// File: /work/erc20-payment/contracts/Payment.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.4.22 <0.8.0;

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

contract Payment {
    address public owner;
    IERC20 public token;

    constructor(address tokenAddress_) public {
        owner = msg.sender;
        token = IERC20(tokenAddress_);
    }

    function pay(string memory ref, uint256 amount)
        external
        returns (bool result)
    {
        result = token.transferFrom(msg.sender, owner, amount);
        require(result, "PaymentFailed");
        emit PaymentDone(ref, msg.sender, amount, block.timestamp);
        return true;
    }

    function transferOwnership(address newOwner_) public restricted {
        owner = newOwner_;
        emit OwnerChanged(msg.sender, newOwner_);
    }

    // Modifier: Allows only
    modifier restricted() {
        require(msg.sender == owner, "Forbidden");
        _;
    }

    // Event: Fired when payment done.
    event PaymentDone(string ref, address payer, uint256 amount, uint256 date);

    // Event: Fired when owner changed.
    event OwnerChanged(address oldOwner, address newOwner);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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);
}