minimumOusdAmount
    ) external whenNotCapitalPaused nonReentrant {
        require(assets[_asset].isSupported, "Asset is not supported");
        require(_amount > 0, "Amount must be greater than 0");

        uint256 price = IOracle(priceProvider).price(_asset);
        if (price > 1e8) {
            price = 1e8;
        }
        require(price >= MINT_MINIMUM_ORACLE, "Asset price below peg");
        uint256 assetDecimals = Helpers.getDecimals(_asset);
        // Scale up to 18 decimal
        uint256 unitAdjustedDeposit = _amount.scaleBy(18, assetDecimals);
        uint256 priceAdjustedDeposit = _amount.mulTruncateScale(
            price.scaleBy(18, 8), // Oracles have 8 decimal precision
            10**assetDecimals
        );

        if (_minimumOusdAmount > 0) {
            require(
                priceAdjustedDeposit >= _minimumOusdAmount,
                "Mint amount lower than minimum"
            );
        }

        emit Mint(msg.sender, priceAdjustedDeposit);

        // Rebase must happen before any transfers occur.
        if (unitAdjustedDeposit >= rebaseThreshold && !rebasePaused) {
            _rebase();
        }

        // Mint matching OUSD
        oUSD.mint(msg.sender, priceAdjustedDeposit);

        // Transfer the deposited coins to the vault
        IERC20 asset = IERC20(_asset);
        asset.safeTransferFrom(msg.sender, address(this), _amount);

        if (unitAdjustedDeposit >= autoAllocateThreshold) {
            _allocate();
        }
    }

    /**
     * @dev Mint OUSD for OUSD Meta Strategy
     * @param _amount Amount of the asset being deposited
     *
     * Notice: can't use `nonReentrant` modifier since the `mint` function can
     * call `allocate`, and that can trigger `ConvexOUSDMetaStrategy` to call this function
     * while the execution of the `mint` has not yet completed -> causing a `nonReentrant` collision.
     *
     * Also important to understand is that this is a limitation imposed by the test suite.
     * Production / mainnet contracts should never be configured in a way where mint/redeem functions
     * that are moving funds between the Vault and end user wallets can influence strategies
     * utilizing this function.
     */
    function mintForStrategy(uint256 _amount)
        external
        whenNotCapitalPaused
        onlyOusdMetaStrategy
    {
        require(_amount < MAX_INT, "Amount too high");

        emit Mint(msg.sender, _amount);

        // Rebase must happen before any transfers occur.
        // TODO: double check the relevance of this
        if (_amount >= rebaseThreshold && !rebasePaused) {
            _rebase();
        }

        // safe to cast because of the require check at the beginning of the function
        netOusdMintedForStrategy += int256(_amount);

        require(
            abs(netOusdMintedForStrategy) < netOusdMintForStrategyThreshold,
            "Minted ousd surpassed netOusdMintForStrategyThreshold."
        );

        // Mint matching OUSD
        oUSD.mint(msg.sender, _amount);
    }

    // In memoriam

    /**
     * @dev Withdraw a supported asset and burn OUSD.
     * @param _amount Amount of OUSD to burn
     * @param _minimumUnitAmount Minimum stablecoin units to receive in return
     */
    function redeem(uint256 _amount, uint256 _minimumUnitAmount)
        external
        whenNotCapitalPaused
        nonReentrant
    {
        _redeem(_amount, _minimumUnitAmount);
    }

    /**
     * @dev Withdraw a supported asset and burn OUSD.
     * @param _amount Amount of OUSD to burn
     * @param _minimumUnitAmount Minimum stablecoin units to receive in return
     */
    function _redeem(uint256 _amount, uint256 _minimumUnitAmount) internal {
        // Calculate redemption outputs
        (
            uint256[] memory outputs,
            uint256 _backingValue
        ) = _calculateRedeemOutputs(_amount);

        // Check that OUSD is backed by enough assets
        uint256 _totalSupply = oUSD.totalSupply();
        if (maxSupplyDiff > 0) {
            // Allow a max difference of maxSupplyDiff% between
            // backing assets value and OUSD total supply
            uint256 diff = _totalSupply.divPrecisely(_backingValue);
            require(
                (diff > 1e18 ? diff.sub(1e18) : uint256(1e18).sub(diff)) <=
                    maxSupplyDiff,
                "Backing supply liquidity error"
            );
        }

        emit Redeem(msg.sender, _amount);

        // Send outputs
        for (uint256 i = 0; i < allAssets.length; i++) {
            if (outputs[i] == 0) continue;

            IERC20 asset = IERC20(allAssets[i]);

            if (asset.balanceOf(address(this)) >= outputs[i]) {
                // Use Vault funds first if sufficient
                asset.safeTransfer(msg.sender, outputs[i]);
            } else {
                address strategyAddr = assetDefaultStrategies[allAssets[i]];
                if (strategyAddr != address(0)) {
                    // Nothing in Vault, but something in Strategy, send from there
                    IStrategy strategy = IStrategy(strategyAddr);
                    strategy.withdraw(msg.sender, allAssets[i], outputs[i]);
                } else {
                    // Cant find funds anywhere
                    revert("Liquidity error");
                }
            }
        }

        if (_minimumUnitAmount > 0) {
            uint256 unitTotal = 0;
            for (uint256 i = 0; i < outputs.length; i++) {
                uint256 assetDecimals = Helpers.getDecimals(allAssets[i]);
                unitTotal = unitTotal.add(
                    outputs[i].scaleBy(18, assetDecimals)
                );
            }
            require(
                unitTotal >= _minimumUnitAmount,
                "Redeem amount lower than minimum"
            );
        }

        oUSD.burn(msg.sender, _amount);

        // Until we can prove that we won't affect the prices of our assets
        // by withdrawing them, this should be here.
        // It's possible that a strategy was off on its asset total, perhaps
        // a reward token sold for more or for less than anticipated.
        if (_amount >= rebaseThreshold && !rebasePaused) {
            _rebase();
        }
    }

    /**
     * @dev Burn OUSD for OUSD Meta Strategy
     * @param _amount Amount of OUSD to burn
     *
     * Notice: can't use `nonReentrant` modifier since the `redeem` function could
     * require withdrawal on `ConvexOUSDMetaStrategy` and that one can call `burnForStrategy`
     * while the execution of the `redeem` has not yet completed -> causing a `nonReentrant` collision.
     *
     * Also important to understand is that this is a limitation imposed by the test suite.
     * Production / mainnet contracts should never be configured in a way where mint/redeem functions
     * that are moving funds between the Vault and end user wallets can influence strategies
     * utilizing this function.
     */
    function burnForStrategy(uint256 _amount)
        external
        whenNotCapitalPaused
        onlyOusdMetaStrategy
    {
        require(_amount < MAX_INT, "Amount too high");

        emit Redeem(msg.sender, _amount);

        // safe to cast because of the require check at the beginning of the function
        netOusdMintedForStrategy -= int256(_amount);

        require(
            abs(netOusdMintedForStrategy) < netOusdMintForStrategyThreshold,
            "Attempting to burn too much OUSD."
        );

        // Burn OUSD
        oUSD.burn(msg.sender, _amount);

        // Until we can prove that we won't affect the prices of our assets
        // by withdrawing them, this should be here.
        // It's possible that a strategy was off on its asset total, perhaps
        // a reward token sold for more or for less than anticipated.
        if (_amount >= rebaseThreshold && !rebasePaused) {
            _rebase();
        }
    }

