contract Spawner {
  
  /// @notice Internal function for spawning an eip-1167 minimal proxy using `CREATE2`.
  /// @param creator address The address of the account creating the proxy.
  /// @param logicContract address The address of the logic contract.
  /// @param initializationCalldata bytes The calldata that will be supplied to
  /// the `DELEGATECALL` from the spawned contract to the logic contract during
  /// contract creation.
  /// @return The address of the newly-spawned contract.
  function _spawn(
    address creator,
    address logicContract,
    bytes memory initializationCalldata
  ) internal returns (address spawnedContract) {

    // get instance code and hash

    bytes memory initCode;
    bytes32 initCodeHash;
    (initCode, initCodeHash) = _getInitCodeAndHash(logicContract, initializationCalldata);

    // get valid create2 target

    (address target, bytes32 safeSalt) = _getNextNonceTargetWithInitCodeHash(creator, initCodeHash);

    // spawn create2 instance and validate

    return _executeSpawnCreate2(initCode, safeSalt, target);
  }

  /// @notice Internal function for spawning an eip-1167 minimal proxy using `CREATE2`.
  /// @param creator address The address of the account creating the proxy.
  /// @param logicContract address The address of the logic contract.
  /// @param initializationCalldata bytes The calldata that will be supplied to
  /// the `DELEGATECALL` from the spawned contract to the logic contract during
  /// contract creation.
  /// @param salt bytes32 A user defined salt.
  /// @return The address of the newly-spawned contract.
  function _spawnSalty(
    address creator,
    address logicContract,
    bytes memory initializationCalldata,
    bytes32 salt
  ) internal returns (address spawnedContract) {

    // get instance code and hash

    bytes memory initCode;
    bytes32 initCodeHash;
    (initCode, initCodeHash) = _getInitCodeAndHash(logicContract, initializationCalldata);

    // get valid create2 target

    (address target, bytes32 safeSalt, bool validity) = _getSaltyTargetWithInitCodeHash(creator, initCodeHash, salt);
    require(validity, "contract already deployed with supplied salt");

    // spawn create2 instance and validate

    return _executeSpawnCreate2(initCode, safeSalt, target);
  }

  /// @notice Private function for spawning an eip-1167 minimal proxy using `CREATE2`.
  /// Reverts with appropriate error string if deployment is unsuccessful.
  /// @param initCode bytes The spawner code and initialization calldata.
  /// @param safeSalt bytes32 A valid salt hashed with creator address.
  /// @param target address The expected address of the proxy.
  /// @return The address of the newly-spawned contract.
  function _executeSpawnCreate2(bytes memory initCode, bytes32 safeSalt, address target) private returns (address spawnedContract) {
    assembly {
      let encoded_data := add(0x20, initCode) // load initialization code.
      let encoded_size := mload(initCode)     // load the init code's length.
      spawnedContract := create2(             // call `CREATE2` w/ 4 arguments.
        callvalue,                            // forward any supplied endowment.
        encoded_data,                         // pass in initialization code.
        encoded_size,                         // pass in init code's length.
        safeSalt                              // pass in the salt value.
      )

      // pass along failure message from failed contract deployment and revert.
      if iszero(spawnedContract) {
        returndatacopy(0, 0, returndatasize)
        revert(0, returndatasize)
      }
    }

    // validate spawned instance matches target
    require(spawnedContract == target, "attempted deployment to unexpected address");

    // explicit return
    return spawnedContract;
  }

  /// @notice Internal view function for finding the expected address of the standard
  /// eip-1167 minimal proxy created using `CREATE2` with a given logic contract,
  /// salt, and initialization calldata payload.
  /// @param creator address The address of the account creating the proxy.
  /// @param logicContract address The address of the logic contract.
  /// @param initializationCalldata bytes The calldata that will be supplied to
  /// the `DELEGATECALL` from the spawned contract to the logic contract during
  /// contract creation.
  /// @param salt bytes32 A user defined salt.
  /// @return target address The address of the newly-spawned contract.
  /// @return validity bool True if the `target` is available.
  function _getSaltyTarget(
    address creator,
    address logicContract,
    bytes memory initializationCalldata,
    bytes32 salt
  ) internal view returns (address target, bool validity) {

