app.py

import json
import torch
import gradio as gr
from transformers import AutoTokenizer, AutoModelForSequenceClassification

# Path to saved fine-tuned model (upload this folder to Hugging Face Space)
MODEL_DIR = "./saved_mbert_prompt_injection"
MAX_LENGTH = 128

# Load label names and threshold saved during training
with open(f"{MODEL_DIR}/label_config.json", "r", encoding="utf-8") as f:
    config = json.load(f)

LABELS = config["labels"]
THRESHOLD = config.get("threshold", 0.5)

# Load tokenizer and model
tokenizer = AutoTokenizer.from_pretrained(MODEL_DIR)
model = AutoModelForSequenceClassification.from_pretrained(MODEL_DIR)
model.eval()

device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model.to(device)


def predict(prompt, threshold=THRESHOLD):
    """Predict 3 attack labels and confidence scores for one prompt."""
    if not prompt.strip():
        return "Please enter text.", {}

    inputs = tokenizer(
        prompt,
        return_tensors="pt",
        truncation=True,
        padding=True,
        max_length=MAX_LENGTH,
    ).to(device)

    with torch.no_grad():
        logits = model(**inputs).logits
        probs = torch.sigmoid(logits).cpu().numpy()[0]

    pred_dict = {label: float(probs[i]) for i, label in enumerate(LABELS)}
    detected = [label for i, label in enumerate(LABELS) if probs[i] >= threshold]

    if not detected:
        detected = ["Benign / No Attack Detected"]

    return "Detected: " + ", ".join(detected), pred_dict


# Professional Gradio UI for Hugging Face Spaces
with gr.Blocks(theme=gr.themes.Soft()) as demo:
    gr.Markdown(
        """
        # Prompt Injection Attack Detector
        Multilingual BERT multi-label classifier for:
        - Direct Injection
        - Goal Hijacking
        - Information Leakage
        """
    )

    with gr.Row():
        prompt_box = gr.Textbox(
            label="Prompt",
            lines=5,
            placeholder="Enter user prompt here...",
        )
        threshold = gr.Slider(
            0.1,
            0.9,
            value=THRESHOLD,
            step=0.05,
            label="Threshold",
        )

    summary = gr.Textbox(label="Prediction")
    scores = gr.Label(label="Confidence Scores", num_top_classes=3)
    run_btn = gr.Button("Analyze Prompt", variant="primary")

    run_btn.click(fn=predict, inputs=[prompt_box, threshold], outputs=[summary, scores])

demo.launch()