// File: src/USDH.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.7.6;
pragma abicoder v2;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import "./interfaces/IERC20Decimals.sol"; 

contract USDH is IERC20, Ownable, ReentrancyGuard {
    uint256 internal constant max256 = type(uint256).max;

    string private constant _name = "Hoard Dollar";
    string private constant _symbol = "USDH";
    uint8 private constant _decimals = 18;

    uint256 public _totalSupply;

    mapping (address => bool) public wasCollateral;
    mapping (address => bool) public collateralWhitelist;

    address[] public collateralTypes;

    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;

    address public governance;

    modifier onlyGovernance() {
        require(msg.sender == governance);
        _;
    }

    constructor() {
        governance = msg.sender;
        _balances[address(this)] = _totalSupply;
        emit Transfer(address(0), address(this), _totalSupply);
    }

    function mint(address _collateral, uint256 _amount) external nonReentrant {
        require(collateralWhitelist[_collateral]);
        require(_amount > 0);

        uint256 _amountStablecoin = _amount;
        IERC20 _Collateral = IERC20(_collateral);
        require(_Collateral.balanceOf(msg.sender) >= _amountStablecoin);
        require(_Collateral.allowance(msg.sender, address(this)) >= _amountStablecoin);
        uint256 _balance = _Collateral.balanceOf(address(this));
        require(_Collateral.transferFrom(msg.sender, address(this), _amountStablecoin), "TF");
        require(_Collateral.balanceOf(address(this)) >= _balance + _amountStablecoin, "TF");

        _totalSupply = _totalSupply + _amount;
        _balances[msg.sender] = _balances[msg.sender] + _amount;
        emit Transfer(address(0), msg.sender, _amount);
    }

    function redeem(uint256 _amount) external nonReentrant returns (address[] memory) {
        require(_balances[msg.sender] >= _amount && _totalSupply >= _amount);
        _balances[msg.sender] = _balances[msg.sender] - _amount;
        emit Transfer(msg.sender, address(0), _amount);
        _totalSupply = _totalSupply - _amount;

        address[] memory _collateralTypes = new address[](9);

        uint256 _amountStablecoin = _amount;
        uint256 _amountStablecoinPaid;
        uint256 _i;
        while (_amountStablecoin > _amountStablecoinPaid) {
            (address _largestCollateral, uint256 _largestBalance) = getLargestBalance();
            uint256 _amountStablecoinRemaining = _amountStablecoin - _amountStablecoinPaid;
            uint256 _amountCollateral = _amountStablecoinRemaining > _largestBalance ? _largestBalance : _amountStablecoinRemaining;
            try IERC20(_largestCollateral).transfer(msg.sender, _amountCollateral) {} catch {}
            _amountStablecoinPaid = _amountStablecoinPaid + _amountCollateral;
            if (_i < 9) {
                _collateralTypes[_i] = _largestCollateral;
                _i = _i + 1;
            }
        }

        return _collateralTypes;
    }

    function getLargestBalance() public view returns (address, uint256) {
        address _largestCollateral;
        uint256 _largestBalance;

        uint256 collateralTypesNum = collateralTypes.length;

        for (uint256 _i = 0; _i < collateralTypesNum; _i++) {
            address _collateral = collateralTypes[_i];
            uint256 _balance = IERC20(_collateral).balanceOf(address(this));
            if (_balance > _largestBalance) {
                _largestCollateral = _collateral;
                _largestBalance = _balance;
            }
        }

        return (_largestCollateral, _largestBalance);
    }

    function getCollateral(address _collateral) external view returns (bool, uint256) {
        return (collateralWhitelist[_collateral], IERC20(_collateral).balanceOf(address(this)));
    }

    function setCollateral(address _collateralAddress, bool _collateralEnabled) external onlyGovernance {
        if (_collateralEnabled) {
            require(IERC20Decimals(_collateralAddress).decimals() == 18);
            if (!wasCollateral[_collateralAddress]) {
                collateralTypes.push(_collateralAddress);
                wasCollateral[_collateralAddress] = true;
            }
        }
        collateralWhitelist[_collateralAddress] = _collateralEnabled;
    }

    function totalSupply() external view override returns (uint256) {
        return _totalSupply;
    }

    function decimals() external pure returns (uint8) {
        return _decimals;
    }

    function symbol() external pure returns (string memory) {
        return _symbol;
    }

    function name() external pure returns (string memory) {
        return _name;
    }

    function getOwner() external view returns (address) {
        return owner();
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function allowance(address holder, address spender) external view override returns (uint256) {
        return _allowances[holder][spender];
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        _allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function approveMax(address spender) external returns (bool) {
        return approve(spender, max256);
    }

    function transfer(address recipient, uint256 amount) external override returns (bool) {
        return _transferFrom(msg.sender, recipient, amount);
    }

    function transferFrom(address sender, address recipient, uint256 amount) external override returns (bool) {
        if (_allowances[sender][msg.sender] != max256) {
            require(_allowances[sender][msg.sender] >= amount, "Insufficient allowance");
            _allowances[sender][msg.sender] = _allowances[sender][msg.sender] - amount;
        }
        return _transferFrom(sender, recipient, amount);
    }

    function _transferFrom(address sender, address recipient, uint256 amount) internal returns (bool) {
        require(_balances[sender] >= amount, "Insufficient balance");
        _balances[sender] = _balances[sender] - amount;
        _balances[recipient] = _balances[recipient] + amount;
        emit Transfer(sender, recipient, amount);
        return true;
    }

    function rescue(address token) external onlyOwner {
        if (token == 0x0000000000000000000000000000000000000000) {
            payable(msg.sender).call{value: address(this).balance}("");
        } else {
            require(!wasCollateral[token], "Can't withdraw collateral");
            IERC20 Token = IERC20(token);
            Token.transfer(msg.sender, Token.balanceOf(address(this)));
        }
    }

    function setGovernance(address governanceContract) external {
        require(msg.sender == governance);
        governance = governanceContract;
    }

    receive() external payable {}
}

// File: lib/openzeppelin-contracts/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <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: lib/openzeppelin-contracts/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: lib/openzeppelin-contracts/contracts/utils/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () internal {
        _status = _NOT_ENTERED;
    }

    /**
     * @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() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: src/interfaces/IERC20Decimals.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.7.6;

interface IERC20Decimals {
    function decimals() external view returns (uint8);
}

// File: lib/openzeppelin-contracts/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}