"""
Training pipeline for emotion recognition models.
"""
import os
import json
from pathlib import Path
from datetime import datetime
from typing import Dict, Optional, Tuple, Callable

import numpy as np
import tensorflow as tf
from tensorflow.keras.models import Model
from tensorflow.keras.optimizers import Adam
from tensorflow.keras.callbacks import (
    EarlyStopping, ModelCheckpoint, ReduceLROnPlateau,
    TensorBoard, Callback
)

import sys
sys.path.append(str(Path(__file__).parent.parent.parent))
from src.config import (
    EPOCHS, LEARNING_RATE, LEARNING_RATE_FINE_TUNE,
    EARLY_STOPPING_PATIENCE, REDUCE_LR_PATIENCE, REDUCE_LR_FACTOR,
    MODELS_DIR, CUSTOM_CNN_PATH, MOBILENET_PATH, VGG_PATH
)


class TrainingProgressCallback(Callback):
    """Custom callback to track and display training progress."""
    
    def __init__(self, total_epochs: int):
        super().__init__()
        self.total_epochs = total_epochs
    
    def on_epoch_end(self, epoch, logs=None):
        logs = logs or {}
        print(f"\nEpoch {epoch + 1}/{self.total_epochs}")
        print(f"  Loss: {logs.get('loss', 0):.4f} - Accuracy: {logs.get('accuracy', 0):.4f}")
        print(f"  Val Loss: {logs.get('val_loss', 0):.4f} - Val Accuracy: {logs.get('val_accuracy', 0):.4f}")


class EmotionModelTrainer:
    """
    Trainer class for emotion recognition models.
    """
    
    def __init__(
        self,
        model: Model,
        model_name: str = "model",
        save_path: Optional[Path] = None,
        logs_dir: Optional[Path] = None
    ):
        """
        Initialize the trainer.
        
        Args:
            model: Keras model to train
            model_name: Name for the model (used for saving)
            save_path: Path to save the trained model
            logs_dir: Directory for TensorBoard logs
        """
        self.model = model
        self.model_name = model_name
        self.save_path = save_path or MODELS_DIR / f"{model_name}.h5"
        self.logs_dir = logs_dir or MODELS_DIR / "logs" / model_name
        
        self.history = None
        self.training_metadata = {}
        
        # Create directories
        Path(self.save_path).parent.mkdir(parents=True, exist_ok=True)
        Path(self.logs_dir).mkdir(parents=True, exist_ok=True)
    
    def compile(
        self,
        learning_rate: float = LEARNING_RATE,
        optimizer: Optional[tf.keras.optimizers.Optimizer] = None,
        loss: str = 'categorical_crossentropy',
        metrics: list = ['accuracy']
    ) -> None:
        """
        Compile the model.
        
        Args:
            learning_rate: Learning rate for optimizer
            optimizer: Custom optimizer (uses Adam if None)
            loss: Loss function
            metrics: Metrics to track
        """
        if optimizer is None:
            optimizer = Adam(learning_rate=learning_rate)
        
        self.model.compile(
            optimizer=optimizer,
            loss=loss,
            metrics=metrics
        )
        
        self.training_metadata['learning_rate'] = learning_rate
        self.training_metadata['loss_function'] = loss
        self.training_metadata['metrics'] = metrics
    
    def get_callbacks(
        self,
        use_early_stopping: bool = True,
        use_reduce_lr: bool = True,
        use_tensorboard: bool = True,
        use_checkpoint: bool = True,
        custom_callbacks: Optional[list] = None
    ) -> list:
        """
        Get training callbacks.
        
        Args:
            use_early_stopping: Whether to use early stopping
            use_reduce_lr: Whether to reduce LR on plateau
            use_tensorboard: Whether to log to TensorBoard
            use_checkpoint: Whether to save best model
            custom_callbacks: Additional custom callbacks
            