    // get initialization code

    bytes32 initCodeHash;
    ( , initCodeHash) = _getInitCodeAndHash(logicContract, initializationCalldata);

    // get valid target

    (target, , validity) = _getSaltyTargetWithInitCodeHash(creator, initCodeHash, salt);

    // explicit return
    return (target, validity);
  }

  /// @notice Internal view function for finding the expected address of the standard
  /// eip-1167 minimal proxy created using `CREATE2` with a given initCodeHash, and salt.
  /// @param creator address The address of the account creating the proxy.
  /// @param initCodeHash bytes32 The hash of initCode.
  /// @param salt bytes32 A user defined salt.
  /// @return target address The address of the newly-spawned contract.
  /// @return safeSalt bytes32 A safe salt. Must include the msg.sender address for front-running protection.
  /// @return validity bool True if the `target` is available.
  function _getSaltyTargetWithInitCodeHash(
    address creator,
    bytes32 initCodeHash,
    bytes32 salt
  ) private view returns (address target, bytes32 safeSalt, bool validity) {
    // get safeSalt from input
    safeSalt = keccak256(abi.encodePacked(creator, salt));

    // get expected target
    target = _computeTargetWithCodeHash(initCodeHash, safeSalt);

    // get target validity
    validity = _getTargetValidity(target);

    // explicit return
    return (target, safeSalt, validity);
  }

  /// @notice Internal view function for finding the expected address of the standard
  /// eip-1167 minimal proxy created using `CREATE2` with a given logic contract,
  /// nonce, and initialization calldata payload.
  /// @param creator address The address of the account creating the proxy.
  /// @param logicContract address The address of the logic contract.
  /// @param initializationCalldata bytes The calldata that will be supplied to
  /// the `DELEGATECALL` from the spawned contract to the logic contract during
  /// contract creation.
  /// @return target address The address of the newly-spawned contract.
  function _getNextNonceTarget(
    address creator,
    address logicContract,
    bytes memory initializationCalldata
  ) internal view returns (address target) {

    // get initialization code

    bytes32 initCodeHash;
    ( , initCodeHash) = _getInitCodeAndHash(logicContract, initializationCalldata);

    // get valid target

    (target, ) = _getNextNonceTargetWithInitCodeHash(creator, initCodeHash);

    // explicit return
    return target;
  }

  /// @notice Internal view function for finding the expected address of the standard
  /// eip-1167 minimal proxy created using `CREATE2` with a given initCodeHash, and nonce.
  /// @param creator address The address of the account creating the proxy.
  /// @param initCodeHash bytes32 The hash of initCode.
  /// @return target address The address of the newly-spawned contract.
  /// @return safeSalt bytes32 A safe salt. Must include the msg.sender address for front-running protection.
  function _getNextNonceTargetWithInitCodeHash(
    address creator,
    bytes32 initCodeHash
  ) private view returns (address target, bytes32 safeSalt) {
    // set the initial nonce to be provided when constructing the salt.
    uint256 nonce = 0;

    while (true) {
      // get safeSalt from nonce
      safeSalt = keccak256(abi.encodePacked(creator, nonce));

      // get expected target
      target = _computeTargetWithCodeHash(initCodeHash, safeSalt);

      // validate no contract already deployed to the target address.
      // exit the loop if no contract is deployed to the target address.
      // otherwise, increment the nonce and derive a new salt.
      if (_getTargetValidity(target))
        break;
      else
        nonce++;
    }
    
