// SPDX-License-Identifier: LGPL-3.0-or-later
pragma solidity ^0.7.6;

import "../interfaces/GPv2EIP1271.sol";
import "../libraries/GPv2Order.sol";
import "../libraries/GPv2Trade.sol";

/// @title Gnosis Protocol v2 Signing Library.
/// @author Gnosis Developers
abstract contract GPv2Signing {
    using GPv2Order for GPv2Order.Data;
    using GPv2Order for bytes;

    /// @dev Recovered trade data containing the extracted order and the
    /// recovered owner address.
    struct RecoveredOrder {
        GPv2Order.Data data;
        bytes uid;
        address owner;
        address receiver;
    }

    /// @dev Signing scheme used for recovery.
    enum Scheme {
        Eip712,
        EthSign,
        Eip1271,
        PreSign
    }

    /// @dev The EIP-712 domain type hash used for computing the domain
    /// separator.
    bytes32 private constant DOMAIN_TYPE_HASH =
        keccak256(
            "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
        );

    /// @dev The EIP-712 domain name used for computing the domain separator.
    bytes32 private constant DOMAIN_NAME = keccak256("Gnosis Protocol");

    /// @dev The EIP-712 domain version used for computing the domain separator.
    bytes32 private constant DOMAIN_VERSION = keccak256("v2");

    /// @dev Marker value indicating an order is pre-signed.
    uint256 private constant PRE_SIGNED =
        uint256(keccak256("GPv2Signing.Scheme.PreSign"));

    /// @dev The domain separator used for signing orders that gets mixed in
    /// making signatures for different domains incompatible. This domain
    /// separator is computed following the EIP-712 standard and has replay
    /// protection mixed in so that signed orders are only valid for specific
    /// GPv2 contracts.
    bytes32 public immutable domainSeparator;

    /// @dev Storage indicating whether or not an order has been signed by a
    /// particular address.
    mapping(bytes => uint256) public preSignature;

    /// @dev Event that is emitted when an account either pre-signs an order or
    /// revokes an existing pre-signature.
    event PreSignature(address indexed owner, bytes orderUid, bool signed);

    constructor() {
        // NOTE: Currently, the only way to get the chain ID in solidity is
        // using assembly.
        uint256 chainId;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            chainId := chainid()
        }

        domainSeparator = keccak256(
            abi.encode(
                DOMAIN_TYPE_HASH,
                DOMAIN_NAME,
                DOMAIN_VERSION,
                chainId,
                address(this)
            )
        );
    }

    /// @dev Sets a presignature for the specified order UID.
    ///
    /// @param orderUid The unique identifier of the order to pre-sign.
    function setPreSignature(bytes calldata orderUid, bool signed) external {
        (, address owner, ) = orderUid.extractOrderUidParams();
        require(owner == msg.sender, "GPv2: cannot presign order");
        if (signed) {
            preSignature[orderUid] = PRE_SIGNED;
        } else {
            preSignature[orderUid] = 0;
        }
        emit PreSignature(owner, orderUid, signed);
    }

    /// @dev Returns an empty recovered order with a pre-allocated buffer for
    /// packing the unique identifier.
    ///
    /// @return recoveredOrder The empty recovered order data.
    function allocateRecoveredOrder()
        internal
        pure
        returns (RecoveredOrder memory recoveredOrder)
    {
        recoveredOrder.uid = new bytes(GPv2Order.UID_LENGTH);
    }

    /// @dev Extracts order data and recovers the signer from the specified
    /// trade.
    ///
    /// @param recoveredOrder Memory location used for writing the recovered order data.
    /// @param tokens The list of tokens included in the settlement. The token
    /// indices in the trade parameters map to tokens in this array.
    /// @param trade The trade data to recover the order data from.
    function recoverOrderFromTrade(
        RecoveredOrder memory recoveredOrder,
        IERC20[] calldata tokens,
        GPv2Trade.Data calldata trade
    ) internal view {
        GPv2Order.Data memory order = recoveredOrder.data;

        Scheme signingScheme = GPv2Trade.extractOrder(trade, tokens, order);
        (bytes32 orderDigest, address owner) = recoverOrderSigner(
            order,
            signingScheme,
            trade.signature
        );

        recoveredOrder.uid.packOrderUidParams(
            orderDigest,
            owner,
            order.validTo
        );
        recoveredOrder.owner = owner;
        recoveredOrder.receiver = order.actualReceiver(owner);
    }

    /// @dev The length of any signature from an externally owned account.
    uint256 private constant ECDSA_SIGNATURE_LENGTH = 65;

    /// @dev Recovers an order's signer from the specified order and signature.
    ///
    /// @param order The order to recover a signature for.
    /// @param signingScheme The signing scheme.
    /// @param signature The signature bytes.
    /// @return orderDigest The computed order hash.
    /// @return owner The recovered address from the specified signature.
    function recoverOrderSigner(
        GPv2Order.Data memory order,
        Scheme signingScheme,
        bytes calldata signature
    ) internal view returns (bytes32 orderDigest, address owner) {
        orderDigest = order.hash(domainSeparator);
        if (signingScheme == Scheme.Eip712) {
            owner = recoverEip712Signer(orderDigest, signature);
        } else if (signingScheme == Scheme.EthSign) {
            owner = recoverEthsignSigner(orderDigest, signature);
        } else if (signingScheme == Scheme.Eip1271) {
            owner = recoverEip1271Signer(orderDigest, signature);
        } else {
            // signingScheme == Scheme.PreSign
            owner = recoverPreSigner(orderDigest, signature, order.validTo);
        }
    }

