# app.py — ZeroGPU-optimised Gradio app (HF Spaces)

import os
import tempfile
from datetime import datetime

import gradio as gr
import pandas as pd
import torch
from transformers import AutoModelForCausalLM, AutoTokenizer

# ---- ZeroGPU decorator ----
try:
    import spaces  # HF Spaces utility (provides @spaces.GPU())
except Exception:
    # Fallback: make a no-op decorator so the app still runs locally/CPU
    class _Noop:
        def GPU(self, *args, **kwargs):
            def deco(fn):
                return fn
            return deco
    spaces = _Noop()

# ---- Optional quantisation (GPU only) ----
try:
    from transformers import BitsAndBytesConfig
    HAS_BNB = True
except Exception:
    HAS_BNB = False

# ----------------------------
# Config
# ----------------------------

DEFAULT_MODELS = [
    "TinyLlama/TinyLlama-1.1B-Chat-v1.0",
    "Qwen/Qwen2.5-1.5B-Instruct",
    "neovalle/tinyllama-1.1B-h4rmony-trained",
]

# Keep batches reasonable on ZeroGPU for low latency
MICROBATCH = 4

# Cap encoder length to avoid wasting time on very long inputs
MAX_INPUT_TOKENS = 1024

# Speed on GPU (TF32 gives extra throughput on Ampere+)
if torch.cuda.is_available():
    torch.backends.cuda.matmul.allow_tf32 = True
    torch.backends.cudnn.allow_tf32 = True
else:
    # On CPU, reducing threads sometimes helps stability/predictability
    try:
        torch.set_num_threads(max(1, (os.cpu_count() or 4) // 2))
    except Exception:
        pass

_MODEL_CACHE = {}  # cache: model_id -> (tokenizer, model)


# ----------------------------
# Helpers
# ----------------------------

def _all_eos_ids(tok):
    """Collect a few likely EOS ids so generation can stop earlier."""
    ids = set()
    if tok.eos_token_id is not None:
        ids.add(tok.eos_token_id)
    for t in ("<|im_end|>", "<|endoftext|>", "</s>"):
        try:
            tid = tok.convert_tokens_to_ids(t)
            if isinstance(tid, int) and tid >= 0:
                ids.add(tid)
        except Exception:
            pass
    return list(ids) if ids else None


def _load_model(model_id: str):
    """Load & cache model/tokenizer. On GPU, prefer 4-bit NF4 with BF16 compute."""
    if model_id in _MODEL_CACHE:
        return _MODEL_CACHE[model_id]

    tok = AutoTokenizer.from_pretrained(model_id, use_fast=True)

    # Ensure a pad token for batch generate()
    if tok.pad_token is None:
        if tok.eos_token is not None:
            tok.pad_token = tok.eos_token
        else:
            tok.add_special_tokens({"pad_token": "<|pad|>"})

    use_gpu = torch.cuda.is_available()
    dtype = (
        torch.bfloat16 if (use_gpu and torch.cuda.is_bf16_supported()) else
        (torch.float16 if use_gpu else torch.float32)
    )

    quant_cfg = None
    if use_gpu and HAS_BNB:
        quant_cfg = BitsAndBytesConfig(
            load_in_4bit=True,
            bnb_4bit_use_double_quant=True,
            bnb_4bit_quant_type="nf4",
            bnb_4bit_compute_dtype=torch.bfloat16 if torch.cuda.is_bf16_supported() else torch.float16,
        )

    model = AutoModelForCausalLM.from_pretrained(
        model_id,
        torch_dtype=(torch.bfloat16 if use_gpu else torch.float32),
        low_cpu_mem_usage=True,
        device_map="auto",
        quantization_config=quant_cfg,  # 4-bit on GPU if available; None on CPU
        trust_remote_code=True,         # helps for chat templates (e.g., Qwen)
        # attn_implementation="flash_attention_2",  # enable only if flash-attn in requirements
    ).eval()

    # Resize if we added new pad token
    if model.get_input_embeddings().num_embeddings != len(tok):
        model.resize_token_embeddings(len(tok))

    # Prefer KV cache
    try:
        model.generation_config.use_cache = True
    except Exception:
        pass

    _MODEL_CACHE[model_id] = (tok, model)
    return tok, model


def _format_prompt(tokenizer, system_prompt: str, user_prompt: str) -> str:
    sys = (system_prompt or "").strip()
    usr = (user_prompt or "").strip()

    if hasattr(tokenizer, "apply_chat_template") and tokenizer.chat_template:
        messages = []
        if sys:
            messages.append({"role": "system", "content": sys})
        messages.append({"role": "user", "content": usr})
        return tokenizer.apply_chat_template(
            messages,
            tokenize=False,
            add_generation_prompt=True,
        )

    prefix = f"<<SYS>>\n{sys}\n<</SYS>>\n\n" if sys else ""
    return f"{prefix}<<USER>>\n{usr}\n<</USER>>\n<<ASSISTANT>>\n"


@torch.inference_mode()
def _generate_microbatch(tok, model, formatted_prompts, gen_kwargs):
    """Generate for a list of formatted prompts. Returns (texts, tokens_out)."""
    device = model.device
    eos_ids = _all_eos_ids(tok)

    enc = tok(
        formatted_prompts,
        return_tensors="pt",
        padding=True,
        truncation=True,
        max_length=MAX_INPUT_TOKENS,
    ).to(device)

    prompt_lens = enc["attention_mask"].sum(dim=1)
    outputs = model.generate(
        **enc,
        eos_token_id=eos_ids,
        pad_token_id=tok.pad_token_id,
        **gen_kwargs,
    )

    texts, toks_out = [], []
    for i in range(outputs.size(0)):
        start = int(prompt_lens[i].item())
        gen_ids = outputs[i, start:]
        texts.append(tok.decode(gen_ids, skip_special_tokens=True).strip())
        toks_out.append(int(gen_ids.numel()))
    return texts, toks_out


def generate_batch_df(
    model_id: str,
    system_prompt: str,
    prompts_multiline: str,
    max_new_tokens: int,
    temperature: float,
    top_p: float,
    top_k: int,
    repetition_penalty: float,
) -> pd.DataFrame:
    tok, model = _load_model(model_id)