    /**
     * @notice Withdraw a supported asset and burn all OUSD.
     * @param _minimumUnitAmount Minimum stablecoin units to receive in return
     */
    function redeemAll(uint256 _minimumUnitAmount)
        external
        whenNotCapitalPaused
        nonReentrant
    {
        _redeem(oUSD.balanceOf(msg.sender), _minimumUnitAmount);
    }

    /**
     * @notice Allocate unallocated funds on Vault to strategies.
     * @dev Allocate unallocated funds on Vault to strategies.
     **/
    function allocate() external whenNotCapitalPaused nonReentrant {
        _allocate();
    }

    /**
     * @notice Allocate unallocated funds on Vault to strategies.
     * @dev Allocate unallocated funds on Vault to strategies.
     **/
    function _allocate() internal {
        uint256 vaultValue = _totalValueInVault();
        // Nothing in vault to allocate
        if (vaultValue == 0) return;
        uint256 strategiesValue = _totalValueInStrategies();
        // We have a method that does the same as this, gas optimisation
        uint256 calculatedTotalValue = vaultValue.add(strategiesValue);

        // We want to maintain a buffer on the Vault so calculate a percentage
        // modifier to multiply each amount being allocated by to enforce the
        // vault buffer
        uint256 vaultBufferModifier;
        if (strategiesValue == 0) {
            // Nothing in Strategies, allocate 100% minus the vault buffer to
            // strategies
            vaultBufferModifier = uint256(1e18).sub(vaultBuffer);
        } else {
            vaultBufferModifier = vaultBuffer.mul(calculatedTotalValue).div(
                vaultValue
            );
            if (1e18 > vaultBufferModifier) {
                // E.g. 1e18 - (1e17 * 10e18)/5e18 = 8e17
                // (5e18 * 8e17) / 1e18 = 4e18 allocated from Vault
                vaultBufferModifier = uint256(1e18).sub(vaultBufferModifier);
            } else {
                // We need to let the buffer fill
                return;
            }
        }
        if (vaultBufferModifier == 0) return;

        // Iterate over all assets in the Vault and allocate to the appropriate
        // strategy
        for (uint256 i = 0; i < allAssets.length; i++) {
            IERC20 asset = IERC20(allAssets[i]);
            uint256 assetBalance = asset.balanceOf(address(this));
            // No balance, nothing to do here
            if (assetBalance == 0) continue;

            // Multiply the balance by the vault buffer modifier and truncate
            // to the scale of the asset decimals
            uint256 allocateAmount = assetBalance.mulTruncate(
                vaultBufferModifier
            );

            address depositStrategyAddr = assetDefaultStrategies[
                address(asset)
            ];

            if (depositStrategyAddr != address(0) && allocateAmount > 0) {
                IStrategy strategy = IStrategy(depositStrategyAddr);
                // Transfer asset to Strategy and call deposit method to
                // mint or take required action
                asset.safeTransfer(address(strategy), allocateAmount);
                strategy.deposit(address(asset), allocateAmount);
                emit AssetAllocated(
                    address(asset),
                    depositStrategyAddr,
                    allocateAmount
                );
            }
        }

        // Trigger OGN Buyback
        address _trusteeAddress = trusteeAddress; // gas savings
        if (_trusteeAddress != address(0)) {
            IBuyback(trusteeAddress).swap();
        }
    }

    /**
     * @dev Calculate the total value of assets held by the Vault and all
     *      strategies and update the supply of OUSD.
     */
    function rebase() external virtual nonReentrant {
        _rebase();
    }

    /**
     * @dev Calculate the total value of assets held by the Vault and all
     *      strategies and update the supply of OUSD, optionally sending a
     *      portion of the yield to the trustee.
     */
    function _rebase() internal whenNotRebasePaused {
        uint256 ousdSupply = oUSD.totalSupply();
        if (ousdSupply == 0) {
            return;
        }
        uint256 vaultValue = _totalValue();

        // Yield fee collection
        address _trusteeAddress = trusteeAddress; // gas savings
        if (_trusteeAddress != address(0) && (vaultValue > ousdSupply)) {
            uint256 yield = vaultValue.sub(ousdSupply);
            uint256 fee = yield.mul(trusteeFeeBps).div(10000);
            require(yield > fee, "Fee must not be greater than yield");
            if (fee > 0) {
                oUSD.mint(_trusteeAddress, fee);
            }
            emit YieldDistribution(_trusteeAddress, yield, fee);
        }

        // Only rachet OUSD supply upwards
        ousdSupply = oUSD.totalSupply(); // Final check should use latest value
        if (vaultValue > ousdSupply) {
            oUSD.changeSupply(vaultValue);
        }
    }

    /**
     * @dev Determine the total value of assets held by the vault and its
     *         strategies.
     * @return value Total value in USD (1e18)
     */
    function totalValue() external view virtual returns (uint256 value) {
        value = _totalValue();
    }

    /**
     * @dev Internal Calculate the total value of the assets held by the
     *         vault and its strategies.
     * @return value Total value in USD (1e18)
     */
    function _totalValue() internal view virtual returns (uint256 value) {
        return _totalValueInVault().add(_totalValueInStrategies());
    }

    /**
     * @dev Internal to calculate total value of all assets held in Vault.
     * @return value Total value in ETH (1e18)
     */
    function _totalValueInVault() internal view returns (uint256 value) {
        for (uint256 y = 0; y < allAssets.length; y++) {
            IERC20 asset = IERC20(allAssets[y]);
            uint256 assetDecimals = Helpers.getDecimals(allAssets[y]);
            uint256 balance = asset.balanceOf(address(this));
            if (balance > 0) {
                value = value.add(balance.scaleBy(18, assetDecimals));
            }
        }
    }

    /**
     * @dev Internal to calculate total value of all assets held in Strategies.
     * @return value Total value in ETH (1e18)
     */
    function _totalValueInStrategies() internal view returns (uint256 value) {
        for (uint256 i = 0; i < allStrategies.length; i++) {
            value = value.add(_totalValueInStrategy(allStrategies[i]));
        }
    }

    /**
     * @dev Internal to calculate total value of all assets held by strategy.
     * @param _strategyAddr Address of the strategy
     * @return value Total value in ETH (1e18)
     */
    function _totalValueInStrategy(address _strategyAddr)
        internal
        view
        returns (uint256 value)
    {
        IStrategy strategy = IStrategy(_strategyAddr);
        for (uint256 y = 0; y < allAssets.length; y++) {
            uint256 assetDecimals = Helpers.getDecimals(allAssets[y]);
            if (strategy.supportsAsset(allAssets[y])) {
                uint256 balance = strategy.checkBalance(allAssets[y]);
                if (balance > 0) {
                    value = value.add(balance.scaleBy(18, assetDecimals));
                }
            }
        }
    }

    /**
     * @notice Get the balance of an asset held in Vault and all strategies.
     * @param _asset Address of asset
     * @return uint256 Balance of asset in decimals of asset
     */
    function checkBalance(address _asset) external view returns (uint256) {
        return _checkBalance(_asset);
    }

    /**
     * @notice Get the balance of an asset held in Vault and all strategies.
     * @param _asset Address of asset
     * @return balance Balance of asset in decimals of asset
     */
    function _checkBalance(address _asset)
        internal
        view
        virtual
        returns (uint256 balance)
    {
        IERC20 asset = IERC20(_asset);
        balance = asset.balanceOf(address(this));
        for (uint256 i = 0; i < allStrategies.length; i++) {
            IStrategy strategy = IStrategy(allStrategies[i]);
            if (strategy.supportsAsset(_asset)) {
                balance = balance.add(strategy.checkBalance(_asset));
            }
        }
    }

