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contracts...random_gen.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/VRFConsumerBase.sol";


/**
 * THIS IS AN EXAMPLE CONTRACT WHICH USES HARDCODED VALUES FOR CLARITY.
 * PLEASE DO NOT USE THIS CODE IN PRODUCTION.
 */

/**
 * Request testnet LINK and ETH here: https://faucets.chain.link/
 * Find information on LINK Token Contracts and get the latest ETH and LINK faucets here: https://docs.chain.link/docs/link-token-contracts/
 */
 
contract RandomNumberConsumer is VRFConsumerBase {
    
    bytes32 internal keyHash;
    uint256 internal fee;
    
    // uint256 public randomResult;
    
    mapping(uint => bytes32) public mapIncrementToRequestId;
    mapping(bytes32 => uint256) public mapRequestIdToResult;
    
    uint public currentIncrement = 1;
    
    /**
     * Constructor inherits VRFConsumerBase
     * 
     * Network: Kovan
     * Chainlink VRF Coordinator address: 0xdD3782915140c8f3b190B5D67eAc6dc5760C46E9
     * LINK token address:                0xa36085F69e2889c224210F603D836748e7dC0088
     * Key Hash: 0x6c3699283bda56ad74f6b855546325b68d482e983852a7a82979cc4807b641f4
     */
    constructor() 
        VRFConsumerBase(
            0xdD3782915140c8f3b190B5D67eAc6dc5760C46E9, // VRF Coordinator
            0xa36085F69e2889c224210F603D836748e7dC0088  // LINK Token
        )
    {
        keyHash = 0x6c3699283bda56ad74f6b855546325b68d482e983852a7a82979cc4807b641f4;
        fee = 0.1 * 10 ** 18; // 0.1 LINK (Varies by network)
    }
    
    /** 
     * Requests randomness 
     */
    function getRandomNumber() public returns (bytes32 requestId) {
        require(LINK.balanceOf(address(this)) >= fee, "Not enough LINK - fill contract with faucet");
        requestId = requestRandomness(keyHash, fee);
        mapIncrementToRequestId[currentIncrement] = requestId;
        currentIncrement += 1;
        return requestId;
    }

    /**
     * Callback function used by VRF Coordinator
     */
    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override {
        mapRequestIdToResult[requestId] = randomness;
    }
    
    function withdrawLink() public {
      address chainlinkTokenAddress = 0xa36085F69e2889c224210F603D836748e7dC0088;
      LinkTokenInterface link = LinkTokenInterface(chainlinkTokenAddress);
      link.transfer(msg.sender, link.balanceOf(address(this)));
    }    
    
    function viewRawGenerateResult(uint incrementId) public view returns(uint256 random)  {
        bytes32 requestId = mapIncrementToRequestId[incrementId];
        random = mapRequestIdToResult[requestId];
        return random;
    }
    
    function viewCoinToss(uint incrementId) public view returns(string memory resultString)  {
        uint256 rawRandom = viewRawGenerateResult(incrementId);
        resultString = "TAIL";
        if (rawRandom % 2 == 0){
            resultString = "HEAD";
        }
        return resultString;
    }
    
    function viewAllCoinToss() public view returns(string memory resultString){
        resultString = "";
        for (uint i = 1; i < currentIncrement; i++) {
            string memory tmp = string(bytes.concat(bytes(resultString), "-", bytes(viewCoinToss(i))));
            resultString = tmp;
        }
        return resultString;
    }

    // function withdrawLink() external {} - Implement a withdraw function to avoid locking your LINK in the contract
}