app.py

import torch
import torch.nn.functional as F
from transformers import AutoTokenizer, AutoModelForSequenceClassification
import re
import pandas as pd
import gradio as gr

# -----------------------------
# STRONGEST AVAILABLE PUBLIC MODEL (WORKING)
# -----------------------------
MODEL_NAME = "openai-community/roberta-base-openai-detector"

# -----------------------------
# LOAD MODEL
# -----------------------------
tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
dtype = torch.bfloat16 if (device.type=="cuda" and torch.cuda.is_bf16_supported()) else torch.float32
model = AutoModelForSequenceClassification.from_pretrained(MODEL_NAME, torch_dtype=dtype)
model.to(device).eval()


# -----------------------------
# PARAGRAPH SPLITTER
# -----------------------------
def paragraph_split(text):
    paragraphs = [p.strip() for p in text.split("\n") if p.strip()]
    return paragraphs


# -----------------------------
# AI DETECTION FUNCTION
# -----------------------------
def classify_text(text):
    if not text.strip():
        return "⚠️ Please enter some text.", None, None

    paragraphs = paragraph_split(text)
    if not paragraphs:
        return "⚠️ No paragraphs detected.", None, None

    # Tokenize paragraphs
    inputs = tokenizer(
        paragraphs,
        return_tensors="pt",
        padding=True,
        truncation=True,
        max_length=model.config.max_position_embeddings
    ).to(device)

    # Predict
    with torch.no_grad():
        logits = model(**inputs).logits
        probs = F.softmax(logits, dim=-1).cpu()
        preds = torch.argmax(probs, dim=-1).cpu()

    # -----------------------------
    # BUILD RESULTS
    # -----------------------------
    results = []
    highlighted_paragraphs = []

    for i, p in enumerate(paragraphs):
        pred_label = preds[i].item()
        confidence = probs[i, pred_label].item()

        label = "AI" if pred_label == 1 else "Human"  
        # NOTE: roberta-base-openai-detector → label 1 = Fake (AI), 0 = Real (Human)

        conf_text = f"{confidence:.2f}"

        results.append([p, label, conf_text])

        if label == "AI":
            highlighted_paragraphs.append(
                f"<p style='color:red; font-weight:bold; margin-bottom:10px'>{p}</p>"
            )
        else:
            highlighted_paragraphs.append(
                f"<p style='color:green; font-weight:bold; margin-bottom:10px'>{p}</p>"
            )

    # -----------------------------
    # DOCUMENT LEVEL SCORE
    # -----------------------------
    avg = torch.mean(probs, dim=0)
    ai_likelihood = avg[1].item() * 100   # class 1 = AI

    highlighted_html = "\n".join(highlighted_paragraphs)
    df = pd.DataFrame(results, columns=["Paragraph", "Classification", "Confidence"])

    return f"⚖️ Document AI Likelihood: {ai_likelihood:.1f}%", highlighted_html, df


# -----------------------------
# GRADIO UI
# -----------------------------
with gr.Blocks() as demo:
    gr.Markdown("## 🧠 Writenix Advanced AI Detection (Paragraph-Level)")

    with gr.Row():
        text_input = gr.Textbox(
            label="Enter text",
            lines=14,
            placeholder="Paste your essay, article, or content here…"
        )

    classify_btn = gr.Button("🚀 Detect AI")

    ai_score = gr.Label(label="Overall AI Likelihood")
    highlighted = gr.HTML()
    table = gr.Dataframe(headers=["Paragraph", "Classification", "Confidence"], wrap=True)

    classify_btn.click(classify_text, inputs=text_input, outputs=[ai_score, highlighted, table])

if __name__ == "__main__":
    demo.launch()