// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.0.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.20;

/**
 * @dev Interface of the ERC-20 standard as defined in the ERC.
 */
interface IERC20 {
    /**
     * @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);

    /**
     * @dev Returns the value of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

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

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

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "./IERC20.sol";

contract SwapDVT {
    address public owner;
    address public old_token;
    address public new_token;
    uint256 public rate;

    event Swapped(address indexed user, uint256 sent, uint256 received);

    constructor(address _old, address _new, uint256 _rate) {
        owner = msg.sender;
        old_token = _old;
        new_token = _new;
        rate = _rate == 0 ? 10: _rate;   // default value is 10.
    }

    function old_token_balance_of(address _user) public view returns (uint256) {
        return IERC20(old_token).balanceOf(_user);
    }

    function new_token_balance_of(address _user) public view returns (uint256) {
        return IERC20(new_token).balanceOf(_user);
    }

    function swap(uint256 _amount) external {
        require(_amount > rate, "Amount must be greater than rate value");
        uint256 received_amount = _amount / rate;
        IERC20(old_token).transferFrom(msg.sender, address(this), _amount);
        IERC20(new_token).transfer(msg.sender, received_amount);
        emit Swapped(msg.sender, _amount, received_amount);
    }
}

{
  "compilationTarget": {
    "contracts/SwapDVT.sol": "SwapDVT"
  },
  "evmVersion": "paris",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 800
  },
  "remappings": []
}