"""
Training script for conditional diffusion on CAMELS LH (6 cosmological parameters).

Same training theory as DDPM_HI_Emulation_improved (2-label): DDPM noise prediction,
DDIM sampling, ConditionalUNet with time + label embeddings, label z-score from train split,
EMA, optional AMP, cosine LR, early stopping.

Changes from original:
- EMA weights are now applied before validation and sampling
- Training args are saved to args.txt for evaluation script
- Fixed --normalize_labels and --use_ddim flags (were un-disableable)
- Added mixed-precision (AMP) training support
- Fixed loss averaging to be per-sample rather than per-batch
- Added weights_only=True to torch.load for security
"""

import argparse
import json
import os
import random
import time

import matplotlib.pyplot as plt
import numpy as np
import torch
import torch.optim as optim
from tqdm import tqdm

from dataset_conditional import DEFAULT_DATA_DIR, get_conditional_dataloaders
from diffusion_conditional import ConditionalDiffusionModel, GaussianDiffusion
from unet_conditional import ConditionalUNet

# Weights & Biases (optional)
try:
    import wandb

    WANDB_AVAILABLE = True
except ImportError:
    WANDB_AVAILABLE = False
    print("Warning: wandb not available. Install with: pip install wandb")


class EMA:
    """Exponential Moving Average for model parameters"""

    def __init__(self, model, decay=0.9999):
        self.model = model
        self.decay = decay
        self.shadow = {}
        for name, param in model.named_parameters():
            if param.requires_grad:
                self.shadow[name] = param.data.clone()

    def update(self):
        for name, param in self.model.named_parameters():
            if param.requires_grad:
                self.shadow[name] = self.decay * self.shadow[name] + (1 - self.decay) * param.data

    def apply_shadow(self):
        self.backup = {
            name: param.data.clone() for name, param in self.model.named_parameters() if param.requires_grad
        }
        for name, param in self.model.named_parameters():
            if param.requires_grad:
                param.data = self.shadow[name]

    def restore(self):
        for name, param in self.model.named_parameters():
            if param.requires_grad:
                param.data = self.backup[name]
        self.backup = {}


def train_epoch(model, dataloader, optimizer, device, epoch, ema=None, use_wandb=False, scaler=None):
    model.train()
    total_loss = 0.0
    total_samples = 0
    pbar = tqdm(dataloader, desc=f"Epoch {epoch}")

    for batch_idx, (images, labels) in enumerate(pbar):
        images = images.to(device)
        labels = labels.to(device)
        batch_size = images.shape[0]

        optimizer.zero_grad()

        if scaler is not None:
            with torch.amp.autocast("cuda"):
                loss = model.get_loss(images, labels)
            scaler.scale(loss).backward()
            scaler.unscale_(optimizer)
            torch.nn.utils.clip_grad_norm_(model.parameters(), 1.0)
            scaler.step(optimizer)
            scaler.update()
        else:
            loss = model.get_loss(images, labels)
            loss.backward()
            torch.nn.utils.clip_grad_norm_(model.parameters(), 1.0)
            optimizer.step()

        if ema is not None:
            ema.update()

        total_loss += loss.item() * batch_size
        total_samples += batch_size
        pbar.set_postfix({"loss": f"{loss.item():.4f}"})

        if use_wandb and batch_idx % 10 == 0:
            wandb.log({"batch_loss": loss.item(), "epoch": epoch, "batch": epoch * len(dataloader) + batch_idx})

    return total_loss / total_samples


def validate(model, dataloader, device):
    model.eval()
    total_loss = 0.0
    total_samples = 0
    with torch.no_grad():
        for images, labels in tqdm(dataloader, desc="Validating"):
            images = images.to(device)
            labels = labels.to(device)
            batch_size = images.shape[0]
            loss = model.get_loss(images, labels)
            total_loss += loss.item() * batch_size
            total_samples += batch_size
    return total_loss / total_samples


