using System.Data;
using System.Text.Json;
using Confluent.Kafka;
using Npgsql;

namespace GeoPulse_Pipeline;

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

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

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

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

		var consumerConfig = new ConsumerConfig
		{
			BootstrapServers = _kafkaHost,
			GroupId = "telemetry-db-writer-group", // 💡 建議換個名字，強迫 Kafka 重置 Offset
			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 // 💡 關鍵修正：try 放在 while 裡面
			{
				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);

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

					_logger.LogInformation($"✅ [成功] 已寫入 {buffer.Count} 筆資料至 PostgreSQL。");

					buffer.Clear();
					lastBatchTime = DateTime.UtcNow;
				}
			}
			catch (Exception ex)
			{
				// 💡 就算這裡噴錯，程式也只是印出 Log，然後回到 while 頂部繼續跑下一輪
				_logger.LogError(ex, "❌ [失敗] 批次處理發生錯誤！原因: {Message}", ex.Message);

				// 發生錯誤後，為了避免壞資料卡死 buffer 導致無窮重試，這裡建議清空
				buffer.Clear();
				lastBatchTime = DateTime.UtcNow;

				// 稍微停 2 秒，避免在連續錯誤時瘋狂刷屏
				await Task.Delay(2000, stoppingToken);
			}
		}
	}

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

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

			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);
	}
}