utils.py

import torch
from transformers import BitsAndBytesConfig, AutoModelForCausalLM, PreTrainedTokenizerFast
from peft import PeftModel

#-----------------------------------------
# Quantization Config
#-----------------------------------------
def get_bnb_config():
    return BitsAndBytesConfig(
        load_in_4bit=True,
        bnb_4bit_quant_type="nf4",
        bnb_4bit_compute_dtype=torch.float16,
        bnb_4bit_use_double_quant=True,
        bnb_4bit_quant_storage=torch.float16
    )

#-----------------------------------------
# Base Model Loader
#-----------------------------------------
def load_base_model(base_model_path: str):
    """
    Loads a base LLM model with 4-bit quantization and tokenizer.
    
    Args:
        base_model_path (str): HF model path
    
    Returns:
        model (AutoModelForCausalLM)
        tokenizer (PreTrainedTokenizerFast)
    """
    bnb_config = get_bnb_config()

    tokenizer = PreTrainedTokenizerFast.from_pretrained(base_model_path, return_tensors="pt")

    model = AutoModelForCausalLM.from_pretrained(
        base_model_path,
        quantization_config=bnb_config,
        trust_remote_code=True,
        attn_implementation="eager",
        torch_dtype=torch.float16
    )

    return model, tokenizer

#-----------------------------------------
# Fine-Tuned Model Loader
#-----------------------------------------
def load_fine_tuned_model(adapter_path: str, base_model_path: str):
    """
    Loads the fine-tuned model by applying LoRA adapter to a base model.
    
    Args:
        adapter_path (str): Local or HF adapter path
        base_model_path (str): Base LLM model path
    
    Returns:
        fine_tuned_model (PeftModel)
        tokenizer (PreTrainedTokenizerFast)
    """
    bnb_config = get_bnb_config()

    tokenizer = PreTrainedTokenizerFast.from_pretrained(base_model_path, return_tensors="pt")

    base_model = AutoModelForCausalLM.from_pretrained(
        base_model_path,
        quantization_config=bnb_config,
        trust_remote_code=True,
        attn_implementation="eager",
        torch_dtype=torch.float16
    )

    fine_tuned_model = PeftModel.from_pretrained(
        base_model,
        adapter_path,
        device_map="auto"
    )

    return fine_tuned_model, tokenizer

#-----------------------------------------
# Inference Function
#-----------------------------------------
@torch.no_grad()
def generate_response(
    model: AutoModelForCausalLM,
    tokenizer: PreTrainedTokenizerFast,
    messages: list,
    do_sample: bool = False,
    temperature: float = 0.7,
    top_k: int = 50,
    top_p: float = 0.95,
    num_beams: int = 1,
    max_new_tokens: int = 500
) -> str:
    """
    Runs inference on an LLM model.

    Args:
        model (AutoModelForCausalLM)
        tokenizer (PreTrainedTokenizerFast)
        messages (list): List of dicts containing 'role' and 'content'
    
    Returns:
        str: Model response
    """
    # Ensure pad token exists
    tokenizer.pad_token = "<|reserved_special_token_5|>"

    # Create chat prompt
    input_text = tokenizer.apply_chat_template(
        messages,
        add_generation_prompt=True,
        tokenize=False
    )

    # Tokenize input
    inputs = tokenizer(
        input_text,
        max_length=500,
        truncation=True,
        return_tensors="pt"
    ).to(model.device)

    generation_params = {
        "do_sample": do_sample,
        "temperature": temperature if do_sample else None,
        "top_k": top_k if do_sample else None,
        "top_p": top_p if do_sample else None,
        "num_beams": num_beams if not do_sample else 1,
        "max_new_tokens": max_new_tokens
    }

    output = model.generate(**inputs, **generation_params)

    # Decode and clean up response
    response = tokenizer.decode(output[0], skip_special_tokens=True)

    if 'assistant' in response:
        response = response.split('assistant')[1].strip()

    return response