def save_checkpoint(model, optimizer, ema, epoch, loss, save_dir, is_best=False, last_improvement_epoch=None, scheduler=None):
    checkpoint = {
        "epoch": epoch,
        "model_state_dict": model.state_dict(),
        "optimizer_state_dict": optimizer.state_dict(),
        "loss": loss,
    }
    if ema is not None:
        checkpoint["ema_shadow"] = ema.shadow
    if last_improvement_epoch is not None:
        checkpoint["last_improvement_epoch"] = last_improvement_epoch
    if scheduler is not None:
        checkpoint["scheduler_state_dict"] = scheduler.state_dict()

    torch.save(checkpoint, os.path.join(save_dir, "checkpoint_latest.pt"))
    if is_best:
        torch.save(checkpoint, os.path.join(save_dir, "best_model.pt"))
        print(f"Saved best model at epoch {epoch+1}")

    if (epoch + 1) % 20 == 0:
        torch.save(checkpoint, os.path.join(save_dir, f"checkpoint_epoch_{epoch+1}.pt"))

    print(f"Saved checkpoint at epoch {epoch+1}")


def sample_images(model, diffusion, device, save_path, test_labels, ema=None, n_samples=8, epoch=0, use_ddim=True, ddim_steps=50, use_wandb=False):
    if ema is not None:
        ema.apply_shadow()

    model.eval()
    labels = test_labels[:n_samples].to(device)

    with torch.no_grad():
        samples = diffusion.sample(
            model,
            labels=labels,
            channels=1,
            height=256,
            width=256,
            device=device,
            progress=True,
            use_ddim=use_ddim,
            ddim_steps=ddim_steps,
            eta=0.0,
        )

    if ema is not None:
        ema.restore()

    n_cols = min(n_samples, 4)
    n_rows = (n_samples + n_cols - 1) // n_cols
    fig, axes = plt.subplots(n_rows, n_cols, figsize=(4.5 * n_cols, 4.5 * n_rows))
    if n_rows == 1 and n_cols == 1:
        axes = np.array([[axes]])
    elif n_rows == 1:
        axes = axes[np.newaxis, :]
    elif n_cols == 1:
        axes = axes[:, np.newaxis]
    for i in range(n_rows * n_cols):
        ax = axes[i // n_cols, i % n_cols]
        if i < n_samples:
            img = samples[i, 0].cpu().numpy()
            label_vals = labels[i].cpu().tolist()
            label_str = ", ".join(f"{v:.2f}" for v in label_vals)
            ax.imshow(img, vmin=-1, vmax=1)
            ax.set_title(label_str, fontsize=10)
        ax.axis("off")

    plt.suptitle(f"Generated Samples - Epoch {epoch}", fontsize=14)
    plt.tight_layout()
    plt.savefig(save_path, dpi=150, bbox_inches="tight")

    if use_wandb:
        wandb.log({"generated_samples": wandb.Image(save_path), "epoch": epoch})
    plt.close()
    print(f"Saved samples to {save_path}")


def save_training_args(args, output_dir):
    """Save training arguments so the evaluation script can reconstruct the model."""
    args_path = os.path.join(output_dir, "args.txt")
    with open(args_path, "w", encoding="utf-8") as f:
        for key, value in vars(args).items():
            f.write(f"{key}: {value}\n")
    args_json_path = os.path.join(output_dir, "args.json")
    with open(args_json_path, "w", encoding="utf-8") as f:
        json.dump(vars(args), f, indent=2)
    print(f"Saved training args to {args_path} and {args_json_path}")


