ERC721.sol

// SPDX-License-Identifier: MIT
// taken from https://github.com/Vectorized/solady/commit/496b9aceb690f2681648f43929f632b8403bfd7f

pragma solidity ^0.8.4;

/// @notice Simple ERC721 implementation with storage hitchhiking.
/// @author Solady (https://github.com/vectorized/solady/blob/main/src/tokens/ERC721.sol)
/// @author Modified from Solmate (https://github.com/transmissions11/solmate/blob/main/src/tokens/ERC721.sol)
/// @author Modified from OpenZeppelin (https://github.com/OpenZeppelin/openzeppelin-contracts/tree/master/contracts/token/ERC721/ERC721.sol)
///
/// @dev Note:
/// - The ERC721 standard allows for self-approvals.
///   For performance, this implementation WILL NOT revert for such actions.
///   Please add any checks with overrides if desired.
/// - For performance, methods are made payable where permitted by the ERC721 standard.
/// - The `safeTransfer` functions use the identity precompile (0x4)
///   to copy memory internally.
///
/// If you are overriding:
/// - NEVER violate the ERC721 invariant:
///   the balance of an owner MUST always be equal to their number of ownership slots.
///   The transfer functions do not have an underflow guard for user token balances.
/// - Make sure all variables written to storage are properly cleaned
//    (e.g. the bool value for `isApprovedForAll` MUST be either 1 or 0 under the hood).
/// - Check that the overridden function is actually used in the function you want to
///   change the behavior of. Much of the code has been manually inlined for performance.
abstract contract ERC721 {
    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                         CONSTANTS                          */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev An account can hold up to 4294967295 tokens.
    uint256 internal constant _MAX_ACCOUNT_BALANCE = 0xffffffff;

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                       CUSTOM ERRORS                        */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Only the token owner or an approved account can manage the token.
    error NotOwnerNorApproved();

    /// @dev The token does not exist.
    error TokenDoesNotExist();

    /// @dev The token already exists.
    error TokenAlreadyExists();

    /// @dev Cannot query the balance for the zero address.
    error BalanceQueryForZeroAddress();

    /// @dev Cannot mint or transfer to the zero address.
    error TransferToZeroAddress();

    /// @dev The token must be owned by `from`.
    error TransferFromIncorrectOwner();

    /// @dev The recipient's balance has overflowed.
    error AccountBalanceOverflow();

    /// @dev Cannot safely transfer to a contract that does not implement
    /// the ERC721Receiver interface.
    error TransferToNonERC721ReceiverImplementer();

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                           EVENTS                           */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Emitted when token `id` is transferred from `from` to `to`.
    event Transfer(address indexed from, address indexed to, uint256 indexed id);

    /// @dev Emitted when `owner` enables `account` to manage the `id` token.
    event Approval(address indexed owner, address indexed account, uint256 indexed id);

    /// @dev Emitted when `owner` enables or disables `operator` to manage all of their tokens.
    event ApprovalForAll(address indexed owner, address indexed operator, bool isApproved);

    /// @dev `keccak256(bytes("Transfer(address,address,uint256)"))`.
    uint256 private constant _TRANSFER_EVENT_SIGNATURE =
        0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;

    /// @dev `keccak256(bytes("Approval(address,address,uint256)"))`.
    uint256 private constant _APPROVAL_EVENT_SIGNATURE =
        0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925;

    /// @dev `keccak256(bytes("ApprovalForAll(address,address,bool)"))`.
    uint256 private constant _APPROVAL_FOR_ALL_EVENT_SIGNATURE =
        0x17307eab39ab6107e8899845ad3d59bd9653f200f220920489ca2b5937696c31;

