// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.16;

import {IAutomationRegistryConsumer} from "./interfaces/IAutomationRegistryConsumer.sol";

uint256 constant PERFORM_GAS_CUSHION = 5000;

/**
 * @title AutomationForwarder is a relayer that sits between the registry and the customer's target contract
 * @dev The purpose of the forwarder is to give customers a consistent address to authorize against,
 * which stays consistent between migrations. The Forwarder also exposes the registry address, so that users who
 * want to programatically interact with the registry (ie top up funds) can do so.
 */
contract AutomationForwarder {
  /// @notice the user's target contract address
  address private immutable i_target;

  /// @notice the shared logic address
  address private immutable i_logic;

  IAutomationRegistryConsumer private s_registry;

  constructor(address target, address registry, address logic) {
    s_registry = IAutomationRegistryConsumer(registry);
    i_target = target;
    i_logic = logic;
  }

  /**
   * @notice forward is called by the registry and forwards the call to the target
   * @param gasAmount is the amount of gas to use in the call
   * @param data is the 4 bytes function selector + arbitrary function data
   * @return success indicating whether the target call succeeded or failed
   */
  function forward(uint256 gasAmount, bytes memory data) external returns (bool success, uint256 gasUsed) {
    if (msg.sender != address(s_registry)) revert();
    address target = i_target;
    gasUsed = gasleft();
    assembly {
      let g := gas()
      // Compute g -= PERFORM_GAS_CUSHION and check for underflow
      if lt(g, PERFORM_GAS_CUSHION) { revert(0, 0) }
      g := sub(g, PERFORM_GAS_CUSHION)
      // if g - g//64 <= gasAmount, revert
      // (we subtract g//64 because of EIP-150)
      if iszero(gt(sub(g, div(g, 64)), gasAmount)) { revert(0, 0) }
      // solidity calls check that a contract actually exists at the destination, so we do the same
      if iszero(extcodesize(target)) { revert(0, 0) }
      // call with exact gas
      success := call(gasAmount, target, 0, add(data, 0x20), mload(data), 0, 0)
    }
    gasUsed = gasUsed - gasleft();
    return (success, gasUsed);
  }

  function getTarget() external view returns (address) {
    return i_target;
  }

  fallback() external {
    // copy to memory for assembly access
    address logic = i_logic;
    // copied directly from OZ's Proxy contract
    assembly {
      // Copy msg.data. We take full control of memory in this inline assembly
      // block because it will not return to Solidity code. We overwrite the
      // Solidity scratch pad at memory position 0.
      calldatacopy(0, 0, calldatasize())

      // out and outsize are 0 because we don't know the size yet.
      let result := delegatecall(gas(), logic, 0, calldatasize(), 0, 0)

      // Copy the returned data.
      returndatacopy(0, 0, returndatasize())

      switch result
      // delegatecall returns 0 on error.
      case 0 { revert(0, returndatasize()) }
      default { return(0, returndatasize()) }
    }
  }
}