app.py

import gradio as gr
import tensorflow as tf
import numpy as np
from tensorflow.keras.preprocessing import image
from PIL import Image
import cv2
import traceback

# Load the trained model
try:
    model = tf.keras.models.load_model("./model/deepfake_mobilenet_model.h5")
except Exception as e:
    print(f"Error loading model. Make sure the path is correct. Error: {e}")
    # Fallback dummy model for deployment debugging
    inputs = tf.keras.Input(shape=(224, 224, 3))
    outputs = tf.keras.layers.Dense(1, activation="sigmoid")(tf.keras.layers.GlobalAveragePooling2D()(inputs))
    model = tf.keras.Model(inputs, outputs)

# ==============================================================================
# --- Grad-CAM Heatmap Generation Functions (with safety check restored) ---
# ==============================================================================

def get_last_conv_layer_name(model):
    """Finds the name of the last convolutional layer in the model."""
    for layer in reversed(model.layers):
        if len(layer.output.shape) == 4:
            return layer.name
    raise ValueError("Could not find a conv layer in the model")

def make_gradcam_heatmap(img_array, model, last_conv_layer_name):
    """Generates the Grad-CAM heatmap with a stability check."""
    grad_model = tf.keras.models.Model(
        model.inputs, [model.get_layer(last_conv_layer_name).output, model.output]
    )
    with tf.GradientTape() as tape:
        last_conv_layer_output, preds = grad_model([img_array], training=False)
        
        preds_tensor = preds[0]
        if tf.rank(preds_tensor) > 1:
            class_channel = preds_tensor[:, 0]
        else:
            class_channel = preds_tensor
            
    grads = tape.gradient(class_channel, last_conv_layer_output)
    
    # <-- FIX: The critical safety check is restored here.
    # This prevents the "None to a Tensor" crash without changing the logic.
    if grads is None:
        print("Warning: Gradient is None. Cannot compute heatmap for this image. Returning a blank map.")
        h, w = last_conv_layer_output.shape[1:3]
        return np.zeros((h, w), dtype=np.float32)
    
    pooled_grads = tf.reduce_mean(grads, axis=(0, 1, 2))
    last_conv_layer_output = last_conv_layer_output[0]
    heatmap = last_conv_layer_output @ pooled_grads[..., tf.newaxis]
    heatmap = tf.squeeze(heatmap)
    heatmap = tf.maximum(heatmap, 0) / (tf.math.reduce_max(heatmap) + 1e-8)
    return heatmap.numpy()

def superimpose_gradcam(original_img_pil, heatmap):
    """Overlays the heatmap on the original image."""
    original_img = np.array(original_img_pil)
    heatmap = cv2.resize(heatmap, (original_img.shape[1], original_img.shape[0]))
    heatmap = np.uint8(255 * heatmap)
    heatmap = cv2.applyColorMap(heatmap, cv2.COLORMAP_JET) 
    superimposed_img = cv2.addWeighted(original_img, 0.6, heatmap, 0.4, 0) 
    return Image.fromarray(superimposed_img)

# ==============================================================================
# --- Main Prediction Function ---
# ==============================================================================
last_conv_layer_name = get_last_conv_layer_name(model)

def predict_and_visualize(img):
    """Performs prediction and generates Grad-CAM heatmap."""
    try:
        if img is None:
            return None, None

        img_resized = img.resize((224, 224))
        img_array = image.img_to_array(img_resized) / 255.0
        img_array_expanded = np.expand_dims(img_array, axis=0)
        
        prediction = model.predict(img_array_expanded, verbose=0)[0][0]
        real_conf = float(prediction)
        fake_conf = float(1 - prediction)
        labels = {"Real Image": real_conf, "Fake Image": fake_conf}
        
        heatmap = make_gradcam_heatmap(img_array_expanded, model, last_conv_layer_name)
        superimposed_image = superimpose_gradcam(img, heatmap)
        
        return labels, superimposed_image
        
    except Exception as e:
        print("--- GRADIO APP ERROR ---")
        traceback.print_exc()
        print("------------------------")
        error_msg = f"Error: {e}"
        return {error_msg: 0.0}, None

# ==============================================================================
# --- Gradio Interface ---
# ==============================================================================
gr.Interface(
    fn=predict_and_visualize,
    inputs=gr.Image(type="pil", label="📷 Upload a Face Image"),
    outputs=[
        gr.Label(num_top_classes=2, label="🧠 Model Prediction"),
        gr.Image(label="🔥 Grad-CAM Heatmap Overlay")
    ],
    title="✨ Deepfake Image Detector with Visual Explanation ✨",
    description="""
    **Detect whether an uploaded image is Real or AI-Generated (Deepfake).** The confidence bars show the model's certainty for both **Real** and **Fake** categories.  

    Below, the **Grad-CAM heatmap** highlights the regions the model focused on (red = most important).  

    ⚡ **Instructions:** 1. Upload a face image (JPEG/PNG).  
    2. Wait a few seconds for the prediction and heatmap.  
    3. Observe the confidence bars and heatmap for model explanation.
    """,
    theme="default"
).launch()