main.py

from fastapi import FastAPI, HTTPException
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel
import torch
import torch.nn.functional as F
from transformers import AutoTokenizer, AutoModelForSequenceClassification
from lime.lime_text import LimeTextExplainer
import numpy as np
import os

app = FastAPI(title="MedGuard API")

# --- NUCLEAR CORS FIX ---
# Allow EVERYTHING. This rules out CORS as the problem.
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"], 
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# --- CONFIGURATION ---
MODEL_PATH = "./model"
DEVICE = "cpu"

print(f"🔄 Loading Model from {MODEL_PATH}...")
model = None
tokenizer = None

try:
    tokenizer = AutoTokenizer.from_pretrained(MODEL_PATH)
    model = AutoModelForSequenceClassification.from_pretrained(MODEL_PATH)
    model.to(DEVICE)
    model.eval()
    print("✅ Model Loaded Successfully!")
except Exception as e:
    print(f"❌ Error loading local model: {e}")
    MODEL_NAME = "csebuetnlp/banglabert"
    tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)
    model = AutoModelForSequenceClassification.from_pretrained(MODEL_NAME, num_labels=3)

# --- DATA MODELS ---
class QueryRequest(BaseModel):
    text: str

class PredictionResponse(BaseModel):
    label: str
    confidence: float
    probs: dict
    explanation: list = None

LABELS = ["Highly Relevant", "Partially Relevant", "Not Relevant"]

def predict_proba_lime(texts):
    inputs = tokenizer(texts, return_tensors="pt", padding=True, truncation=True, max_length=128).to(DEVICE)
    with torch.no_grad():
        outputs = model(**inputs)
    return torch.nn.functional.softmax(outputs.logits, dim=-1).cpu().numpy()

@app.get("/")
def health_check():
    return {"status": "active", "model": "MedGuard v1.0"}

@app.post("/predict", response_model=PredictionResponse)
def predict(request: QueryRequest):
    if not model or not tokenizer:
        raise HTTPException(status_code=503, detail="Model not loaded")
    
    try:
        inputs = tokenizer(request.text, return_tensors="pt", truncation=True, max_length=128).to(DEVICE)
        with torch.no_grad():
            outputs = model(**inputs)
            probs = F.softmax(outputs.logits, dim=-1).cpu().numpy()[0]
        
        pred_idx = np.argmax(probs)
        
        # LIME (Reduced to 20 samples for speed testing)
        explainer = LimeTextExplainer(class_names=LABELS, split_expression=lambda x: x.split())
        exp = explainer.explain_instance(request.text, predict_proba_lime, num_features=6, num_samples=20, labels=[pred_idx])
        lime_features = exp.as_list(label=pred_idx) 
        
        return {
            "label": LABELS[pred_idx],
            "confidence": round(float(probs[pred_idx]) * 100, 2),
            "probs": {l: round(float(p), 4) for l, p in zip(LABELS, probs)},
            "explanation": lime_features
        }
    except Exception as e:
        print(f"Server Error: {e}") # Print error to backend terminal
        raise HTTPException(status_code=500, detail=str(e))

if __name__ == "__main__":
    import uvicorn
    # Bind to localhost specifically
    uvicorn.run(app, host="127.0.0.1", port=8000)