using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using MarketAlly.AIPlugin.Context.Configuration;
using System.Collections.Concurrent;
using System.Security.Cryptography;
using System.Text;

namespace MarketAlly.AIPlugin.Context.Performance
{
	/// <summary>
	/// Manages caching for search results and frequently accessed context data
	/// </summary>
	public class CacheManager : IDisposable
	{
		private readonly MemoryCache _searchCache;
		private readonly MemoryCache _contextCache;
		private readonly ContextConfiguration _configuration;
		private readonly ILogger<CacheManager> _logger;
		private readonly ConcurrentDictionary<string, SemaphoreSlim> _cacheLocks;
		private readonly Timer _cleanupTimer;

		public CacheManager(ContextConfiguration configuration, ILogger<CacheManager> logger)
		{
			_configuration = configuration;
			_logger = logger;
			_cacheLocks = new ConcurrentDictionary<string, SemaphoreSlim>();

			var cacheOptions = new MemoryCacheOptions
			{
				SizeLimit = _configuration.Performance.CacheSizeLimit,
				CompactionPercentage = _configuration.Performance.CacheCompactionPercentage
			};

			_searchCache = new MemoryCache(cacheOptions);
			_contextCache = new MemoryCache(cacheOptions);

			// Setup cleanup timer to run every 10 minutes
			_cleanupTimer = new Timer(CleanupExpiredEntries, null, TimeSpan.FromMinutes(10), TimeSpan.FromMinutes(10));

			_logger.LogDebug("Cache manager initialized with size limit: {SizeLimit}", cacheOptions.SizeLimit);
		}

		/// <summary>
		/// Gets cached search results for a query
		/// </summary>
		public async Task<SearchResults?> GetCachedSearchResultsAsync(string query, string projectPath, SearchParameters parameters)
		{
			if (!_configuration.Search.EnableCaching)
				return null;

			var cacheKey = GenerateSearchCacheKey(query, projectPath, parameters);
			
			if (_searchCache.TryGetValue(cacheKey, out SearchResults? results))
			{
				_logger.LogDebug("Cache hit for search query: {Query}", query);
				return results;
			}

			_logger.LogDebug("Cache miss for search query: {Query}", query);
			return null;
		}

		/// <summary>
		/// Caches search results for future use
		/// </summary>
		public async Task CacheSearchResultsAsync(string query, string projectPath, SearchParameters parameters, SearchResults results)
		{
			if (!_configuration.Search.EnableCaching)
				return;

			var cacheKey = GenerateSearchCacheKey(query, projectPath, parameters);
			var lockKey = $"search_{cacheKey}";
			
			var lockObject = _cacheLocks.GetOrAdd(lockKey, _ => new SemaphoreSlim(1, 1));
			
			await lockObject.WaitAsync();
			try
			{
				var cacheEntryOptions = new MemoryCacheEntryOptions
				{
					AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(_configuration.Search.CacheExpirationMinutes),
					Size = EstimateSearchResultsSize(results),
					Priority = CacheItemPriority.Normal
				};

				_searchCache.Set(cacheKey, results, cacheEntryOptions);
				_logger.LogDebug("Cached search results for query: {Query}, expires in {Minutes} minutes", 
					query, _configuration.Search.CacheExpirationMinutes);
			}
			finally
			{
				lockObject.Release();
			}
		}

		/// <summary>
		/// Gets cached context entries for a file
		/// </summary>
		public async Task<List<StoredContextEntry>?> GetCachedContextEntriesAsync(string filePath)
		{
			var cacheKey = GenerateFileCacheKey(filePath);
			
			if (_contextCache.TryGetValue(cacheKey, out List<StoredContextEntry>? entries))
			{
				var fileInfo = new System.IO.FileInfo(filePath);
				if (_contextCache.TryGetValue($"{cacheKey}_timestamp", out DateTime cachedTimestamp) &&
					cachedTimestamp >= fileInfo.LastWriteTime)
				{
					_logger.LogDebug("Cache hit for context file: {FilePath}", filePath);
					return entries;
				}
				else
				{
					// File has been modified, remove from cache
					_contextCache.Remove(cacheKey);
					_contextCache.Remove($"{cacheKey}_timestamp");
				}
			}

			_logger.LogDebug("Cache miss for context file: {FilePath}", filePath);
			return null;
		}

		/// <summary>
		/// Caches context entries for a file
		/// </summary>
		public async Task CacheContextEntriesAsync(string filePath, List<StoredContextEntry> entries)
		{
			var cacheKey = GenerateFileCacheKey(filePath);
			var lockKey = $"context_{cacheKey}";
			
			var lockObject = _cacheLocks.GetOrAdd(lockKey, _ => new SemaphoreSlim(1, 1));
			
			await lockObject.WaitAsync();
			try
			{
				var cacheEntryOptions = new MemoryCacheEntryOptions
				{
					SlidingExpiration = TimeSpan.FromMinutes(30), // Keep in cache if accessed within 30 minutes
					Size = EstimateContextEntriesSize(entries),
					Priority = CacheItemPriority.High // Context entries are high priority
				};