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                          STORAGE                           */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev The ownership data slot of `id` is given by:
    /// ```
    ///     mstore(0x00, id)
    ///     mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
    ///     let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
    /// ```
    /// Bits Layout:
    /// - [0..159]   `addr`
    /// - [160..255] `extraData`
    ///
    /// The approved address slot is given by: `add(1, ownershipSlot)`.
    ///
    /// See: https://notes.ethereum.org/%40vbuterin/verkle_tree_eip
    ///
    /// The balance slot of `owner` is given by:
    /// ```
    ///     mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
    ///     mstore(0x00, owner)
    ///     let balanceSlot := keccak256(0x0c, 0x1c)
    /// ```
    /// Bits Layout:
    /// - [0..31]   `balance`
    /// - [32..255] `aux`
    ///
    /// The `operator` approval slot of `owner` is given by:
    /// ```
    ///     mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, operator))
    ///     mstore(0x00, owner)
    ///     let operatorApprovalSlot := keccak256(0x0c, 0x30)
    /// ```
    uint256 private constant _ERC721_MASTER_SLOT_SEED = 0x7d8825530a5a2e7a << 192;

    /// @dev Pre-shifted and pre-masked constant.
    uint256 private constant _ERC721_MASTER_SLOT_SEED_MASKED = 0x0a5a2e7a00000000;

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                      ERC721 METADATA                       */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Returns the token collection name.
    function name() public view virtual returns (string memory);

    /// @dev Returns the token collection symbol.
    function symbol() public view virtual returns (string memory);

    /// @dev Returns the Uniform Resource Identifier (URI) for token `id`.
    function tokenURI(uint256 id) public view virtual returns (string memory);

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                           ERC721                           */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Returns the owner of token `id`.
    ///
    /// Requirements:
    /// - Token `id` must exist.
    function ownerOf(uint256 id) public view virtual returns (address result) {
        result = _ownerOf(id);
        /// @solidity memory-safe-assembly
        assembly {
            if iszero(result) {
                mstore(0x00, 0xceea21b6) // `TokenDoesNotExist()`.
                revert(0x1c, 0x04)
            }
        }
    }

    /// @dev Returns the number of tokens owned by `owner`.
    ///
    /// Requirements:
    /// - `owner` must not be the zero address.
    function balanceOf(address owner) public view virtual returns (uint256 result) {
        /// @solidity memory-safe-assembly
        assembly {
            // Revert if the `owner` is the zero address.
            if iszero(owner) {
                mstore(0x00, 0x8f4eb604) // `BalanceQueryForZeroAddress()`.
                revert(0x1c, 0x04)
            }
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            mstore(0x00, owner)
            result := and(sload(keccak256(0x0c, 0x1c)), _MAX_ACCOUNT_BALANCE)
        }
    }

    /// @dev Returns the account approved to manage token `id`.
    ///
    /// Requirements:
    /// - Token `id` must exist.
    function getApproved(uint256 id) public view virtual returns (address result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            if iszero(shl(96, sload(ownershipSlot))) {
                mstore(0x00, 0xceea21b6) // `TokenDoesNotExist()`.
                revert(0x1c, 0x04)
            }
            result := sload(add(1, ownershipSlot))
        }
    }

    /// @dev Sets `account` as the approved account to manage token `id`.
    ///
    /// Requirements:
    /// - Token `id` must exist.
    /// - The caller must be the owner of the token,
    ///   or an approved operator for the token owner.
    ///
    /// Emits an {Approval} event.
    function approve(address account, uint256 id) public payable virtual {
        _approve(msg.sender, account, id);
    }

    /// @dev Returns whether `operator` is approved to manage the tokens of `owner`.
    function isApprovedForAll(address owner, address operator)
        public
        view
        virtual
        returns (bool result)
    {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x1c, operator)
            mstore(0x08, _ERC721_MASTER_SLOT_SEED_MASKED)
            mstore(0x00, owner)
            result := sload(keccak256(0x0c, 0x30))
        }
    }

    /// @dev Sets whether `operator` is approved to manage the tokens of the caller.
    ///
    /// Emits an {ApprovalForAll} event.
    function setApprovalForAll(address operator, bool isApproved) public virtual {
        /// @solidity memory-safe-assembly
        assembly {
            // Convert to 0 or 1.
            isApproved := iszero(iszero(isApproved))
            // Update the `isApproved` for (`msg.sender`, `operator`).
            mstore(0x1c, operator)
            mstore(0x08, _ERC721_MASTER_SLOT_SEED_MASKED)
            mstore(0x00, caller())
            sstore(keccak256(0x0c, 0x30), isApproved)
            // Emit the {ApprovalForAll} event.
            mstore(0x00, isApproved)
            // forgefmt: disable-next-item
            log3(0x00, 0x20, _APPROVAL_FOR_ALL_EVENT_SIGNATURE, caller(), shr(96, shl(96, operator)))
        }
    }

