import os, json
from datasets import Dataset
from sklearn.model_selection import train_test_split
from transformers import T5Tokenizer, T5ForConditionalGeneration, TrainingArguments, Trainer, DataCollatorForSeq2Seq


def load_squad(path: str):
    with open(path, "r", encoding="utf-8") as f:
        d = json.load(f)

    data = []
    for a in d.get("data", []):
        for p in a.get("paragraphs", []):
            ctx = p.get("context", "")
            for qa in p.get("qas", []):
                if qa.get("is_impossible") or not qa.get("answers"):
                    continue
                ans = qa["answers"][0].get("text", "")
                q = qa.get("question", "")
                if ans and q and ctx:
                    data.append({"input": f"answer: {ans} context: {ctx}", "target": q})
    return data


def tokenize(batch, tok, max_in=512, max_out=64):
    x = tok(batch["input"], max_length=max_in, truncation=True)
    y = tok(text_target=batch["target"], max_length=max_out, truncation=True)
    x["labels"] = y["input_ids"]
    return x


def latest_ckpt(out_dir: str):
    if not os.path.isdir(out_dir):
        return None

    best_step, best_path = -1, None
    for name in os.listdir(out_dir):
        if not name.startswith("checkpoint-"):
            continue
        try:
            step = int(name.split("-")[-1])
        except ValueError:
            continue
        if step > best_step:
            best_step, best_path = step, os.path.join(out_dir, name)

    return best_path


def main():
    data_path = "39k_train.json"
    out_dir = "t5-viet-qg-finetuned"
    logs_dir = "logs"
    model_name = "VietAI/vit5-base"

    print("Tải mô hình và tokenizer...")
    tok = T5Tokenizer.from_pretrained(model_name)
    model = T5ForConditionalGeneration.from_pretrained(model_name)

    print("Đọc và chia dữ liệu...")
    data = load_squad(data_path)
    tr, va = train_test_split(data, test_size=0.2, random_state=42)

    print("Tokenize dữ liệu...")
    tr_ds = Dataset.from_list(tr).map(
        lambda b: tokenize(b, tok),
        batched=True,
        remove_columns=["input", "target"],
    )
    va_ds = Dataset.from_list(va).map(
        lambda b: tokenize(b, tok),
        batched=True,
        remove_columns=["input", "target"],
    )

    print("Cấu hình huấn luyện (checkpoint + resume)...")
    args = TrainingArguments(
        output_dir=out_dir,
        overwrite_output_dir=False,
        per_device_train_batch_size=1,
        gradient_accumulation_steps=1,
        num_train_epochs=3,
        learning_rate=2e-4,
        weight_decay=0.01,
        warmup_steps=0,
        save_strategy="steps",
        save_steps=500,
        save_total_limit=100,
        eval_strategy="steps",
        eval_steps=500,
        load_best_model_at_end=True,
        metric_for_best_model="eval_loss",
        greater_is_better=False,
        logging_dir=logs_dir,
        logging_steps=10,
        fp16=True,
        report_to="none",
    )

    trainer = Trainer(
        model=model,
        args=args,
        train_dataset=tr_ds,
        eval_dataset=va_ds,
        tokenizer=tok,
        data_collator=DataCollatorForSeq2Seq(tokenizer=tok, model=model),
    )

    ckpt = latest_ckpt(out_dir)
    if ckpt:
        print(f"Phát hiện checkpoint: {ckpt} → Resume training")
        trainer.train(resume_from_checkpoint=ckpt)
    else:
        print("Không có checkpoint → Train từ đầu")
        trainer.train()

    print("Lưu mô hình cuối cùng...")
    trainer.save_model(out_dir)
    tok.save_pretrained(out_dir)

    print("Huấn luyện hoàn tất!")


if __name__ == "__main__":
    main()