// File: contracts/JamEth.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;

import './UsingLiquidityProtectionService.sol';
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";


contract JamEth is ERC20, Ownable, UsingLiquidityProtectionService(0x80A703aD8f590035f2A18BD433a847694c83c069) {

    constructor(address geojamTeam) ERC20("Geojam", "JAM") Ownable() {
        transferOwnership(geojamTeam);
        _mint(owner(), 8000000000  * 1e18);
    }

    function token_transfer(address _from, address _to, uint _amount) internal override {
        _transfer(_from, _to, _amount); // Expose low-level token transfer function.
    }
    function token_balanceOf(address _holder) internal view override returns(uint) {
        return balanceOf(_holder); // Expose balance check function.
    }
    function protectionAdminCheck() internal view override onlyOwner {} // Must revert to deny access.
    function uniswapVariety() internal pure override returns(bytes32) {
        return UNISWAP; // UNISWAP / PANCAKESWAP / QUICKSWAP / SUSHISWAP.
    }
    function uniswapVersion() internal pure override returns(UniswapVersion) {
        return UniswapVersion.V2; // V2 or V3.
    }
    function uniswapFactory() internal pure override returns(address) {
        return 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f; // Replace with the correct address.
    }
    function _beforeTokenTransfer(address _from, address _to, uint _amount) internal override {
        super._beforeTokenTransfer(_from, _to, _amount);
        LiquidityProtection_beforeTokenTransfer(_from, _to, _amount);
    }
    // All the following overrides are optional, if you want to modify default behavior.

    // How the protection gets disabled.
    function protectionChecker() internal view override returns(bool) {
        return ProtectionSwitch_timestamp(1642291199); // Switch off protection on Saturday, January 15, 2022 11:59:59 PM GMT.
        // return ProtectionSwitch_block(13000000); // Switch off protection on block 13000000.
        // return ProtectionSwitch_manual(); // Switch off protection by calling disableProtection(); from owner. Default.
    }

    // This token will be pooled in pair with:
    function counterToken() internal pure override returns(address) {
        return 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2; // WETH
    }
}
// File: contracts/UsingLiquidityProtectionService.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import './external/UniswapV2Library.sol';
import './external/UniswapV3Library.sol';
import './IPLPS.sol';

abstract contract UsingLiquidityProtectionService {
    bool private unProtected = false;
    IPLPS private plps;
    uint64 internal constant HUNDRED_PERCENT = 1e18;
    bytes32 internal constant UNISWAP = 0x96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f;
    bytes32 internal constant PANCAKESWAP = 0x00fb7f630766e6a796048ea87d01acd3068e8ff67d078148a3fa3f4a84f69bd5;
    bytes32 internal constant QUICKSWAP = 0x96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f;
    bytes32 internal constant SUSHISWAP = 0xe18a34eb0e04b04f7a0ac29a6e80748dca96319b42c54d679cb821dca90c6303;

    enum UniswapVersion {
        V2,
        V3
    }

    enum UniswapV3Fees {
        _005, // 0.05%
        _03, // 0.3%
        _1 // 1%
    }

    modifier onlyProtectionAdmin() {
        protectionAdminCheck();
        _;
    }

    constructor (address _plps) {
        plps = IPLPS(_plps);
    }

    function LiquidityProtection_setLiquidityProtectionService(IPLPS _plps) external onlyProtectionAdmin() {
        require(token_balanceOf(getLiquidityPool()) == 0, 'UsingLiquidityProtectionService: liquidity already added');
        plps = _plps;
    }

    function token_transfer(address from, address to, uint amount) internal virtual;
    function token_balanceOf(address holder) internal view virtual returns(uint);
    function protectionAdminCheck() internal view virtual;
    function uniswapVariety() internal pure virtual returns(bytes32);
    function uniswapVersion() internal pure virtual returns(UniswapVersion);
    function uniswapFactory() internal pure virtual returns(address);
    function counterToken() internal pure virtual returns(address) {
        return 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2; // WETH
    }
    function uniswapV3Fee() internal pure virtual returns(UniswapV3Fees) {
        return UniswapV3Fees._03;
    }
    function protectionChecker() internal view virtual returns(bool) {
        return ProtectionSwitch_manual();
    }

    function lps() private view returns(IPLPS) {
        return plps;
    }

    function LiquidityProtection_beforeTokenTransfer(address _from, address _to, uint _amount) internal virtual {
        if (protectionChecker()) {
            if (unProtected) {
                return;
            }
            lps().LiquidityProtection_beforeTokenTransfer(getLiquidityPool(), _from, _to, _amount);
        }
    }

    function revokeBlocked(address[] calldata _holders, address _revokeTo) external onlyProtectionAdmin() {
        require(protectionChecker(), 'UsingLiquidityProtectionService: protection removed');
        bool unProtectedOld = unProtected;
        unProtected = true;
        address pool = getLiquidityPool();
        for (uint i = 0; i < _holders.length; i++) {
            address holder = _holders[i];
            if (lps().isBlocked(pool, holder)) {
                token_transfer(holder, _revokeTo, token_balanceOf(holder));
            }
        }
        unProtected = unProtectedOld;
    }

    function LiquidityProtection_unblock(address[] calldata _holders) external onlyProtectionAdmin() {
        require(protectionChecker(), 'UsingLiquidityProtectionService: protection removed');
        address pool = getLiquidityPool();
        lps().unblock(pool, _holders);
    }