				_contextCache.Set(cacheKey, entries, cacheEntryOptions);
				_contextCache.Set($"{cacheKey}_timestamp", File.GetLastWriteTime(filePath), cacheEntryOptions);
				
				_logger.LogDebug("Cached {Count} context entries for file: {FilePath}", entries.Count, filePath);
			}
			finally
			{
				lockObject.Release();
			}
		}

		/// <summary>
		/// Invalidates cache entries for a specific file
		/// </summary>
		public void InvalidateFileCache(string filePath)
		{
			var cacheKey = GenerateFileCacheKey(filePath);
			_contextCache.Remove(cacheKey);
			_contextCache.Remove($"{cacheKey}_timestamp");
			_logger.LogDebug("Invalidated cache for file: {FilePath}", filePath);
		}

		/// <summary>
		/// Invalidates all search cache entries for a project
		/// </summary>
		public void InvalidateProjectSearchCache(string projectPath)
		{
			// Unfortunately, MemoryCache doesn't support wildcard removal
			// In a production system, you might want to use a more sophisticated cache like Redis
			_searchCache.Clear();
			_logger.LogInformation("Cleared search cache for project changes");
		}

		/// <summary>
		/// Gets cache statistics
		/// </summary>
		public CacheStatistics GetStatistics()
		{
			// Note: MemoryCache doesn't expose detailed statistics
			// In production, you might want to track these manually
			return new CacheStatistics
			{
				SearchCacheEnabled = _configuration.Search.EnableCaching,
				ContextCacheEnabled = true,
				CacheSizeLimit = _configuration.Performance.CacheSizeLimit,
				CompactionPercentage = _configuration.Performance.CacheCompactionPercentage
			};
		}

		private string GenerateSearchCacheKey(string query, string projectPath, SearchParameters parameters)
		{
			var keyBuilder = new StringBuilder();
			keyBuilder.Append($"search_{query}_{projectPath}");
			keyBuilder.Append($"_{parameters.ContextType}_{parameters.Priority}");
			keyBuilder.Append($"_{parameters.DaysBack}_{parameters.MaxResults}");
			keyBuilder.Append($"_{parameters.IncludeContent}");
			
			if (!string.IsNullOrEmpty(parameters.Tags))
			{
				keyBuilder.Append($"_{parameters.Tags}");
			}

			return GenerateHashKey(keyBuilder.ToString());
		}

		private string GenerateFileCacheKey(string filePath)
		{
			return GenerateHashKey($"file_{filePath}");
		}

		private string GenerateHashKey(string input)
		{
			using var sha256 = SHA256.Create();
			var hashBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(input));
			return Convert.ToBase64String(hashBytes).Replace("/", "_").Replace("+", "-").TrimEnd('=');
		}

		private long EstimateSearchResultsSize(SearchResults results)
		{
			// Rough estimation: each result ~1KB
			return results.Results.Count * 1024;
		}

		private long EstimateContextEntriesSize(List<StoredContextEntry> entries)
		{
			// Rough estimation based on content length
			return entries.Sum(e => e.Content.Length + e.Summary.Length + 500); // 500 bytes overhead per entry
		}

		private void CleanupExpiredEntries(object? state)
		{
			try
			{
				_searchCache.Compact(1.0); // Force cleanup of expired entries
				_contextCache.Compact(1.0);
				_logger.LogDebug("Completed cache cleanup cycle");
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Error during cache cleanup");
			}
		}

		public void Dispose()
		{
			_cleanupTimer?.Dispose();
			_searchCache?.Dispose();
			_contextCache?.Dispose();
			
			foreach (var lockObject in _cacheLocks.Values)
			{
				lockObject.Dispose();
			}
			_cacheLocks.Clear();
		}
	}

	/// <summary>
	/// Parameters for search operations used in cache key generation
	/// </summary>
	public class SearchParameters
	{
		public string ContextType { get; set; } = "all";
		public string Priority { get; set; } = "all";
		public int DaysBack { get; set; } = 0;
		public int MaxResults { get; set; } = 10;
		public bool IncludeContent { get; set; } = true;
		public string? Tags { get; set; }
	}

	/// <summary>
	/// Cache performance and configuration statistics
	/// </summary>
	public class CacheStatistics
	{
		public bool SearchCacheEnabled { get; set; }
		public bool ContextCacheEnabled { get; set; }
		public int CacheSizeLimit { get; set; }
		public double CompactionPercentage { get; set; }
	}
}