"""
Training script for TTV-1B Text-to-Video Model
Supports distributed training, mixed precision, and gradient checkpointing
"""

import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.utils.data import Dataset, DataLoader
from torch.cuda.amp import autocast, GradScaler
from torch.optim import AdamW
from torch.optim.lr_scheduler import CosineAnnealingLR
import os
import json
from pathlib import Path
from tqdm import tqdm
import numpy as np
from typing import Dict, List, Optional
import logging

from video_ttv_1b import VideoTTV1B, DDPMScheduler


# Configure logging
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
logger = logging.getLogger(__name__)


class VideoTextDataset(Dataset):
    """Dataset for video-text pairs"""
    def __init__(self, video_dir: str, annotation_file: str, 
                 num_frames: int = 16, img_size: tuple = (256, 256)):
        self.video_dir = Path(video_dir)
        self.num_frames = num_frames
        self.img_size = img_size
        
        # Load annotations
        with open(annotation_file, 'r') as f:
            self.annotations = json.load(f)
        
        self.video_ids = list(self.annotations.keys())
        logger.info(f"Loaded {len(self.video_ids)} video-text pairs")
        
    def __len__(self):
        return len(self.video_ids)
    
    def tokenize(self, text: str, max_length: int = 256) -> torch.Tensor:
        """Simple character-level tokenization (replace with proper tokenizer)"""
        tokens = [ord(c) % 50257 for c in text[:max_length]]
        tokens = tokens + [0] * (max_length - len(tokens))  # Pad
        return torch.tensor(tokens, dtype=torch.long)
    
    def load_video(self, video_path: Path) -> torch.Tensor:
        """Load and preprocess video (placeholder - implement with actual video loading)"""
        # In production, use libraries like torchvision.io or decord
        # This is a placeholder that generates synthetic data
        video = torch.randn(3, self.num_frames, *self.img_size)
        # Normalize to [-1, 1]
        video = (video - video.min()) / (video.max() - video.min()) * 2 - 1
        return video
    
    def __getitem__(self, idx: int):
        video_id = self.video_ids[idx]
        annotation = self.annotations[video_id]
        
        # Load video
        video_path = self.video_dir / f"{video_id}.mp4"
        video = self.load_video(video_path)
        
        # Tokenize text
        text = annotation['caption']
        text_tokens = self.tokenize(text)
        
        return {
            'video': video,
            'text_tokens': text_tokens,
            'text': text  # Keep original text for logging
        }


class Trainer:
    """Trainer class for TTV-1B model"""
    def __init__(
        self,
        model: nn.Module,
        train_dataset: Dataset,
        val_dataset: Optional[Dataset] = None,
        batch_size: int = 4,
        num_workers: int = 4,
        learning_rate: float = 1e-4,
        weight_decay: float = 0.01,
        num_epochs: int = 100,
        gradient_accumulation_steps: int = 4,
        mixed_precision: bool = True,
        gradient_checkpointing: bool = True,
        save_dir: str = './checkpoints',
        log_every: int = 100,
        save_every: int = 5000,
        device: str = 'cuda',
    ):
        self.model = model
        self.device = device
        self.batch_size = batch_size
        self.num_epochs = num_epochs
        self.gradient_accumulation_steps = gradient_accumulation_steps
        self.mixed_precision = mixed_precision
        self.log_every = log_every
        self.save_every = save_every
        self.save_dir = Path(save_dir)
        self.save_dir.mkdir(parents=True, exist_ok=True)
        
        # Enable gradient checkpointing to save memory
        if gradient_checkpointing:
            logger.info("Enabling gradient checkpointing")
            # Note: Requires implementing checkpointing in model blocks
        
        # Create dataloaders
        self.train_loader = DataLoader(
            train_dataset,
            batch_size=batch_size,
            shuffle=True,
            num_workers=num_workers,
            pin_memory=True,
            drop_last=True
        )
        
        self.val_loader = None
        if val_dataset:
            self.val_loader = DataLoader(
                val_dataset,
                batch_size=batch_size,
                shuffle=False,
                num_workers=num_workers,
                pin_memory=True
            )
        
        # Optimizer
        self.optimizer = AdamW(
            model.parameters(),
            lr=learning_rate,
            weight_decay=weight_decay,
            betas=(0.9, 0.999)
        )
        