        Returns:
            List of callbacks
        """
        callbacks = []
        
        if use_early_stopping:
            callbacks.append(EarlyStopping(
                monitor='val_loss',
                patience=EARLY_STOPPING_PATIENCE,
                restore_best_weights=True,
                verbose=1
            ))
        
        if use_reduce_lr:
            callbacks.append(ReduceLROnPlateau(
                monitor='val_loss',
                factor=REDUCE_LR_FACTOR,
                patience=REDUCE_LR_PATIENCE,
                min_lr=1e-7,
                verbose=1
            ))
        
        if use_tensorboard:
            callbacks.append(TensorBoard(
                log_dir=str(self.logs_dir),
                histogram_freq=1,
                write_graph=True
            ))
        
        if use_checkpoint:
            callbacks.append(ModelCheckpoint(
                filepath=str(self.save_path),
                monitor='val_accuracy',
                save_best_only=True,
                mode='max',
                verbose=1
            ))
        
        if custom_callbacks:
            callbacks.extend(custom_callbacks)
        
        return callbacks
    
    def train(
        self,
        train_generator,
        val_generator,
        epochs: int = EPOCHS,
        class_weights: Optional[Dict] = None,
        callbacks: Optional[list] = None,
        verbose: int = 1
    ) -> Dict:
        """
        Train the model.
        
        Args:
            train_generator: Training data generator
            val_generator: Validation data generator
            epochs: Number of epochs
            class_weights: Optional class weights for imbalanced data
            callbacks: Optional custom callbacks (uses defaults if None)
            verbose: Verbosity mode
            
        Returns:
            Training history dictionary
        """
        if callbacks is None:
            callbacks = self.get_callbacks()
        
        # Add progress callback
        callbacks.append(TrainingProgressCallback(epochs))
        
        # Record training start
        start_time = datetime.now()
        self.training_metadata['training_started'] = start_time.isoformat()
        self.training_metadata['epochs_requested'] = epochs
        
        print(f"\n{'='*60}")
        print(f"Training {self.model_name}")
        print(f"{'='*60}")
        print(f"Epochs: {epochs}")
        print(f"Training samples: {train_generator.samples}")
        print(f"Validation samples: {val_generator.samples}")
        print(f"{'='*60}\n")
        
        # Train
        self.history = self.model.fit(
            train_generator,
            epochs=epochs,
            validation_data=val_generator,
            class_weight=class_weights,
            callbacks=callbacks,
            verbose=verbose
        )
        
        # Record training end
        end_time = datetime.now()
        duration = (end_time - start_time).total_seconds()
        
        self.training_metadata['training_ended'] = end_time.isoformat()
        self.training_metadata['training_duration_seconds'] = duration
        self.training_metadata['epochs_completed'] = len(self.history.history['loss'])
        self.training_metadata['final_accuracy'] = float(self.history.history['accuracy'][-1])
        self.training_metadata['final_val_accuracy'] = float(self.history.history['val_accuracy'][-1])
        self.training_metadata['best_val_accuracy'] = float(max(self.history.history['val_accuracy']))
        
        print(f"\n{'='*60}")
        print(f"Training Complete!")
        print(f"Duration: {duration/60:.2f} minutes")
        print(f"Best Validation Accuracy: {self.training_metadata['best_val_accuracy']:.4f}")
        print(f"{'='*60}\n")
        
        return self.history.history
    
    def fine_tune(
        self,
        train_generator,
        val_generator,
        epochs: int = 20,
        learning_rate: float = LEARNING_RATE_FINE_TUNE,
        unfreeze_layers: int = 30
    ) -> Dict:
        """
        Fine-tune a transfer learning model.
        
        Args:
            train_generator: Training data generator
            val_generator: Validation data generator
            epochs: Number of fine-tuning epochs
            learning_rate: Learning rate for fine-tuning
            unfreeze_layers: Number of layers to unfreeze
            
        Returns:
            Fine-tuning history
        """
        # Unfreeze top layers
        for layer in self.model.layers[-unfreeze_layers:]:
            layer.trainable = True
        
        # Recompile with lower learning rate
        self.compile(learning_rate=learning_rate)
        
        print(f"\nFine-tuning with learning rate: {learning_rate}")
        print(f"Unfrozen {unfreeze_layers} top layers")
        
        # Continue training
        return self.train(train_generator, val_generator, epochs=epochs)
    
    def save_training_history(self) -> None:
        """Save training history and metadata to files."""
        if self.history is None:
            print("No training history to save.")
            return
        
        # Save history as JSON
        history_path = self.save_path.with_suffix('.history.json')
        with open(history_path, 'w') as f:
            json.dump(self.history.history, f, indent=2)
        
        # Save metadata
        metadata_path = self.save_path.with_suffix('.meta.json')
        with open(metadata_path, 'w') as f:
            json.dump(self.training_metadata, f, indent=2)
        
        print(f"Training history saved to: {history_path}")
        print(f"Training metadata saved to: {metadata_path}")
    
    def get_training_summary(self) -> Dict:
        """
        Get a summary of the training results.
        