    // explicit return
    return (target, safeSalt);
  }

  /// @notice Private pure function for obtaining the initCode and the initCodeHash of `logicContract` and `initializationCalldata`.
  /// @param logicContract address The address of the logic contract.
  /// @param initializationCalldata bytes The calldata that will be supplied to
  /// the `DELEGATECALL` from the spawned contract to the logic contract during
  /// contract creation.
  /// @return initCode bytes The spawner code and initialization calldata.
  /// @return initCodeHash bytes32 The hash of initCode.
  function _getInitCodeAndHash(
    address logicContract,
    bytes memory initializationCalldata
  ) private pure returns (bytes memory initCode, bytes32 initCodeHash) {
    // place creation code and constructor args of contract to spawn in memory.
    initCode = abi.encodePacked(
      type(Spawn).creationCode,
      abi.encode(logicContract, initializationCalldata)
    );

    // get the keccak256 hash of the init code for address derivation.
    initCodeHash = keccak256(initCode);

    // explicit return
    return (initCode, initCodeHash);
  }
  
  /// @notice Private view function for finding the expected address of the standard
  /// eip-1167 minimal proxy created using `CREATE2` with a given logic contract,
  /// salt, and initialization calldata payload.
  /// @param initCodeHash bytes32 The hash of initCode.
  /// @param safeSalt bytes32 A safe salt. Must include the msg.sender address for front-running protection.
  /// @return The address of the proxy contract with the given parameters.
  function _computeTargetWithCodeHash(
    bytes32 initCodeHash,
    bytes32 safeSalt
  ) private view returns (address target) {
    return address(    // derive the target deployment address.
      uint160(                   // downcast to match the address type.
        uint256(                 // cast to uint to truncate upper digits.
          keccak256(             // compute CREATE2 hash using 4 inputs.
            abi.encodePacked(    // pack all inputs to the hash together.
              bytes1(0xff),      // pass in the control character.
              address(this),     // pass in the address of this contract.
              safeSalt,          // pass in the safeSalt from above.
              initCodeHash       // pass in hash of contract creation code.
            )
          )
        )
      )
    );
  }

  /// @notice Private view function to validate if the `target` address is an available deployment address.
  /// @param target address The address to validate.
  /// @return validity bool True if the `target` is available.
  function _getTargetValidity(address target) private view returns (bool validity) {
    // validate no contract already deployed to the target address.
    uint256 codeSize;
    assembly { codeSize := extcodesize(target) }
    return codeSize == 0;
  }
}
/// @title Spawner
/// @author 0age (@0age) and Stephane Gosselin (@thegostep) for Numerai Inc
/// @dev Security contact: security@numer.ai
/// @dev Version: 1.2.0
/// @notice This contract spawns and initializes eip-1167 minimal proxies that
/// point to existing logic contracts. The logic contracts need to have an
/// initializer function that should only callable when no contract exists at
/// their current address (i.e. it is being `DELEGATECALL`ed from a constructor).
function _executeSpawnCreate2(bytes memory initCode, bytes32 safeSalt, address target) private returns (address spawnedContract) {
  assembly {
    let encoded_data := add(0x20, initCode) // load initialization code.
    let encoded_size := mload(initCode)     // load the init code's length.
    spawnedContract := create2(             // call `CREATE2` w/ 4 arguments.
      callvalue,                            // forward any supplied endowment.
      encoded_data,                         // pass in initialization code.
      encoded_size,                         // pass in init code's length.
      safeSalt                              // pass in the salt value.
    )

    // pass along failure message from failed contract deployment and revert.
    if iszero(spawnedContract) {
      returndatacopy(0, 0, returndatasize)
      revert(0, returndatasize)
    }
  }

  // validate spawned instance matches target
  require(spawnedContract == target, "attempted deployment to unexpected address");

  // explicit return
  return spawnedContract;
}

/// @notice Private function for spawning an eip-1167 minimal proxy using `CREATE2`.
/// Reverts with appropriate error string if deployment is unsuccessful.
/// @param initCode bytes The spawner code and initialization calldata.
/// @param safeSalt bytes32 A valid salt hashed with creator address.
/// @param target address The expected address of the proxy.
/// @return The address of the newly-spawned contract.