app.py

# app.py
import os
import math
import requests
from langdetect import detect
import gradio as gr

# -----------------------------------------------------------------------------
# Configuration
# -----------------------------------------------------------------------------
HF_API_URL = "https://api-inference.huggingface.co/models/YOUR_USERNAME/YOUR_MODEL"
HF_TOKEN = os.getenv("HF_TOKEN")

if HF_TOKEN is None:
    raise ValueError("HF_TOKEN environment variable not set!")

HEADERS = {
    "Authorization": f"Bearer {HF_TOKEN}",
    "Content-Type": "application/json"
}

# -----------------------------------------------------------------------------
# Utility Functions
# -----------------------------------------------------------------------------
def entropy(probs):
    """Shannon entropy as epistemic uncertainty indicator."""
    return -sum(p * math.log2(p) for p in probs if p > 0)

def normalize_labels(hf_output):
    """
    Normalize Hugging Face output into a stable schema.
    Expected HF format:
    [
      {"label": "HUMAN", "score": 0.73},
      {"label": "AI", "score": 0.27}
    ]
    """
    result = {item["label"].lower(): float(item["score"]) for item in hf_output}
    human_p = result.get("human", 0.0)
    ai_p = result.get("ai", 0.0)
    return human_p, ai_p

def hf_inference(text):
    payload = {"inputs": text}
    r = requests.post(HF_API_URL, headers=HEADERS, json=payload, timeout=30)
    r.raise_for_status()
    return r.json()

# -----------------------------------------------------------------------------
# Gradio Prediction Function
# -----------------------------------------------------------------------------
def analyze_text(text):
    text = text.strip()
    if not text:
        return {"error": "Empty input"}

    # 1. Language detection
    try:
        language = detect(text)
    except Exception:
        language = "unknown"

    # 2. Hugging Face inference
    hf_raw = hf_inference(text)
    if not isinstance(hf_raw, list):
        return {"error": "Unexpected model response", "raw": hf_raw}

    human_p, ai_p = normalize_labels(hf_raw)

    # 3. Decision
    label = "Human" if human_p >= ai_p else "Machine"
    confidence = max(human_p, ai_p)

    # 4. Epistemic uncertainty
    H = entropy([human_p, ai_p])

    # 5. Explainability placeholder
    explainability_stub = {
        "method": "pending",
        "note": (
            "This model endpoint does not natively expose SHAP/LIME. "
            "Post-hoc explainability must be computed locally using a "
            "replicated model or proxy explainer."
        ),
        "token_attributions": []
    }

    # 6. Fairness metadata
    fairness_context = {
        "language": language,
        "human_probability": human_p,
        "ai_probability": ai_p,
        "entropy": H
    }

    response = {
        "prediction": {
            "label": label,
            "confidence": round(confidence, 4)
        },
        "probabilities": {
            "human": round(human_p, 4),
            "machine": round(ai_p, 4)
        },
        "uncertainty": {
            "entropy": round(H, 4),
            "interpretation": (
                "High entropy indicates epistemic ambiguity; "
                "classification should be treated cautiously."
            )
        },
        "linguistic_context": {
            "detected_language": language
        },
        "explainability": explainability_stub,
        "fairness_audit_fields": fairness_context
    }

    return response

# -----------------------------------------------------------------------------
# Gradio Interface
# -----------------------------------------------------------------------------
iface = gr.Interface(
    fn=analyze_text,
    inputs=gr.Textbox(lines=5, placeholder="Enter text here..."),
    outputs=gr.JSON(),
    title="HATA: Human-AI Text Attribution",
    description=(
        "Detect whether text is human-written or AI-generated.\n"
        "Supports uncertainty estimation, language-aware auditing, "
        "and XAI-ready outputs."
    )
)

# -----------------------------------------------------------------------------
# Launch Gradio App
# -----------------------------------------------------------------------------
if __name__ == "__main__":
    iface.launch(server_name="0.0.0.0", server_port=7860)