using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using BITKit;
using Cysharp.Threading.Tasks;

namespace Net.BITKit.Chat
{
    public interface IChatService
    {
        UniTask SendMessage(ChatMessage message);
        UniTask<IReadOnlyList<ChatMessage>> GetMessages(string userId);
         UniTask<IReadOnlyList<ChatMessage>> GetMessages(string userId1, string userId2);
        UniTask<IReadOnlyList<ChatMessage>> GetChatList(string userId);
        public event Action<ChatMessage> OnMessageReceived;
    }

    public interface IChatVoiceService
    {
    }
 
    public class ChatService : IChatService
    {
        private readonly IDictionary<int,ChatMessage> _messages;

        public ChatService(IDictionary<int, ChatMessage> messages)
        {
            _messages = messages;

            if (_messages.Count is 0)
            {
                foreach (var chatMessage in ChatMockDataGenerator.GenerateMockMessages())
                {
                    _messages.Add(chatMessage.Id,chatMessage);
                }
            }
        }

        public UniTask SendMessage(ChatMessage message)
        {
            if (_messages.ContainsKey(message.Id))
            {
                message.Id = Guid.NewGuid().GetHashCode();
            }
            _messages.Add(message.Id,message);
            
            OnMessageReceived?.Invoke(message);
            
            return UniTask.CompletedTask;
        }

        public UniTask<IReadOnlyList<ChatMessage>> GetMessages(string userId)
        {
            var list = new List<ChatMessage>();
            
            list.AddRange(_messages.Values.Where(x=>x.FromUserId==userId));

            list.Sort((a, b) => a.Timestamp.CompareTo(b.Timestamp));
            
            return UniTask.FromResult<IReadOnlyList<ChatMessage>>(list);
        }

        public UniTask<IReadOnlyList<ChatMessage>> GetMessages(string userId1, string userId2)
        {
            var list = new List<ChatMessage>();
            
            list.AddRange(_messages.Values.Where(x=>(x.FromUserId==userId1&&x.ToUserId==userId2) || (x.FromUserId==userId2&&x.ToUserId==userId1)));

            list.Sort((a, b) => a.Timestamp.CompareTo(b.Timestamp));
            
            return UniTask.FromResult<IReadOnlyList<ChatMessage>>(list);
        }

        public  UniTask<IReadOnlyList<ChatMessage>> GetChatList(string userId)
        {
            var result = new List<ChatMessage>();
            
            foreach (var chatMessage in _messages.Values)
            {
                if (chatMessage.FromUserId == userId || chatMessage.ToUserId == userId)
                {
                    result.Add(chatMessage);
                }
            }

            #if NET5_0_OR_GREATER
            result = result.OrderByDescending(m => m.Timestamp).DistinctBy(x=>new
            {
                x.FromUserId,
                x.ToUserId
            }).ToList();
            #else
            result = result
                .OrderByDescending(m => m.Timestamp)
                .GroupBy(x => new { x.FromUserId, x.ToUserId }) // 按这两个字段分组
                .Select(g => g.First()) // 每组取最新的一条
                .ToList();

#endif
            
            return UniTask.FromResult<IReadOnlyList<ChatMessage>>(result);
        }

        public event Action<ChatMessage> OnMessageReceived;
    }
    
    public static class ChatMockDataGenerator
    {
        private static int _count;
        public static List<ChatMessage> GenerateMockMessages(int countPerUser = 10)
        {
            var systemUserId = Environment.UserName;
            var otherUsers = new[] { "bob", "alice", "lucy", "john", "eva" };
            var messages = new List<ChatMessage>();
            var rnd = new Random();

            foreach (var otherUser in otherUsers)
            {
                for (int i = 0; i < countPerUser; i++)
                {
                    // 随机决定谁说话
                    bool fromSystem = rnd.NextDouble() < 0.5;

                    messages.Add(new ChatMessage
                    {
                        Id = _count++,
                        FromUserId = fromSystem ? systemUserId : otherUser,
                        ToUserId = fromSystem ? otherUser : systemUserId,
                        Content = fromSystem
                            ? $"Hi {otherUser}, message {i}"
                            : $"Hey {systemUserId}, reply {i}",
                        Timestamp = DateTime.Now.AddMinutes(-rnd.Next(0, 60 * 24 * 3)) // 过去3天内
                    });
                }
            }

            return messages.OrderBy(m => m.Timestamp).ToList();
        }
    }
}