    # Split user inputs
    prompts = [p.strip() for p in prompts_multiline.splitlines() if p.strip()]
    if not prompts:
        return pd.DataFrame([{"user_prompt": "", "response": "", "tokens_out": 0}])

    formatted = [_format_prompt(tok, system_prompt, p) for p in prompts]

    # Micro-batch multi-line input to keep latency low on ZeroGPU
    B = MICROBATCH if len(formatted) > MICROBATCH else len(formatted)

    # Greedy is fine (and fastest). If temp > 0, enable sampling knobs.
    do_sample = bool(temperature > 0.0)
    gen_kwargs = dict(
        max_new_tokens=int(max_new_tokens),
        do_sample=do_sample,
        temperature=float(temperature) if do_sample else None,
        top_p=float(top_p) if do_sample else None,
        top_k=int(top_k) if (do_sample and int(top_k) > 0) else None,
        repetition_penalty=float(repetition_penalty),
        num_beams=1,
        return_dict_in_generate=False,
        use_cache=True,
    )

    all_texts, all_toks = [], []
    for i in range(0, len(formatted), B):
        batch_prompts = formatted[i : i + B]
        texts, toks = _generate_microbatch(tok, model, batch_prompts, gen_kwargs)
        all_texts.extend(texts)
        all_toks.extend(toks)

    return pd.DataFrame(
        {"user_prompt": prompts, "response": all_texts, "tokens_out": all_toks}
    )


def write_csv_path(df: pd.DataFrame) -> str:
    ts = datetime.utcnow().strftime("%Y%m%d-%H%M%S")
    tmp = tempfile.NamedTemporaryFile(prefix=f"Output_{ts}_", suffix=".csv", delete=False, dir="/tmp")
    df.to_csv(tmp.name, index=False)
    return tmp.name


# ----------------------------
# Gradio UI
# ----------------------------

with gr.Blocks(title="Multi-Prompt Chat (ZeroGPU-optimised)") as demo:
    gr.Markdown(
        """
        # Multi-Prompt Chat to test system prompt effects (ZeroGPU-optimised)
        Pick a small model, set a **system prompt**, and enter **multiple user prompts** (one per line).
        Click **Generate** to get batched responses and a **downloadable CSV**.
        """
    )

    with gr.Row():
        with gr.Column(scale=1):
            model_id = gr.Dropdown(
                choices=DEFAULT_MODELS,
                value=DEFAULT_MODELS[0],
                label="Model",
                info="ZeroGPU attaches an H200 dynamically. 4-bit is used automatically on GPU.",
            )
            system_prompt = gr.Textbox(
                label="System prompt",
                placeholder="e.g., You are an ecolinguistics-aware assistant...",
                lines=5,
            )
            prompts_multiline = gr.Textbox(
                label="User prompts (one per line)",
                placeholder="One query per line.\nExample:\nExplain transformers in simple terms\nGive 3 eco-friendly tips\nSummarise benefits of multilingual models",
                lines=10,
            )

            with gr.Accordion("Generation settings", open=False):
                max_new_tokens = gr.Slider(16, 1024, value=200, step=1, label="max_new_tokens")
                temperature = gr.Slider(0.0, 2.0, value=0.0, step=0.05, label="temperature (0 = greedy, fastest)")
                top_p = gr.Slider(0.1, 1.0, value=0.9, step=0.05, label="top_p (used if temp > 0)")
                top_k = gr.Slider(0, 200, value=40, step=1, label="top_k (0 disables; used if temp > 0)")
                repetition_penalty = gr.Slider(1.0, 2.0, value=1.1, step=0.01, label="repetition_penalty")

            run_btn = gr.Button("Generate", variant="primary")

        with gr.Column(scale=1):
            out_df = gr.Dataframe(
                headers=["user_prompt", "response", "tokens_out"],
                datatype=["str", "str", "number"],
                label="Results",
                wrap=True,
                interactive=False,
                row_count=(0, "dynamic"),
                type="pandas",
            )
            csv_out = gr.File(label="CSV output", interactive=False, type="filepath")

    # -------- Callback: GPU-decorated for ZeroGPU --------

    @spaces.GPU()  # <— This tells ZeroGPU to attach a GPU for this request
    def _generate_cb(model_id, system_prompt, prompts_multiline,
                     max_new_tokens, temperature, top_p, top_k, repetition_penalty,
                     progress=gr.Progress(track_tqdm=True)):

        progress(0.05, desc="Requesting ZeroGPU…")
        df = generate_batch_df(
            model_id=model_id,
            system_prompt=system_prompt,
            prompts_multiline=prompts_multiline,
            max_new_tokens=int(max_new_tokens),
            temperature=float(temperature),
            top_p=float(top_p),
            top_k=int(top_k),
            repetition_penalty=float(repetition_penalty),
        )
        progress(0.95, desc="Preparing CSV…")
        csv_path = write_csv_path(df)
        progress(1.0, desc="Done")
        return df, csv_path

    run_btn.click(
        _generate_cb,
        inputs=[model_id, system_prompt, prompts_multiline, max_new_tokens, temperature, top_p, top_k, repetition_penalty],
        outputs=[out_df, csv_out],
        api_name="generate_batch",
    )

if __name__ == "__main__":
    demo.launch()