using System.Data;
using System.Text.Json;
using Confluent.Kafka;
using Elastic.Clients.Elasticsearch;
using Npgsql;

namespace GeoPulse_Pipeline;

public class KafkaConsumer : BackgroundService
{
	private readonly ILogger<KafkaConsumer> _logger;
	private readonly NpgsqlDataSource _dataSource;
	private readonly PartitionManager _partitionManager;
	private readonly string _kafkaHost;
	private readonly ElasticsearchClient _esClient;

	private const int BatchSize = 1000;
	private readonly TimeSpan MaxWaitTime = TimeSpan.FromSeconds(2);


	public KafkaConsumer(
		ILogger<KafkaConsumer> logger,
		IConfiguration configuration,
		NpgsqlDataSource dataSource,
		PartitionManager partitionManager,
		ElasticsearchClient esClient)
	{
		_logger = logger;
		_kafkaHost = configuration["KafkaHost"];
		_dataSource = dataSource;
		_partitionManager = partitionManager;
		_esClient = esClient;
	}

	protected override async Task ExecuteAsync(CancellationToken stoppingToken)
	{
		await Task.Yield();

		var consumerConfig = new ConsumerConfig
		{
			BootstrapServers = _kafkaHost,
			GroupId = "telemetry-db-writer-group",
			AutoOffsetReset = AutoOffsetReset.Earliest,
			EnableAutoCommit = false
		};

		using var consumer = new ConsumerBuilder<Ignore, string>(consumerConfig)
			.SetErrorHandler((_, e) => _logger.LogError($"Kafka 底層錯誤: {e.Reason}"))
			.Build();

		consumer.Subscribe("telemetry-events");

		var buffer = new List<ConsumeResult<Ignore, string>>();
		var lastBatchTime = DateTime.UtcNow;

		_logger.LogInformation("Consumer 已啟動，開始監控 Kafka 訊息...");

		while (!stoppingToken.IsCancellationRequested)
		{
			try
			{
				var consumeResult = consumer.Consume(TimeSpan.FromMilliseconds(500));

				if (consumeResult != null)
				{
					buffer.Add(consumeResult);
				}

				bool isBatchFull = buffer.Count >= BatchSize;
				bool isTimeUp = buffer.Count > 0 && (DateTime.UtcNow - lastBatchTime) >= MaxWaitTime;

				if (isBatchFull || isTimeUp)
				{
					_logger.LogInformation($"[處理中] 準備批次寫入 {buffer.Count} 筆資料...");

					await BulkInsertToDatabaseAsync(buffer, stoppingToken);
					await BulkInsertToElasticsearchAsync(buffer, stoppingToken);

					var offsets = buffer.GroupBy(msg => msg.TopicPartition)
						.Select(g => new TopicPartitionOffset(g.Key, g.Last().Offset + 1)).ToList();
					consumer.Commit(offsets);

					_logger.LogInformation($"Kafka已寫入DB {buffer.Count} 筆資料至 PostgreSQL。");

					buffer.Clear();
					lastBatchTime = DateTime.UtcNow;
				}
			}
			catch (Exception ex)
			{
				_logger.LogError(ex, "Kafka寫入DB批次處理發生錯誤！原因: {Message}", ex.Message);

				buffer.Clear();
				lastBatchTime = DateTime.UtcNow;

				await Task.Delay(2000, stoppingToken);
			}
		}
	}

	private async Task BulkInsertToDatabaseAsync(List<ConsumeResult<Ignore, string>> buffer,
		CancellationToken stoppingToken)
	{
		var jsonOptions = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };

		// 先收集所有不重複的日期並確保分區表存在
		var uniqueDates = new HashSet<DateTimeOffset>();
		var processedMessages = new List<(TelemetryRequest Data, ConsumeResult<Ignore, string> Msg)>();

		foreach (var msg in buffer)
		{
			var data = JsonSerializer.Deserialize<TelemetryRequest>(msg.Message.Value, jsonOptions);
			if (data == null) continue;
			
			uniqueDates.Add(data.Timestamp);
			processedMessages.Add((data, msg));
		}

		foreach (var timestamp in uniqueDates)
		{
			await _partitionManager.EnsurePartitionExistsAsync(timestamp);
		}

		await using var batch = _dataSource.CreateBatch();

		foreach (var (data, msg) in processedMessages)
		{
			var cmd = batch.CreateBatchCommand();
			cmd.CommandText =
				@"INSERT INTO telemetry_history (id, device_id, geom, timestamp) VALUES (gen_random_uuid(), $1, ST_SetSRID(ST_MakePoint($2, $3), 4326), $4)";

			cmd.Parameters.AddWithValue(data.DeviceId ?? string.Empty);
			cmd.Parameters.AddWithValue(data.Lng);
			cmd.Parameters.AddWithValue(data.Lat);
			cmd.Parameters.AddWithValue(data.Timestamp);

			batch.BatchCommands.Add(cmd);
		}

		await batch.ExecuteNonQueryAsync(stoppingToken);
	}

	private async Task BulkInsertToElasticsearchAsync(List<ConsumeResult<Ignore, string>> buffer,
		CancellationToken stoppingToken)
	{
		var jsonOptions = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };

		var documents = new List<object>();

		foreach (var msg in buffer)
		{
			var data = JsonSerializer.Deserialize<TelemetryRequest>(msg.Message.Value, jsonOptions);
			if (data == null) continue;

			documents.Add(new
			{
				deviceId = data.DeviceId,
				timestamp = data.Timestamp,
				location = new { lat = data.Lat, lon = data.Lng }
			});
		}

		var indexName = $"geopulse-telemetry-{DateTime.UtcNow:yyyy.MM.dd}";

		var response = await _esClient.BulkAsync(b => b
			.Index(indexName)
			.CreateMany(documents), stoppingToken);

		if (!response.IsValidResponse)
		{
			_logger.LogError("寫入 Elasticsearch 失敗: {Error}", response.DebugInformation);
		}
	}
}