    /// @dev Transfers token `id` from `from` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - `from` must be the owner of the token.
    /// - `to` cannot be the zero address.
    /// - The caller must be the owner of the token, or be approved to manage the token.
    ///
    /// Emits a {Transfer} event.
    function transferFrom(address from, address to, uint256 id) public payable virtual {
        _beforeTokenTransfer(from, to, id);
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            let bitmaskAddress := shr(96, not(0))
            from := and(bitmaskAddress, from)
            to := and(bitmaskAddress, to)
            // Load the ownership data.
            mstore(0x00, id)
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, caller()))
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let ownershipPacked := sload(ownershipSlot)
            let owner := and(bitmaskAddress, ownershipPacked)
            // Revert if the token does not exist, or if `from` is not the owner.
            if iszero(mul(owner, eq(owner, from))) {
                // `TokenDoesNotExist()`, `TransferFromIncorrectOwner()`.
                mstore(shl(2, iszero(owner)), 0xceea21b6a1148100)
                revert(0x1c, 0x04)
            }
            // Load, check, and update the token approval.
            {
                mstore(0x00, from)
                let approvedAddress := sload(add(1, ownershipSlot))
                // Revert if the caller is not the owner, nor approved.
                if iszero(or(eq(caller(), from), eq(caller(), approvedAddress))) {
                    if iszero(sload(keccak256(0x0c, 0x30))) {
                        mstore(0x00, 0x4b6e7f18) // `NotOwnerNorApproved()`.
                        revert(0x1c, 0x04)
                    }
                }
                // Delete the approved address if any.
                if approvedAddress { sstore(add(1, ownershipSlot), 0) }
            }
            // Update with the new owner.
            sstore(ownershipSlot, xor(ownershipPacked, xor(from, to)))
            // Decrement the balance of `from`.
            {
                let fromBalanceSlot := keccak256(0x0c, 0x1c)
                sstore(fromBalanceSlot, sub(sload(fromBalanceSlot), 1))
            }
            // Increment the balance of `to`.
            {
                mstore(0x00, to)
                let toBalanceSlot := keccak256(0x0c, 0x1c)
                let toBalanceSlotPacked := add(sload(toBalanceSlot), 1)
                // Revert if `to` is the zero address, or if the account balance overflows.
                if iszero(mul(to, and(toBalanceSlotPacked, _MAX_ACCOUNT_BALANCE))) {
                    // `TransferToZeroAddress()`, `AccountBalanceOverflow()`.
                    mstore(shl(2, iszero(to)), 0xea553b3401336cea)
                    revert(0x1c, 0x04)
                }
                sstore(toBalanceSlot, toBalanceSlotPacked)
            }
            // Emit the {Transfer} event.
            log4(codesize(), 0x00, _TRANSFER_EVENT_SIGNATURE, from, to, id)
        }
        _afterTokenTransfer(from, to, id);
    }

    /// @dev Equivalent to `safeTransferFrom(from, to, id, "")`.
    function safeTransferFrom(address from, address to, uint256 id) public payable virtual {
        transferFrom(from, to, id);
        if (_hasCode(to)) _checkOnERC721Received(from, to, id, "");
    }

    /// @dev Transfers token `id` from `from` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - `from` must be the owner of the token.
    /// - `to` cannot be the zero address.
    /// - The caller must be the owner of the token, or be approved to manage the token.
    /// - If `to` refers to a smart contract, it must implement
    ///   {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
    ///
    /// Emits a {Transfer} event.
    function safeTransferFrom(address from, address to, uint256 id, bytes calldata data)
        public
        payable
        virtual
    {
        transferFrom(from, to, id);
        if (_hasCode(to)) _checkOnERC721Received(from, to, id, data);
    }

