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"""
train_clf.py β€” InceptionV3 binary classification on BDAPPV (panel / no panel).

Usage:
    python train_clf.py --provider google
    python train_clf.py --provider ign
    python train_clf.py --provider google --checkpoint weights/inception_google_best.pth
"""

import argparse
import os

import torch
from tqdm import tqdm
import torch.nn as nn
from torch.utils.data import DataLoader
from torchvision.models import inception_v3, Inception_V3_Weights

from datasets import load_dataset

from dataset import ClassificationDataset


# ── Metrics ───────────────────────────────────────────────────────────────────

def accuracy_f1(logits, labels, threshold=0.0):
    preds   = (logits > threshold).float()
    correct = (preds == labels).float().mean().item()
    tp = (preds * labels).sum().item()
    fp = (preds * (1 - labels)).sum().item()
    fn = ((1 - preds) * labels).sum().item()
    prec = tp / max(tp + fp, 1e-6)
    rec  = tp / max(tp + fn, 1e-6)
    f1   = 2 * prec * rec / max(prec + rec, 1e-6)
    return correct, f1


# ── Main ──────────────────────────────────────────────────────────────────────

def train(args):
    device = (
        torch.device("mps")  if torch.backends.mps.is_available() else
        torch.device("cuda") if torch.cuda.is_available() else
        torch.device("cpu")
    )
    print(f"Device : {device}")
    print(f"Provider: {args.provider}  |  effective batch: {args.batch_size * args.grad_accum}")

    # ── Data ──────────────────────────────────────────────────────────────────
    print("Loading dataset from HuggingFace Hub...")
    ds = load_dataset("gabrielkasmi/bdappv", args.provider)

    train_ds = ClassificationDataset(ds["train"],      img_size=299, augment=True)
    val_ds   = ClassificationDataset(ds["validation"], img_size=299, augment=False)

    print(f"  train : {len(train_ds):,}  |  val : {len(val_ds):,}")

    train_loader = DataLoader(
        train_ds, batch_size=args.batch_size, shuffle=True,
        num_workers=args.num_workers, pin_memory=(device.type != "mps"),
    )
    val_loader = DataLoader(
        val_ds, batch_size=args.batch_size, shuffle=False,
        num_workers=args.num_workers, pin_memory=(device.type != "mps"),
    )

    # ── Model ─────────────────────────────────────────────────────────────────
    model = inception_v3(weights=Inception_V3_Weights.DEFAULT)

    if args.checkpoint:
        # Poids issus d'un modΓ¨le Γ  2 classes β€” on charge avec la tΓͺte originale
        # puis on la remplace par une tΓͺte binaire (1 sortie, BCEWithLogitsLoss)
        model.fc           = nn.Linear(model.fc.in_features, 2)
        model.AuxLogits.fc = nn.Linear(model.AuxLogits.fc.in_features, 2)
        ckpt  = torch.load(args.checkpoint, map_location="cpu", weights_only=False)
        state = ckpt["model_state_dict"] if isinstance(ckpt, dict) else ckpt
        model.load_state_dict(state, strict=True)
        print(f"Loaded checkpoint: {args.checkpoint}")

    # Remplace la tΓͺte par 1 sortie pour BCEWithLogitsLoss
    model.fc           = nn.Linear(model.fc.in_features, 1)
    model.AuxLogits.fc = nn.Linear(model.AuxLogits.fc.in_features, 1)

    model = model.to(device)

    # ── Optimizer + scheduler ─────────────────────────────────────────────────
    optimizer = torch.optim.AdamW(model.parameters(), lr=args.lr, weight_decay=1e-4)
    scheduler = torch.optim.lr_scheduler.CosineAnnealingLR(optimizer, T_max=args.epochs)
    criterion = nn.BCEWithLogitsLoss()

    # ── Training loop ─────────────────────────────────────────────────────────
    os.makedirs(args.out_dir, exist_ok=True)
    best_f1      = 0.0
    patience_ctr = 0

    for epoch in range(1, args.epochs + 1):
        model.train()
        total_loss = 0.0
        optimizer.zero_grad()

        pbar = tqdm(train_loader, desc=f"Epoch {epoch}/{args.epochs}", leave=False)
        for step, (images, labels) in enumerate(pbar):
            images = images.to(device)
            labels = labels.to(device).unsqueeze(1)

            out    = model(images)
            logits = out.logits if hasattr(out, "logits") else out[0]
            aux    = out.aux_logits if hasattr(out, "aux_logits") else out[1]

            loss = (criterion(logits, labels) + 0.4 * criterion(aux, labels)) / args.grad_accum
            loss.backward()
            total_loss += loss.item() * args.grad_accum
            pbar.set_postfix(loss=f"{loss.item() * args.grad_accum:.4f}")

            if (step + 1) % args.grad_accum == 0 or (step + 1) == len(train_loader):
                optimizer.step()
                optimizer.zero_grad()

        # ── Validation ────────────────────────────────────────────────────────
        model.eval()
        all_logits, all_labels = [], []
        with torch.no_grad():
            for images, labels in val_loader:
                images = images.to(device)
                logits = model(images)
                if hasattr(logits, "logits"):
                    logits = logits.logits
                all_logits.append(logits.cpu())
                all_labels.append(labels.unsqueeze(1))

        all_logits = torch.cat(all_logits)
        all_labels = torch.cat(all_labels)
        acc, f1    = accuracy_f1(all_logits, all_labels)
        avg_loss   = total_loss / len(train_loader)

        print(f"Epoch {epoch:3d}/{args.epochs}  loss={avg_loss:.4f}  val_acc={acc:.4f}  val_f1={f1:.4f}")

        scheduler.step()

        if f1 > best_f1:
            best_f1      = f1
            patience_ctr = 0
            ckpt_path    = os.path.join(args.out_dir, f"inception_{args.provider}_best.pth")
            torch.save(model.state_dict(), ckpt_path)
            print(f"  β†’ checkpoint saved (F1={best_f1:.4f})")
        else:
            patience_ctr += 1
            if patience_ctr >= args.patience:
                print(f"\nEarly stopping β€” no improvement for {args.patience} epochs.")
                break

    print(f"\nDone. Best val F1: {best_f1:.4f}")
    print(f"Weights: {os.path.join(args.out_dir, f'inception_{args.provider}_best.pth')}")


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("--provider",    default="google", choices=["google", "ign"])
    parser.add_argument("--epochs",      type=int,   default=50)
    parser.add_argument("--batch_size",  type=int,   default=8)
    parser.add_argument("--grad_accum",  type=int,   default=4,   help="Gradient accumulation steps")
    parser.add_argument("--lr",          type=float, default=1e-4)
    parser.add_argument("--num_workers", type=int,   default=2,   help="Workers pour le dataloader")
    parser.add_argument("--checkpoint",  default=None)
    parser.add_argument("--out_dir",     default="weights")
    parser.add_argument("--patience",    type=int,   default=7,   help="Early stopping patience (epochs)")
    args = parser.parse_args()
    train(args)