def main():
    parser = argparse.ArgumentParser(description="Train conditional diffusion (LH 6-parameter)")
    # Model
    parser.add_argument("--label_dim", type=int, default=6)
    parser.add_argument("--base_channels", type=int, default=64)
    parser.add_argument("--channel_multipliers", type=int, nargs="+", default=[1, 2, 4, 8])
    parser.add_argument("--attention_levels", type=int, nargs="+", default=[2, 3])
    parser.add_argument("--dropout", type=float, default=0.1)
    # Diffusion
    parser.add_argument("--timesteps", type=int, default=1500)
    parser.add_argument("--beta_start", type=float, default=1e-4)
    parser.add_argument("--beta_end", type=float, default=0.02)
    parser.add_argument("--schedule_type", type=str, default="linear")
    # Training
    parser.add_argument("--epochs", type=int, default=100)
    parser.add_argument("--batch_size", type=int, default=8)
    parser.add_argument("--lr", type=float, default=2e-4)
    parser.add_argument("--ema_decay", type=float, default=0.9999)
    parser.add_argument("--num_workers", type=int, default=4)
    parser.add_argument("--early_stop_patience", type=int, default=30)
    parser.add_argument(
        "--use_amp",
        action="store_true",
        default=False,
        help="Enable mixed-precision training (recommended for GPU)",
    )
    # Data
    parser.add_argument(
        "--data_dir",
        type=str,
        default=DEFAULT_DATA_DIR,
        help="Directory with *_LH_6.npy and *_labels_LH.npy (same rule as improved repo: e.g. .../LH_data/params_6)",
    )
    parser.add_argument("--normalize_labels", action=argparse.BooleanOptionalAction, default=True)
    # Output
    parser.add_argument("--output_dir", type=str, default="outputs_conditional_6param")
    parser.add_argument("--resume", type=str, default="")
    parser.add_argument(
        "--resume_refresh_scheduler",
        action="store_true",
        help="On resume, rebuild cosine LR scheduler for --epochs (last_epoch=start-1) instead of loading saved scheduler; use when extending training beyond the original epoch count",
    )
    parser.add_argument("--sample_every", type=int, default=10)
    parser.add_argument("--use_ddim", action=argparse.BooleanOptionalAction, default=True)
    parser.add_argument("--ddim_steps", type=int, default=50)
    # WandB
    parser.add_argument("--use_wandb", action="store_true", default=False)
    parser.add_argument("--wandb_project", type=str, default="ddpm_cosmology")
    parser.add_argument("--wandb_entity", type=str, default="")
    parser.add_argument("--wandb_run_name", type=str, default="")

    args = parser.parse_args()

    seed = 42
    random.seed(seed)
    np.random.seed(seed)
    torch.manual_seed(seed)
    if torch.cuda.is_available():
        torch.cuda.manual_seed_all(seed)
        torch.backends.cudnn.deterministic = True
        torch.backends.cudnn.benchmark = False

    use_wandb = args.use_wandb and WANDB_AVAILABLE
    if use_wandb:
        run_name = args.wandb_run_name or f"conditional_diffusion_{time.strftime('%Y%m%d_%H%M%S')}"
        wandb.init(project=args.wandb_project, entity=args.wandb_entity or None, name=run_name, config=vars(args))
        print(f"W&B run: {run_name}")

    timestamp = time.strftime("%Y%m%d_%H%M%S")
    output_dir = f"{args.output_dir}_{timestamp}"
    os.makedirs(output_dir, exist_ok=True)
    os.makedirs(os.path.join(output_dir, "checkpoints"), exist_ok=True)
    os.makedirs(os.path.join(output_dir, "samples"), exist_ok=True)

    save_training_args(args, output_dir)

    device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
    print(f"Using device: {device}")

    scaler = torch.amp.GradScaler("cuda") if args.use_amp and torch.cuda.is_available() else None
    if scaler:
        print("Mixed-precision training enabled (AMP)")

    print("\nLoading data...")
    train_loader, val_loader, test_loader = get_conditional_dataloaders(
        data_dir=args.data_dir,
        batch_size=args.batch_size,
        num_workers=args.num_workers,
        normalize_labels=args.normalize_labels,
        label_dim=args.label_dim,
    )
    _, test_labels = next(iter(test_loader))

    print("\nCreating model...")
    unet = ConditionalUNet(
        in_channels=1,
        out_channels=1,
        label_dim=args.label_dim,
        base_channels=args.base_channels,
        channel_multipliers=args.channel_multipliers,
        attention_levels=args.attention_levels,
        dropout=args.dropout,
    )
    diffusion = GaussianDiffusion(
        timesteps=args.timesteps,
        beta_start=args.beta_start,
        beta_end=args.beta_end,
        schedule_type=args.schedule_type,
    )

    model = ConditionalDiffusionModel(unet, diffusion).to(device)
    print(f"Model parameters: {sum(p.numel() for p in model.parameters()):,}")

