"""
Offline quantization of base models to AWQ / GPTQ with a FIXED calibration set,
using llmcompressor (Neural Magic). Output is compressed-tensors format, which
vLLM loads natively.

Must be run from the `sonthh-stepprobe-quant` conda env (vLLM's main env has
incompatible dep pins with llmcompressor).

Usage:
    /home/aiteam1/anaconda3/envs/sonthh-stepprobe-quant/bin/python \
        scripts/quantize_models.py \
        --model deepseek-ai/DeepSeek-R1-Distill-Qwen-7B \
        --method gptq --bits 4 --group-size 128 \
        --output results/quantized_models/r1-qwen-7b_gptq_w4
"""
import argparse
import os
import random


CALIB_N_SAMPLES = 128
CALIB_SEQ_LEN = 512
CALIB_SEED = 42


def load_calib_dataset(tokenizer):
    """Fixed WikiText-2 calibration set, same for every (model, method, bits)."""
    from datasets import load_dataset

    ds = load_dataset("wikitext", "wikitext-2-raw-v1", split="train")
    ds = ds.filter(lambda x: len(x["text"].strip()) > 200)
    ds = ds.shuffle(seed=CALIB_SEED).select(range(min(CALIB_N_SAMPLES, len(ds))))

    def tokenize(example):
        return tokenizer(
            example["text"],
            padding=False,
            max_length=CALIB_SEQ_LEN,
            truncation=True,
            add_special_tokens=False,
        )

    ds = ds.map(tokenize, remove_columns=ds.column_names)
    return ds


def build_recipe(method: str, bits: int, group_size: int):
    """Build an llmcompressor recipe for the given (method, bits)."""
    from compressed_tensors.quantization import (
        QuantizationArgs,
        QuantizationScheme,
        QuantizationStrategy,
        QuantizationType,
    )
    from llmcompressor.modifiers.quantization import GPTQModifier

    weights_args = QuantizationArgs(
        num_bits=bits,
        type=QuantizationType.INT,
        symmetric=True,
        strategy=QuantizationStrategy.GROUP,
        group_size=group_size,
    )
    scheme = QuantizationScheme(targets=["Linear"], weights=weights_args)

    if method == "gptq":
        return GPTQModifier(
            config_groups={"group_0": scheme},
            ignore=["lm_head"],
        )
    elif method == "awq":
        if bits != 4:
            raise ValueError(f"AWQ path only supports 4-bit; got bits={bits}")
        from llmcompressor.modifiers.awq import AWQModifier
        return AWQModifier(
            config_groups={"group_0": scheme},
            ignore=["lm_head"],
        )
    else:
        raise ValueError(f"Unknown method: {method}")


def quantize(model_name: str, method: str, bits: int, group_size: int, output_dir: str):
    from llmcompressor import oneshot
    from transformers import AutoModelForCausalLM, AutoTokenizer

    print(f"Loading base model: {model_name}")
    model = AutoModelForCausalLM.from_pretrained(
        model_name,
        torch_dtype="auto",
        device_map="auto",
        trust_remote_code=True,
    )
    tokenizer = AutoTokenizer.from_pretrained(model_name, trust_remote_code=True)

    print(f"Loading calibration set: WikiText-2 ({CALIB_N_SAMPLES} samples, seq_len={CALIB_SEQ_LEN}, seed={CALIB_SEED})")
    ds = load_calib_dataset(tokenizer)

    recipe = build_recipe(method, bits, group_size)
    print(f"Running {method.upper()} oneshot: bits={bits}, group_size={group_size}")

    oneshot(
        model=model,
        dataset=ds,
        recipe=recipe,
        output_dir=output_dir,
        max_seq_length=CALIB_SEQ_LEN,
        num_calibration_samples=CALIB_N_SAMPLES,
    )

    tokenizer.save_pretrained(output_dir)


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--model", required=True, help="HuggingFace model name or local path")
    parser.add_argument("--method", choices=["awq", "gptq"], required=True)
    parser.add_argument("--bits", type=int, required=True)
    parser.add_argument("--group-size", type=int, default=128)
    parser.add_argument("--output", required=True, help="Output directory for quantized model")
    args = parser.parse_args()

    if os.path.isfile(os.path.join(args.output, "config.json")):
        print(f"[SKIP] Already quantized: {args.output}")
        return

    os.makedirs(args.output, exist_ok=True)
    print(f"Quantizing {args.model} -> {args.method} w{args.bits} (group={args.group_size})")
    print(f"Output: {args.output}")

    quantize(args.model, args.method, args.bits, args.group_size, args.output)

    print(f"Done: {args.output}")


if __name__ == "__main__":
    main()