using System;
using System.Collections.Generic;
using System.IO;
using AI.Models;
using AI.Models.Store;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NamingConventions;

namespace AI.Service
{
    /// <summary>
    /// 会话文件持久化 DTO（YAML 格式：元数据 + entries）
    /// </summary>
    public class SessionFileDto
    {
        public string SessionId { get; set; } = string.Empty;
        public string Title { get; set; } = "新会话";
        public DateTime CreatedAt { get; set; }
        public DateTime UpdatedAt { get; set; }
        public string WorkflowMode { get; set; } = "Ask";
        public List<ConversationEntryDto> Entries { get; set; } = new();
    }

    /// <summary>
    /// 会话存储的 YAML 文件持久化：按会话 ID 保存到目录下的 {sessionId}.yaml，支持加载全部会话。
    /// </summary>
    public class SessionStorage
    {
        private readonly string _directory;
        private static readonly ISerializer _serializer = new SerializerBuilder()
            .WithNamingConvention(CamelCaseNamingConvention.Instance)
            .Build();
        private static readonly IDeserializer _deserializer = new DeserializerBuilder()
            .WithNamingConvention(CamelCaseNamingConvention.Instance)
            .IgnoreUnmatchedProperties()
            .Build();

        public SessionStorage(string? baseDirectory = null)
        {
            _directory = string.IsNullOrWhiteSpace(baseDirectory)
                ? Path.Combine(AppContext.BaseDirectory, "Sessions")
                : Path.Combine(baseDirectory, "Sessions");
        }

        /// <summary>
        /// 确保会话目录存在
        /// </summary>
        public void EnsureDirectory()
        {
            if (!Directory.Exists(_directory))
                Directory.CreateDirectory(_directory);
        }

        /// <summary>
        /// 获取指定会话的 YAML 文件路径
        /// </summary>
        public string GetFilePath(string sessionId)
        {
            EnsureDirectory();
            return Path.Combine(_directory, $"{sessionId}.yaml");
        }

        /// <summary>
        /// 将会话保存为 YAML 文件
        /// </summary>
        public void Save(ChatSession session)
        {
            if (session == null) return;
            var dto = new SessionFileDto
            {
                SessionId = session.Id,
                Title = session.Title ?? "新会话",
                CreatedAt = session.CreatedAt,
                UpdatedAt = session.UpdatedAt,
                WorkflowMode = session.WorkflowMode.ToString(),
                Entries = ConversationEntryMapper.ToDtoList(session.Store.Entries)
            };
            var yaml = _serializer.Serialize(dto);
            var path = GetFilePath(session.Id);
            File.WriteAllText(path, yaml);
        }

        /// <summary>
        /// 从 YAML 文件加载一个会话；文件不存在或解析失败时返回 null
        /// </summary>
        public ChatSession? Load(string sessionId)
        {
            var path = GetFilePath(sessionId);
            if (!File.Exists(path))
            {
                return null;
            }
            try
            {
                var yaml = File.ReadAllText(path);
                return LoadFromYaml(yaml);
            }
            catch
            {
                return null;
            }
        }

        /// <summary>
        /// 从 YAML 字符串反序列化并构造 ChatSession（用于单文件加载或测试）
        /// </summary>
        public ChatSession? LoadFromYaml(string yaml)
        {
            if (string.IsNullOrWhiteSpace(yaml))
            {
                return null;
            }

            try
            {
                var dto = _deserializer.Deserialize<SessionFileDto>(yaml);
                if (dto == null)
                {
                    return null;
                }

                var store = new ConversationStore();
                store.LoadFromEntries(dto.Entries ?? new List<ConversationEntryDto>());
                var mode = WorkflowMode.Ask;
                if (!string.IsNullOrEmpty(dto.WorkflowMode) && Enum.TryParse<WorkflowMode>(dto.WorkflowMode, true, out var m))
                {
                    mode = m;
                }
                return new ChatSession(
                    dto.SessionId,
                    dto.Title,
                    dto.CreatedAt,
                    dto.UpdatedAt,
                    mode,
                    store);
            }
            catch
            {
                return null;
            }
        }

        /// <summary>
        /// 从会话目录加载所有会话文件，返回按 UpdatedAt 倒序的会话列表
        /// </summary>
        public IEnumerable<ChatSession> LoadAll()
        {
            EnsureDirectory();
            var list = new List<ChatSession>();
            foreach (var path in Directory.EnumerateFiles(_directory, "*.yaml"))
            {
                try
                {
                    var yaml = File.ReadAllText(path);
                    var session = LoadFromYaml(yaml);
                    if (session != null)
                    {
                        list.Add(session);
                    }
                }
                catch
                {
                    // 单文件失败则跳过
                }
            }
            list.Sort((a, b) => b.UpdatedAt.CompareTo(a.UpdatedAt));
            return list;
        }

        /// <summary>
        /// 删除指定会话的持久化文件
        /// </summary>
        public void Delete(string sessionId)
        {
            var path = GetFilePath(sessionId);
            if (File.Exists(path))
                File.Delete(path);
        }
    }
}