    /// @dev Returns true if this contract implements the interface defined by `interfaceId`.
    /// See: https://eips.ethereum.org/EIPS/eip-165
    /// This function call must use less than 30000 gas.
    function supportsInterface(bytes4 interfaceId) public view virtual returns (bool result) {
        /// @solidity memory-safe-assembly
        assembly {
            let s := shr(224, interfaceId)
            // ERC165: 0x01ffc9a7, ERC721: 0x80ac58cd, ERC721Metadata: 0x5b5e139f.
            result := or(or(eq(s, 0x01ffc9a7), eq(s, 0x80ac58cd)), eq(s, 0x5b5e139f))
        }
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                  INTERNAL QUERY FUNCTIONS                  */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Returns if token `id` exists.
    function _exists(uint256 id) internal view virtual returns (bool result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            result := iszero(iszero(shl(96, sload(add(id, add(id, keccak256(0x00, 0x20)))))))
        }
    }

    /// @dev Returns the owner of token `id`.
    /// Returns the zero address instead of reverting if the token does not exist.
    function _ownerOf(uint256 id) internal view virtual returns (address result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            result := shr(96, shl(96, sload(add(id, add(id, keccak256(0x00, 0x20))))))
        }
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*            INTERNAL DATA HITCHHIKING FUNCTIONS             */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    // For performance, no events are emitted for the hitchhiking setters.
    // Please emit your own events if required.

    /// @dev Returns the auxiliary data for `owner`.
    /// Minting, transferring, burning the tokens of `owner` will not change the auxiliary data.
    /// Auxiliary data can be set for any address, even if it does not have any tokens.
    function _getAux(address owner) internal view virtual returns (uint224 result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            mstore(0x00, owner)
            result := shr(32, sload(keccak256(0x0c, 0x1c)))
        }
    }

    /// @dev Set the auxiliary data for `owner` to `value`.
    /// Minting, transferring, burning the tokens of `owner` will not change the auxiliary data.
    /// Auxiliary data can be set for any address, even if it does not have any tokens.
    function _setAux(address owner, uint224 value) internal virtual {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            mstore(0x00, owner)
            let balanceSlot := keccak256(0x0c, 0x1c)
            let packed := sload(balanceSlot)
            sstore(balanceSlot, xor(packed, shl(32, xor(value, shr(32, packed)))))
        }
    }

    /// @dev Returns the extra data for token `id`.
    /// Minting, transferring, burning a token will not change the extra data.
    /// The extra data can be set on a non-existent token.
    function _getExtraData(uint256 id) internal view virtual returns (uint96 result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            result := shr(160, sload(add(id, add(id, keccak256(0x00, 0x20)))))
        }
    }

    /// @dev Sets the extra data for token `id` to `value`.
    /// Minting, transferring, burning a token will not change the extra data.
    /// The extra data can be set on a non-existent token.
    function _setExtraData(uint256 id, uint96 value) internal virtual {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let packed := sload(ownershipSlot)
            sstore(ownershipSlot, xor(packed, shl(160, xor(value, shr(160, packed)))))
        }
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                  INTERNAL MINT FUNCTIONS                   */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Mints token `id` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must not exist.
    /// - `to` cannot be the zero address.
    ///
    /// Emits a {Transfer} event.
    function _mint(address to, uint256 id) internal virtual {
        _beforeTokenTransfer(address(0), to, id);
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            to := shr(96, shl(96, to))
            // Load the ownership data.
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let ownershipPacked := sload(ownershipSlot)
            // Revert if the token already exists.
            if shl(96, ownershipPacked) {
                mstore(0x00, 0xc991cbb1) // `TokenAlreadyExists()`.
                revert(0x1c, 0x04)
            }
            // Update with the owner.
            sstore(ownershipSlot, or(ownershipPacked, to))
            // Increment the balance of the owner.
            {
                mstore(0x00, to)
                let balanceSlot := keccak256(0x0c, 0x1c)
                let balanceSlotPacked := add(sload(balanceSlot), 1)
                // Revert if `to` is the zero address, or if the account balance overflows.
                if iszero(mul(to, and(balanceSlotPacked, _MAX_ACCOUNT_BALANCE))) {
                    // `TransferToZeroAddress()`, `AccountBalanceOverflow()`.
                    mstore(shl(2, iszero(to)), 0xea553b3401336cea)
                    revert(0x1c, 0x04)
                }
                sstore(balanceSlot, balanceSlotPacked)
            }
            // Emit the {Transfer} event.
            log4(codesize(), 0x00, _TRANSFER_EVENT_SIGNATURE, 0, to, id)
        }
        _afterTokenTransfer(address(0), to, id);
    }

