using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Reflection;
using System.Security.Cryptography;
using System.Text;
using WTelegram;

namespace TL
{
	public interface ITLObject { }
	public delegate string ITLFunction(BinaryWriter writer);

	public static partial class Schema
	{
		internal static byte[] Serialize(this ITLObject msg)
		{
			using var memStream = new MemoryStream(1024);
			using (var writer = new BinaryWriter(memStream))
				WriteTLObject(writer, msg);
			return memStream.ToArray();
		}

		internal static T Deserialize<T>(byte[] bytes) where T : ITLObject
		{
			using var memStream = new MemoryStream(bytes);
			using var reader = new BinaryReader(memStream);
			return (T)reader.ReadTLObject();
		}

		internal static void WriteTLObject(this BinaryWriter writer, ITLObject obj)
		{
			if (obj == null) { writer.Write(NullCtor); return; }
			var type = obj.GetType();
			var ctorNb = type.GetCustomAttribute<TLDefAttribute>().CtorNb;
			writer.Write(ctorNb);
			var fields = obj.GetType().GetFields().GroupBy(f => f.DeclaringType).Reverse().SelectMany(g => g);
			int flags = 0;
			IfFlagAttribute ifFlag;
			foreach (var field in fields)
			{
				if (((ifFlag = field.GetCustomAttribute<IfFlagAttribute>()) != null) && (flags & (1 << ifFlag.Bit)) == 0) continue;
				object value = field.GetValue(obj);
				if (value == null)
					writer.WriteTLNull(field.FieldType);
				else
					writer.WriteTLValue(value);
				if (field.Name.Equals("Flags", StringComparison.OrdinalIgnoreCase)) flags = (int)value;
			}
		}

		internal static ITLObject ReadTLObject(this BinaryReader reader, Func<Type, bool> customRead = null)
		{
			var ctorNb = reader.ReadUInt32();
			if (ctorNb == NullCtor) return null;
			if (!Table.TryGetValue(ctorNb, out var type))
				throw new ApplicationException($"Cannot find type for ctor #{ctorNb:x}");
			var obj = Activator.CreateInstance(type);
			if (customRead?.Invoke(type) == true) return (ITLObject)obj;
			var fields = obj.GetType().GetFields().GroupBy(f => f.DeclaringType).Reverse().SelectMany(g => g);
			int flags = 0;
			IfFlagAttribute ifFlag;
			foreach (var field in fields)
			{
				if (((ifFlag = field.GetCustomAttribute<IfFlagAttribute>()) != null) && (flags & (1 << ifFlag.Bit)) == 0) continue;
				object value = reader.ReadTLValue(field.FieldType);
				field.SetValue(obj, value);
				if (field.Name.Equals("Flags", StringComparison.OrdinalIgnoreCase)) flags = (int)value;
			}
			return type == typeof(GzipPacked) ? UnzipPacket((GzipPacked)obj) : (ITLObject)obj;
		}

		internal static void WriteTLValue(this BinaryWriter writer, object value)
		{
			var type = value.GetType();
			switch (Type.GetTypeCode(type))
			{
				case TypeCode.Int32: writer.Write((int)value); break;
				case TypeCode.UInt32: writer.Write((uint)value); break;
				case TypeCode.Int64: writer.Write((long)value); break;
				case TypeCode.UInt64: writer.Write((ulong)value); break;
				case TypeCode.Double: writer.Write((double)value); break;
				case TypeCode.String: writer.WriteTLString((string)value); break;
				case TypeCode.DateTime: writer.WriteTLStamp((DateTime)value); break;
				case TypeCode.Boolean: writer.Write((bool)value ? 0x997275B5 : 0xBC799737); break;
				case TypeCode.Object:
					if (type.IsArray)
						if (value is byte[] bytes)
							writer.WriteTLBytes(bytes);
						else
							writer.WriteTLVector((Array)value);
					else if (value is Int128 int128)
						writer.Write(int128);
					else if (value is Int256 int256)
						writer.Write(int256);
					else if (value is ITLObject tlObject)
						WriteTLObject(writer, tlObject);
					else
						ShouldntBeHere();
					break;
				default:
					ShouldntBeHere();
					break;
			}
		}