    function disableProtection() external onlyProtectionAdmin() {
        unProtected = true;
    }

    function isProtected() public view returns(bool) {
        return not(unProtected);
    }

    function ProtectionSwitch_manual() internal view returns(bool) {
        return isProtected();
    }

    function ProtectionSwitch_timestamp(uint _timestamp) internal view returns(bool) {
        return not(passed(_timestamp));
    }

    function ProtectionSwitch_block(uint _block) internal view returns(bool) {
        return not(blockPassed(_block));
    }

    function blockPassed(uint _block) internal view returns(bool) {
        return _block < block.number;
    }

    function passed(uint _timestamp) internal view returns(bool) {
        return _timestamp < block.timestamp;
    }

    function not(bool _condition) internal pure returns(bool) {
        return !_condition;
    }

    function feeToUint24(UniswapV3Fees _fee) internal pure returns(uint24) {
        if (_fee == UniswapV3Fees._03) return 3000;
        if (_fee == UniswapV3Fees._005) return 500;
        return 10000;
    }

    function getLiquidityPool() public view returns(address) {
        if (uniswapVersion() == UniswapVersion.V2) {
            return UniswapV2Library.pairFor(uniswapVariety(), uniswapFactory(), address(this), counterToken());
        }
        require(uniswapVariety() == UNISWAP, 'LiquidityProtection: uniswapVariety() can only be UNISWAP for V3.');
        return UniswapV3Library.computeAddress(uniswapFactory(),
            UniswapV3Library.getPoolKey(address(this), counterToken(), feeToUint24(uniswapV3Fee())));
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * The default value of {decimals} is 18. To select a different value for
     * {decimals} you should overload it.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override 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. This is the value {ERC20} uses, unless this function is
     * overridden;
     *
     * 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 virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, _msgSender(), currentAllowance - amount);
        }

        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(_msgSender(), spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `sender` to `recipient`.
     *
     * This internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;

        emit Transfer(sender, recipient, amount);

        _afterTokenTransfer(sender, recipient, 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:
     *
     * - `account` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(address(0), 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 virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        _totalSupply -= amount;

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^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() {
        _setOwner(_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 {
        _setOwner(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");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: contracts/external/UniswapV2Library.sol



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

// Exempt from the original UniswapV2Library.
library UniswapV2Library {
    // returns sorted token addresses, used to handle return values from pairs sorted in this order
    function sortTokens(address tokenA, address tokenB) internal pure returns (address token0, address token1) {
        require(tokenA != tokenB, 'UniswapV2Library: IDENTICAL_ADDRESSES');
        (token0, token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
        require(token0 != address(0), 'UniswapV2Library: ZERO_ADDRESS');
    }

    // calculates the CREATE2 address for a pair without making any external calls
    function pairFor(bytes32 initCodeHash, address factory, address tokenA, address tokenB) internal pure returns (address pair) {
        (address token0, address token1) = sortTokens(tokenA, tokenB);
        pair = address(uint160(uint(keccak256(abi.encodePacked(
                hex'ff',
                factory,
                keccak256(abi.encodePacked(token0, token1)),
                initCodeHash // init code hash
            )))));
    }
}

// File: contracts/external/UniswapV3Library.sol



// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity ^0.8.0;

/// @notice based on https://github.com/Uniswap/uniswap-v3-periphery/blob/v1.0.0/contracts/libraries/PoolAddress.sol
/// @notice changed compiler version and lib name.

/// @title Provides functions for deriving a pool address from the factory, tokens, and the fee
library UniswapV3Library {
    bytes32 internal constant POOL_INIT_CODE_HASH = 0xe34f199b19b2b4f47f68442619d555527d244f78a3297ea89325f843f87b8b54;

    /// @notice The identifying key of the pool
    struct PoolKey {
        address token0;
        address token1;
        uint24 fee;
    }

    /// @notice Returns PoolKey: the ordered tokens with the matched fee levels
    /// @param tokenA The first token of a pool, unsorted
    /// @param tokenB The second token of a pool, unsorted
    /// @param fee The fee level of the pool
    /// @return Poolkey The pool details with ordered token0 and token1 assignments
    function getPoolKey(
        address tokenA,
        address tokenB,
        uint24 fee
    ) internal pure returns (PoolKey memory) {
        if (tokenA > tokenB) (tokenA, tokenB) = (tokenB, tokenA);
        return PoolKey({token0: tokenA, token1: tokenB, fee: fee});
    }

    /// @notice Deterministically computes the pool address given the factory and PoolKey
    /// @param factory The Uniswap V3 factory contract address
    /// @param key The PoolKey
    /// @return pool The contract address of the V3 pool
    function computeAddress(address factory, PoolKey memory key) internal pure returns (address pool) {
        require(key.token0 < key.token1);
        pool = address(
            uint160(
                uint256(
                    keccak256(
                        abi.encodePacked(
                            hex'ff',
                            factory,
                            keccak256(abi.encode(key.token0, key.token1, key.fee)),
                            POOL_INIT_CODE_HASH
                        )
                    )
                )
            )
        );
    }
}

// File: contracts/IPLPS.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IPLPS {
    function LiquidityProtection_beforeTokenTransfer(
        address _pool, address _from, address _to, uint _amount) external;
    function isBlocked(address _pool, address _who) external view returns(bool);
    function unblock(address pool, address[] calldata whos) external;
}

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



// SPDX-License-Identifier: MIT

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/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^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 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}