using System;
using System.Collections.Generic;
using System.IO;
using System.Text.Json;

namespace leak_test_project.Services
{
    /// <summary>
    /// 로트번호(Lot No)별 각인 순번을 저장하고 관리하는 서비스.
    /// DB COUNT(*) 의존성을 제거하고, Lot No별로 검사할 때마다 무조건 +1씩 증가하며,
    /// Lot No 변경 시 1부터 시작하고, 기존 Lot No로 복귀 시 이전 진행 번호부터 이어받아 증가합니다.
    /// </summary>
    public class LotEngravingService
    {
        private static readonly object _fileLock = new object();
        private static LotEngravingService _instance;
        public static LotEngravingService Instance => _instance ??= new LotEngravingService();

        private readonly string _filePath;
        private readonly Dictionary<string, int> _sequences = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);

        public LotEngravingService()
        {
            string appDir = AppDomain.CurrentDomain.BaseDirectory;
            _filePath = Path.Combine(appDir, "lot_sequences.json");
            LoadSequences();
        }

        private void LoadSequences()
        {
            lock (_fileLock)
            {
                try
                {
                    if (File.Exists(_filePath))
                    {
                        string json = File.ReadAllText(_filePath);
                        var data = JsonSerializer.Deserialize<Dictionary<string, int>>(json);
                        if (data != null)
                        {
                            _sequences.Clear();
                            foreach (var kvp in data)
                            {
                                _sequences[kvp.Key] = kvp.Value;
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    System.Diagnostics.Debug.WriteLine($"[LotEngravingService] LoadSequences Error: {ex.Message}");
                }
            }
        }

        private void SaveSequences()
        {
            lock (_fileLock)
            {
                try
                {
                    string json = JsonSerializer.Serialize(_sequences, new JsonSerializerOptions { WriteIndented = true });
                    File.WriteAllText(_filePath, json);
                }
                catch (Exception ex)
                {
                    System.Diagnostics.Debug.WriteLine($"[LotEngravingService] SaveSequences Error: {ex.Message}");
                }
            }
        }

        /// <summary>
        /// 지정한 Lot No의 현재 마지막 각인 순번을 조회합니다. (없을 경우 0)
        /// </summary>
        public int GetLastSequence(string lotNo)
        {
            if (string.IsNullOrWhiteSpace(lotNo)) return 0;
            string key = lotNo.Trim();

            lock (_fileLock)
            {
                return _sequences.TryGetValue(key, out int seq) ? seq : 0;
            }
        }

        /// <summary>
        /// 지정한 Lot No의 다음 각인 순번을 가져오고, 카운터를 +1 증가시켜 영구 저장합니다.
        /// </summary>
        public int GetNextSequence(string lotNo)
        {
            if (string.IsNullOrWhiteSpace(lotNo)) lotNo = "DEFAULT";
            string key = lotNo.Trim();

            lock (_fileLock)
            {
                int current = _sequences.TryGetValue(key, out int seq) ? seq : 0;
                int next = current + 1;
                _sequences[key] = next;
                SaveSequences();
                return next;
            }
        }
    }
}