// SPDX-License-Identifier: GPL-3.0-or-later
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity ^0.7.0;
pragma experimental ABIEncoderV2;

import "./CodeDeployer.sol";

/**
 * @dev Base factory for contracts whose creation code is so large that the factory cannot hold it. This happens when
 * the contract's creation code grows close to 24kB.
 *
 * Note that this factory cannot help with contracts that have a *runtime* (deployed) bytecode larger than 24kB.
 */
abstract contract BaseSplitCodeFactory {
    // The contract's creation code is stored as code in two separate addresses, and retrieved via `extcodecopy`. This
    // means this factory supports contracts with creation code of up to 48kB.
    // We rely on inline-assembly to achieve this, both to make the entire operation highly gas efficient, and because
    // `extcodecopy` is not available in Solidity.

    // solhint-disable no-inline-assembly

    address private immutable _creationCodeContractA;
    uint256 private immutable _creationCodeSizeA;

    address private immutable _creationCodeContractB;
    uint256 private immutable _creationCodeSizeB;

    /**
     * @dev The creation code of a contract Foo can be obtained inside Solidity with `type(Foo).creationCode`.
     */
    constructor(bytes memory creationCode) {
        uint256 creationCodeSize = creationCode.length;

        // We are going to deploy two contracts: one with approximately the first half of `creationCode`'s contents
        // (A), and another with the remaining half (B).
        // We store the lengths in both immutable and stack variables, since immutable variables cannot be read during
        // construction.
        uint256 creationCodeSizeA = creationCodeSize / 2;
        _creationCodeSizeA = creationCodeSizeA;

        uint256 creationCodeSizeB = creationCodeSize - creationCodeSizeA;
        _creationCodeSizeB = creationCodeSizeB;

        // To deploy the contracts, we're going to use `CodeDeployer.deploy()`, which expects a memory array with
        // the code to deploy. Note that we cannot simply create arrays for A and B's code by copying or moving
        // `creationCode`'s contents as they are expected to be very large (> 24kB), so we must operate in-place.

        // Memory: [ code length ] [ A.data ] [ B.data ]

        // Creating A's array is simple: we simply replace `creationCode`'s length with A's length. We'll later restore
        // the original length.

        bytes memory creationCodeA;
        assembly {
            creationCodeA := creationCode
            mstore(creationCodeA, creationCodeSizeA)
        }

        // Memory: [ A.length ] [ A.data ] [ B.data ]
        //         ^ creationCodeA

        _creationCodeContractA = CodeDeployer.deploy(creationCodeA);

        // Creating B's array is a bit more involved: since we cannot move B's contents, we are going to create a 'new'
        // memory array starting at A's last 32 bytes, which will be replaced with B's length. We'll back-up this last
        // byte to later restore it.

        bytes memory creationCodeB;
        bytes32 lastByteA;

        assembly {
            // `creationCode` points to the array's length, not data, so by adding A's length to it we arrive at A's
            // last 32 bytes.
            creationCodeB := add(creationCode, creationCodeSizeA)
            lastByteA := mload(creationCodeB)
            mstore(creationCodeB, creationCodeSizeB)
        }

        // Memory: [ A.length ] [ A.data[ : -1] ] [ B.length ][ B.data ]
        //         ^ creationCodeA                ^ creationCodeB

        _creationCodeContractB = CodeDeployer.deploy(creationCodeB);

        // We now restore the original contents of `creationCode` by writing back the original length and A's last byte.
        assembly {
            mstore(creationCodeA, creationCodeSize)
            mstore(creationCodeB, lastByteA)
        }
    }

    /**
     * @dev Returns the two addresses where the creation code of the contract crated by this factory is stored.
     */
    function getCreationCodeContracts() public view returns (address contractA, address contractB) {
        return (_creationCodeContractA, _creationCodeContractB);
    }

    /**
     * @dev Returns the creation code of the contract this factory creates.
     */
    function getCreationCode() public view returns (bytes memory) {
        return _getCreationCodeWithArgs("");
    }