        # Learning rate scheduler
        self.scheduler = CosineAnnealingLR(
            self.optimizer,
            T_max=num_epochs * len(self.train_loader),
            eta_min=learning_rate * 0.1
        )
        
        # Mixed precision scaler
        self.scaler = GradScaler() if mixed_precision else None
        
        # Diffusion scheduler
        self.noise_scheduler = DDPMScheduler(num_steps=1000)
        
        # Training state
        self.global_step = 0
        self.epoch = 0
        self.best_val_loss = float('inf')
        
    def train_step(self, batch: Dict[str, torch.Tensor]) -> float:
        """Single training step"""
        videos = batch['video'].to(self.device)
        text_tokens = batch['text_tokens'].to(self.device)
        
        # Sample random timesteps
        timesteps = torch.randint(
            0, self.noise_scheduler.num_steps,
            (videos.shape[0],),
            device=self.device
        )
        
        # Add noise to videos
        noise = torch.randn_like(videos)
        noisy_videos = self.noise_scheduler.add_noise(videos, timesteps, noise)
        
        # Forward pass
        if self.mixed_precision:
            with autocast():
                predicted_noise = self.model(noisy_videos, timesteps, text_tokens)
                loss = F.mse_loss(predicted_noise, noise)
                loss = loss / self.gradient_accumulation_steps
        else:
            predicted_noise = self.model(noisy_videos, timesteps, text_tokens)
            loss = F.mse_loss(predicted_noise, noise)
            loss = loss / self.gradient_accumulation_steps
        
        # Backward pass
        if self.mixed_precision:
            self.scaler.scale(loss).backward()
        else:
            loss.backward()
        
        return loss.item() * self.gradient_accumulation_steps
    
    @torch.no_grad()
    def validate(self) -> float:
        """Validation loop"""
        if self.val_loader is None:
            return 0.0
        
        self.model.eval()
        total_loss = 0.0
        num_batches = 0
        
        for batch in tqdm(self.val_loader, desc="Validating"):
            videos = batch['video'].to(self.device)
            text_tokens = batch['text_tokens'].to(self.device)
            
            timesteps = torch.randint(
                0, self.noise_scheduler.num_steps,
                (videos.shape[0],),
                device=self.device
            )
            
            noise = torch.randn_like(videos)
            noisy_videos = self.noise_scheduler.add_noise(videos, timesteps, noise)
            
            predicted_noise = self.model(noisy_videos, timesteps, text_tokens)
            loss = F.mse_loss(predicted_noise, noise)
            
            total_loss += loss.item()
            num_batches += 1
        
        avg_loss = total_loss / num_batches
        self.model.train()
        return avg_loss
    
    def save_checkpoint(self, suffix: str = ""):
        """Save model checkpoint"""
        checkpoint_path = self.save_dir / f"checkpoint_step_{self.global_step}{suffix}.pt"
        
        checkpoint = {
            'model_state_dict': self.model.state_dict(),
            'optimizer_state_dict': self.optimizer.state_dict(),
            'scheduler_state_dict': self.scheduler.state_dict(),
            'global_step': self.global_step,
            'epoch': self.epoch,
            'best_val_loss': self.best_val_loss,
        }
        
        if self.scaler:
            checkpoint['scaler_state_dict'] = self.scaler.state_dict()
        
        torch.save(checkpoint, checkpoint_path)
        logger.info(f"Saved checkpoint to {checkpoint_path}")
        
        # Save model config
        config_path = self.save_dir / "model_config.json"
        config = {
            'architecture': 'VideoTTV1B',
            'parameters': self.model.count_parameters(),
            'img_size': self.model.img_size,
            'num_frames': self.model.num_frames,
            'patch_size': self.model.patch_size,
            'hidden_dim': self.model.hidden_dim,
        }
        with open(config_path, 'w') as f:
            json.dump(config, f, indent=2)
    
    def load_checkpoint(self, checkpoint_path: str):
        """Load model checkpoint"""
        checkpoint = torch.load(checkpoint_path, map_location=self.device)
        
        self.model.load_state_dict(checkpoint['model_state_dict'])
        self.optimizer.load_state_dict(checkpoint['optimizer_state_dict'])
        self.scheduler.load_state_dict(checkpoint['scheduler_state_dict'])
        self.global_step = checkpoint['global_step']
        self.epoch = checkpoint['epoch']
        self.best_val_loss = checkpoint['best_val_loss']
        
