pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see `ERC20Detailed`.
 */
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.
     *
     * > 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);
}

contract TreasureHunt {
  bool public isActive;
  bytes32 hashedSecret;
  address DGX_TOKEN_ADDRESS;

  // this function runs when the contract is deployed
  // it initializes the contract storage
  constructor(bytes32 _hashedSecret, address _dgx_token_address) public {
    // set the hashed secret
    hashedSecret = _hashedSecret;

    // set the DGX contract address
    DGX_TOKEN_ADDRESS = _dgx_token_address;

    // set the treasure hunt as active
    isActive = true;
  }

  function unlockTreasure(bytes32 _secret) public {
    // only if this treasure hunt is active
    require(isActive, "treasure inactive");

    // make sure the keccak256 hash of the _secret
    // matches the hashedSecret
    require(keccak256(abi.encodePacked(_secret)) == hashedSecret, "incorrect secret");

    // transfer the DGX to the address
    // that called this function
    uint256 _dgxBalance = IERC20(DGX_TOKEN_ADDRESS).balanceOf(address(this));
    require(IERC20(DGX_TOKEN_ADDRESS).transfer(msg.sender, _dgxBalance), "could not transfer DGX");

    // set the treasure hunt to be inactive
    isActive = false;
  }
}