FeatherMC/src/PacketReader.h

#pragma once

#include "Common.h"
#include "util/ByteUtil.h"

#include <cstdio>
#include <cstdint>
#include <string>

using std::string;

namespace Feather
{
    // Class to read packet data, such as is produced by NetworkMessage
    class PacketReader
    {
    public:
        PacketReader(const uint8_t *const dataPtr)
          : m_data(dataPtr), m_offset(0), m_length(ReadLength())
        {
        }

        // Peek the next value to be read
        // If big endian (the default), will reverse byte order.
        template <typename T, Endian endianMode = Endian::Big>
        inline T Peek()
        {
            T value = *reinterpret_cast<const T *const>(&m_data[m_offset]);

            return (endianMode == Endian::Big) ? ReverseBytes(value) : value;
        }

        // Read the next value
        // If big endian (the default), will reverse byte order.
        template <typename T, Endian endianMode = Endian::Big>
        inline T Read()
        {
            T value = Peek<T, endianMode>();
            m_offset += sizeof(T);
            return value;
        }

        // Read bool as 1 byte
        template <>
        inline bool Read<bool>()
        {
            // TODO: Could warn on non-bool value
            return (ReadByte() != 0x00);
        }

        // Fast way to peek the next byte
        inline uint8_t PeekByte() { return m_data[m_offset]; }

        // Fast way to read a byte
        inline uint8_t ReadByte() { return m_data[m_offset++]; }

        inline int32_t ReadLength()
        {
            int32_t length = ReadVarInt(&m_lengthSize);

            // HACK: handle Legacy Server List Ping
            m_legacy = length == 0xFE && PeekByte() == 0x01;
            if (m_legacy)
                return 1;

            return length;
        }

        template <typename T = int32_t>
        inline T ReadVarInt(uint32_t* outCount = nullptr)
        {
            uint32_t numRead = 0;
            int32_t result = 0;
            uint8_t read;
            do
            {
                read = ReadByte();
                int value = (read & 0b01111111);
                result |= (value << (7 * numRead));

                numRead++;
                if (numRead > 5)
                {
                    // complain
                    //throw new RuntimeException("VarInt is too big");
                }
            } while ((read & 0b10000000) != 0);

            if (outCount != nullptr)
                *outCount = numRead;

            return static_cast<T>(result);
        }

        // can be assigned to string&, string_view
        string ReadString()
        {
            int size = ReadVarInt();
            string str;

            for (int i = 0; i < size; i++) {
                str += ReadByte();
            }
            
            return str;
        }

        inline BlockPos ReadPosition()
        {
            return BlockPos(Read<int64_t>());
        }

        uint32_t Length() const { return m_length; }
        uint32_t Size()   const { return m_length + m_lengthSize; }

        bool IsLegacyPing() const { return m_legacy; }

    private:
        const uint8_t *const m_data;
        uint32_t             m_offset;
        const uint32_t       m_length;
        uint32_t             m_lengthSize;
        bool                 m_legacy;
    };

    // Use fast Read and Peek for uint8_t

    template <>
    inline uint8_t PacketReader::Peek<uint8_t>() { return PeekByte(); }

    template<>
    inline uint8_t PacketReader::Read<uint8_t>() { return ReadByte(); }
}