    /**
     * @notice Get the balance of all assets held in Vault and all strategies.
     * @return balance Balance of all assets (1e18)
     */
    function _checkBalance() internal view returns (uint256 balance) {
        for (uint256 i = 0; i < allAssets.length; i++) {
            uint256 assetDecimals = Helpers.getDecimals(allAssets[i]);
            balance = balance.add(
                _checkBalance(allAssets[i]).scaleBy(18, assetDecimals)
            );
        }
    }

    /**
     * @notice Calculate the outputs for a redeem function, i.e. the mix of
     * coins that will be returned
     */
    function calculateRedeemOutputs(uint256 _amount)
        external
        view
        returns (uint256[] memory)
    {
        (uint256[] memory outputs, ) = _calculateRedeemOutputs(_amount);
        return outputs;
    }

    /**
     * @notice Calculate the outputs for a redeem function, i.e. the mix of
     * coins that will be returned.
     * @return outputs Array of amounts respective to the supported assets
     * @return totalBalance Total balance of Vault
     */
    function _calculateRedeemOutputs(uint256 _amount)
        internal
        view
        returns (uint256[] memory outputs, uint256 totalBalance)
    {
        // We always give out coins in proportion to how many we have,
        // Now if all coins were the same value, this math would easy,
        // just take the percentage of each coin, and multiply by the
        // value to be given out. But if coins are worth more than $1,
        // then we would end up handing out too many coins. We need to
        // adjust by the total value of coins.
        //
        // To do this, we total up the value of our coins, by their
        // percentages. Then divide what we would otherwise give out by
        // this number.
        //
        // Let say we have 100 DAI at $1.06  and 200 USDT at $1.00.
        // So for every 1 DAI we give out, we'll be handing out 2 USDT
        // Our total output ratio is: 33% * 1.06 + 66% * 1.00 = 1.02
        //
        // So when calculating the output, we take the percentage of
        // each coin, times the desired output value, divided by the
        // totalOutputRatio.
        //
        // For example, withdrawing: 30 OUSD:
        // DAI 33% * 30 / 1.02 = 9.80 DAI
        // USDT = 66 % * 30 / 1.02 = 19.60 USDT
        //
        // Checking these numbers:
        // 9.80 DAI * 1.06 = $10.40
        // 19.60 USDT * 1.00 = $19.60
        //
        // And so the user gets $10.40 + $19.60 = $30 worth of value.

        uint256 assetCount = getAssetCount();
        uint256[] memory assetPrices = _getAssetPrices();
        uint256[] memory assetBalances = new uint256[](assetCount);
        uint256[] memory assetDecimals = new uint256[](assetCount);
        uint256 totalOutputRatio = 0;
        outputs = new uint256[](assetCount);

        // Calculate redeem fee
        if (redeemFeeBps > 0) {
            uint256 redeemFee = _amount.mul(redeemFeeBps).div(10000);
            _amount = _amount.sub(redeemFee);
        }

        // Calculate assets balances and decimals once,
        // for a large gas savings.
        for (uint256 i = 0; i < allAssets.length; i++) {
            uint256 balance = _checkBalance(allAssets[i]);
            uint256 decimals = Helpers.getDecimals(allAssets[i]);
            assetBalances[i] = balance;
            assetDecimals[i] = decimals;
            totalBalance = totalBalance.add(balance.scaleBy(18, decimals));
        }
        // Calculate totalOutputRatio
        for (uint256 i = 0; i < allAssets.length; i++) {
            uint256 price = assetPrices[i];
            // Never give out more than one
            // stablecoin per dollar of OUSD
            if (price < 1e18) {
                price = 1e18;
            }
            uint256 ratio = assetBalances[i]
                .scaleBy(18, assetDecimals[i])
                .mul(price)
                .div(totalBalance);
            totalOutputRatio = totalOutputRatio.add(ratio);
        }
        // Calculate final outputs
        uint256 factor = _amount.divPrecisely(totalOutputRatio);
        for (uint256 i = 0; i < allAssets.length; i++) {
            outputs[i] = assetBalances[i].mul(factor).div(totalBalance);
        }
    }

    /**
     * @notice Get an array of the supported asset prices in USD.
     * @return assetPrices Array of asset prices in USD (1e18)
     */
    function _getAssetPrices()
        internal
        view
        returns (uint256[] memory assetPrices)
    {
        assetPrices = new uint256[](getAssetCount());

        IOracle oracle = IOracle(priceProvider);
        // Price from Oracle is returned with 8 decimals
        // _amount is in assetDecimals
        for (uint256 i = 0; i < allAssets.length; i++) {
            assetPrices[i] = oracle.price(allAssets[i]).scaleBy(18, 8);
        }
    }

    /***************************************
                    Utils
    ****************************************/

    /**
     * @dev Return the number of assets supported by the Vault.
     */
    function getAssetCount() public view returns (uint256) {
        return allAssets.length;
    }

    /**
     * @dev Return all asset addresses in order
     */
    function getAllAssets() external view returns (address[] memory) {
        return allAssets;
    }

    /**
     * @dev Return the number of strategies active on the Vault.
     */
    function getStrategyCount() external view returns (uint256) {
        return allStrategies.length;
    }

    /**
     * @dev Return the array of all strategies
     */
    function getAllStrategies() external view returns (address[] memory) {
        return allStrategies;
    }

    function isSupportedAsset(address _asset) external view returns (bool) {
        return assets[_asset].isSupported;
    }

    /**
     * @dev Falldown to the admin implementation
     * @notice This is a catch all for all functions not declared in core
     */
    // solhint-disable-next-line no-complex-fallback
    fallback() external payable {
        bytes32 slot = adminImplPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // Copy msg.data. We take full control of memory in this inline assembly
            // block because it will not return to Solidity code. We overwrite the
            // Solidity scratch pad at memory position 0.
            calldatacopy(0, 0, calldatasize())

            // Call the implementation.
            // out and outsize are 0 because we don't know the size yet.
            let result := delegatecall(
                gas(),
                sload(slot),
                0,
                calldatasize(),
                0,
                0
            )

            // Copy the returned data.
            returndatacopy(0, 0, returndatasize())

            switch result
            // delegatecall returns 0 on error.
            case 0 {
                revert(0, returndatasize())
            }
            default {
                return(0, returndatasize())
            }
        }
    }

    function abs(int256 x) private pure returns (uint256) {
        require(x < int256(MAX_INT), "Amount too high");
        return x >= 0 ? uint256(x) : uint256(-x);
    }
}

// File: @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/utils/SafeERC20.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - value;
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
        }
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: @openzeppelin/contracts/utils/math/SafeMath.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/math/SafeMath.sol)

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

// File: contracts/utils/StableMath.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

import { SafeMath } from "@openzeppelin/contracts/utils/math/SafeMath.sol";

// Based on StableMath from Stability Labs Pty. Ltd.
// https://github.com/mstable/mStable-contracts/blob/master/contracts/shared/StableMath.sol

library StableMath {
    using SafeMath for uint256;

    /**
     * @dev Scaling unit for use in specific calculations,
     * where 1 * 10**18, or 1e18 represents a unit '1'
     */
    uint256 private constant FULL_SCALE = 1e18;

    /***************************************
                    Helpers
    ****************************************/

    /**
     * @dev Adjust the scale of an integer
     * @param to Decimals to scale to
     * @param from Decimals to scale from
     */
    function scaleBy(
        uint256 x,
        uint256 to,
        uint256 from
    ) internal pure returns (uint256) {
        if (to > from) {
            x = x.mul(10**(to - from));
        } else if (to < from) {
            x = x.div(10**(from - to));
        }
        return x;
    }