    /// @dev Mints token `id` to `to`, and updates the extra data for token `id` to `value`.
    /// Does NOT check if token `id` already exists (assumes `id` is auto-incrementing).
    ///
    /// Requirements:
    ///
    /// - `to` cannot be the zero address.
    ///
    /// Emits a {Transfer} event.
    function _mintAndSetExtraDataUnchecked(address to, uint256 id, uint96 value) internal virtual {
        _beforeTokenTransfer(address(0), to, id);
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            to := shr(96, shl(96, to))
            // Update with the owner and extra data.
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            sstore(add(id, add(id, keccak256(0x00, 0x20))), or(shl(160, value), to))
            // Increment the balance of the owner.
            {
                mstore(0x00, to)
                let balanceSlot := keccak256(0x0c, 0x1c)
                let balanceSlotPacked := add(sload(balanceSlot), 1)
                // Revert if `to` is the zero address, or if the account balance overflows.
                if iszero(mul(to, and(balanceSlotPacked, _MAX_ACCOUNT_BALANCE))) {
                    // `TransferToZeroAddress()`, `AccountBalanceOverflow()`.
                    mstore(shl(2, iszero(to)), 0xea553b3401336cea)
                    revert(0x1c, 0x04)
                }
                sstore(balanceSlot, balanceSlotPacked)
            }
            // Emit the {Transfer} event.
            log4(codesize(), 0x00, _TRANSFER_EVENT_SIGNATURE, 0, to, id)
        }
        _afterTokenTransfer(address(0), to, id);
    }

    /// @dev Equivalent to `_safeMint(to, id, "")`.
    function _safeMint(address to, uint256 id) internal virtual {
        _safeMint(to, id, "");
    }

    /// @dev Mints token `id` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must not exist.
    /// - `to` cannot be the zero address.
    /// - If `to` refers to a smart contract, it must implement
    ///   {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
    ///
    /// Emits a {Transfer} event.
    function _safeMint(address to, uint256 id, bytes memory data) internal virtual {
        _mint(to, id);
        if (_hasCode(to)) _checkOnERC721Received(address(0), to, id, data);
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                  INTERNAL BURN FUNCTIONS                   */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Equivalent to `_burn(address(0), id)`.
    function _burn(uint256 id) internal virtual {
        _burn(address(0), id);
    }

    /// @dev Destroys token `id`, using `by`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - If `by` is not the zero address,
    ///   it must be the owner of the token, or be approved to manage the token.
    ///
    /// Emits a {Transfer} event.
    function _burn(address by, uint256 id) internal virtual {
        address owner = ownerOf(id);
        _beforeTokenTransfer(owner, address(0), id);
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            by := shr(96, shl(96, by))
            // Load the ownership data.
            mstore(0x00, id)
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, by))
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let ownershipPacked := sload(ownershipSlot)
            // Reload the owner in case it is changed in `_beforeTokenTransfer`.
            owner := shr(96, shl(96, ownershipPacked))
            // Revert if the token does not exist.
            if iszero(owner) {
                mstore(0x00, 0xceea21b6) // `TokenDoesNotExist()`.
                revert(0x1c, 0x04)
            }
            // Load and check the token approval.
            {
                mstore(0x00, owner)
                let approvedAddress := sload(add(1, ownershipSlot))
                // If `by` is not the zero address, do the authorization check.
                // Revert if the `by` is not the owner, nor approved.
                if iszero(or(iszero(by), or(eq(by, owner), eq(by, approvedAddress)))) {
                    if iszero(sload(keccak256(0x0c, 0x30))) {
                        mstore(0x00, 0x4b6e7f18) // `NotOwnerNorApproved()`.
                        revert(0x1c, 0x04)
                    }
                }
                // Delete the approved address if any.
                if approvedAddress { sstore(add(1, ownershipSlot), 0) }
            }
            // Clear the owner.
            sstore(ownershipSlot, xor(ownershipPacked, owner))
            // Decrement the balance of `owner`.
            {
                let balanceSlot := keccak256(0x0c, 0x1c)
                sstore(balanceSlot, sub(sload(balanceSlot), 1))
            }
            // Emit the {Transfer} event.
            log4(codesize(), 0x00, _TRANSFER_EVENT_SIGNATURE, owner, 0, id)
        }
        _afterTokenTransfer(owner, address(0), id);
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                INTERNAL APPROVAL FUNCTIONS                 */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Returns whether `account` is the owner of token `id`, or is approved to manage it.
    ///
    /// Requirements:
    /// - Token `id` must exist.
    function _isApprovedOrOwner(address account, uint256 id)
        internal
        view
        virtual
        returns (bool result)
    {
        /// @solidity memory-safe-assembly
        assembly {
            result := 1
            // Clear the upper 96 bits.
            account := shr(96, shl(96, account))
            // Load the ownership data.
            mstore(0x00, id)
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, account))
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let owner := shr(96, shl(96, sload(ownershipSlot)))
            // Revert if the token does not exist.
            if iszero(owner) {
                mstore(0x00, 0xceea21b6) // `TokenDoesNotExist()`.
                revert(0x1c, 0x04)
            }
            // Check if `account` is the `owner`.
            if iszero(eq(account, owner)) {
                mstore(0x00, owner)
                // Check if `account` is approved to manage the token.
                if iszero(sload(keccak256(0x0c, 0x30))) {
                    result := eq(account, sload(add(1, ownershipSlot)))
                }
            }
        }
    }

