// SPDX-License-Identifier: MIT
pragma solidity 0.8.19;

// solhint-disable gas-custom-errors
abstract contract LinkTokenReceiver {
  // @notice Called when LINK is sent to the contract via `transferAndCall`
  // @dev The data payload's first 2 words will be overwritten by the `sender` and `amount`
  // values to ensure correctness. Calls oracleRequest.
  // @param sender Address of the sender
  // @param amount Amount of LINK sent (specified in wei)
  // @param data Payload of the transaction
  function onTokenTransfer(
    address sender,
    uint256 amount,
    bytes memory data
  ) public validateFromLINK permittedFunctionsForLINK(data) {
    assembly {
      // solhint-disable-next-line avoid-low-level-calls
      mstore(add(data, 36), sender) // ensure correct sender is passed
      // solhint-disable-next-line avoid-low-level-calls
      mstore(add(data, 68), amount) // ensure correct amount is passed0.8.19
    }
    // solhint-disable-next-line avoid-low-level-calls
    (bool success,) = address(this).delegatecall(data); // calls oracleRequest
    require(success, "Unable to create request");
  }

  function getChainlinkToken() public view virtual returns (address);

  // @notice Validate the function called on token transfer
  function _validateTokenTransferAction(bytes4 funcSelector, bytes memory data) internal virtual;

  // @dev Reverts if not sent from the LINK token
  modifier validateFromLINK() {
    require(msg.sender == getChainlinkToken(), "Must use LINK token");
    _;
  }

  // @dev Reverts if the given data does not begin with the `oracleRequest` function selector
  // @param data The data payload of the request
  modifier permittedFunctionsForLINK(
    bytes memory data
  ) {
    bytes4 funcSelector;
    assembly {
      // solhint-disable-next-line avoid-low-level-calls
      funcSelector := mload(add(data, 32))
    }
    _validateTokenTransferAction(funcSelector, data);
    _;
  }
}