    /**
     * @dev Returns the creation code that will result in a contract being deployed with `constructorArgs`.
     */
    function _getCreationCodeWithArgs(bytes memory constructorArgs) private view returns (bytes memory code) {
        // This function exists because `abi.encode()` cannot be instructed to place its result at a specific address.
        // We need for the ABI-encoded constructor arguments to be located immediately after the creation code, but
        // cannot rely on `abi.encodePacked()` to perform concatenation as that would involve copying the creation code,
        // which would be prohibitively expensive.
        // Instead, we compute the creation code in a pre-allocated array that is large enough to hold *both* the
        // creation code and the constructor arguments, and then copy the ABI-encoded arguments (which should not be
        // overly long) right after the end of the creation code.

        // Immutable variables cannot be used in assembly, so we store them in the stack first.
        address creationCodeContractA = _creationCodeContractA;
        uint256 creationCodeSizeA = _creationCodeSizeA;
        address creationCodeContractB = _creationCodeContractB;
        uint256 creationCodeSizeB = _creationCodeSizeB;

        uint256 creationCodeSize = creationCodeSizeA + creationCodeSizeB;
        uint256 constructorArgsSize = constructorArgs.length;

        uint256 codeSize = creationCodeSize + constructorArgsSize;

        assembly {
            // First, we allocate memory for `code` by retrieving the free memory pointer and then moving it ahead of
            // `code` by the size of the creation code plus constructor arguments, and 32 bytes for the array length.
            code := mload(0x40)
            mstore(0x40, add(code, add(codeSize, 32)))

            // We now store the length of the code plus constructor arguments.
            mstore(code, codeSize)

            // Next, we concatenate the creation code stored in A and B.
            let dataStart := add(code, 32)
            extcodecopy(creationCodeContractA, dataStart, 0, creationCodeSizeA)
            extcodecopy(creationCodeContractB, add(dataStart, creationCodeSizeA), 0, creationCodeSizeB)
        }

        // Finally, we copy the constructorArgs to the end of the array. Unfortunately there is no way to avoid this
        // copy, as it is not possible to tell Solidity where to store the result of `abi.encode()`.
        uint256 constructorArgsDataPtr;
        uint256 constructorArgsCodeDataPtr;
        assembly {
            constructorArgsDataPtr := add(constructorArgs, 32)
            constructorArgsCodeDataPtr := add(add(code, 32), creationCodeSize)
        }

        _memcpy(constructorArgsCodeDataPtr, constructorArgsDataPtr, constructorArgsSize);
    }

    /**
     * @dev Deploys a contract with constructor arguments. To create `constructorArgs`, call `abi.encode()` with the
     * contract's constructor arguments, in order.
     */
    function _create(bytes memory constructorArgs) internal virtual returns (address) {
        bytes memory creationCode = _getCreationCodeWithArgs(constructorArgs);

        address destination;
        assembly {
            destination := create(0, add(creationCode, 32), mload(creationCode))
        }

        if (destination == address(0)) {
            // Bubble up inner revert reason
            // solhint-disable-next-line no-inline-assembly
            assembly {
                returndatacopy(0, 0, returndatasize())
                revert(0, returndatasize())
            }
        }

        return destination;
    }

    // From
    // https://github.com/Arachnid/solidity-stringutils/blob/b9a6f6615cf18a87a823cbc461ce9e140a61c305/src/strings.sol
    function _memcpy(
        uint256 dest,
        uint256 src,
        uint256 len
    ) private pure {
        // Copy word-length chunks while possible
        for (; len >= 32; len -= 32) {
            assembly {
                mstore(dest, mload(src))
            }
            dest += 32;
            src += 32;
        }

        // Copy remaining bytes
        uint256 mask = 256**(32 - len) - 1;
        assembly {
            let srcpart := and(mload(src), not(mask))
            let destpart := and(mload(dest), mask)
            mstore(dest, or(destpart, srcpart))
        }
    }
}