using System;
using System.Collections.Generic;
using System.Text;

namespace XWorld.Framework.Protocol
{
    // 手写小端二进制写入器：varint(LEB128) + zigzag，无反射，AOT/WASM 友好
    public sealed class PacketWriter
    {
        private readonly List<byte> _buf;

        public PacketWriter(int capacity = 64)
        {
            _buf = new List<byte>(capacity);
        }

        public void WriteByte(byte v) => _buf.Add(v);

        public void WriteBool(bool v) => _buf.Add(v ? (byte)1 : (byte)0);

        public void WriteUInt16(ushort v)
        {
            _buf.Add((byte)(v & 0xFF));
            _buf.Add((byte)((v >> 8) & 0xFF));
        }

        public void WriteVarUInt(uint v)
        {
            while (v >= 0x80)
            {
                _buf.Add((byte)(v | 0x80));
                v >>= 7;
            }
            _buf.Add((byte)v);
        }

        public void WriteVarInt(int v)
        {
            uint zig = (uint)((v << 1) ^ (v >> 31)); // zigzag
            WriteVarUInt(zig);
        }

        public void WriteVarLong(long v)
        {
            ulong zig = (ulong)((v << 1) ^ (v >> 63));
            while (zig >= 0x80)
            {
                _buf.Add((byte)(zig | 0x80));
                zig >>= 7;
            }
            _buf.Add((byte)zig);
        }

        public void WriteSingle(float v)
        {
            byte[] b = BitConverter.GetBytes(v);
            if (!BitConverter.IsLittleEndian) Array.Reverse(b);
            _buf.Add(b[0]); _buf.Add(b[1]); _buf.Add(b[2]); _buf.Add(b[3]);
        }

        public void WriteBytes(byte[] data)
        {
            if (data == null || data.Length == 0)
            {
                WriteVarUInt(0);
                return;
            }
            WriteVarUInt((uint)data.Length);
            _buf.AddRange(data);
        }

        public void WriteString(string s)
        {
            if (string.IsNullOrEmpty(s))
            {
                WriteVarUInt(0);
                return;
            }
            byte[] b = Encoding.UTF8.GetBytes(s);
            WriteVarUInt((uint)b.Length);
            _buf.AddRange(b);
        }

        public byte[] ToArray() => _buf.ToArray();
    }
}