    /// @dev Perform an ECDSA recover for the specified message and calldata
    /// signature.
    ///
    /// The signature is encoded by tighyly packing the following struct:
    /// ```
    /// struct EncodedSignature {
    ///     bytes32 r;
    ///     bytes32 s;
    ///     uint8 v;
    /// }
    /// ```
    ///
    /// @param message The signed message.
    /// @param encodedSignature The encoded signature.
    function ecdsaRecover(bytes32 message, bytes calldata encodedSignature)
        internal
        pure
        returns (address signer)
    {
        require(
            encodedSignature.length == ECDSA_SIGNATURE_LENGTH,
            "GPv2: malformed ecdsa signature"
        );

        bytes32 r;
        bytes32 s;
        uint8 v;

        // NOTE: Use assembly to efficiently decode signature data.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // r = uint256(encodedSignature[0:32])
            r := calldataload(encodedSignature.offset)
            // s = uint256(encodedSignature[32:64])
            s := calldataload(add(encodedSignature.offset, 32))
            // v = uint8(encodedSignature[64])
            v := shr(248, calldataload(add(encodedSignature.offset, 64)))
        }

        signer = ecrecover(message, v, r, s);
        require(signer != address(0), "GPv2: invalid ecdsa signature");
    }

    /// @dev Decodes signature bytes originating from an EIP-712-encoded
    /// signature.
    ///
    /// EIP-712 signs typed data. The specifications are described in the
    /// related EIP (<https://eips.ethereum.org/EIPS/eip-712>).
    ///
    /// EIP-712 signatures are encoded as standard ECDSA signatures as described
    /// in the corresponding decoding function [`ecdsaRecover`].
    ///
    /// @param orderDigest The EIP-712 signing digest derived from the order
    /// parameters.
    /// @param encodedSignature Calldata pointing to tightly packed signature
    /// bytes.
    /// @return owner The address of the signer.
    function recoverEip712Signer(
        bytes32 orderDigest,
        bytes calldata encodedSignature
    ) internal pure returns (address owner) {
        owner = ecdsaRecover(orderDigest, encodedSignature);
    }

    /// @dev Decodes signature bytes originating from the output of the eth_sign
    /// RPC call.
    ///
    /// The specifications are described in the Ethereum documentation
    /// (<https://eth.wiki/json-rpc/API#eth_sign>).
    ///
    /// eth_sign signatures are encoded as standard ECDSA signatures as
    /// described in the corresponding decoding function
    /// [`ecdsaRecover`].
    ///
    /// @param orderDigest The EIP-712 signing digest derived from the order
    /// parameters.
    /// @param encodedSignature Calldata pointing to tightly packed signature
    /// bytes.
    /// @return owner The address of the signer.
    function recoverEthsignSigner(
        bytes32 orderDigest,
        bytes calldata encodedSignature
    ) internal pure returns (address owner) {
        // The signed message is encoded as:
        // `"\x19Ethereum Signed Message:\n" || length || data`, where
        // the length is a constant (32 bytes) and the data is defined as:
        // `orderDigest`.
        bytes32 ethsignDigest = keccak256(
            abi.encodePacked("\x19Ethereum Signed Message:\n32", orderDigest)
        );

        owner = ecdsaRecover(ethsignDigest, encodedSignature);
    }

    /// @dev Verifies the input calldata as an EIP-1271 contract signature and
    /// returns the address of the signer.
    ///
    /// The encoded signature tightly packs the following struct:
    ///
    /// ```
    /// struct EncodedEip1271Signature {
    ///     address owner;
    ///     bytes signature;
    /// }
    /// ```
    ///
    /// This function enforces that the encoded data stores enough bytes to
    /// cover the full length of the decoded signature.
    ///
    /// @param encodedSignature The encoded EIP-1271 signature.
    /// @param orderDigest The EIP-712 signing digest derived from the order
    /// parameters.
    /// @return owner The address of the signer.
    function recoverEip1271Signer(
        bytes32 orderDigest,
        bytes calldata encodedSignature
    ) internal view returns (address owner) {
        // NOTE: Use assembly to read the verifier address from the encoded
        // signature bytes.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // owner = address(encodedSignature[0:20])
            owner := shr(96, calldataload(encodedSignature.offset))
        }

        // NOTE: Configure prettier to ignore the following line as it causes
        // a panic in the Solidity plugin.
        // prettier-ignore
        bytes calldata signature = encodedSignature[20:];

        require(
            EIP1271Verifier(owner).isValidSignature(orderDigest, signature) ==
                GPv2EIP1271.MAGICVALUE,
            "GPv2: invalid eip1271 signature"
        );
    }

    /// @dev Verifies the order has been pre-signed. The signature is the
    /// address of the signer of the order.
    ///
    /// @param orderDigest The EIP-712 signing digest derived from the order
    /// parameters.
    /// @param encodedSignature The pre-sign signature reprenting the order UID.
    /// @param validTo The order expiry timestamp.
    /// @return owner The address of the signer.
    function recoverPreSigner(
        bytes32 orderDigest,
        bytes calldata encodedSignature,
        uint32 validTo
    ) internal view returns (address owner) {
        require(encodedSignature.length == 20, "GPv2: malformed presignature");
        // NOTE: Use assembly to read the owner address from the encoded
        // signature bytes.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // owner = address(encodedSignature[0:20])
            owner := shr(96, calldataload(encodedSignature.offset))
        }

        bytes memory orderUid = new bytes(GPv2Order.UID_LENGTH);
        orderUid.packOrderUidParams(orderDigest, owner, validTo);

        require(
            preSignature[orderUid] == PRE_SIGNED,
            "GPv2: order not presigned"
        );
    }
}