// File: @openzeppelin/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: contracts/xMigration.sol

pragma solidity 0.6.2;


interface IXKNC is IERC20 {
    function mintWithToken(uint256 kncAmountTwei) external;

    function burn(
        uint256 sourceTokenBal,
        bool redeemForKnc,
        uint256 minRate
    ) external;
}

contract xMigration {
    IERC20 private knc;
    IXKNC private sourceToken;
    IXKNC private targetToken;

    uint256 constant MAX_UINT = 2**256 - 1;

    event MigrateToken(
        address indexed userAccount,
        uint256 tokenAmount,
        uint256 kncAmount
    );

    constructor(
        IXKNC _sourceToken,
        IXKNC _targetToken,
        IERC20 _knc
    ) public {
        sourceToken = _sourceToken;
        targetToken = _targetToken;
        knc = _knc;
    }

    function migrate() external {
        uint256 sourceTokenBal = sourceToken.balanceOf(msg.sender);
        require(
            sourceTokenBal > 0,
            "xMigration: sourceToken balance cant be 0"
        );

        // transfer source xKNC from user to here
        sourceToken.transferFrom(msg.sender, address(this), sourceTokenBal);

        // burn source xKNC for KNC
        sourceToken.burn(sourceTokenBal, true, 0);

        // mint target xKNC for KNC
        uint256 kncBal = knc.balanceOf(address(this));
        targetToken.mintWithToken(kncBal);

        // transfer back the target xKNC to user
        uint256 xkncBal = targetToken.balanceOf(address(this));
        targetToken.transfer(msg.sender, xkncBal);

        emit MigrateToken(msg.sender, sourceTokenBal, kncBal);
    }

    // run once before exposing to users
    function approveTarget() external {
        knc.approve(address(targetToken), MAX_UINT);
    }
}

{
  "compilationTarget": {
    "xMigration.sol": "xMigration"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}