using System.Collections.Concurrent;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using MarketAlly.AIPlugin.Context.Configuration;

namespace MarketAlly.AIPlugin.Context.Concurrency
{
	/// <summary>
	/// Thread-safe storage manager for context operations
	/// </summary>
	public class ThreadSafeStorage : IDisposable
	{
		private readonly ContextConfiguration _configuration;
		private readonly ILogger<ThreadSafeStorage> _logger;
		private readonly ConcurrentDictionary<string, SemaphoreSlim> _fileLocks;
		private readonly ConcurrentDictionary<string, DateTime> _fileTimestamps;
		private readonly SemaphoreSlim _globalWriteLock;
		private readonly ReaderWriterLockSlim _indexLock;
		private readonly Timer _lockCleanupTimer;

		public ThreadSafeStorage(ContextConfiguration configuration, ILogger<ThreadSafeStorage> logger)
		{
			_configuration = configuration;
			_logger = logger;
			_fileLocks = new ConcurrentDictionary<string, SemaphoreSlim>();
			_fileTimestamps = new ConcurrentDictionary<string, DateTime>();
			_globalWriteLock = new SemaphoreSlim(_configuration.Performance.MaxConcurrentOperations, _configuration.Performance.MaxConcurrentOperations);
			_indexLock = new ReaderWriterLockSlim();
			
			// Clean up unused locks every 5 minutes
			_lockCleanupTimer = new Timer(CleanupUnusedLocks, null, TimeSpan.FromMinutes(5), TimeSpan.FromMinutes(5));
		}

		/// <summary>
		/// Safely stores a context entry with optimistic concurrency control
		/// </summary>
		public async Task<StorageResult> StoreContextEntryAsync(StoredContextEntry entry, string storagePath, CancellationToken cancellationToken = default)
		{
			var fileName = $"context-{DateTime.UtcNow:yyyy-MM}.json";
			var filePath = Path.Combine(storagePath, fileName);
			
			// Acquire global write semaphore to limit concurrent operations
			await _globalWriteLock.WaitAsync(cancellationToken);
			
			try
			{
				// Get or create file-specific lock
				var fileLock = _fileLocks.GetOrAdd(filePath, _ => new SemaphoreSlim(1, 1));
				
				await fileLock.WaitAsync(cancellationToken);
				try
				{
					var result = await StoreEntryWithRetryAsync(entry, filePath, cancellationToken);
					
					if (result.Success)
					{
						// Update index in a thread-safe manner
						await UpdateIndexSafelyAsync(entry, storagePath, cancellationToken);
						_fileTimestamps[filePath] = DateTime.UtcNow;
					}
					
					return result;
				}
				finally
				{
					fileLock.Release();
				}
			}
			finally
			{
				_globalWriteLock.Release();
			}
		}

		/// <summary>
		/// Safely reads context entries from a file
		/// </summary>
		public async Task<ReadResult> ReadContextEntriesAsync(string filePath, CancellationToken cancellationToken = default)
		{
			if (!File.Exists(filePath))
			{
				return new ReadResult { Success = false, Error = "File not found" };
			}

			// Get or create file-specific lock for reading
			var fileLock = _fileLocks.GetOrAdd(filePath, _ => new SemaphoreSlim(1, 1));
			
			await fileLock.WaitAsync(cancellationToken);
			try
			{
				var fileInfo = new System.IO.FileInfo(filePath);
				var entries = new List<StoredContextEntry>();

				// Check if file has been modified since our last read
				if (_fileTimestamps.TryGetValue(filePath, out var lastRead) && lastRead >= fileInfo.LastWriteTime)
				{
					_logger.LogDebug("File {FilePath} unchanged since last read", filePath);
				}

				using var fileStream = File.OpenRead(filePath);
				var jsonContent = await new StreamReader(fileStream).ReadToEndAsync();
				
				var deserializedEntries = JsonSerializer.Deserialize<List<StoredContextEntry>>(jsonContent);
				if (deserializedEntries != null)
				{
					entries.AddRange(deserializedEntries);
				}

