using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ChatRoomServer.Main.Entities
{
	using System.IO;
	using System.Threading;

	class EntityUtility
	{
		static readonly string EncryptKey = "iFishMessagePack";
		static readonly byte[] EncryptKeyBuffer = Encoding.ASCII.GetBytes(EncryptKey);
		static readonly int EncStart = 1;
		static readonly Random Random = new Random();

		public static MessageItem FromBuffer(byte[] buffer)
		{
			if (buffer.Length < 1 + EncryptKeyBuffer.Length || buffer[0] >= EncryptKeyBuffer.Length)
				return null;

			//decrypt key
			var key = EncryptKeyBuffer[buffer[0]];
			for (int i = EncStart; i < buffer.Length; i++)
			{
				var tkey = key;
				key = buffer[i];
				buffer[i] ^= tkey;
			}

			//read prefix
			var index = 1;
			if (Encoding.ASCII.GetString(buffer, index, EncryptKeyBuffer.Length) != EncryptKey)
				return null;
			index += EncryptKeyBuffer.Length;

			var item = new MessageItem();
			item.Action = ReadString(buffer, ref index);
			item.Success = buffer[index++] == 1;
			item.Time = System.FishDateTimeExtension.JsTicksStartBase.AddTicks(BitConverter.ToInt64(buffer, index) * 10000);
			index += 8;
			item.SystemMessage = buffer[index++] == 1;
			item.SysMsgType = (SystemMessageType)BitConverter.ToInt32(buffer, index);
			index += 4;
			item.UserMsgType = (UserMessageType)BitConverter.ToInt32(buffer, index);
			index += 4;
			item.Content = ReadString(buffer, ref index);
			item.Color = ReadString(buffer, ref index);
			//images
			var imgCount = BitConverter.ToInt32(buffer, index);
			index += 4;
			if (imgCount > 0)
			{
				item.Images = new string[imgCount];
				for (int i = 0; i < imgCount; i++)
				{
					item.Images[i] = ReadString(buffer, ref index);
				}
			}
			//from
			item.From = ReadString(buffer, ref index);
			//to
			var tousersCount = BitConverter.ToInt32(buffer, index);
			index += 4;
			if (tousersCount > 0)
			{
				item.ToUsers = new string[tousersCount];
				for (int i = 0; i < tousersCount; i++)
				{
					item.ToUsers[i] = ReadString(buffer, ref index);
				}
			}

			return item;
		}

		static string ReadString(byte[] data, ref int index)
		{
			var unicode = data[index++] == 1;
			var length = BitConverter.ToInt32(data, index);
			index += 4;

			var result = (unicode ? Encoding.Unicode : Encoding.ASCII).GetString(data, index, length);
			index += length;

			return result;
		}

		public static byte[] ToBuffer(MessageItem item)
		{
			var length = (item.Content?.Length ?? 0) * 3 + 100;
			var randomKeyIndex = Random.Next(EncryptKey.Length);
			var randomKey = (byte)EncryptKey[randomKeyIndex];

			using (var ms = new MemoryStream(length))
			{
				//1. write encrypt key
				ms.Write(new byte[] { (byte)randomKeyIndex });
				//1. write package header
				ms.Write(EncryptKeyBuffer);

				//3. write action
				Write(ms, item.Action, false);
				//4. write success
				ms.Write(new[] { (byte)(item.Success ? 1 : 0) });
				//5. write time
				ms.Write(item.Time.ToJsTicks());
				//6. system message
				ms.Write(new[] { (byte)(item.SystemMessage ? 1 : 0) });
				//7.
				ms.Write((int)item.SysMsgType);
				//8.
				ms.Write((int)item.UserMsgType);
				//9. content
				Write(ms, item.Content, true);
				//10. color
				Write(ms, item.Color, false);
				//11. images
				ms.Write(item.Images?.Length ?? 0);
				if (item.Images != null)
				{
					foreach (var image in item.Images)
					{
						Write(ms, image, false);
					}
				}
				//12. from user
				Write(ms, item.From, false);
				//13. to user
				ms.Write(item.ToUsers?.Length ?? 0);
				if (item.ToUsers != null)
				{
					foreach (var user in item.ToUsers)
					{
						Write(ms, user, false);
					}
				}


				var data = ms.ToArray();
				for (int i = EncStart; i < data.Length; i++)
				{
					randomKey = data[i] ^= randomKey;
				}

				return data;
			}
		}

		static void Write(Stream stream, string text, bool unicode = true)
		{
			text = text ?? "";

			var buffer = unicode ? Encoding.Unicode.GetBytes(text) : Encoding.ASCII.GetBytes(text);
			stream.Write(new[] { (byte)(unicode ? 1 : 0) });
			stream.Write(buffer.Length);
			stream.Write(buffer);
		}
	}
}