    /***************************************
               Precise Arithmetic
    ****************************************/

    /**
     * @dev Multiplies two precise units, and then truncates by the full scale
     * @param x Left hand input to multiplication
     * @param y Right hand input to multiplication
     * @return Result after multiplying the two inputs and then dividing by the shared
     *         scale unit
     */
    function mulTruncate(uint256 x, uint256 y) internal pure returns (uint256) {
        return mulTruncateScale(x, y, FULL_SCALE);
    }

    /**
     * @dev Multiplies two precise units, and then truncates by the given scale. For example,
     * when calculating 90% of 10e18, (10e18 * 9e17) / 1e18 = (9e36) / 1e18 = 9e18
     * @param x Left hand input to multiplication
     * @param y Right hand input to multiplication
     * @param scale Scale unit
     * @return Result after multiplying the two inputs and then dividing by the shared
     *         scale unit
     */
    function mulTruncateScale(
        uint256 x,
        uint256 y,
        uint256 scale
    ) internal pure returns (uint256) {
        // e.g. assume scale = fullScale
        // z = 10e18 * 9e17 = 9e36
        uint256 z = x.mul(y);
        // return 9e36 / 1e18 = 9e18
        return z.div(scale);
    }

    /**
     * @dev Multiplies two precise units, and then truncates by the full scale, rounding up the result
     * @param x Left hand input to multiplication
     * @param y Right hand input to multiplication
     * @return Result after multiplying the two inputs and then dividing by the shared
     *          scale unit, rounded up to the closest base unit.
     */
    function mulTruncateCeil(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        // e.g. 8e17 * 17268172638 = 138145381104e17
        uint256 scaled = x.mul(y);
        // e.g. 138145381104e17 + 9.99...e17 = 138145381113.99...e17
        uint256 ceil = scaled.add(FULL_SCALE.sub(1));
        // e.g. 13814538111.399...e18 / 1e18 = 13814538111
        return ceil.div(FULL_SCALE);
    }

    /**
     * @dev Precisely divides two units, by first scaling the left hand operand. Useful
     *      for finding percentage weightings, i.e. 8e18/10e18 = 80% (or 8e17)
     * @param x Left hand input to division
     * @param y Right hand input to division
     * @return Result after multiplying the left operand by the scale, and
     *         executing the division on the right hand input.
     */
    function divPrecisely(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        // e.g. 8e18 * 1e18 = 8e36
        uint256 z = x.mul(FULL_SCALE);
        // e.g. 8e36 / 10e18 = 8e17
        return z.div(y);
    }
}

// File: contracts/interfaces/IOracle.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

interface IOracle {
    /**
     * @dev returns the asset price in USD, 8 decimal digits.
     */
    function price(address asset) external view returns (uint256);
}

// File: contracts/interfaces/IVault.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

interface IVault {
    event AssetSupported(address _asset);
    event AssetDefaultStrategyUpdated(address _asset, address _strategy);
    event AssetAllocated(address _asset, address _strategy, uint256 _amount);
    event StrategyApproved(address _addr);
    event StrategyRemoved(address _addr);
    event Mint(address _addr, uint256 _value);
    event Redeem(address _addr, uint256 _value);
    event CapitalPaused();
    event CapitalUnpaused();
    event RebasePaused();
    event RebaseUnpaused();
    event VaultBufferUpdated(uint256 _vaultBuffer);
    event RedeemFeeUpdated(uint256 _redeemFeeBps);
    event PriceProviderUpdated(address _priceProvider);
    event AllocateThresholdUpdated(uint256 _threshold);
    event RebaseThresholdUpdated(uint256 _threshold);
    event StrategistUpdated(address _address);
    event MaxSupplyDiffChanged(uint256 maxSupplyDiff);
    event YieldDistribution(address _to, uint256 _yield, uint256 _fee);
    event TrusteeFeeBpsChanged(uint256 _basis);
    event TrusteeAddressChanged(address _address);

    // Governable.sol
    function transferGovernance(address _newGovernor) external;

    function claimGovernance() external;

    function governor() external view returns (address);

    // VaultAdmin.sol
    function setPriceProvider(address _priceProvider) external;

    function priceProvider() external view returns (address);

    function setRedeemFeeBps(uint256 _redeemFeeBps) external;

    function redeemFeeBps() external view returns (uint256);

    function setVaultBuffer(uint256 _vaultBuffer) external;

    function vaultBuffer() external view returns (uint256);

    function setAutoAllocateThreshold(uint256 _threshold) external;

    function autoAllocateThreshold() external view returns (uint256);

    function setRebaseThreshold(uint256 _threshold) external;

    function rebaseThreshold() external view returns (uint256);

    function setStrategistAddr(address _address) external;

    function strategistAddr() external view returns (address);

    function setMaxSupplyDiff(uint256 _maxSupplyDiff) external;

    function maxSupplyDiff() external view returns (uint256);

    function setTrusteeAddress(address _address) external;

    function trusteeAddress() external view returns (address);

    function setTrusteeFeeBps(uint256 _basis) external;

    function trusteeFeeBps() external view returns (uint256);

    function ousdMetaStrategy() external view returns (address);

    function supportAsset(address _asset) external;

    function approveStrategy(address _addr) external;

    function removeStrategy(address _addr) external;

    function setAssetDefaultStrategy(address _asset, address _strategy)
        external;

    function assetDefaultStrategies(address _asset)
        external
        view
        returns (address);

    function pauseRebase() external;

    function unpauseRebase() external;

    function rebasePaused() external view returns (bool);

    function pauseCapital() external;

    function unpauseCapital() external;

    function capitalPaused() external view returns (bool);

    function transferToken(address _asset, uint256 _amount) external;

    function priceUSDMint(address asset) external view returns (uint256);

    function priceUSDRedeem(address asset) external view returns (uint256);

    function withdrawAllFromStrategy(address _strategyAddr) external;

    function withdrawAllFromStrategies() external;

    function reallocate(
        address _strategyFromAddress,
        address _strategyToAddress,
        address[] calldata _assets,
        uint256[] calldata _amounts
    ) external;

    // VaultCore.sol
    function mint(
        address _asset,
        uint256 _amount,
        uint256 _minimumOusdAmount
    ) external;

    function mintForStrategy(uint256 _amount) external;

    function redeem(uint256 _amount, uint256 _minimumUnitAmount) external;

    function burnForStrategy(uint256 _amount) external;

    function redeemAll(uint256 _minimumUnitAmount) external;

    function allocate() external;

    function rebase() external;

    function totalValue() external view returns (uint256 value);

    function checkBalance(address _asset) external view returns (uint256);

    function calculateRedeemOutputs(uint256 _amount)
        external
        view
        returns (uint256[] memory);

    function getAssetCount() external view returns (uint256);

    function getAllAssets() external view returns (address[] memory);

    function getStrategyCount() external view returns (uint256);

    function getAllStrategies() external view returns (address[] memory);

    function isSupportedAsset(address _asset) external view returns (bool);

    function netOusdMintForStrategyThreshold() external view returns (uint256);

    function setOusdMetaStrategy(address _ousdMetaStrategy) external;

    function setNetOusdMintForStrategyThreshold(uint256 _threshold) external;

    function netOusdMintedForStrategy() external view returns (int256);
}

// File: contracts/interfaces/IBuyback.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

interface IBuyback {
    function swap() external;
}

// File: contracts/vault/VaultStorage.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

