using System.Text;
using System.Text.Json;
using DatabaseSnapshotsService.Models;

namespace DatabaseSnapshotsService.Services
{
    public class EventStore
    {
        private readonly EventStoreConfig _config;
        private readonly string _eventsPath;
        private readonly string _indexPath;
        private readonly object _writeLock = new object();
        private long _currentEventId = 0;
        private string _currentEventFile = string.Empty;
        private StreamWriter? _currentWriter;
        private long _currentFileSize = 0;

        public EventStore(EventStoreConfig config)
        {
            _config = config;
            _eventsPath = Path.GetFullPath(config.Path);
            _indexPath = Path.Combine(_eventsPath, "index");
            
            // Ensure directories exist
            Directory.CreateDirectory(_eventsPath);
            Directory.CreateDirectory(_indexPath);
            
            // Load next event ID and initialize current file
            LoadNextEventId();
            InitializeCurrentFile();
        }

        public async Task<long> StoreEventAsync(DatabaseEvent evt)
        {
            lock (_writeLock)
            {
                evt.Id = ++_currentEventId;
                evt.Timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
                evt.Checksum = CalculateEventChecksum(evt);
                
                // Check if we need to rotate the file
                if (_currentFileSize > _config.MaxFileSize || _currentWriter == null)
                {
                    RotateEventFile();
                }
                
                // Write event to current file
                var json = JsonSerializer.Serialize(evt);
                _currentWriter?.WriteLine(json);
                _currentWriter?.Flush();
                _currentFileSize += json.Length + Environment.NewLine.Length;
                
                // Update index
                UpdateEventIndex(evt);
                
                return evt.Id;
            }
        }

        public async Task<long> GetLastEventIdAsync()
        {
            var eventFiles = Directory.GetFiles(_eventsPath, "events_*.json");
            long lastId = 0;
            
            foreach (var file in eventFiles.OrderByDescending(f => f))
            {
                var lines = await File.ReadAllLinesAsync(file);
                if (lines.Length > 0)
                {
                    var lastLine = lines.Last();
                    try
                    {
                        var lastEvent = JsonSerializer.Deserialize<DatabaseEvent>(lastLine);
                        if (lastEvent != null && lastEvent.Id > lastId)
                        {
                            lastId = lastEvent.Id;
                        }
                    }
                    catch (JsonException)
                    {
                        // Skip malformed JSON
                        continue;
                    }
                }
            }
            
            return lastId;
        }

        private void LoadNextEventId()
        {
            var lastId = GetLastEventIdAsync().GetAwaiter().GetResult();
            _currentEventId = lastId;
        }

        private void InitializeCurrentFile()
        {
            var timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
            _currentEventFile = Path.Combine(_eventsPath, $"events_{timestamp}.json");
            _currentWriter = new StreamWriter(_currentEventFile, true, Encoding.UTF8);
            _currentFileSize = 0;
        }

        private void RotateEventFile()
        {
            // Close current writer and delete file if empty
            if (_currentWriter != null)
            {
                _currentWriter.Close();
                if (!string.IsNullOrEmpty(_currentEventFile) && File.Exists(_currentEventFile))
                {
                    var fileInfo = new FileInfo(_currentEventFile);
                    if (fileInfo.Length == 0)
                    {
                        File.Delete(_currentEventFile);
                    }
                }
            }
            _currentEventFile = Path.Combine(_eventsPath, $"events_{DateTime.UtcNow:yyyyMMdd_HHmmss}_{_currentEventId}.json");
            _currentWriter = new StreamWriter(_currentEventFile, append: false, Encoding.UTF8);
            _currentFileSize = 0;
        }

        private string CalculateEventChecksum(DatabaseEvent evt)
        {
            var data = $"{evt.Id}{evt.Timestamp}{evt.Type}{evt.Table}{evt.Operation}{evt.Data}{evt.BinlogPosition}{evt.ServerId}";
            using var sha256 = System.Security.Cryptography.SHA256.Create();
            var hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(data));
            return Convert.ToHexString(hash).ToLower();
        }

        private void UpdateEventIndex(DatabaseEvent evt)
        {
            var indexFile = Path.Combine(_indexPath, Path.GetFileNameWithoutExtension(_currentEventFile) + ".idx");
            var indexEntry = $"{evt.Id},{evt.Timestamp},{evt.Table},{evt.Operation}";
            
            File.AppendAllText(indexFile, indexEntry + Environment.NewLine);
        }
    }
}