"""
Chat Template Helper
Auto-detect format: native chat template (Qwen/Llama/Mistral) atau simple (GPT-2).
Dipakai oleh chat.py, rag_module.py, dan trainer.py.
"""

FORMAT_NATIVE = "native"
FORMAT_SIMPLE = "simple"

DEFAULT_SYSTEM_PROMPT = "Anda adalah asisten AI yang ramah dan informatif."


def detect_format(tokenizer) -> str:
    """Deteksi format yang didukung tokenizer."""
    if getattr(tokenizer, "chat_template", None):
        return FORMAT_NATIVE
    return FORMAT_SIMPLE


def format_inference_prompt(tokenizer, user_message, system_message=None, history=None):
    """Format prompt untuk inference/chat."""
    fmt = detect_format(tokenizer)
    system_message = system_message or DEFAULT_SYSTEM_PROMPT

    if fmt == FORMAT_NATIVE:
        messages = [{"role": "system", "content": system_message}]
        if history:
            for turn in history[-5:]:
                u = (turn.get("user") or "").strip()
                a = (turn.get("ai") or "").strip()
                if u and a:
                    messages.append({"role": "user", "content": u})
                    messages.append({"role": "assistant", "content": a})
        messages.append({"role": "user", "content": user_message})
        return tokenizer.apply_chat_template(
            messages, tokenize=False, add_generation_prompt=True
        )

    # Fallback: format lama "User: / AI:"
    parts = [system_message]
    if history:
        for turn in history[-2:]:
            u = (turn.get("user") or "").strip()
            a = (turn.get("ai") or "").strip()
            if u and a:
                parts.append(f"User: {u}")
                parts.append(f"AI: {a}")
    parts.append(f"User: {user_message}")
    parts.append("AI:")
    return "\n".join(parts)


def format_training_sample(tokenizer, user_message, ai_response, system_message=None):
    """Format 1 Q&A untuk training."""
    fmt = detect_format(tokenizer)
    system_message = system_message or DEFAULT_SYSTEM_PROMPT

    if fmt == FORMAT_NATIVE:
        messages = [
            {"role": "system", "content": system_message},
            {"role": "user", "content": user_message},
            {"role": "assistant", "content": ai_response},
        ]
        return tokenizer.apply_chat_template(
            messages, tokenize=False, add_generation_prompt=False
        )

    eos = tokenizer.eos_token or ""
    return f"User: {user_message}\nAI: {ai_response}{eos}"


def tokenize_for_training(tokenizer, text, max_length):
    """Tokenize + prompt masking untuk training."""
    enc = tokenizer(
        text,
        truncation=True,
        max_length=max_length,
        padding=False,
        return_tensors=None,
    )
    ids = enc["input_ids"]
    labels = list(ids)
    fmt = detect_format(tokenizer)

    marker = "<|im_start|>assistant\n" if fmt == FORMAT_NATIVE else "AI:"
    marker_ids = tokenizer.encode(marker, add_special_tokens=False)
    mlen = len(marker_ids)

    if mlen > 0 and len(ids) > mlen:
        pos = -1
        for i in range(len(ids) - mlen, -1, -1):
            if ids[i:i + mlen] == marker_ids:
                pos = i + mlen
                break
        if pos > 0:
            for i in range(min(pos, len(labels))):
                labels[i] = -100

    return {
        "input_ids": ids,
        "attention_mask": enc["attention_mask"],
        "labels": labels,
    }


def tokenize_batch_for_training(examples, tokenizer, max_length):
    """Tokenize batch (untuk dataset.map)."""
    result = {"input_ids": [], "attention_mask": [], "labels": []}
    for text in examples["text"]:
        out = tokenize_for_training(tokenizer, text, max_length)
        result["input_ids"].append(out["input_ids"])
        result["attention_mask"].append(out["attention_mask"])
        result["labels"].append(out["labels"])
    return result