/**
 * @title OUSD VaultStorage Contract
 * @notice The VaultStorage contract defines the storage for the Vault contracts
 * @author Origin Protocol Inc
 */

import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import { SafeMath } from "@openzeppelin/contracts/utils/math/SafeMath.sol";
import { Address } from "@openzeppelin/contracts/utils/Address.sol";

import { IStrategy } from "../interfaces/IStrategy.sol";
import { Governable } from "../governance/Governable.sol";
import { OUSD } from "../token/OUSD.sol";
import { Initializable } from "../utils/Initializable.sol";
import "../utils/Helpers.sol";
import { StableMath } from "../utils/StableMath.sol";

contract VaultStorage is Initializable, Governable {
    using SafeMath for uint256;
    using StableMath for uint256;
    using SafeMath for int256;
    using SafeERC20 for IERC20;

    event AssetSupported(address _asset);
    event AssetDefaultStrategyUpdated(address _asset, address _strategy);
    event AssetAllocated(address _asset, address _strategy, uint256 _amount);
    event StrategyApproved(address _addr);
    event StrategyRemoved(address _addr);
    event Mint(address _addr, uint256 _value);
    event Redeem(address _addr, uint256 _value);
    event CapitalPaused();
    event CapitalUnpaused();
    event RebasePaused();
    event RebaseUnpaused();
    event VaultBufferUpdated(uint256 _vaultBuffer);
    event OusdMetaStrategyUpdated(address _ousdMetaStrategy);
    event RedeemFeeUpdated(uint256 _redeemFeeBps);
    event PriceProviderUpdated(address _priceProvider);
    event AllocateThresholdUpdated(uint256 _threshold);
    event RebaseThresholdUpdated(uint256 _threshold);
    event StrategistUpdated(address _address);
    event MaxSupplyDiffChanged(uint256 maxSupplyDiff);
    event YieldDistribution(address _to, uint256 _yield, uint256 _fee);
    event TrusteeFeeBpsChanged(uint256 _basis);
    event TrusteeAddressChanged(address _address);
    event NetOusdMintForStrategyThresholdChanged(uint256 _threshold);

    // Assets supported by the Vault, i.e. Stablecoins
    struct Asset {
        bool isSupported;
    }
    mapping(address => Asset) internal assets;
    address[] internal allAssets;

    // Strategies approved for use by the Vault
    struct Strategy {
        bool isSupported;
        uint256 _deprecated; // Deprecated storage slot
    }
    mapping(address => Strategy) internal strategies;
    address[] internal allStrategies;

    // Address of the Oracle price provider contract
    address public priceProvider;
    // Pausing bools
    bool public rebasePaused = false;
    bool public capitalPaused = true;
    // Redemption fee in basis points
    uint256 public redeemFeeBps;
    // Buffer of assets to keep in Vault to handle (most) withdrawals
    uint256 public vaultBuffer;
    // Mints over this amount automatically allocate funds. 18 decimals.
    uint256 public autoAllocateThreshold;
    // Mints over this amount automatically rebase. 18 decimals.
    uint256 public rebaseThreshold;

    OUSD internal oUSD;

    //keccak256("OUSD.vault.governor.admin.impl");
    bytes32 constant adminImplPosition =
        0xa2bd3d3cf188a41358c8b401076eb59066b09dec5775650c0de4c55187d17bd9;

    // Address of the contract responsible for post rebase syncs with AMMs
    address private _deprecated_rebaseHooksAddr = address(0);

    // Deprecated: Address of Uniswap
    // slither-disable-next-line constable-states
    address private _deprecated_uniswapAddr = address(0);

    // Address of the Strategist
    address public strategistAddr = address(0);

    // Mapping of asset address to the Strategy that they should automatically
    // be allocated to
    mapping(address => address) public assetDefaultStrategies;

    uint256 public maxSupplyDiff;

    // Trustee contract that can collect a percentage of yield
    address public trusteeAddress;

    // Amount of yield collected in basis points
    uint256 public trusteeFeeBps;

    // Deprecated: Tokens that should be swapped for stablecoins
    address[] private _deprecated_swapTokens;

    uint256 constant MINT_MINIMUM_ORACLE = 99800000;

    // Meta strategy that is allowed to mint/burn OUSD without changing collateral
    address public ousdMetaStrategy = address(0);

    // How much OUSD is currently minted by the strategy
    int256 public netOusdMintedForStrategy = 0;

    // How much net total OUSD is allowed to be minted by all strategies
    uint256 public netOusdMintForStrategyThreshold = 0;

    /**
     * @dev set the implementation for the admin, this needs to be in a base class else we cannot set it
     * @param newImpl address of the implementation
     */
    function setAdminImpl(address newImpl) external onlyGovernor {
        require(
            Address.isContract(newImpl),
            "new implementation is not a contract"
        );
        bytes32 position = adminImplPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(position, newImpl)
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Address.sol)

pragma solidity ^0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: contracts/interfaces/IStrategy.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

/**
 * @title Platform interface to integrate with lending platform like Compound, AAVE etc.
 */
interface IStrategy {
    /**
     * @dev Deposit the given asset to platform
     * @param _asset asset address
     * @param _amount Amount to deposit
     */
    function deposit(address _asset, uint256 _amount) external;

    /**
     * @dev Deposit the entire balance of all supported assets in the Strategy
     *      to the platform
     */
    function depositAll() external;

    /**
     * @dev Withdraw given asset from Lending platform
     */
    function withdraw(
        address _recipient,
        address _asset,
        uint256 _amount
    ) external;

    /**
     * @dev Liquidate all assets in strategy and return them to Vault.
     */
    function withdrawAll() external;

    /**
     * @dev Returns the current balance of the given asset.
     */
    function checkBalance(address _asset)
        external
        view
        returns (uint256 balance);

    /**
     * @dev Returns bool indicating whether strategy supports asset.
     */
    function supportsAsset(address _asset) external view returns (bool);

    /**
     * @dev Collect reward tokens from the Strategy.
     */
    function collectRewardTokens() external;

    /**
     * @dev The address array of the reward tokens for the Strategy.
     */
    function getRewardTokenAddresses() external view returns (address[] memory);
}

// File: contracts/governance/Governable.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

/**
 * @title OUSD Governable Contract
 * @dev Copy of the openzeppelin Ownable.sol contract with nomenclature change
 *      from owner to governor and renounce methods removed. Does not use
 *      Context.sol like Ownable.sol does for simplification.
 * @author Origin Protocol Inc
 */
contract Governable {
    // Storage position of the owner and pendingOwner of the contract
    // keccak256("OUSD.governor");
    bytes32 private constant governorPosition =
        0x7bea13895fa79d2831e0a9e28edede30099005a50d652d8957cf8a607ee6ca4a;

    // keccak256("OUSD.pending.governor");
    bytes32 private constant pendingGovernorPosition =
        0x44c4d30b2eaad5130ad70c3ba6972730566f3e6359ab83e800d905c61b1c51db;

    // keccak256("OUSD.reentry.status");
    bytes32 private constant reentryStatusPosition =
        0x53bf423e48ed90e97d02ab0ebab13b2a235a6bfbe9c321847d5c175333ac4535;

    // See OpenZeppelin ReentrancyGuard implementation
    uint256 constant _NOT_ENTERED = 1;
    uint256 constant _ENTERED = 2;

    event PendingGovernorshipTransfer(
        address indexed previousGovernor,
        address indexed newGovernor
    );

    event GovernorshipTransferred(
        address indexed previousGovernor,
        address indexed newGovernor
    );