				_fileTimestamps[filePath] = DateTime.UtcNow;

				return new ReadResult 
				{ 
					Success = true, 
					Entries = entries,
					LastModified = fileInfo.LastWriteTime
				};
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Failed to read context entries from {FilePath}", filePath);
				return new ReadResult { Success = false, Error = ex.Message };
			}
			finally
			{
				fileLock.Release();
			}
		}

		/// <summary>
		/// Safely deletes context entries with optimistic concurrency control
		/// </summary>
		public async Task<DeletionResult> DeleteContextEntriesAsync(string filePath, Func<StoredContextEntry, bool> predicate, CancellationToken cancellationToken = default)
		{
			if (!File.Exists(filePath))
			{
				return new DeletionResult { Success = false, Error = "File not found" };
			}

			// Acquire global write semaphore
			await _globalWriteLock.WaitAsync(cancellationToken);
			
			try
			{
				var fileLock = _fileLocks.GetOrAdd(filePath, _ => new SemaphoreSlim(1, 1));
				
				await fileLock.WaitAsync(cancellationToken);
				try
				{
					return await DeleteEntriesWithRetryAsync(filePath, predicate, cancellationToken);
				}
				finally
				{
					fileLock.Release();
				}
			}
			finally
			{
				_globalWriteLock.Release();
			}
		}

		/// <summary>
		/// Safely updates the context index
		/// </summary>
		public async Task<bool> UpdateIndexSafelyAsync(StoredContextEntry entry, string storagePath, CancellationToken cancellationToken = default)
		{
			var indexPath = Path.Combine(storagePath, "context-index.json");
			
			_indexLock.EnterWriteLock();
			try
			{
				var indexEntries = new List<ContextIndexEntry>();

				// Load existing index
				if (File.Exists(indexPath))
				{
					var indexJson = await File.ReadAllTextAsync(indexPath, cancellationToken);
					var existing = JsonSerializer.Deserialize<List<ContextIndexEntry>>(indexJson);
					if (existing != null)
					{
						indexEntries = existing;
					}
				}

				// Add new index entry
				var indexEntry = new ContextIndexEntry
				{
					Id = entry.Id,
					Type = entry.Type,
					Summary = entry.Summary,
					Tags = entry.Tags,
					Priority = entry.Priority,
					Timestamp = entry.Timestamp,
					FileName = $"context-{entry.Timestamp:yyyy-MM}.json"
				};

				indexEntries.Add(indexEntry);

				// Keep only the most recent entries
				indexEntries = indexEntries.OrderByDescending(e => e.Timestamp)
										  .Take(1000)
										  .ToList();

				// Save index atomically
				var tempIndexPath = indexPath + ".tmp";
				var indexJsonString = JsonSerializer.Serialize(indexEntries, new JsonSerializerOptions
				{
					WriteIndented = true
				});

				await File.WriteAllTextAsync(tempIndexPath, indexJsonString, cancellationToken);
				File.Move(tempIndexPath, indexPath, overwrite: true);

				return true;
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Failed to update index for entry {EntryId}", entry.Id);
				return false;
			}
			finally
			{
				_indexLock.ExitWriteLock();
			}
		}

		/// <summary>
		/// Safely reads the context index
		/// </summary>
		public async Task<List<ContextIndexEntry>> ReadIndexSafelyAsync(string storagePath, CancellationToken cancellationToken = default)
		{
			var indexPath = Path.Combine(storagePath, "context-index.json");
			
			if (!File.Exists(indexPath))
			{
				return new List<ContextIndexEntry>();
			}

			_indexLock.EnterReadLock();
			try
			{
				var indexJson = await File.ReadAllTextAsync(indexPath, cancellationToken);
				var entries = JsonSerializer.Deserialize<List<ContextIndexEntry>>(indexJson);
				return entries ?? new List<ContextIndexEntry>();
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Failed to read index from {IndexPath}", indexPath);
				return new List<ContextIndexEntry>();
			}
			finally
			{
				_indexLock.ExitReadLock();
			}
		}