		internal static object ReadTLValue(this BinaryReader reader, Type type)
		{
			switch (Type.GetTypeCode(type))
			{
				case TypeCode.Int32: return reader.ReadInt32();
				case TypeCode.UInt32: return reader.ReadUInt32();
				case TypeCode.Int64: return reader.ReadInt64();
				case TypeCode.UInt64: return reader.ReadUInt64();
				case TypeCode.Double: return reader.ReadDouble();
				case TypeCode.String: return reader.ReadTLString();
				case TypeCode.DateTime: return reader.ReadTLStamp();
				case TypeCode.Boolean:
					return reader.ReadUInt32() switch
					{
						0x997275b5 => true,
						0xbc799737 => false,
						var value => throw new ApplicationException($"Invalid boolean value #{value:x}")
					};
				case TypeCode.Object:
					if (type.IsArray)
					{
						if (type == typeof(byte[]))
							return reader.ReadTLBytes();
						else if (type == typeof(_Message[]))
							return reader.ReadTLMessages();
						else
							return reader.ReadTLVector(type);
					}
					else if (type == typeof(Int128))
						return new Int128(reader);
					else if (type == typeof(Int256))
						return new Int256(reader);
					else
						return ReadTLObject(reader);
				default:
					ShouldntBeHere();
					return null;
			}
		}

		internal static void WriteTLVector(this BinaryWriter writer, Array array)
		{
			writer.Write(VectorCtor);
			if (array == null) { writer.Write(0); return; }
			int count = array.Length;
			writer.Write(count);
			for (int i = 0; i < count; i++)
				writer.WriteTLValue(array.GetValue(i));
		}

		internal static Array ReadTLVector(this BinaryReader reader, Type type)
		{
			var ctorNb = reader.ReadInt32();
			if (ctorNb != VectorCtor) throw new ApplicationException($"Cannot deserialize {type.Name} with ctor #{ctorNb:x}");
			var elementType = type.GetElementType();
			int count = reader.ReadInt32();
			Array array = (Array)Activator.CreateInstance(type, count);
			for (int i = 0; i < count; i++)
				array.SetValue(reader.ReadTLValue(elementType), i);
			return array;
		}

		internal static void WriteTLStamp(this BinaryWriter writer, DateTime datetime)
			=> writer.Write((uint)(datetime.ToUniversalTime().Ticks / 10000000 - 62135596800L));

		internal static DateTime ReadTLStamp(this BinaryReader reader)
			=> new((reader.ReadUInt32() + 62135596800L) * 10000000, DateTimeKind.Utc);

		internal static void WriteTLString(this BinaryWriter writer, string str)
		{
			if (str == null)
				writer.Write(0);
			else
				writer.WriteTLBytes(Encoding.UTF8.GetBytes(str));
		}

		internal static string ReadTLString(this BinaryReader reader)
			=> Encoding.UTF8.GetString(reader.ReadTLBytes());

		internal static void WriteTLBytes(this BinaryWriter writer, byte[] bytes)
		{
			if (bytes == null) { writer.Write(0); return; }
			int length = bytes.Length;
			if (length < 254)
				writer.Write((byte)length);
			else
			{
				writer.Write(length << 8 | 254);
				length += 3;
			}
			writer.Write(bytes);
			while (++length % 4 != 0) writer.Write((byte)0);
		}

		internal static byte[] ReadTLBytes(this BinaryReader reader)
		{
			byte[] bytes;
			int length = reader.ReadByte();
			if (length < 254)
				bytes = reader.ReadBytes(length);
			else
			{
				length = reader.ReadInt16() + (reader.ReadByte() << 16);
				bytes = reader.ReadBytes(length);
				length += 3;
			}
			while (++length % 4 != 0) reader.ReadByte();
			return bytes;
		}

