Create app.py

app.py

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+from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from pydantic import BaseModel
+import requests
+import os  # for reading environment variables
+
+app = FastAPI()
+
+# Enable CORS
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],  # Allow all origins, or replace with your frontend URL
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Read OpenRouter API key from environment variable (HF Secret)
+OPENROUTER_API_KEY = os.environ.get("OPENROUTER_API_KEY")
+if not OPENROUTER_API_KEY:
+    raise RuntimeError("OPENROUTER_API_KEY environment variable not set!")
+
+# Request schema
+class ExplainRequest(BaseModel):
+    message: str
+    label: str  # "Phishing" or "Safe"
+
+@app.post("/explain")
+def explain(req: ExplainRequest):
+    user_message = req.message.strip()
+    label = req.label.strip()
+
+    if not user_message or not label:
+        raise HTTPException(status_code=400, detail="Missing message or label")
+
+    # Updated system prompt with bullet-point format
+    system_prompt = (
+        f"You are a robot that identifies phishing and safe messages. "
+        f"The message was classified as '{label}'. "
+        "Explain why this decision was made and point out any words or patterns that led to it. "
+        "Limit your answer to 2–3 sentences. No greetings, introductions, or closing remarks. "
+        "Don't restate the message or its classification. Output only the explanation as bullet points. "
+        f"Message:\n\n{user_message}"
+    )
+
+    url = "https://openrouter.ai/api/v1/chat/completions"
+    headers = {
+        "Authorization": f"Bearer {OPENROUTER_API_KEY}",
+        "Content-Type": "application/json"
+    }
+    payload = {
+        "model": "x-ai/grok-4-fast:free",
+        "messages": [
+            {"role": "system", "content": system_prompt},
+            {"role": "user", "content": user_message}
+        ]
+    }
+
+    try:
+        response = requests.post(url, headers=headers, json=payload, timeout=20)
+        response.raise_for_status()
+        result = response.json()
+        reply = result.get("choices", [{}])[0].get("message", {}).get("content", "").strip()
+        if not reply:
+            reply = "[No explanation returned]"
+        return {"reply": reply}
+    except requests.RequestException as e:
+        raise HTTPException(status_code=500, detail=f"Error contacting OpenRouter: {e}")