from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from transformers import AutoModelForCausalLM, AutoTokenizer
import torch
from huggingface_hub import snapshot_download

class ModelInput(BaseModel):
    prompt: str
    max_new_tokens: int = 50

app = FastAPI()

# Define model paths
base_model_path = "HuggingFaceTB/SmolLM2-135M-Instruct"
adapter_path = "khurrameycon/SmolLM-135M-Instruct-qa_pairs_converted.json-25epochs"

try:
    # First load the base model
    print("Loading base model...")
    model = AutoModelForCausalLM.from_pretrained(
        base_model_path,
        torch_dtype=torch.float16,
        trust_remote_code=True,
        device_map="auto"
    )
    
    # Load tokenizer from base model
    print("Loading tokenizer...")
    tokenizer = AutoTokenizer.from_pretrained(base_model_path)
    
    # Download and load adapter weights
    print("Loading adapter weights...")
    adapter_path_local = snapshot_download(adapter_path)
    
    # Load the adapter weights
    state_dict = torch.load(f"{adapter_path_local}/adapter_model.safetensors")
    model.load_state_dict(state_dict, strict=False)
    
    print("Model and adapter loaded successfully!")

except Exception as e:
    print(f"Error during model loading: {e}")
    raise

def generate_response(model, tokenizer, instruction, max_new_tokens=128):
    """Generate a response from the model based on an instruction."""
    try:
        messages = [{"role": "user", "content": instruction}]
        input_text = tokenizer.apply_chat_template(
            messages, tokenize=False, add_generation_prompt=True
        )
        
        inputs = tokenizer.encode(input_text, return_tensors="pt").to(model.device)
        outputs = model.generate(
            inputs,
            max_new_tokens=max_new_tokens,
            temperature=0.2,
            top_p=0.9,
            do_sample=True,
        )
        
        response = tokenizer.decode(outputs[0], skip_special_tokens=True)
        return response
    
    except Exception as e:
        raise ValueError(f"Error generating response: {e}")

@app.post("/generate")
async def generate_text(input: ModelInput):
    try:
        response = generate_response(
            model=model,
            tokenizer=tokenizer,
            instruction=input.prompt,
            max_new_tokens=input.max_new_tokens
        )
        return {"generated_text": response}
    
    except Exception as e:
        raise HTTPException(status_code=500, detail=str(e))

@app.get("/")
async def root():
    return {"message": "Welcome to the Model API!"}