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

namespace MarketAlly.AIPlugin.Context.Performance
{
	/// <summary>
	/// Provides streaming JSON processing capabilities for large context files
	/// </summary>
	public class StreamingJsonProcessor
	{
		private readonly ContextConfiguration _configuration;
		private readonly ILogger<StreamingJsonProcessor> _logger;

		public StreamingJsonProcessor(ContextConfiguration configuration, ILogger<StreamingJsonProcessor> logger)
		{
			_configuration = configuration;
			_logger = logger;
		}

		/// <summary>
		/// Streams context entries from a file without loading the entire file into memory
		/// </summary>
		public async IAsyncEnumerable<StoredContextEntry> StreamContextEntriesAsync(string filePath, CancellationToken cancellationToken = default)
		{
			if (!File.Exists(filePath))
			{
				_logger.LogWarning("Context file not found: {FilePath}", filePath);
				yield break;
			}

			using var fileStream = File.OpenRead(filePath);
			using var document = await JsonDocument.ParseAsync(fileStream, cancellationToken: cancellationToken);

			if (document.RootElement.ValueKind != JsonValueKind.Array)
			{
				_logger.LogError("Invalid JSON format in context file: {FilePath}", filePath);
				yield break;
			}

			var entriesProcessed = 0;
			foreach (var element in document.RootElement.EnumerateArray())
			{
				if (cancellationToken.IsCancellationRequested)
				{
					_logger.LogInformation("Streaming operation cancelled after processing {Count} entries from {FilePath}", 
						entriesProcessed, filePath);
					yield break;
				}

				StoredContextEntry? entry = null;
				try
				{
					entry = JsonSerializer.Deserialize<StoredContextEntry>(element.GetRawText());
				}
				catch (JsonException ex)
				{
					_logger.LogWarning(ex, "Failed to deserialize context entry at index {Index} in file {FilePath}", 
						entriesProcessed, filePath);
					continue;
				}

				if (entry != null)
				{
					entriesProcessed++;
					yield return entry;
				}
			}

			_logger.LogDebug("Streamed {Count} entries from {FilePath}", entriesProcessed, filePath);
		}

		/// <summary>
		/// Streams and filters context entries based on search criteria
		/// </summary>
		public async IAsyncEnumerable<StoredContextEntry> StreamAndFilterEntriesAsync(
			string filePath, 
			Func<StoredContextEntry, bool> filter, 
			CancellationToken cancellationToken = default)
		{
			await foreach (var entry in StreamContextEntriesAsync(filePath, cancellationToken))
			{
				if (filter(entry))
				{
					yield return entry;
				}
			}
		}

		/// <summary>
		/// Processes multiple context files in parallel using streaming
		/// </summary>
		public async Task<IEnumerable<StoredContextEntry>> ProcessMultipleFilesAsync(
			IEnumerable<string> filePaths, 
			Func<StoredContextEntry, bool> filter, 
			int maxConcurrency = 5,
			CancellationToken cancellationToken = default)
		{
			var results = new List<StoredContextEntry>();
			var semaphore = new SemaphoreSlim(maxConcurrency, maxConcurrency);

			var tasks = filePaths.Select(async filePath =>
			{
				await semaphore.WaitAsync(cancellationToken);
				try
				{
					var fileResults = new List<StoredContextEntry>();
					await foreach (var entry in StreamAndFilterEntriesAsync(filePath, filter, cancellationToken))
					{
						fileResults.Add(entry);
					}
					return fileResults;
				}
				finally
				{
					semaphore.Release();
				}
			});

			var fileResults = await Task.WhenAll(tasks);
			return fileResults.SelectMany(entries => entries);
		}

		/// <summary>
		/// Writes context entries to a file using streaming approach
		/// </summary>
		public async Task WriteContextEntriesStreamAsync(
			string filePath, 
			IAsyncEnumerable<StoredContextEntry> entries, 
			CancellationToken cancellationToken = default)
		{
			using var fileStream = File.Create(filePath);
			using var writer = new Utf8JsonWriter(fileStream, new JsonWriterOptions 
			{ 
				Indented = true,
				Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping
			});

			writer.WriteStartArray();

			var entryCount = 0;
			await foreach (var entry in entries)
			{
				if (cancellationToken.IsCancellationRequested)
				{
					_logger.LogInformation("Write operation cancelled after processing {Count} entries", entryCount);
					break;
				}

				var entryJson = JsonSerializer.Serialize(entry);
				writer.WriteRawValue(entryJson);
				entryCount++;

				// Flush periodically to avoid memory buildup
				if (entryCount % 100 == 0)
				{
					await writer.FlushAsync(cancellationToken);
				}
			}

			writer.WriteEndArray();
			await writer.FlushAsync(cancellationToken);

			_logger.LogDebug("Wrote {Count} entries to {FilePath}", entryCount, filePath);
		}

		/// <summary>
		/// Compresses a context file by removing entries older than the retention period
		/// </summary>
		public async Task<CompactionResult> CompactFileAsync(string filePath, CancellationToken cancellationToken = default)
		{
			var originalSize = new System.IO.FileInfo(filePath).Length;
			var cutoffDate = DateTime.UtcNow.AddDays(-_configuration.Retention.RetentionDays);
			var tempFilePath = filePath + ".tmp";

			var retainedEntries = 0;
			var removedEntries = 0;

			try
			{
				var filteredEntries = StreamAndFilterEntriesAsync(filePath, entry =>
				{
					if (entry.Timestamp >= cutoffDate)
					{
						retainedEntries++;
						return true;
					}
					else
					{
						removedEntries++;
						return false;
					}
				}, cancellationToken);

				await WriteContextEntriesStreamAsync(tempFilePath, filteredEntries, cancellationToken);

				// Replace original file with compacted version
				File.Move(tempFilePath, filePath, overwrite: true);

				var newSize = new System.IO.FileInfo(filePath).Length;
				var result = new CompactionResult
				{
					OriginalSizeBytes = originalSize,
					NewSizeBytes = newSize,
					EntriesRetained = retainedEntries,
					EntriesRemoved = removedEntries,
					SpaceSavedBytes = originalSize - newSize,
					Success = true
				};

				_logger.LogInformation("Compacted {FilePath}: removed {RemovedEntries} entries, saved {SpaceSaved} bytes",
					filePath, removedEntries, result.SpaceSavedBytes);

				return result;
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Failed to compact context file: {FilePath}", filePath);
				
				// Clean up temp file if it exists
				if (File.Exists(tempFilePath))
				{
					File.Delete(tempFilePath);
				}

				return new CompactionResult { Success = false, Error = ex.Message };
			}
		}
	}

	/// <summary>
	/// Result of a file compaction operation
	/// </summary>
	public class CompactionResult
	{
		public bool Success { get; set; }
		public string? Error { get; set; }
		public long OriginalSizeBytes { get; set; }
		public long NewSizeBytes { get; set; }
		public int EntriesRetained { get; set; }
		public int EntriesRemoved { get; set; }
		public long SpaceSavedBytes { get; set; }
		public double CompressionRatio => OriginalSizeBytes > 0 ? (double)NewSizeBytes / OriginalSizeBytes : 1.0;
	}
}