main.py

from fastapi import FastAPI, HTTPException
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel
from contextlib import asynccontextmanager
from transformers import AutoTokenizer
from optimum.onnxruntime import ORTModelForSeq2SeqLM
import time


# ==========================================
# 1. GLOBAL STATE & LIFESPAN
# ==========================================
# We store the model in a global dictionary so it stays in memory
ml_models = {}

@asynccontextmanager
async def lifespan(app: FastAPI):
    # --- STARTUP LOGIC ---
    print("⚡ Loading Quantized Model into RAM...")
    model_path = "./tone_slider_model_quantized"
    
    try:
        # Load Tokenizer
        ml_models["tokenizer"] = AutoTokenizer.from_pretrained(model_path)
        
        # Load ONNX Model (Explicit filenames to avoid warnings)
        ml_models["model"] = ORTModelForSeq2SeqLM.from_pretrained(
            model_path,
            encoder_file_name="encoder_model_quantized.onnx",
            decoder_file_name="decoder_model_quantized.onnx",
            decoder_with_past_file_name="decoder_with_past_model_quantized.onnx",
            provider="CPUExecutionProvider"
        )
        print("✅ Model loaded and ready!")
    except Exception as e:
        print(f"❌ Failed to load model: {e}")
        
    yield
    
    # --- SHUTDOWN LOGIC ---
    ml_models.clear()
    print("🛑 Model unloaded.")

# ==========================================
# 2. APP SETUP
# ==========================================
app = FastAPI(lifespan=lifespan, title="Tone Slider API")

# Enable CORS (Allows your frontend to talk to this API)
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"], # In production, replace "*" with your frontend URL
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# ==========================================
# 3. DATA MODELS
# ==========================================
class ToneRequest(BaseModel):
    text: str
    style: str  # Expecting "casual" or "formal"

class ToneResponse(BaseModel):
    original: str
    transformed: str
    latency_ms: float

# ==========================================
# 4. THE ENDPOINT
# ==========================================
@app.post("/transform", response_model=ToneResponse)
async def transform_text(request: ToneRequest):
    if "model" not in ml_models:
        raise HTTPException(status_code=503, detail="Model not loaded")

    tokenizer = ml_models["tokenizer"]
    model = ml_models["model"]
    
    start_time = time.time()

    # 1. Preprocess Input
    # Validating style to prevent injection
    style_prefix = "casual: " if request.style.lower() == "casual" else "formal: "
    input_text = style_prefix + request.text

    # 2. Inference
    inputs = tokenizer(input_text, return_tensors="pt")
    
    # Generate (Greedy search is fastest for CPU)
    outputs = model.generate(
        **inputs, 
        max_length=64,
        do_sample=False 
    )

    # 3. Decode
    result = tokenizer.decode(outputs[0], skip_special_tokens=True)
    
    duration = (time.time() - start_time) * 1000

    return ToneResponse(
        original=request.text,
        transformed=result,
        latency_ms=round(duration, 2)
    )

# Run with: uvicorn main:app --reload