        if self.scaler and 'scaler_state_dict' in checkpoint:
            self.scaler.load_state_dict(checkpoint['scaler_state_dict'])
        
        logger.info(f"Loaded checkpoint from {checkpoint_path}")
    
    def train(self):
        """Main training loop"""
        logger.info("Starting training...")
        logger.info(f"Total parameters: {self.model.count_parameters():,}")
        logger.info(f"Batch size: {self.batch_size}")
        logger.info(f"Gradient accumulation steps: {self.gradient_accumulation_steps}")
        logger.info(f"Effective batch size: {self.batch_size * self.gradient_accumulation_steps}")
        
        self.model.train()
        
        for epoch in range(self.epoch, self.num_epochs):
            self.epoch = epoch
            epoch_loss = 0.0
            num_batches = 0
            
            pbar = tqdm(self.train_loader, desc=f"Epoch {epoch+1}/{self.num_epochs}")
            
            for step, batch in enumerate(pbar):
                loss = self.train_step(batch)
                epoch_loss += loss
                num_batches += 1
                
                # Gradient accumulation
                if (step + 1) % self.gradient_accumulation_steps == 0:
                    # Clip gradients
                    if self.mixed_precision:
                        self.scaler.unscale_(self.optimizer)
                    torch.nn.utils.clip_grad_norm_(self.model.parameters(), 1.0)
                    
                    # Optimizer step
                    if self.mixed_precision:
                        self.scaler.step(self.optimizer)
                        self.scaler.update()
                    else:
                        self.optimizer.step()
                    
                    self.scheduler.step()
                    self.optimizer.zero_grad()
                    self.global_step += 1
                    
                    # Logging
                    if self.global_step % self.log_every == 0:
                        avg_loss = epoch_loss / num_batches
                        lr = self.scheduler.get_last_lr()[0]
                        logger.info(
                            f"Step {self.global_step} | "
                            f"Loss: {avg_loss:.4f} | "
                            f"LR: {lr:.2e}"
                        )
                    
                    # Save checkpoint
                    if self.global_step % self.save_every == 0:
                        self.save_checkpoint()
                
                # Update progress bar
                pbar.set_postfix({'loss': f'{loss:.4f}'})
            
            # Validation
            if self.val_loader:
                val_loss = self.validate()
                logger.info(f"Epoch {epoch+1} | Validation loss: {val_loss:.4f}")
                
                if val_loss < self.best_val_loss:
                    self.best_val_loss = val_loss
                    self.save_checkpoint(suffix="_best")
            
            # Save epoch checkpoint
            self.save_checkpoint(suffix=f"_epoch_{epoch+1}")
        
        logger.info("Training completed!")


def main():
    """Main training script"""
    # Configuration
    config = {
        'data_dir': './data/videos',
        'annotation_file': './data/annotations.json',
        'batch_size': 2,  # Small batch size for 1B model
        'num_workers': 4,
        'learning_rate': 1e-4,
        'weight_decay': 0.01,
        'num_epochs': 100,
        'gradient_accumulation_steps': 8,  # Effective batch size = 16
        'mixed_precision': True,
        'gradient_checkpointing': True,
        'save_dir': './checkpoints',
        'device': 'cuda' if torch.cuda.is_available() else 'cpu',
    }
    
    logger.info("Configuration:")
    for key, value in config.items():
        logger.info(f"  {key}: {value}")
    
    # Create synthetic dataset for demonstration
    # In production, replace with actual video dataset
    logger.warning("Using synthetic dataset - replace with real data for training")
    
    class SyntheticDataset(Dataset):
        def __init__(self, size=1000):
            self.size = size
        
        def __len__(self):
            return self.size
        
        def __getitem__(self, idx):
            return {
                'video': torch.randn(3, 16, 256, 256),
                'text_tokens': torch.randint(0, 50257, (256,)),
                'text': f"Sample video {idx}"
            }
    
    train_dataset = SyntheticDataset(size=10000)
    val_dataset = SyntheticDataset(size=1000)
    
    # Create model
    from video_ttv_1b import create_model
    model = create_model(config['device'])
    
    # Create trainer
    trainer = Trainer(
        model=model,
        train_dataset=train_dataset,
        val_dataset=val_dataset,
        **{k: v for k, v in config.items() if k not in ['data_dir', 'annotation_file', 'device']}
    )
    
    # Train
    trainer.train()


if __name__ == "__main__":
    main()