StandardHookMetadata Library

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.8.0;

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/**
 * Format of metadata:
 *
 * [0:2] variant
 * [2:34] msg.value
 * [34:66] Gas limit for message (IGP)
 * [66:86] Refund address for message (IGP)
 * [86:] Custom metadata
 */
library StandardHookMetadata {
    struct Metadata {
        uint16 variant;
        uint256 msgValue;
        uint256 gasLimit;
        address refundAddress;
    }

    uint8 private constant VARIANT_OFFSET = 0;
    uint8 private constant MSG_VALUE_OFFSET = 2;
    uint8 private constant GAS_LIMIT_OFFSET = 34;
    uint8 private constant REFUND_ADDRESS_OFFSET = 66;
    uint256 private constant MIN_METADATA_LENGTH = 86;

    uint16 public constant VARIANT = 1;

    /**
     * @notice Returns the variant of the metadata.
     * @param _metadata ABI encoded standard hook metadata.
     * @return variant of the metadata as uint8.
     */
    function variant(bytes calldata _metadata) internal pure returns (uint16) {
        if (_metadata.length < VARIANT_OFFSET + 2) return 0;
        return uint16(bytes2(_metadata[VARIANT_OFFSET:VARIANT_OFFSET + 2]));
    }

    /**
     * @notice Returns the specified value for the message.
     * @param _metadata ABI encoded standard hook metadata.
     * @param _default Default fallback value.
     * @return Value for the message as uint256.
     */
    function msgValue(
        bytes calldata _metadata,
        uint256 _default
    ) internal pure returns (uint256) {
        if (_metadata.length < MSG_VALUE_OFFSET + 32) return _default;
        return
            uint256(bytes32(_metadata[MSG_VALUE_OFFSET:MSG_VALUE_OFFSET + 32]));
    }

    /**
     * @notice Returns the specified gas limit for the message.
     * @param _metadata ABI encoded standard hook metadata.
     * @param _default Default fallback gas limit.
     * @return Gas limit for the message as uint256.
     */
    function gasLimit(
        bytes calldata _metadata,
        uint256 _default
    ) internal pure returns (uint256) {
        if (_metadata.length < GAS_LIMIT_OFFSET + 32) return _default;
        return
            uint256(bytes32(_metadata[GAS_LIMIT_OFFSET:GAS_LIMIT_OFFSET + 32]));
    }

    /**
     * @notice Returns the specified refund address for the message.
     * @param _metadata ABI encoded standard hook metadata.
     * @param _default Default fallback refund address.
     * @return Refund address for the message as address.
     */
    function refundAddress(
        bytes calldata _metadata,
        address _default
    ) internal pure returns (address) {
        if (_metadata.length < REFUND_ADDRESS_OFFSET + 20) return _default;
        return
            address(
                bytes20(
                    _metadata[REFUND_ADDRESS_OFFSET:REFUND_ADDRESS_OFFSET + 20]
                )
            );
    }

    /**
     * @notice Returns any custom metadata.
     * @param _metadata ABI encoded standard hook metadata.
     * @return Custom metadata.
     */
    function getCustomMetadata(
        bytes calldata _metadata
    ) internal pure returns (bytes calldata) {
        if (_metadata.length < MIN_METADATA_LENGTH) return _metadata[0:0];
        return _metadata[MIN_METADATA_LENGTH:];
    }

    /**
     * @notice Formats the specified gas limit and refund address into standard hook metadata.
     * @param _msgValue msg.value for the message.
     * @param _gasLimit Gas limit for the message.
     * @param _refundAddress Refund address for the message.
     * @param _customMetadata Additional metadata to include in the standard hook metadata.
     * @return ABI encoded standard hook metadata.
     */
    function formatMetadata(
        uint256 _msgValue,
        uint256 _gasLimit,
        address _refundAddress,
        bytes memory _customMetadata
    ) internal pure returns (bytes memory) {
        return
            abi.encodePacked(
                VARIANT,
                _msgValue,
                _gasLimit,
                _refundAddress,
                _customMetadata
            );
    }

    /**
     * @notice Formats the specified gas limit and refund address into standard hook metadata.
     * @param _msgValue msg.value for the message.
     * @return ABI encoded standard hook metadata.
     */
    function overrideMsgValue(
        uint256 _msgValue
    ) internal view returns (bytes memory) {
        return formatMetadata(_msgValue, uint256(0), msg.sender, "");
    }

    /**
     * @notice Formats the specified gas limit and refund address into standard hook metadata.
     * @param _gasLimit Gas limit for the message.
     * @return ABI encoded standard hook metadata.
     */
    function overrideGasLimit(
        uint256 _gasLimit
    ) internal view returns (bytes memory) {
        return formatMetadata(uint256(0), _gasLimit, msg.sender, "");
    }

    /**
     * @notice Formats the specified refund address into standard hook metadata.
     * @param _refundAddress Refund address for the message.
     * @return ABI encoded standard hook metadata.
     */
    function overrideRefundAddress(
        address _refundAddress
    ) internal pure returns (bytes memory) {
        return formatMetadata(uint256(0), uint256(0), _refundAddress, "");
    }
}