		/// <summary>
		/// Performs parallel processing of multiple files with concurrency control
		/// </summary>
		public async Task<List<T>> ProcessFilesInParallelAsync<T>(
			IEnumerable<string> filePaths, 
			Func<string, CancellationToken, Task<T>> processor,
			CancellationToken cancellationToken = default)
		{
			var results = new List<T>();
			var semaphore = new SemaphoreSlim(_configuration.Performance.MaxConcurrentOperations, _configuration.Performance.MaxConcurrentOperations);

			var tasks = filePaths.Select(async filePath =>
			{
				await semaphore.WaitAsync(cancellationToken);
				try
				{
					return await processor(filePath, cancellationToken);
				}
				finally
				{
					semaphore.Release();
				}
			});

			var completedResults = await Task.WhenAll(tasks);
			return completedResults.ToList();
		}

		/// <summary>
		/// Stores entry with retry logic for handling concurrent modifications
		/// </summary>
		private async Task<StorageResult> StoreEntryWithRetryAsync(StoredContextEntry entry, string filePath, CancellationToken cancellationToken, int maxRetries = 3)
		{
			var attempt = 0;
			while (attempt < maxRetries)
			{
				try
				{
					var entries = new List<StoredContextEntry>();

					// Load existing entries if file exists
					if (File.Exists(filePath))
					{
						var existingJson = await File.ReadAllTextAsync(filePath, cancellationToken);
						var existing = JsonSerializer.Deserialize<List<StoredContextEntry>>(existingJson);
						if (existing != null)
						{
							entries = existing;
						}
					}

					// Add new entry
					entries.Add(entry);

					// Sort by timestamp (newest first)
					entries = entries.OrderByDescending(e => e.Timestamp).ToList();

					// Check file size limits
					if (entries.Count > _configuration.Retention.MaxEntriesPerFile)
					{
						entries = entries.Take(_configuration.Retention.MaxEntriesPerFile).ToList();
					}

					// Write atomically using temporary file
					var tempFilePath = filePath + $".tmp.{Guid.NewGuid():N}";
					var json = JsonSerializer.Serialize(entries, new JsonSerializerOptions
					{
						WriteIndented = true,
						Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping
					});

					await File.WriteAllTextAsync(tempFilePath, json, cancellationToken);
					File.Move(tempFilePath, filePath, overwrite: true);

					return new StorageResult 
					{ 
						Success = true, 
						EntryId = entry.Id,
						FilePath = filePath,
						EntriesInFile = entries.Count
					};
				}
				catch (IOException ex) when (attempt < maxRetries - 1)
				{
					// File might be locked by another process, retry after a short delay
					_logger.LogWarning(ex, "IO error storing entry {EntryId}, attempt {Attempt} of {MaxRetries}", 
						entry.Id, attempt + 1, maxRetries);
					
					await Task.Delay(TimeSpan.FromMilliseconds(100 * (attempt + 1)), cancellationToken);
					attempt++;
				}
				catch (Exception ex)
				{
					_logger.LogError(ex, "Failed to store entry {EntryId} after {Attempts} attempts", entry.Id, attempt + 1);
					return new StorageResult { Success = false, Error = ex.Message };
				}
			}

			return new StorageResult { Success = false, Error = $"Failed after {maxRetries} attempts" };
		}

		/// <summary>
		/// Deletes entries with retry logic
		/// </summary>
		private async Task<DeletionResult> DeleteEntriesWithRetryAsync(string filePath, Func<StoredContextEntry, bool> predicate, CancellationToken cancellationToken, int maxRetries = 3)
		{
			var attempt = 0;
			while (attempt < maxRetries)
			{
				try
				{
					var fileContent = await File.ReadAllTextAsync(filePath, cancellationToken);
					var entries = JsonSerializer.Deserialize<List<StoredContextEntry>>(fileContent);

					if (entries == null)
					{
						return new DeletionResult { Success = false, Error = "Failed to parse file content" };
					}

					var originalCount = entries.Count;
					var deletedEntries = entries.Where(predicate).ToList();
					entries.RemoveAll(entry => predicate(entry));

