contract ChainlinkClient {
  using Chainlink for Chainlink.Request;
  using SafeMath for uint256;

  uint256 constant internal LINK = 10**18;
  uint256 constant private AMOUNT_OVERRIDE = 0;
  address constant private SENDER_OVERRIDE = 0x0;
  uint256 constant private ARGS_VERSION = 1;
  bytes32 constant private ENS_TOKEN_SUBNAME = keccak256("link");
  bytes32 constant private ENS_ORACLE_SUBNAME = keccak256("oracle");
  address constant private LINK_TOKEN_POINTER = 0xC89bD4E1632D3A43CB03AAAd5262cbe4038Bc571;

  ENSInterface private ens;
  bytes32 private ensNode;
  LinkTokenInterface private link;
  ChainlinkRequestInterface private oracle;
  uint256 private requests = 1;
  mapping(bytes32 => address) private pendingRequests;

  event ChainlinkRequested(bytes32 indexed id);
  event ChainlinkFulfilled(bytes32 indexed id);
  event ChainlinkCancelled(bytes32 indexed id);

  /**
   * @notice Creates a request that can hold additional parameters
   * @param _specId The Job Specification ID that the request will be created for
   * @param _callbackAddress The callback address that the response will be sent to
   * @param _callbackFunctionSignature The callback function signature to use for the callback address
   * @return A Chainlink Request struct in memory
   */
  function buildChainlinkRequest(
    bytes32 _specId,
    address _callbackAddress,
    bytes4 _callbackFunctionSignature
  ) internal pure returns (Chainlink.Request memory) {
    Chainlink.Request memory req;
    return req.initialize(_specId, _callbackAddress, _callbackFunctionSignature);
  }

  /**
   * @notice Creates a Chainlink request to the stored oracle address
   * @dev Calls `chainlinkRequestTo` with the stored oracle address
   * @param _req The initialized Chainlink Request
   * @param _payment The amount of LINK to send for the request
   * @return The request ID
   */
  function sendChainlinkRequest(Chainlink.Request memory _req, uint256 _payment)
    internal
    returns (bytes32)
  {
    return sendChainlinkRequestTo(oracle, _req, _payment);
  }

  /**
   * @notice Creates a Chainlink request to the specified oracle address
   * @dev Generates and stores a request ID, increments the local nonce, and uses `transferAndCall` to
   * send LINK which creates a request on the target oracle contract.
   * Emits ChainlinkRequested event.
   * @param _oracle The address of the oracle for the request
   * @param _req The initialized Chainlink Request
   * @param _payment The amount of LINK to send for the request
   * @return The request ID
   */
  function sendChainlinkRequestTo(address _oracle, Chainlink.Request memory _req, uint256 _payment)
    internal
    returns (bytes32 requestId)
  {
    requestId = keccak256(abi.encodePacked(this, requests));
    _req.nonce = requests;
    pendingRequests[requestId] = _oracle;
    emit ChainlinkRequested(requestId);
    require(link.transferAndCall(_oracle, _payment, encodeRequest(_req)), "unable to transferAndCall to oracle");
    requests += 1;

    return requestId;
  }

  /**
   * @notice Allows a request to be cancelled if it has not been fulfilled
   * @dev Requires keeping track of the expiration value emitted from the oracle contract.
   * Deletes the request from the `pendingRequests` mapping.
   * Emits ChainlinkCancelled event.
   * @param _requestId The request ID
   * @param _payment The amount of LINK sent for the request
   * @param _callbackFunc The callback function specified for the request
   * @param _expiration The time of the expiration for the request
   */
  function cancelChainlinkRequest(
    bytes32 _requestId,
    uint256 _payment,
    bytes4 _callbackFunc,
    uint256 _expiration
  )
    internal
  {
    ChainlinkRequestInterface requested = ChainlinkRequestInterface(pendingRequests[_requestId]);
    delete pendingRequests[_requestId];
    emit ChainlinkCancelled(_requestId);
    requested.cancelOracleRequest(_requestId, _payment, _callbackFunc, _expiration);
  }

  /**
   * @notice Sets the stored oracle address
   * @param _oracle The address of the oracle contract
   */
  function setChainlinkOracle(address _oracle) internal {
    oracle = ChainlinkRequestInterface(_oracle);
  }

  /**
   * @notice Sets the LINK token address
   * @param _link The address of the LINK token contract
   */
  function setChainlinkToken(address _link) internal {
    link = LinkTokenInterface(_link);
  }

  /**
   * @notice Sets the Chainlink token address for the public
   * network as given by the Pointer contract
   */
  function setPublicChainlinkToken() internal {
    setChainlinkToken(PointerInterface(LINK_TOKEN_POINTER).getAddress());
  }

  /**
   * @notice Retrieves the stored address of the LINK token
   * @return The address of the LINK token
   */
  function chainlinkTokenAddress()
    internal
    view
    returns (address)
  {
    return address(link);
  }