    /**
     * @dev Initializes the contract setting the deployer as the initial Governor.
     */
    constructor() {
        _setGovernor(msg.sender);
        emit GovernorshipTransferred(address(0), _governor());
    }

    /**
     * @dev Returns the address of the current Governor.
     */
    function governor() public view returns (address) {
        return _governor();
    }

    /**
     * @dev Returns the address of the current Governor.
     */
    function _governor() internal view returns (address governorOut) {
        bytes32 position = governorPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            governorOut := sload(position)
        }
    }

    /**
     * @dev Returns the address of the pending Governor.
     */
    function _pendingGovernor()
        internal
        view
        returns (address pendingGovernor)
    {
        bytes32 position = pendingGovernorPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            pendingGovernor := sload(position)
        }
    }

    /**
     * @dev Throws if called by any account other than the Governor.
     */
    modifier onlyGovernor() {
        require(isGovernor(), "Caller is not the Governor");
        _;
    }

    /**
     * @dev Returns true if the caller is the current Governor.
     */
    function isGovernor() public view returns (bool) {
        return msg.sender == _governor();
    }

    function _setGovernor(address newGovernor) internal {
        bytes32 position = governorPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(position, newGovernor)
        }
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        bytes32 position = reentryStatusPosition;
        uint256 _reentry_status;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            _reentry_status := sload(position)
        }

        // On the first call to nonReentrant, _notEntered will be true
        require(_reentry_status != _ENTERED, "Reentrant call");

        // Any calls to nonReentrant after this point will fail
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(position, _ENTERED)
        }

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(position, _NOT_ENTERED)
        }
    }

    function _setPendingGovernor(address newGovernor) internal {
        bytes32 position = pendingGovernorPosition;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(position, newGovernor)
        }
    }

    /**
     * @dev Transfers Governance of the contract to a new account (`newGovernor`).
     * Can only be called by the current Governor. Must be claimed for this to complete
     * @param _newGovernor Address of the new Governor
     */
    function transferGovernance(address _newGovernor) external onlyGovernor {
        _setPendingGovernor(_newGovernor);
        emit PendingGovernorshipTransfer(_governor(), _newGovernor);
    }

    /**
     * @dev Claim Governance of the contract to a new account (`newGovernor`).
     * Can only be called by the new Governor.
     */
    function claimGovernance() external {
        require(
            msg.sender == _pendingGovernor(),
            "Only the pending Governor can complete the claim"
        );
        _changeGovernor(msg.sender);
    }

    /**
     * @dev Change Governance of the contract to a new account (`newGovernor`).
     * @param _newGovernor Address of the new Governor
     */
    function _changeGovernor(address _newGovernor) internal {
        require(_newGovernor != address(0), "New Governor is address(0)");
        emit GovernorshipTransferred(_governor(), _newGovernor);
        _setGovernor(_newGovernor);
    }
}

// File: contracts/token/OUSD.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

/**
 * @title OUSD Token Contract
 * @dev ERC20 compatible contract for OUSD
 * @dev Implements an elastic supply
 * @author Origin Protocol Inc
 */
import { SafeMath } from "@openzeppelin/contracts/utils/math/SafeMath.sol";
import { Address } from "@openzeppelin/contracts/utils/Address.sol";

import { Initializable } from "../utils/Initializable.sol";
import { InitializableERC20Detailed } from "../utils/InitializableERC20Detailed.sol";
import { StableMath } from "../utils/StableMath.sol";
import { Governable } from "../governance/Governable.sol";

/**
 * NOTE that this is an ERC20 token but the invariant that the sum of
 * balanceOf(x) for all x is not >= totalSupply(). This is a consequence of the
 * rebasing design. Any integrations with OUSD should be aware.
 */

contract OUSD is Initializable, InitializableERC20Detailed, Governable {
    using SafeMath for uint256;
    using StableMath for uint256;

    event TotalSupplyUpdatedHighres(
        uint256 totalSupply,
        uint256 rebasingCredits,
        uint256 rebasingCreditsPerToken
    );

    enum RebaseOptions {
        NotSet,
        OptOut,
        OptIn
    }

    uint256 private constant MAX_SUPPLY = ~uint128(0); // (2^128) - 1
    uint256 public _totalSupply;
    mapping(address => mapping(address => uint256)) private _allowances;
    address public vaultAddress = address(0);
    mapping(address => uint256) private _creditBalances;
    uint256 private _rebasingCredits;
    uint256 private _rebasingCreditsPerToken;
    // Frozen address/credits are non rebasing (value is held in contracts which
    // do not receive yield unless they explicitly opt in)
    uint256 public nonRebasingSupply;
    mapping(address => uint256) public nonRebasingCreditsPerToken;
    mapping(address => RebaseOptions) public rebaseState;
    mapping(address => uint256) public isUpgraded;

    uint256 private constant RESOLUTION_INCREASE = 1e9;

    function initialize(
        string calldata _nameArg,
        string calldata _symbolArg,
        address _vaultAddress
    ) external onlyGovernor initializer {
        InitializableERC20Detailed._initialize(_nameArg, _symbolArg, 18);
        _rebasingCreditsPerToken = 1e18;
        vaultAddress = _vaultAddress;
    }

    /**
     * @dev Verifies that the caller is the Vault contract
     */
    modifier onlyVault() {
        require(vaultAddress == msg.sender, "Caller is not the Vault");
        _;
    }

    /**
     * @return The total supply of OUSD.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @return Low resolution rebasingCreditsPerToken
     */
    function rebasingCreditsPerToken() public view returns (uint256) {
        return _rebasingCreditsPerToken / RESOLUTION_INCREASE;
    }

    /**
     * @return Low resolution total number of rebasing credits
     */
    function rebasingCredits() public view returns (uint256) {
        return _rebasingCredits / RESOLUTION_INCREASE;
    }

    /**
     * @return High resolution rebasingCreditsPerToken
     */
    function rebasingCreditsPerTokenHighres() public view returns (uint256) {
        return _rebasingCreditsPerToken;
    }

    /**
     * @return High resolution total number of rebasing credits
     */
    function rebasingCreditsHighres() public view returns (uint256) {
        return _rebasingCredits;
    }

    /**
     * @dev Gets the balance of the specified address.
     * @param _account Address to query the balance of.
     * @return A uint256 representing the amount of base units owned by the
     *         specified address.
     */
    function balanceOf(address _account)
        public
        view
        override
        returns (uint256)
    {
        if (_creditBalances[_account] == 0) return 0;
        return
            _creditBalances[_account].divPrecisely(_creditsPerToken(_account));
    }

    /**
     * @dev Gets the credits balance of the specified address.
     * @dev Backwards compatible with old low res credits per token.
     * @param _account The address to query the balance of.
     * @return (uint256, uint256) Credit balance and credits per token of the
     *         address
     */
    function creditsBalanceOf(address _account)
        public
        view
        returns (uint256, uint256)
    {
        uint256 cpt = _creditsPerToken(_account);
        if (cpt == 1e27) {
            // For a period before the resolution upgrade, we created all new
            // contract accounts at high resolution. Since they are not changing
            // as a result of this upgrade, we will return their true values
            return (_creditBalances[_account], cpt);
        } else {
            return (
                _creditBalances[_account] / RESOLUTION_INCREASE,
                cpt / RESOLUTION_INCREASE
            );
        }
    }