					// Write back atomically
					var tempFilePath = filePath + $".tmp.{Guid.NewGuid():N}";
					var updatedJson = JsonSerializer.Serialize(entries, new JsonSerializerOptions
					{
						WriteIndented = true,
						Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping
					});

					await File.WriteAllTextAsync(tempFilePath, updatedJson, cancellationToken);
					File.Move(tempFilePath, filePath, overwrite: true);

					return new DeletionResult
					{
						Success = true,
						DeletedCount = originalCount - entries.Count,
						RemainingCount = entries.Count,
						DeletedEntries = deletedEntries.Select(e => e.Id).ToList()
					};
				}
				catch (IOException ex) when (attempt < maxRetries - 1)
				{
					_logger.LogWarning(ex, "IO error deleting entries from {FilePath}, attempt {Attempt} of {MaxRetries}", 
						filePath, attempt + 1, maxRetries);
					
					await Task.Delay(TimeSpan.FromMilliseconds(100 * (attempt + 1)), cancellationToken);
					attempt++;
				}
				catch (Exception ex)
				{
					_logger.LogError(ex, "Failed to delete entries from {FilePath} after {Attempts} attempts", filePath, attempt + 1);
					return new DeletionResult { Success = false, Error = ex.Message };
				}
			}

			return new DeletionResult { Success = false, Error = $"Failed after {maxRetries} attempts" };
		}

		/// <summary>
		/// Cleans up unused file locks to prevent memory leaks
		/// </summary>
		private void CleanupUnusedLocks(object? state)
		{
			try
			{
				var cutoffTime = DateTime.UtcNow.AddMinutes(-10); // Remove locks unused for 10+ minutes
				var locksToRemove = new List<string>();

				foreach (var kvp in _fileTimestamps)
				{
					if (kvp.Value < cutoffTime)
					{
						locksToRemove.Add(kvp.Key);
					}
				}

				foreach (var filePath in locksToRemove)
				{
					if (_fileLocks.TryRemove(filePath, out var lockObject))
					{
						lockObject.Dispose();
					}
					_fileTimestamps.TryRemove(filePath, out _);
				}

				if (locksToRemove.Count > 0)
				{
					_logger.LogDebug("Cleaned up {Count} unused file locks", locksToRemove.Count);
				}
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Error during lock cleanup");
			}
		}

		public void Dispose()
		{
			_lockCleanupTimer?.Dispose();
			_globalWriteLock?.Dispose();
			_indexLock?.Dispose();

			foreach (var lockObject in _fileLocks.Values)
			{
				lockObject.Dispose();
			}
			_fileLocks.Clear();
		}
	}

	/// <summary>
	/// Result of a storage operation
	/// </summary>
	public class StorageResult
	{
		public bool Success { get; set; }
		public string? Error { get; set; }
		public string EntryId { get; set; } = "";
		public string FilePath { get; set; } = "";
		public int EntriesInFile { get; set; }
	}

	/// <summary>
	/// Result of a read operation
	/// </summary>
	public class ReadResult
	{
		public bool Success { get; set; }
		public string? Error { get; set; }
		public List<StoredContextEntry> Entries { get; set; } = new();
		public DateTime LastModified { get; set; }
	}

	/// <summary>
	/// Result of a deletion operation
	/// </summary>
	public class DeletionResult
	{
		public bool Success { get; set; }
		public string? Error { get; set; }
		public int DeletedCount { get; set; }
		public int RemainingCount { get; set; }
		public List<string> DeletedEntries { get; set; } = new();
	}
}