// SPDX-License-Identifier: BSD-2-Clause
// https://github.com/ensdomains/buffer

pragma solidity ^0.7.0;

/**
 * @dev A library for working with mutable byte buffers in Solidity.
 *
 * Byte buffers are mutable and expandable, and provide a variety of primitives
 * for writing to them. At any time you can fetch a bytes object containing the
 * current contents of the buffer. The bytes object should not be stored between
 * operations, as it may change due to resizing of the buffer.
 */
library Buffer {
    /**
     * @dev Represents a mutable buffer. Buffers have a current value (buf) and
     *      a capacity. The capacity may be longer than the current value, in
     *      which case it can be extended without the need to allocate more memory.
     */
    struct buffer {
        bytes buf;
        uint capacity;
    }

    /**
     * @dev Initializes a buffer with an initial capacity.a co
     * @param buf The buffer to initialize.
     * @param capacity The number of bytes of space to allocate the buffer.
     * @return The buffer, for chaining.
     */
    function init(buffer memory buf, uint capacity) internal pure returns (buffer memory) {
        if (capacity % 32 != 0) {
            capacity += 32 - (capacity % 32);
        }
        // Allocate space for the buffer data
        buf.capacity = capacity;
        assembly {
            let ptr := mload(0x40)
            mstore(buf, ptr)
            mstore(ptr, 0)
            mstore(0x40, add(32, add(ptr, capacity)))
        }
        return buf;
    }


    /**
     * @dev Writes a byte string to a buffer. Resizes if doing so would exceed
     *      the capacity of the buffer.
     * @param buf The buffer to append to.
     * @param off The start offset to write to.
     * @param rawData The data to append.
     * @param len The number of bytes to copy.
     * @return The original buffer, for chaining.
     */
    function writeRawBytes(
        buffer memory buf,
        uint off,
        bytes memory rawData,
        uint offData,
        uint len
    ) internal pure returns (buffer memory) {
        if (off + len > buf.capacity) {
            resize(buf, max(buf.capacity, len + off) * 2);
        }

        uint dest;
        uint src;
        assembly {
            // Memory address of the buffer data
            let bufptr := mload(buf)
            // Length of existing buffer data
            let buflen := mload(bufptr)
            // Start address = buffer address + offset + sizeof(buffer length)
            dest := add(add(bufptr, 32), off)
            // Update buffer length if we're extending it
            if gt(add(len, off), buflen) {
                mstore(bufptr, add(len, off))
            }
            src := add(rawData, offData)
        }

        // Copy word-length chunks while possible
        for (; len >= 32; len -= 32) {
            assembly {
                mstore(dest, mload(src))
            }
            dest += 32;
            src += 32;
        }

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

        return buf;
    }

    /**
     * @dev Writes a byte string to a buffer. Resizes if doing so would exceed
     *      the capacity of the buffer.
     * @param buf The buffer to append to.
     * @param off The start offset to write to.
     * @param data The data to append.
     * @param len The number of bytes to copy.
     * @return The original buffer, for chaining.
     */
    function write(buffer memory buf, uint off, bytes memory data, uint len) internal pure returns (buffer memory) {
        require(len <= data.length);

        if (off + len > buf.capacity) {
            resize(buf, max(buf.capacity, len + off) * 2);
        }

        uint dest;
        uint src;
        assembly {
        // Memory address of the buffer data
            let bufptr := mload(buf)
        // Length of existing buffer data
            let buflen := mload(bufptr)
        // Start address = buffer address + offset + sizeof(buffer length)
            dest := add(add(bufptr, 32), off)
        // Update buffer length if we're extending it
            if gt(add(len, off), buflen) {
                mstore(bufptr, add(len, off))
            }
            src := add(data, 32)
        }

        // Copy word-length chunks while possible
        for (; len >= 32; len -= 32) {
            assembly {
                mstore(dest, mload(src))
            }
            dest += 32;
            src += 32;
        }

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

        return buf;
    }

    function append(buffer memory buf, bytes memory data) internal pure returns (buffer memory) {
        return write(buf, buf.buf.length, data, data.length);
    }

    function resize(buffer memory buf, uint capacity) private pure {
        bytes memory oldbuf = buf.buf;
        init(buf, capacity);
        append(buf, oldbuf);
    }

    function max(uint a, uint b) private pure returns (uint) {
        if (a > b) {
            return a;
        }
        return b;
    }
}