    /**
     * @dev Gets the credits balance of the specified address.
     * @param _account The address to query the balance of.
     * @return (uint256, uint256, bool) Credit balance, credits per token of the
     *         address, and isUpgraded
     */
    function creditsBalanceOfHighres(address _account)
        public
        view
        returns (
            uint256,
            uint256,
            bool
        )
    {
        return (
            _creditBalances[_account],
            _creditsPerToken(_account),
            isUpgraded[_account] == 1
        );
    }

    /**
     * @dev Transfer tokens to a specified address.
     * @param _to the address to transfer to.
     * @param _value the amount to be transferred.
     * @return true on success.
     */
    function transfer(address _to, uint256 _value)
        public
        override
        returns (bool)
    {
        require(_to != address(0), "Transfer to zero address");
        require(
            _value <= balanceOf(msg.sender),
            "Transfer greater than balance"
        );

        _executeTransfer(msg.sender, _to, _value);

        emit Transfer(msg.sender, _to, _value);

        return true;
    }

    /**
     * @dev Transfer tokens from one address to another.
     * @param _from The address you want to send tokens from.
     * @param _to The address you want to transfer to.
     * @param _value The amount of tokens to be transferred.
     */
    function transferFrom(
        address _from,
        address _to,
        uint256 _value
    ) public override returns (bool) {
        require(_to != address(0), "Transfer to zero address");
        require(_value <= balanceOf(_from), "Transfer greater than balance");

        _allowances[_from][msg.sender] = _allowances[_from][msg.sender].sub(
            _value
        );

        _executeTransfer(_from, _to, _value);

        emit Transfer(_from, _to, _value);

        return true;
    }

    /**
     * @dev Update the count of non rebasing credits in response to a transfer
     * @param _from The address you want to send tokens from.
     * @param _to The address you want to transfer to.
     * @param _value Amount of OUSD to transfer
     */
    function _executeTransfer(
        address _from,
        address _to,
        uint256 _value
    ) internal {
        bool isNonRebasingTo = _isNonRebasingAccount(_to);
        bool isNonRebasingFrom = _isNonRebasingAccount(_from);

        // Credits deducted and credited might be different due to the
        // differing creditsPerToken used by each account
        uint256 creditsCredited = _value.mulTruncate(_creditsPerToken(_to));
        uint256 creditsDeducted = _value.mulTruncate(_creditsPerToken(_from));

        _creditBalances[_from] = _creditBalances[_from].sub(
            creditsDeducted,
            "Transfer amount exceeds balance"
        );
        _creditBalances[_to] = _creditBalances[_to].add(creditsCredited);

        if (isNonRebasingTo && !isNonRebasingFrom) {
            // Transfer to non-rebasing account from rebasing account, credits
            // are removed from the non rebasing tally
            nonRebasingSupply = nonRebasingSupply.add(_value);
            // Update rebasingCredits by subtracting the deducted amount
            _rebasingCredits = _rebasingCredits.sub(creditsDeducted);
        } else if (!isNonRebasingTo && isNonRebasingFrom) {
            // Transfer to rebasing account from non-rebasing account
            // Decreasing non-rebasing credits by the amount that was sent
            nonRebasingSupply = nonRebasingSupply.sub(_value);
            // Update rebasingCredits by adding the credited amount
            _rebasingCredits = _rebasingCredits.add(creditsCredited);
        }
    }

    /**
     * @dev Function to check the amount of tokens that _owner has allowed to
     *      `_spender`.
     * @param _owner The address which owns the funds.
     * @param _spender The address which will spend the funds.
     * @return The number of tokens still available for the _spender.
     */
    function allowance(address _owner, address _spender)
        public
        view
        override
        returns (uint256)
    {
        return _allowances[_owner][_spender];
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens
     *      on behalf of msg.sender. This method is included for ERC20
     *      compatibility. `increaseAllowance` and `decreaseAllowance` should be
     *      used instead.
     *
     *      Changing an allowance with this method brings the risk that someone
     *      may transfer both the old and the new allowance - if they are both
     *      greater than zero - if a transfer transaction is mined before the
     *      later approve() call is mined.
     * @param _spender The address which will spend the funds.
     * @param _value The amount of tokens to be spent.
     */
    function approve(address _spender, uint256 _value)
        public
        override
        returns (bool)
    {
        _allowances[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner has allowed to
     *      `_spender`.
     *      This method should be used instead of approve() to avoid the double
     *      approval vulnerability described above.
     * @param _spender The address which will spend the funds.
     * @param _addedValue The amount of tokens to increase the allowance by.
     */
    function increaseAllowance(address _spender, uint256 _addedValue)
        public
        returns (bool)
    {
        _allowances[msg.sender][_spender] = _allowances[msg.sender][_spender]
            .add(_addedValue);
        emit Approval(msg.sender, _spender, _allowances[msg.sender][_spender]);
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner has allowed to
            `_spender`.
     * @param _spender The address which will spend the funds.
     * @param _subtractedValue The amount of tokens to decrease the allowance
     *        by.
     */
    function decreaseAllowance(address _spender, uint256 _subtractedValue)
        public
        returns (bool)
    {
        uint256 oldValue = _allowances[msg.sender][_spender];
        if (_subtractedValue >= oldValue) {
            _allowances[msg.sender][_spender] = 0;
        } else {
            _allowances[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        emit Approval(msg.sender, _spender, _allowances[msg.sender][_spender]);
        return true;
    }

    /**
     * @dev Mints new tokens, increasing totalSupply.
     */
    function mint(address _account, uint256 _amount) external onlyVault {
        _mint(_account, _amount);
    }

    /**
     * @dev Creates `_amount` tokens and assigns them to `_account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address _account, uint256 _amount) internal nonReentrant {
        require(_account != address(0), "Mint to the zero address");

        bool isNonRebasingAccount = _isNonRebasingAccount(_account);

        uint256 creditAmount = _amount.mulTruncate(_creditsPerToken(_account));
        _creditBalances[_account] = _creditBalances[_account].add(creditAmount);

        // If the account is non rebasing and doesn't have a set creditsPerToken
        // then set it i.e. this is a mint from a fresh contract
        if (isNonRebasingAccount) {
            nonRebasingSupply = nonRebasingSupply.add(_amount);
        } else {
            _rebasingCredits = _rebasingCredits.add(creditAmount);
        }

        _totalSupply = _totalSupply.add(_amount);

        require(_totalSupply < MAX_SUPPLY, "Max supply");

        emit Transfer(address(0), _account, _amount);
    }

    /**
     * @dev Burns tokens, decreasing totalSupply.
     */
    function burn(address account, uint256 amount) external onlyVault {
        _burn(account, amount);
    }

    /**
     * @dev Destroys `_amount` tokens from `_account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `_account` cannot be the zero address.
     * - `_account` must have at least `_amount` tokens.
     */
    function _burn(address _account, uint256 _amount) internal nonReentrant {
        require(_account != address(0), "Burn from the zero address");
        if (_amount == 0) {
            return;
        }

        bool isNonRebasingAccount = _isNonRebasingAccount(_account);
        uint256 creditAmount = _amount.mulTruncate(_creditsPerToken(_account));
        uint256 currentCredits = _creditBalances[_account];

        // Remove the credits, burning rounding errors
        if (
            currentCredits == creditAmount || currentCredits - 1 == creditAmount
        ) {
            // Handle dust from rounding
            _creditBalances[_account] = 0;
        } else if (currentCredits > creditAmount) {
            _creditBalances[_account] = _creditBalances[_account].sub(
                creditAmount
            );
        } else {
            revert("Remove exceeds balance");
        }