    optimizer = optim.AdamW(model.parameters(), lr=args.lr, weight_decay=0.01)
    ema = EMA(model, decay=args.ema_decay)
    scheduler = optim.lr_scheduler.CosineAnnealingLR(optimizer, T_max=args.epochs)

    start_epoch = 0
    best_val_loss = float("inf")
    last_improvement_epoch = -1
    if args.resume:
        print(f"Resuming from {args.resume}")
        checkpoint = torch.load(args.resume, map_location=device, weights_only=False)
        model.load_state_dict(checkpoint["model_state_dict"])
        optimizer.load_state_dict(checkpoint["optimizer_state_dict"])
        if "ema_shadow" in checkpoint:
            ema.shadow = checkpoint["ema_shadow"]
        start_epoch = checkpoint["epoch"] + 1
        best_val_loss = checkpoint.get("loss", float("inf"))
        last_improvement_epoch = checkpoint.get("last_improvement_epoch", -1)
        if args.resume_refresh_scheduler:
            scheduler = optim.lr_scheduler.CosineAnnealingLR(
                optimizer, T_max=args.epochs, last_epoch=start_epoch - 1
            )
            print(
                f"Rebuilt LR scheduler for extended run: T_max={args.epochs}, "
                f"resume at epoch {start_epoch + 1} (last_epoch={start_epoch - 1})"
            )
        elif "scheduler_state_dict" in checkpoint:
            scheduler.load_state_dict(checkpoint["scheduler_state_dict"])

    print("\nStarting training...")
    losses = {"train": [], "val": []}

    for epoch in range(start_epoch, args.epochs):
        train_loss = train_epoch(model, train_loader, optimizer, device, epoch, ema, use_wandb, scaler=scaler)

        if ema is not None:
            ema.apply_shadow()
        val_loss = validate(model, val_loader, device)
        if ema is not None:
            ema.restore()

        losses["train"].append(train_loss)
        losses["val"].append(val_loss)
        scheduler.step()

        if use_wandb:
            wandb.log(
                {
                    "epoch": epoch + 1,
                    "train_loss": train_loss,
                    "val_loss": val_loss,
                    "learning_rate": optimizer.param_groups[0]["lr"],
                }
            )

        print(
            f"\nEpoch {epoch+1}/{args.epochs} | Train: {train_loss:.6f} | Val: {val_loss:.6f} | "
            f"LR: {optimizer.param_groups[0]['lr']:.6e}"
        )

        is_best = val_loss < best_val_loss
        if is_best:
            best_val_loss = val_loss
            last_improvement_epoch = epoch

        save_checkpoint(
            model,
            optimizer,
            ema,
            epoch,
            val_loss,
            os.path.join(output_dir, "checkpoints"),
            is_best=is_best,
            last_improvement_epoch=last_improvement_epoch,
            scheduler=scheduler,
        )

        if epoch - last_improvement_epoch >= args.early_stop_patience:
            print(f"Early stopping at epoch {epoch+1}")
            break

        if (epoch + 1) % args.sample_every == 0:
            sample_path = os.path.join(output_dir, "samples", f"samples_epoch_{epoch+1}.png")
            sample_images(
                model,
                diffusion,
                device,
                sample_path,
                test_labels,
                ema=ema,
                epoch=epoch + 1,
                use_ddim=args.use_ddim,
                ddim_steps=args.ddim_steps,
                use_wandb=use_wandb,
            )

        if (epoch + 1) % 5 == 0:
            plt.figure(figsize=(10, 5))
            plt.plot(losses["train"], label="Train Loss")
            plt.plot(losses["val"], label="Val Loss")
            plt.yscale("log")
            plt.xlabel("Epoch")
            plt.ylabel("Loss")
            plt.title("Training Progress")
            plt.legend()
            plt.grid(True, alpha=0.3)
            plt.savefig(os.path.join(output_dir, "losses.png"), dpi=150)
            plt.close()

    print(f"\nTraining completed! Best val loss: {best_val_loss:.6f}")
    print(f"Results saved to: {output_dir}")
    if use_wandb:
        wandb.finish()


if __name__ == "__main__":
    main()