  /**
   * @notice Retrieves the stored address of the oracle contract
   * @return The address of the oracle contract
   */
  function chainlinkOracleAddress()
    internal
    view
    returns (address)
  {
    return address(oracle);
  }

  /**
   * @notice Allows for a request which was created on another contract to be fulfilled
   * on this contract
   * @param _oracle The address of the oracle contract that will fulfill the request
   * @param _requestId The request ID used for the response
   */
  function addChainlinkExternalRequest(address _oracle, bytes32 _requestId)
    internal
    notPendingRequest(_requestId)
  {
    pendingRequests[_requestId] = _oracle;
  }

  /**
   * @notice Sets the stored oracle and LINK token contracts with the addresses resolved by ENS
   * @dev Accounts for subnodes having different resolvers
   * @param _ens The address of the ENS contract
   * @param _node The ENS node hash
   */
  function useChainlinkWithENS(address _ens, bytes32 _node)
    internal
  {
    ens = ENSInterface(_ens);
    ensNode = _node;
    bytes32 linkSubnode = keccak256(abi.encodePacked(ensNode, ENS_TOKEN_SUBNAME));
    ENSResolver resolver = ENSResolver(ens.resolver(linkSubnode));
    setChainlinkToken(resolver.addr(linkSubnode));
    updateChainlinkOracleWithENS();
  }

  /**
   * @notice Sets the stored oracle contract with the address resolved by ENS
   * @dev This may be called on its own as long as `useChainlinkWithENS` has been called previously
   */
  function updateChainlinkOracleWithENS()
    internal
  {
    bytes32 oracleSubnode = keccak256(abi.encodePacked(ensNode, ENS_ORACLE_SUBNAME));
    ENSResolver resolver = ENSResolver(ens.resolver(oracleSubnode));
    setChainlinkOracle(resolver.addr(oracleSubnode));
  }

  /**
   * @notice Encodes the request to be sent to the oracle contract
   * @dev The Chainlink node expects values to be in order for the request to be picked up. Order of types
   * will be validated in the oracle contract.
   * @param _req The initialized Chainlink Request
   * @return The bytes payload for the `transferAndCall` method
   */
  function encodeRequest(Chainlink.Request memory _req)
    private
    view
    returns (bytes memory)
  {
    return abi.encodeWithSelector(
      oracle.oracleRequest.selector,
      SENDER_OVERRIDE, // Sender value - overridden by onTokenTransfer by the requesting contract's address
      AMOUNT_OVERRIDE, // Amount value - overridden by onTokenTransfer by the actual amount of LINK sent
      _req.id,
      _req.callbackAddress,
      _req.callbackFunctionId,
      _req.nonce,
      ARGS_VERSION,
      _req.buf.buf);
  }

  /**
   * @notice Ensures that the fulfillment is valid for this contract
   * @dev Use if the contract developer prefers methods instead of modifiers for validation
   * @param _requestId The request ID for fulfillment
   */
  function validateChainlinkCallback(bytes32 _requestId)
    internal
    recordChainlinkFulfillment(_requestId)
    // solhint-disable-next-line no-empty-blocks
  {}

  /**
   * @dev Reverts if the sender is not the oracle of the request.
   * Emits ChainlinkFulfilled event.
   * @param _requestId The request ID for fulfillment
   */
  modifier recordChainlinkFulfillment(bytes32 _requestId) {
    require(msg.sender == pendingRequests[_requestId], "Source must be the oracle of the request");
    delete pendingRequests[_requestId];
    emit ChainlinkFulfilled(_requestId);
    _;
  }

  /**
   * @dev Reverts if the request is already pending
   * @param _requestId The request ID for fulfillment
   */
  modifier notPendingRequest(bytes32 _requestId) {
    require(pendingRequests[_requestId] == address(0), "Request is already pending");
    _;
  }
}
/**
 * @title The ChainlinkClient contract
 * @notice Contract writers can inherit this contract in order to create requests for the
 * Chainlink network
 */
function sendChainlinkRequestTo(address _oracle, Chainlink.Request memory _req, uint256 _payment)
  internal
  returns (bytes32 requestId)
{
  requestId = keccak256(abi.encodePacked(this, requests));
  _req.nonce = requests;
  pendingRequests[requestId] = _oracle;
  emit ChainlinkRequested(requestId);
  require(link.transferAndCall(_oracle, _payment, encodeRequest(_req)), "unable to transferAndCall to oracle");
  requests += 1;

  return requestId;
}

/**
 * @notice Creates a Chainlink request to the specified oracle address
 * @dev Generates and stores a request ID, increments the local nonce, and uses `transferAndCall` to
 * send LINK which creates a request on the target oracle contract.
 * Emits ChainlinkRequested event.
 * @param _oracle The address of the oracle for the request
 * @param _req The initialized Chainlink Request
 * @param _payment The amount of LINK to send for the request
 * @return The request ID
 */