using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Newtonsoft.Json;
using UnityEngine;

namespace OnDeviceAgent.AgentCore
{
    public sealed class JsonlConversationStore : IConversationStore
    {
        readonly IPersistentPathProvider _paths;
        readonly AgentMemoryCompactionPolicy _policy;
        readonly string _conversationFileName;
        readonly string _summaryFileName;
        readonly SemaphoreSlim _fileLock = new SemaphoreSlim(1, 1);

        public JsonlConversationStore(
            IPersistentPathProvider paths,
            AgentMemoryCompactionPolicy compactionPolicy,
            string conversationFileName = "conversation.jsonl",
            string summaryFileName = "summary.md")
        {
            _paths = paths ?? throw new ArgumentNullException(nameof(paths));
            _policy = compactionPolicy ?? throw new ArgumentNullException(nameof(compactionPolicy));
            _conversationFileName = conversationFileName;
            _summaryFileName = summaryFileName;
        }

        public async Task AppendAsync(ConversationTurn turn, CancellationToken ct)
        {
            if (turn == null) throw new ArgumentNullException(nameof(turn));
            ct.ThrowIfCancellationRequested();

            await _fileLock.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                await Task.Run(() =>
                {
                    EnsureDirectory();

                    var line = JsonConvert.SerializeObject(turn);
                    File.AppendAllText(GetLogPath(), line + Environment.NewLine, Encoding.UTF8);

                    var turns = LoadTurnsFromDisk();
                    if (!_policy.ShouldCompact(turns))
                        return;

                    var recentCount = Mathf.Max(1, _policy.RecentTurnCount);
                    var olderCount = turns.Count - recentCount;
                    if (olderCount > 0)
                        CompactToDisk(turns, olderCount);
                }, ct).ConfigureAwait(false);
            }
            finally
            {
                _fileLock.Release();
            }
        }

        public async Task<string> BuildSummaryAsync(CancellationToken ct)
        {
            ct.ThrowIfCancellationRequested();

            await _fileLock.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                return await Task.Run(() =>
                {
                    var summary = LoadSummaryFromDisk();
                    var turns = LoadTurnsFromDisk();

                    if (string.IsNullOrWhiteSpace(summary) && turns.Count == 0)
                        return string.Empty;

                    return _policy.BuildContext(summary, turns);
                }, ct).ConfigureAwait(false);
            }
            finally
            {
                _fileLock.Release();
            }
        }

        public async Task CompactNowAsync(CancellationToken ct)
        {
            ct.ThrowIfCancellationRequested();

            await _fileLock.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                await Task.Run(() =>
                {
                    var turns = LoadTurnsFromDisk();
                    var recentCount = Mathf.Max(1, _policy.RecentTurnCount);
                    var olderCount = turns.Count - recentCount;
                    if (olderCount > 0)
                        CompactToDisk(turns, olderCount);
                }, ct).ConfigureAwait(false);
            }
            finally
            {
                _fileLock.Release();
            }
        }

        public void ResetSession()
        {
            _fileLock.Wait();
            try
            {
                DeleteIfExists(GetLogPath());
                DeleteIfExists(GetSummaryPath());
            }
            finally
            {
                _fileLock.Release();
            }
        }

        string GetLogPath() => Path.Combine(_paths.GetPersistentDataPath(), _conversationFileName);

        string GetSummaryPath() => Path.Combine(_paths.GetPersistentDataPath(), _summaryFileName);

        void EnsureDirectory()
        {
            var dir = _paths.GetPersistentDataPath();
            if (!string.IsNullOrEmpty(dir))
                Directory.CreateDirectory(dir);
        }

        void CompactToDisk(List<ConversationTurn> turns, int olderCount)
        {
            var olderTurns = turns.GetRange(0, olderCount);
            File.WriteAllText(GetSummaryPath(), _policy.BuildSummary(olderTurns), Encoding.UTF8);

            var recentTurns = turns.GetRange(olderCount, turns.Count - olderCount);
            var sb = new StringBuilder(recentTurns.Count * 256);
            for (var i = 0; i < recentTurns.Count; i++)
                sb.Append(JsonConvert.SerializeObject(recentTurns[i])).Append(Environment.NewLine);
            File.WriteAllText(GetLogPath(), sb.ToString(), Encoding.UTF8);
        }

        List<ConversationTurn> LoadTurnsFromDisk()
        {
            var turns = new List<ConversationTurn>();
            var path = GetLogPath();
            if (!File.Exists(path))
                return turns;

            foreach (var line in File.ReadAllLines(path))
            {
                if (string.IsNullOrWhiteSpace(line))
                    continue;

                try
                {
                    var turn = JsonConvert.DeserializeObject<ConversationTurn>(line);
                    if (turn != null)
                        turns.Add(turn);
                }
                catch (Exception ex)
                {
                    Debug.LogWarning("[JsonlConversationStore] Skipped invalid memory line: " + ex.Message);
                }
            }

            return turns;
        }

        string LoadSummaryFromDisk()
        {
            var path = GetSummaryPath();
            return File.Exists(path) ? File.ReadAllText(path, Encoding.UTF8) : string.Empty;
        }

        static void DeleteIfExists(string path)
        {
            if (File.Exists(path))
                File.Delete(path);
        }

    }
}