    /// @dev Returns the account approved to manage token `id`.
    /// Returns the zero address instead of reverting if the token does not exist.
    function _getApproved(uint256 id) internal view virtual returns (address result) {
        /// @solidity memory-safe-assembly
        assembly {
            mstore(0x00, id)
            mstore(0x1c, _ERC721_MASTER_SLOT_SEED)
            result := sload(add(1, add(id, add(id, keccak256(0x00, 0x20)))))
        }
    }

    /// @dev Equivalent to `_approve(address(0), account, id)`.
    function _approve(address account, uint256 id) internal virtual {
        _approve(address(0), account, id);
    }

    /// @dev Sets `account` as the approved account to manage token `id`, using `by`.
    ///
    /// Requirements:
    /// - Token `id` must exist.
    /// - If `by` is not the zero address, `by` must be the owner
    ///   or an approved operator for the token owner.
    ///
    /// Emits a {Approval} event.
    function _approve(address by, address account, uint256 id) internal virtual {
        assembly {
            // Clear the upper 96 bits.
            let bitmaskAddress := shr(96, not(0))
            account := and(bitmaskAddress, account)
            by := and(bitmaskAddress, by)
            // Load the owner of the token.
            mstore(0x00, id)
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, by))
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let owner := and(bitmaskAddress, sload(ownershipSlot))
            // Revert if the token does not exist.
            if iszero(owner) {
                mstore(0x00, 0xceea21b6) // `TokenDoesNotExist()`.
                revert(0x1c, 0x04)
            }
            // If `by` is not the zero address, do the authorization check.
            // Revert if `by` is not the owner, nor approved.
            if iszero(or(iszero(by), eq(by, owner))) {
                mstore(0x00, owner)
                if iszero(sload(keccak256(0x0c, 0x30))) {
                    mstore(0x00, 0x4b6e7f18) // `NotOwnerNorApproved()`.
                    revert(0x1c, 0x04)
                }
            }
            // Sets `account` as the approved account to manage `id`.
            sstore(add(1, ownershipSlot), account)
            // Emit the {Approval} event.
            log4(codesize(), 0x00, _APPROVAL_EVENT_SIGNATURE, owner, account, id)
        }
    }

