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pragma solidity ^0.4.24;
import "openzeppelin-solidity/contracts/ownership/Ownable.sol";
import "chainlink/contracts/Chainlinked.sol";
@dev WolframAlpha Short Answers API Docs:
contract WolframAlphaConsumer is Chainlinked, Ownable {
// solium-disable-next-line zeppelin/no-arithmetic-operations
uint256 constant private ORACLE_PAYMENT = 1 * LINK;
string constant public BASE_URL = "";
bytes32 public jobId;
event RequestFulfilled(
bytes32 indexed requestId,
bytes32 indexed hash,
int256 distance
event WolframAlphaQuery(
string url
mapping(bytes32 => bytes32) requests;
mapping(bytes32 => int256) public distances;
constructor(address _token, address _oracle, bytes32 _jobId) public {
jobId = _jobId;
@dev Request the distance between two location in miles
@param _from The location from, eg: London
@param _to The location to, eg: Sydney
function requestDistance(string _from, string _to) public {
string memory query = string(abi.encodePacked("What's the distance between ", _from, " and ", _to, "?"));
Chainlink.Request memory req = newRequest(jobId, this, this.fulfill.selector);
req.add("query", query);
req.addInt("index", 1);
req.add("copyPath", "result");
bytes32 requestId = chainlinkRequest(req, ORACLE_PAYMENT);
requests[requestId] = keccak256(abi.encodePacked(_from, _to));
emit WolframAlphaQuery(string(abi.encodePacked(BASE_URL, query)));
function cancelRequest(
bytes32 _requestId,
uint256 _payment,
bytes4 _callbackFunctionId,
uint256 _expiration
cancelChainlinkRequest(_requestId, _payment, _callbackFunctionId, _expiration);
function fulfill(bytes32 _requestId, int256 _distance)
emit RequestFulfilled(_requestId, requests[_requestId], _distance);
distances[requests[_requestId]] = _distance;
delete requests[_requestId];
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