        Returns:
            Dictionary with training summary
        """
        if self.history is None:
            return {"status": "Not trained"}
        
        return {
            "model_name": self.model_name,
            "epochs_completed": len(self.history.history['loss']),
            "final_accuracy": self.history.history['accuracy'][-1],
            "final_val_accuracy": self.history.history['val_accuracy'][-1],
            "best_val_accuracy": max(self.history.history['val_accuracy']),
            "final_loss": self.history.history['loss'][-1],
            "final_val_loss": self.history.history['val_loss'][-1],
            "training_duration": self.training_metadata.get('training_duration_seconds', 0)
        }


def train_custom_cnn(
    train_generator,
    val_generator,
    epochs: int = EPOCHS,
    class_weights: Optional[Dict] = None
) -> Tuple[Model, Dict]:
    """
    Train the custom CNN model.
    
    Args:
        train_generator: Training data generator
        val_generator: Validation data generator
        epochs: Number of epochs
        class_weights: Optional class weights
        
    Returns:
        Tuple of (trained model, training history)
    """
    from src.models.custom_cnn import build_custom_cnn
    
    model = build_custom_cnn()
    trainer = EmotionModelTrainer(model, "custom_cnn", CUSTOM_CNN_PATH)
    trainer.compile()
    history = trainer.train(train_generator, val_generator, epochs, class_weights)
    trainer.save_training_history()
    
    return model, history


def train_mobilenet(
    train_generator,
    val_generator,
    epochs: int = EPOCHS,
    fine_tune_epochs: int = 20,
    class_weights: Optional[Dict] = None
) -> Tuple[Model, Dict]:
    """
    Train the MobileNetV2 model with fine-tuning.
    
    Args:
        train_generator: Training data generator (RGB, 96x96)
        val_generator: Validation data generator
        epochs: Initial training epochs
        fine_tune_epochs: Fine-tuning epochs
        class_weights: Optional class weights
        
    Returns:
        Tuple of (trained model, training history)
    """
    from src.models.mobilenet_model import build_mobilenet_model
    
    model = build_mobilenet_model()
    trainer = EmotionModelTrainer(model, "mobilenet_v2", MOBILENET_PATH)
    
    # Initial training with frozen base
    trainer.compile()
    history = trainer.train(train_generator, val_generator, epochs, class_weights)
    
    # Fine-tuning
    if fine_tune_epochs > 0:
        fine_tune_history = trainer.fine_tune(
            train_generator, val_generator, fine_tune_epochs
        )
        # Merge histories
        for key in history:
            history[key].extend(fine_tune_history[key])
    
    trainer.save_training_history()
    
    return model, history


def train_vgg(
    train_generator,
    val_generator,
    epochs: int = EPOCHS,
    fine_tune_epochs: int = 15,
    class_weights: Optional[Dict] = None
) -> Tuple[Model, Dict]:
    """
    Train the VGG-19 model with fine-tuning.
    
    Args:
        train_generator: Training data generator (RGB, 96x96)
        val_generator: Validation data generator
        epochs: Initial training epochs
        fine_tune_epochs: Fine-tuning epochs
        class_weights: Optional class weights
        
    Returns:
        Tuple of (trained model, training history)
    """
    from src.models.vgg_model import build_vgg_model
    
    model = build_vgg_model()
    trainer = EmotionModelTrainer(model, "vgg19", VGG_PATH)
    
    # Initial training with frozen base
    trainer.compile()
    history = trainer.train(train_generator, val_generator, epochs, class_weights)
    
    # Fine-tuning
    if fine_tune_epochs > 0:
        fine_tune_history = trainer.fine_tune(
            train_generator, val_generator, fine_tune_epochs
        )
        for key in history:
            history[key].extend(fine_tune_history[key])
    
    trainer.save_training_history()
    
    return model, history