    /// @dev Approve or remove the `operator` as an operator for `by`,
    /// without authorization checks.
    ///
    /// Emits an {ApprovalForAll} event.
    function _setApprovalForAll(address by, address operator, bool isApproved) internal virtual {
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            by := shr(96, shl(96, by))
            operator := shr(96, shl(96, operator))
            // Convert to 0 or 1.
            isApproved := iszero(iszero(isApproved))
            // Update the `isApproved` for (`by`, `operator`).
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, operator))
            mstore(0x00, by)
            sstore(keccak256(0x0c, 0x30), isApproved)
            // Emit the {ApprovalForAll} event.
            mstore(0x00, isApproved)
            log3(0x00, 0x20, _APPROVAL_FOR_ALL_EVENT_SIGNATURE, by, operator)
        }
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                INTERNAL TRANSFER FUNCTIONS                 */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Equivalent to `_transfer(address(0), from, to, id)`.
    function _transfer(address from, address to, uint256 id) internal virtual {
        _transfer(address(0), from, to, id);
    }

    /// @dev Transfers token `id` from `from` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - `from` must be the owner of the token.
    /// - `to` cannot be the zero address.
    /// - If `by` is not the zero address,
    ///   it must be the owner of the token, or be approved to manage the token.
    ///
    /// Emits a {Transfer} event.
    function _transfer(address by, address from, address to, uint256 id) internal virtual {
        _beforeTokenTransfer(from, to, id);
        /// @solidity memory-safe-assembly
        assembly {
            // Clear the upper 96 bits.
            let bitmaskAddress := shr(96, not(0))
            from := and(bitmaskAddress, from)
            to := and(bitmaskAddress, to)
            by := and(bitmaskAddress, by)
            // Load the ownership data.
            mstore(0x00, id)
            mstore(0x1c, or(_ERC721_MASTER_SLOT_SEED, by))
            let ownershipSlot := add(id, add(id, keccak256(0x00, 0x20)))
            let ownershipPacked := sload(ownershipSlot)
            let owner := and(bitmaskAddress, ownershipPacked)
            // Revert if the token does not exist, or if `from` is not the owner.
            if iszero(mul(owner, eq(owner, from))) {
                // `TokenDoesNotExist()`, `TransferFromIncorrectOwner()`.
                mstore(shl(2, iszero(owner)), 0xceea21b6a1148100)
                revert(0x1c, 0x04)
            }
            // Load, check, and update the token approval.
            {
                mstore(0x00, from)
                let approvedAddress := sload(add(1, ownershipSlot))
                // If `by` is not the zero address, do the authorization check.
                // Revert if the `by` is not the owner, nor approved.
                if iszero(or(iszero(by), or(eq(by, from), eq(by, approvedAddress)))) {
                    if iszero(sload(keccak256(0x0c, 0x30))) {
                        mstore(0x00, 0x4b6e7f18) // `NotOwnerNorApproved()`.
                        revert(0x1c, 0x04)
                    }
                }
                // Delete the approved address if any.
                if approvedAddress { sstore(add(1, ownershipSlot), 0) }
            }
            // Update with the new owner.
            sstore(ownershipSlot, xor(ownershipPacked, xor(from, to)))
            // Decrement the balance of `from`.
            {
                let fromBalanceSlot := keccak256(0x0c, 0x1c)
                sstore(fromBalanceSlot, sub(sload(fromBalanceSlot), 1))
            }
            // Increment the balance of `to`.
            {
                mstore(0x00, to)
                let toBalanceSlot := keccak256(0x0c, 0x1c)
                let toBalanceSlotPacked := add(sload(toBalanceSlot), 1)
                // Revert if `to` is the zero address, or if the account balance overflows.
                if iszero(mul(to, and(toBalanceSlotPacked, _MAX_ACCOUNT_BALANCE))) {
                    // `TransferToZeroAddress()`, `AccountBalanceOverflow()`.
                    mstore(shl(2, iszero(to)), 0xea553b3401336cea)
                    revert(0x1c, 0x04)
                }
                sstore(toBalanceSlot, toBalanceSlotPacked)
            }
            // Emit the {Transfer} event.
            log4(codesize(), 0x00, _TRANSFER_EVENT_SIGNATURE, from, to, id)
        }
        _afterTokenTransfer(from, to, id);
    }

    /// @dev Equivalent to `_safeTransfer(from, to, id, "")`.
    function _safeTransfer(address from, address to, uint256 id) internal virtual {
        _safeTransfer(from, to, id, "");
    }