		internal static void WriteTLNull(this BinaryWriter writer, Type type)
		{
			if (!type.IsArray)
				writer.Write(NullCtor);
			else if (type != typeof(byte[]))
				writer.Write(VectorCtor);
			writer.Write(0);    // null arrays are serialized as empty
		}

		internal static _Message[] ReadTLMessages(this BinaryReader reader)
		{
			int count = reader.ReadInt32();
			var array = new _Message[count];
			for (int i = 0; i < count; i++)
			{
				array[i] = new _Message
				{
					msg_id = reader.ReadInt64(),
					seqno = reader.ReadInt32(),
					bytes = reader.ReadInt32(),
				};
				var pos = reader.BaseStream.Position;
				try
				{
					array[i].body = reader.ReadTLObject();
				}
				catch (Exception ex)
				{
					Helpers.Log(4, ex.ToString());
				}
				reader.BaseStream.Position = pos + array[i].bytes;
			}
			return array;
		}

		internal static ITLObject UnzipPacket(GzipPacked obj)
		{
			using var reader = new BinaryReader(new GZipStream(new MemoryStream(obj.packed_data), CompressionMode.Decompress));
			var result = ReadTLObject(reader);
			Helpers.Log(1, $"            → {result.GetType().Name}");
			return result;
		}

#if DEBUG
		private static void ShouldntBeHere() => System.Diagnostics.Debugger.Break();
#else
		private static void ShouldntBeHere() => throw new NotImplementedException("You've reached an unexpected point in code");
#endif
	}

	[AttributeUsage(AttributeTargets.Class)]
	public class TLDefAttribute : Attribute
	{
		public readonly uint CtorNb;
		public TLDefAttribute(uint ctorNb) => CtorNb = ctorNb;
		/*public TLDefAttribute(string def)
		{
			var hash = def.IndexOfAny(new[] { '#', ' ' });
			CtorNb = def[hash] == ' ' ? Force.Crc32.Crc32Algorithm.Compute(System.Text.Encoding.UTF8.GetBytes(def))
									  : uint.Parse(def[(hash + 1)..def.IndexOf(' ', hash)], System.Globalization.NumberStyles.HexNumber);
		}*/
	}

	[AttributeUsage(AttributeTargets.Field)]
	public class IfFlagAttribute : Attribute
	{
		public readonly int Bit;
		public IfFlagAttribute(int bit) => Bit = bit;
	}

	public struct Int128
	{
		public byte[] raw;

		public Int128(BinaryReader reader) => raw = reader.ReadBytes(16);
		public Int128(RNGCryptoServiceProvider rng) => rng.GetBytes(raw = new byte[16]);
		public static bool operator ==(Int128 left, Int128 right) { for (int i = 0; i < 16; i++) if (left.raw[i] != right.raw[i]) return false; return true; }
		public static bool operator !=(Int128 left, Int128 right) { for (int i = 0; i < 16; i++) if (left.raw[i] != right.raw[i]) return true; return false; }
		public override bool Equals(object obj) => obj is Int128 other && this == other;
		public override int GetHashCode() => HashCode.Combine(raw[0], raw[1]);
		public static implicit operator byte[](Int128 int128) => int128.raw;
	}

	public struct Int256
	{
		public byte[] raw;

		public Int256(BinaryReader reader) => raw = reader.ReadBytes(32);
		public Int256(RNGCryptoServiceProvider rng) => rng.GetBytes(raw = new byte[32]);
		public static bool operator ==(Int256 left, Int256 right) { for (int i = 0; i < 32; i++) if (left.raw[i] != right.raw[i]) return false; return true; }
		public static bool operator !=(Int256 left, Int256 right) { for (int i = 0; i < 32; i++) if (left.raw[i] != right.raw[i]) return true; return false; }
		public override bool Equals(object obj) => obj is Int256 other && this == other;
		public override int GetHashCode() => HashCode.Combine(raw[0], raw[1]);
		public static implicit operator byte[](Int256 int256) => int256.raw;
	}
}