        // Remove from the credit tallies and non-rebasing supply
        if (isNonRebasingAccount) {
            nonRebasingSupply = nonRebasingSupply.sub(_amount);
        } else {
            _rebasingCredits = _rebasingCredits.sub(creditAmount);
        }

        _totalSupply = _totalSupply.sub(_amount);

        emit Transfer(_account, address(0), _amount);
    }

    /**
     * @dev Get the credits per token for an account. Returns a fixed amount
     *      if the account is non-rebasing.
     * @param _account Address of the account.
     */
    function _creditsPerToken(address _account)
        internal
        view
        returns (uint256)
    {
        if (nonRebasingCreditsPerToken[_account] != 0) {
            return nonRebasingCreditsPerToken[_account];
        } else {
            return _rebasingCreditsPerToken;
        }
    }

    /**
     * @dev Is an account using rebasing accounting or non-rebasing accounting?
     *      Also, ensure contracts are non-rebasing if they have not opted in.
     * @param _account Address of the account.
     */
    function _isNonRebasingAccount(address _account) internal returns (bool) {
        bool isContract = Address.isContract(_account);
        if (isContract && rebaseState[_account] == RebaseOptions.NotSet) {
            _ensureRebasingMigration(_account);
        }
        return nonRebasingCreditsPerToken[_account] > 0;
    }

    /**
     * @dev Ensures internal account for rebasing and non-rebasing credits and
     *      supply is updated following deployment of frozen yield change.
     */
    function _ensureRebasingMigration(address _account) internal {
        if (nonRebasingCreditsPerToken[_account] == 0) {
            if (_creditBalances[_account] == 0) {
                // Since there is no existing balance, we can directly set to
                // high resolution, and do not have to do any other bookkeeping
                nonRebasingCreditsPerToken[_account] = 1e27;
            } else {
                // Migrate an existing account:

                // Set fixed credits per token for this account
                nonRebasingCreditsPerToken[_account] = _rebasingCreditsPerToken;
                // Update non rebasing supply
                nonRebasingSupply = nonRebasingSupply.add(balanceOf(_account));
                // Update credit tallies
                _rebasingCredits = _rebasingCredits.sub(
                    _creditBalances[_account]
                );
            }
        }
    }

    /**
     * @dev Add a contract address to the non-rebasing exception list. The
     * address's balance will be part of rebases and the account will be exposed
     * to upside and downside.
     */
    function rebaseOptIn() public nonReentrant {
        require(_isNonRebasingAccount(msg.sender), "Account has not opted out");

        // Convert balance into the same amount at the current exchange rate
        uint256 newCreditBalance = _creditBalances[msg.sender]
            .mul(_rebasingCreditsPerToken)
            .div(_creditsPerToken(msg.sender));

        // Decreasing non rebasing supply
        nonRebasingSupply = nonRebasingSupply.sub(balanceOf(msg.sender));

        _creditBalances[msg.sender] = newCreditBalance;

        // Increase rebasing credits, totalSupply remains unchanged so no
        // adjustment necessary
        _rebasingCredits = _rebasingCredits.add(_creditBalances[msg.sender]);

        rebaseState[msg.sender] = RebaseOptions.OptIn;

        // Delete any fixed credits per token
        delete nonRebasingCreditsPerToken[msg.sender];
    }

    /**
     * @dev Explicitly mark that an address is non-rebasing.
     */
    function rebaseOptOut() public nonReentrant {
        require(!_isNonRebasingAccount(msg.sender), "Account has not opted in");

        // Increase non rebasing supply
        nonRebasingSupply = nonRebasingSupply.add(balanceOf(msg.sender));
        // Set fixed credits per token
        nonRebasingCreditsPerToken[msg.sender] = _rebasingCreditsPerToken;

        // Decrease rebasing credits, total supply remains unchanged so no
        // adjustment necessary
        _rebasingCredits = _rebasingCredits.sub(_creditBalances[msg.sender]);

        // Mark explicitly opted out of rebasing
        rebaseState[msg.sender] = RebaseOptions.OptOut;
    }

    /**
     * @dev Modify the supply without minting new tokens. This uses a change in
     *      the exchange rate between "credits" and OUSD tokens to change balances.
     * @param _newTotalSupply New total supply of OUSD.
     */
    function changeSupply(uint256 _newTotalSupply)
        external
        onlyVault
        nonReentrant
    {
        require(_totalSupply > 0, "Cannot increase 0 supply");

        if (_totalSupply == _newTotalSupply) {
            emit TotalSupplyUpdatedHighres(
                _totalSupply,
                _rebasingCredits,
                _rebasingCreditsPerToken
            );
            return;
        }

        _totalSupply = _newTotalSupply > MAX_SUPPLY
            ? MAX_SUPPLY
            : _newTotalSupply;

        _rebasingCreditsPerToken = _rebasingCredits.divPrecisely(
            _totalSupply.sub(nonRebasingSupply)
        );

        require(_rebasingCreditsPerToken > 0, "Invalid change in supply");

        _totalSupply = _rebasingCredits
            .divPrecisely(_rebasingCreditsPerToken)
            .add(nonRebasingSupply);

        emit TotalSupplyUpdatedHighres(
            _totalSupply,
            _rebasingCredits,
            _rebasingCreditsPerToken
        );
    }
}

// File: contracts/utils/Initializable.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

abstract contract Initializable {
    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(
            initializing || !initialized,
            "Initializable: contract is already initialized"
        );

        bool isTopLevelCall = !initializing;
        if (isTopLevelCall) {
            initializing = true;
            initialized = true;
        }

        _;

        if (isTopLevelCall) {
            initializing = false;
        }
    }

    uint256[50] private ______gap;
}

// File: contracts/utils/Helpers.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

import { IBasicToken } from "../interfaces/IBasicToken.sol";

library Helpers {
    /**
     * @notice Fetch the `symbol()` from an ERC20 token
     * @dev Grabs the `symbol()` from a contract
     * @param _token Address of the ERC20 token
     * @return string Symbol of the ERC20 token
     */
    function getSymbol(address _token) internal view returns (string memory) {
        string memory symbol = IBasicToken(_token).symbol();
        return symbol;
    }

    /**
     * @notice Fetch the `decimals()` from an ERC20 token
     * @dev Grabs the `decimals()` from a contract and fails if
     *      the decimal value does not live within a certain range
     * @param _token Address of the ERC20 token
     * @return uint256 Decimals of the ERC20 token
     */
    function getDecimals(address _token) internal view returns (uint256) {
        uint256 decimals = IBasicToken(_token).decimals();
        require(
            decimals >= 4 && decimals <= 18,
            "Token must have sufficient decimal places"
        );

        return decimals;
    }
}

// File: contracts/utils/InitializableERC20Detailed.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

/**
 * @dev Optional functions from the ERC20 standard.
 * Converted from openzeppelin/contracts/token/ERC20/ERC20Detailed.sol
 */
abstract contract InitializableERC20Detailed is IERC20 {
    // Storage gap to skip storage from prior to OUSD reset
    uint256[100] private _____gap;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for `name`, `symbol`, and `decimals`. All three of
     * these values are immutable: they can only be set once during
     * construction.
     * @notice To avoid variable shadowing appended `Arg` after arguments name.
     */
    function _initialize(
        string memory nameArg,
        string memory symbolArg,
        uint8 decimalsArg
    ) internal {
        _name = nameArg;
        _symbol = symbolArg;
        _decimals = decimalsArg;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
}

// File: contracts/interfaces/IBasicToken.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.8.0;

interface IBasicToken {
    function symbol() external view returns (string memory);

    function decimals() external view returns (uint8);
}