"""
Caso de uso para Backtesting.

Implementa la lógica de aplicación para evaluar la precisión
de pronósticos usando datos históricos.
"""

import math
from typing import List
from app.domain.services.forecast_service import ForecastService
from app.domain.models.time_series import TimeSeries
from app.domain.models.forecast_config import ForecastConfig
from app.application.dtos.backtest_dtos import (
    BacktestInputDTO,
    BacktestOutputDTO,
    BacktestMetricsDTO
)
from app.utils.logger import setup_logger

logger = setup_logger(__name__)


class BacktestUseCase:
    """
    Caso de uso: Backtesting.
    
    Responsabilidad: Evaluar precisión del modelo usando datos históricos.
    Divide los datos en train/test y calcula métricas de error.
    """
    
    def __init__(self, forecast_service: ForecastService):
        """
        Inicializa el caso de uso.
        
        Args:
            forecast_service: Servicio de dominio para forecasting
        """
        self.forecast_service = forecast_service
        logger.info("BacktestUseCase initialized")
    
    def execute(self, input_dto: BacktestInputDTO) -> BacktestOutputDTO:
        """
        Ejecuta el caso de uso de backtesting.
        
        Args:
            input_dto: Datos de entrada con serie completa y tamaño de test
        
        Returns:
            BacktestOutputDTO: Resultados del backtest con métricas
        
        Raises:
            ValueError: Si los datos son inválidos
            RuntimeError: Si falla el backtest
        """
        logger.info(
            f"Executing backtest: {len(input_dto.values)} total points, "
            f"{input_dto.test_size} test points"
        )
        
        # Validar entrada
        input_dto.validate()
        
        # Dividir en train/test
        train_values = input_dto.values[:-input_dto.test_size]
        test_values = input_dto.values[-input_dto.test_size:]
        
        train_timestamps = None
        test_timestamps = None
        
        if input_dto.timestamps:
            train_timestamps = input_dto.timestamps[:-input_dto.test_size]
            test_timestamps = input_dto.timestamps[-input_dto.test_size:]
        
        logger.info(f"Train size: {len(train_values)}, Test size: {len(test_values)}")
        
        # Crear modelos de dominio para train
        train_series = TimeSeries(
            values=train_values,
            timestamps=train_timestamps,
            freq=input_dto.freq
        )
        
        config = ForecastConfig(
            prediction_length=input_dto.test_size,
            quantile_levels=input_dto.quantile_levels,
            freq=input_dto.freq
        )
        
        # Ejecutar pronóstico sobre datos de train
        try:
            result = self.forecast_service.forecast_univariate(train_series, config)
            logger.info(f"Forecast completed: {len(result.median)} predictions")
        except Exception as e:
            logger.error(f"Backtest forecast failed: {e}", exc_info=True)
            raise RuntimeError(f"Backtest forecast failed: {str(e)}") from e
        
        # Comparar con valores reales
        forecast_values = result.median
        actual_values = test_values
        
        # Calcular errores
        errors = [
            actual - forecast
            for actual, forecast in zip(actual_values, forecast_values)
        ]
        
        # Calcular métricas
        metrics = self._calculate_metrics(actual_values, forecast_values)
        
        logger.info(
            f"Backtest metrics - MAE: {metrics.mae:.2f}, "
            f"MAPE: {metrics.mape:.2f}%, RMSE: {metrics.rmse:.2f}"
        )
        
        # Preparar timestamps de salida
        if test_timestamps:
            output_timestamps = test_timestamps
        else:
            output_timestamps = result.timestamps
        
        # Crear DTO de salida
        output_dto = BacktestOutputDTO(
            forecast_values=forecast_values,
            actual_values=actual_values,
            errors=errors,
            metrics=metrics,
            timestamps=output_timestamps,
            quantiles=result.quantiles if result.quantiles else None
        )
        
        return output_dto
    
    def _calculate_metrics(
        self,
        actual: List[float],
        forecast: List[float]
    ) -> BacktestMetricsDTO:
        """
        Calcula métricas de error para el backtest.
        
        Args:
            actual: Valores reales
            forecast: Valores pronosticados
        
        Returns:
            BacktestMetricsDTO: Métricas calculadas
        """
        n = len(actual)
        
        # Mean Absolute Error
        mae = sum(abs(a - f) for a, f in zip(actual, forecast)) / n
        
        # Mean Absolute Percentage Error
        mape_values = []
        for a, f in zip(actual, forecast):
            if a != 0:
                mape_values.append(abs((a - f) / a))
        
        mape = (sum(mape_values) / len(mape_values) * 100) if mape_values else 0.0
        
        # Mean Squared Error
        mse = sum((a - f) ** 2 for a, f in zip(actual, forecast)) / n
        
        # Root Mean Squared Error
        rmse = math.sqrt(mse)
        
        return BacktestMetricsDTO(
            mae=mae,
            mape=mape,
            rmse=rmse,
            mse=mse
        )