ai_text_detector_valid_final.py

import os
import torch
from transformers import AutoTokenizer, AutoModelForSequenceClassification
import numpy as np
import re

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

# ---------------------------
# ModernBERT Models (SzegedAI)
# ---------------------------
model1_path = "modernbert.bin"
model2_path = "https://huggingface.co/mihalykiss/modernbert_2/resolve/main/Model_groups_3class_seed12"
model3_path = "https://huggingface.co/mihalykiss/modernbert_2/resolve/main/Model_groups_3class_seed22"

tokenizer_modernbert = AutoTokenizer.from_pretrained("answerdotai/ModernBERT-base")

model_1 = AutoModelForSequenceClassification.from_pretrained("answerdotai/ModernBERT-base", num_labels=41)
model_1.load_state_dict(torch.load(model1_path, map_location=device))
model_1.to(device).eval()

model_2 = AutoModelForSequenceClassification.from_pretrained("answerdotai/ModernBERT-base", num_labels=41)
model_2.load_state_dict(torch.hub.load_state_dict_from_url(model2_path, map_location=device))
model_2.to(device).eval()

model_3 = AutoModelForSequenceClassification.from_pretrained("answerdotai/ModernBERT-base", num_labels=41)
model_3.load_state_dict(torch.hub.load_state_dict_from_url(model3_path, map_location=device))
model_3.to(device).eval()

label_mapping = {
    0: '13B', 1: '30B', 2: '65B', 3: '7B', 4: 'GLM130B', 5: 'bloom_7b',
    6: 'bloomz', 7: 'cohere', 8: 'davinci', 9: 'dolly', 10: 'dolly-v2-12b',
    11: 'flan_t5_base', 12: 'flan_t5_large', 13: 'flan_t5_small',
    14: 'flan_t5_xl', 15: 'flan_t5_xxl', 16: 'gemma-7b-it', 17: 'gemma2-9b-it',
    18: 'gpt-3.5-turbo', 19: 'gpt-35', 20: 'gpt4', 21: 'gpt4o',
    22: 'gpt_j', 23: 'gpt_neox', 24: 'human', 25: 'llama3-70b', 26: 'llama3-8b',
    27: 'mixtral-8x7b', 28: 'opt_1.3b', 29: 'opt_125m', 30: 'opt_13b',
    31: 'opt_2.7b', 32: 'opt_30b', 33: 'opt_350m', 34: 'opt_6.7b',
    35: 'opt_iml_30b', 36: 'opt_iml_max_1.3b', 37: 't0_11b', 38: 't0_3b',
    39: 'text-davinci-002', 40: 'text-davinci-003'
}

def clean_text(text: str) -> str:
    """Normalize text for ModernBERT"""
    text = text.replace("\xa0", " ").replace("\u200b", "")
    text = re.sub(r"\s{2,}", " ", text)
    text = re.sub(r"\s+([,.;:?!])", r"\1", text)
    return text.strip()

def classify_szegedai(text: str):
    """
    ModernBERT ensemble detector with:
    - Human label boost
    - Short text handling (<30 words ignored)
    """
    cleaned_text = clean_text(text)
    if not cleaned_text.strip():
        return {"error": "Empty text"}

    word_count = len(cleaned_text.split())
    if word_count < 30:
        # For very short texts, skip AI classification and assume mostly human
        return {"Please Enter at least 30 words"}

    inputs = tokenizer_modernbert(cleaned_text, return_tensors="pt", truncation=True, padding=True).to(device)
    
    with torch.no_grad():
        logits_1 = model_1(**inputs).logits
        logits_2 = model_2(**inputs).logits
        logits_3 = model_3(**inputs).logits

        probs1 = torch.softmax(logits_1, dim=1)
        probs2 = torch.softmax(logits_2, dim=1)
        probs3 = torch.softmax(logits_3, dim=1)

        human_index = 24
        for p in [probs1, probs2, probs3]:
            p[:, human_index] *= 2.0  # Boost human label
            p = p / p.sum(dim=1, keepdim=True)  # Re-normalize

        probs = (probs1 + probs2 + probs3) / 3

    human_prob = probs[0][human_index].item() * 100
    ai_prob = 100 - human_prob

    return {"Human Probability": round(human_prob, 2), "AI Probability": round(ai_prob, 2)}

# ---------------------------
# HuggingFace other models
# ---------------------------
MODELS = {
    "MonkeyDAnh": "MonkeyDAnh/my-awesome-ai-detector-roberta-base-v4-human-vs-machine-finetune",
}

def run_hf_model(model_id, text):
    try:
        tokenizer = AutoTokenizer.from_pretrained(model_id)
        model = AutoModelForSequenceClassification.from_pretrained(model_id)
        inputs = tokenizer(text, return_tensors="pt", truncation=True, padding=True)
        with torch.no_grad():
            logits = model(**inputs).logits
        probs = torch.softmax(logits, dim=-1).cpu().numpy()[0]
        return {"Human Probability": float(probs[0]*100), "AI Probability": float(probs[1]*100)}
    except Exception as e:
        return {"error": str(e)}

# ---------------------------
# Verdict logic
# ---------------------------
def verdict(ai_prob):
    if ai_prob < 20:
        return "Most likely human-written."
    elif 20 <= ai_prob < 40:
        return "Possibly human-written with minimal AI assistance."
    elif 40 <= ai_prob < 60:
        return "Unclear – could be either human or AI-assisted."
    elif 60 <= ai_prob < 80:
        return "Possibly AI-generated, or a human using AI assistance."
    else:
        return "Likely AI-generated or heavily AI-assisted."

def detect_text(text):
    results = {}

    # Run other HuggingFace detectors
    for name, model_id in MODELS.items():
        results[name] = run_hf_model(model_id, text)

    # Run ModernBERT ensemble
    results["SzegedAI Detector"] = classify_szegedai(text)

    # Compute average AI probability
    ai_probs = []
    strong_ai_detector = None
    for v in results.values():
        if "AI Probability" in v:
            ai_probs.append(v["AI Probability"])
            if v["AI Probability"] > 90:   # strong AI flag
                strong_ai_detector = v

    avg_ai = np.mean(ai_probs) if ai_probs else 0

    if strong_ai_detector:
        final_verdict = verdict(strong_ai_detector["AI Probability"])
    else:
        final_verdict = verdict(avg_ai)

    results["Final Score"] = {"Verdict": final_verdict}
    return results

# ---------------------------
# Test Example
# ---------------------------
if __name__ == "__main__":
    sample = "This is a test sentence written by a human."
    print(detect_text(sample))