from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from transformers import pipeline, AutoModelForCausalLM, AutoTokenizer
from safetensors.torch import load_file
import torch

# Define the input schema
class ModelInput(BaseModel):
    prompt: str
    max_new_tokens: int = 50  # Optional: Defaults to 50 tokens

# Initialize FastAPI app
app = FastAPI()

# Load the base model and tokenizer
base_model_path = "HuggingFaceTB/SmolLM2-135M-Instruct"  # Base model
adapter_weights_path = "https://huggingface.co/khurrameycon/SmolLM-135M-Instruct-qa_pairs_converted.json-25epochs/resolve/main/adapter_model.safetensors"
# Path to the adapter weights

tokenizer = AutoTokenizer.from_pretrained(base_model_path)
model = AutoModelForCausalLM.from_pretrained(base_model_path)

# Load the adapter weights
def load_adapter_weights(model, adapter_weights_path):
    adapter_weights = load_file(adapter_weights_path)
    model.load_state_dict(adapter_weights, strict=False)  # Apply the weights
    return model

# Apply adapter weights to the model
model = load_adapter_weights(model, adapter_weights_path)

# Ensure the model is in evaluation mode
model.eval()

# Initialize the pipeline
generator = pipeline("text-generation", model=model, tokenizer=tokenizer)

# Helper function to generate a response
def generate_response(model, tokenizer, instruction, max_new_tokens=128):
    """Generate a response from the model based on an instruction."""
    try:
        # Tokenize and generate the output
        inputs = tokenizer(instruction, return_tensors="pt")
        inputs = {key: value.to(model.device) for key, value in inputs.items()}  # Move tensors to the model's device
        outputs = model.generate(
            **inputs,
            max_new_tokens=max_new_tokens,
            temperature=0.7,
            top_p=0.9,
            do_sample=True,
        )
        # Decode the output
        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")
def generate_text(input: ModelInput):
    """API endpoint to generate text."""
    try:
        # Call the helper function
        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("/")
def root():
    return {"message": "Welcome to the Hugging Face Model API with Adapter Support!"}