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

namespace GeoPulse_Pipeline;

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

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

	public KafkaConsumer(ILogger<KafkaConsumer> logger, IConfiguration configuration)
	{
		_logger = logger;
		_connectionString = configuration.GetConnectionString("DefaultConnection")
		                    ?? throw new ArgumentNullException("資料庫連線字串未設定");
		_kafkaHost = configuration["KafkaHost"];
	}

	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).Build();
		consumer.Subscribe("telemetry-events");

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

		try
		{
			while (!stoppingToken.IsCancellationRequested)
			{
				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)
				{
					await BulkInsertToDatabaseAsync(buffer, stoppingToken);

					var latestOffset = buffer.Last();
					consumer.Commit(latestOffset);

					_logger.LogInformation($"成功批次寫入 {buffer.Count} 筆資料至 PostgreSQL。");

					buffer.Clear();
					lastBatchTime = DateTime.UtcNow;
				}
			}
		}
		catch (Exception ex)
		{
			_logger.LogError($"發生錯誤: {ex.Message} \n {ex.StackTrace}");

			buffer.Clear();
		}
		finally
		{
			consumer.Close();
		}
	}

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