    /// @dev Transfers token `id` from `from` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - `from` must be the owner of the token.
    /// - `to` cannot be the zero address.
    /// - The caller must be the owner of the token, or be approved to manage the token.
    /// - If `to` refers to a smart contract, it must implement
    ///   {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
    ///
    /// Emits a {Transfer} event.
    function _safeTransfer(address from, address to, uint256 id, bytes memory data)
        internal
        virtual
    {
        _transfer(address(0), from, to, id);
        if (_hasCode(to)) _checkOnERC721Received(from, to, id, data);
    }

    /// @dev Equivalent to `_safeTransfer(by, from, to, id, "")`.
    function _safeTransfer(address by, address from, address to, uint256 id) internal virtual {
        _safeTransfer(by, from, to, id, "");
    }

    /// @dev Transfers token `id` from `from` to `to`.
    ///
    /// Requirements:
    ///
    /// - Token `id` must exist.
    /// - `from` must be the owner of the token.
    /// - `to` cannot be the zero address.
    /// - If `by` is not the zero address,
    ///   it must be the owner of the token, or be approved to manage the token.
    /// - If `to` refers to a smart contract, it must implement
    ///   {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
    ///
    /// Emits a {Transfer} event.
    function _safeTransfer(address by, address from, address to, uint256 id, bytes memory data)
        internal
        virtual
    {
        _transfer(by, from, to, id);
        if (_hasCode(to)) _checkOnERC721Received(from, to, id, data);
    }

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                    HOOKS FOR OVERRIDING                    */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Hook that is called before any token transfers, including minting and burning.
    function _beforeTokenTransfer(address from, address to, uint256 id) internal virtual {}

    /// @dev Hook that is called after any token transfers, including minting and burning.
    function _afterTokenTransfer(address from, address to, uint256 id) internal virtual {}

    /*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
    /*                      PRIVATE HELPERS                       */
    /*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/

    /// @dev Returns if `a` has bytecode of non-zero length.
    function _hasCode(address a) private view returns (bool result) {
        /// @solidity memory-safe-assembly
        assembly {
            result := extcodesize(a) // Can handle dirty upper bits.
        }
    }

    /// @dev Perform a call to invoke {IERC721Receiver-onERC721Received} on `to`.
    /// Reverts if the target does not support the function correctly.
    function _checkOnERC721Received(address from, address to, uint256 id, bytes memory data)
        private
    {
        /// @solidity memory-safe-assembly
        assembly {
            // Prepare the calldata.
            let m := mload(0x40)
            let onERC721ReceivedSelector := 0x150b7a02
            mstore(m, onERC721ReceivedSelector)
            mstore(add(m, 0x20), caller()) // The `operator`, which is always `msg.sender`.
            mstore(add(m, 0x40), shr(96, shl(96, from)))
            mstore(add(m, 0x60), id)
            mstore(add(m, 0x80), 0x80)
            let n := mload(data)
            mstore(add(m, 0xa0), n)
            if n { pop(staticcall(gas(), 4, add(data, 0x20), n, add(m, 0xc0), n)) }
            // Revert if the call reverts.
            if iszero(call(gas(), to, 0, add(m, 0x1c), add(n, 0xa4), m, 0x20)) {
                if returndatasize() {
                    // Bubble up the revert if the call reverts.
                    returndatacopy(m, 0x00, returndatasize())
                    revert(m, returndatasize())
                }
            }
            // Load the returndata and compare it.
            if iszero(eq(mload(m), shl(224, onERC721ReceivedSelector))) {
                mstore(0x00, 0xd1a57ed6) // `TransferToNonERC721ReceiverImplementer()`.
                revert(0x1c, 0x04)
            }
        }
    }
}


// a minimal implementation of soladys ERC721 with a mint function
contract MockERC721 is ERC721 {
    function mint(address to, uint256 tokenUri) external {
        _mint(to, tokenUri);
    }

    function name() public view override returns (string memory) {
        return "";
    }

    /// @dev Returns the token collection symbol.
    function symbol() public view override returns (string memory) {
        return "";
    }

    /// @dev Returns the Uniform Resource Identifier (URI) for token `id`.
    function tokenURI(uint256 id) public view override returns (string memory) {
        return "";
    }

}