app.py

import gradio as gr
import shap
import numpy as np
import pandas as pd
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.linear_model import LogisticRegression
from sklearn.pipeline import Pipeline
from sklearn.model_selection import train_test_split

# ============================================================
# 1. FAKE TRAINING DATA (Replace with your real clinical notes)
# ============================================================

data = pd.DataFrame({
    "note": [
        "Patient experienced surgical site drainage, elevated pain, difficulty ambulating, high BMI.",
        "Uncomplicated post-op course, normal vitals, ambulating independently.",
        "Severe swelling, infection suspected, fever noted post-op day 3.",
        "Routine knee replacement recovery, discharged home POD2.",
        "History of diabetes, hypertension, wound healing slow, required re-evaluation.",
        "Strong recovery, no complications, outpatient follow-up scheduled."
    ],
    "readmit_30d": [1, 0, 1, 0, 1, 0]
})

X = data["note"]
y = data["readmit_30d"]

# ================================
# 2. BUILD PIPELINE & EXTRACT COMPONENTS
# ================================
vectorizer = TfidfVectorizer(stop_words="english", max_features=3000)
classifier = LogisticRegression(max_iter=500)

# Transform text to features
X_vectorized = vectorizer.fit_transform(X)
classifier.fit(X_vectorized, y)

# Create pipeline for easy prediction
model = Pipeline([
    ("tfidf", vectorizer),
    ("clf", classifier)
])

# ================================
# 3. SHAP EXPLAINER SETUP
# ================================
# Use LinearExplainer for linear models (much faster and more appropriate)
# Use a sample of vectorized features as background
background_data = X_vectorized[:3].toarray()  # Use first 3 samples as background
explainer = shap.LinearExplainer(
    classifier,
    background_data
)

# ================================
# 4. PREDICTION + SHAP FUNCTION
# ================================
def predict_note(note):
    proba = model.predict_proba([note])[0][1]
    label = "High Readmission Risk" if proba >= 0.5 else "Low Readmission Risk"
    return float(proba), label


def explain_note(note):
    try:
        # Ensure note is a string
        note_str = str(note)
        
        # Transform the note to vectorized features
        note_vectorized = vectorizer.transform([note_str]).toarray()
        
        # Get SHAP values for the vectorized features
        shap_values = explainer.shap_values(note_vectorized)
        
        # Handle binary classification
        if isinstance(shap_values, list):
            shap_vals = shap_values[1]  # Get class 1 (positive class) SHAP values
        else:
            shap_vals = shap_values
        
        # Get feature names (words) from vectorizer
        feature_names = vectorizer.get_feature_names_out()
        
        # Get top contributing features
        shap_vals_flat = shap_vals[0]  # Flatten to 1D
        
        # Get indices sorted by absolute SHAP value
        top_indices = np.argsort(np.abs(shap_vals_flat))[-20:][::-1]  # Top 20 features
        
        # Create HTML explanation showing top contributing words
        html_parts = ["<div style='font-family: monospace; padding: 10px;'>"]
        html_parts.append("<h4>Top Contributing Words:</h4>")
        html_parts.append("<table border='1' style='border-collapse: collapse; width: 100%;'>")
        html_parts.append("<tr><th>Word</th><th>SHAP Value</th><th>Impact</th></tr>")
        
        for idx in top_indices:
            word = feature_names[idx]
            shap_val = shap_vals_flat[idx]
            color = "red" if shap_val > 0 else "blue"
            impact = "↑ Increases" if shap_val > 0 else "↓ Decreases"
            html_parts.append(
                f"<tr><td>{word}</td><td style='color: {color};'>{shap_val:.4f}</td><td>{impact}</td></tr>"
            )
        
        html_parts.append("</table>")
        # Get expected value (base prediction)
        if isinstance(explainer.expected_value, (list, np.ndarray)):
            base_val = explainer.expected_value[1] if len(explainer.expected_value) > 1 else explainer.expected_value[0]
        else:
            base_val = explainer.expected_value
        html_parts.append(f"<p><strong>Base value:</strong> {base_val:.4f}</p>")
        html_parts.append("</div>")
        
        return "".join(html_parts)
        
    except Exception as e:
        return f"Error generating explanation: {str(e)}\nPlease try a different note."


# ================================
# 5. GRADIO UI
# ================================
def full_pipeline(note):
    proba, label = predict_note(note)
    shap_html = explain_note(note)
    return (
        f"Readmission Probability: {proba:.3f}\nPrediction: {label}",
        shap_html
    )


with gr.Blocks() as demo:
    gr.Markdown("# 🏥 Knee Replacement 30-Day Readmission Predictor\n### NLP + SHAP Explainability")

    input_note = gr.Textbox(
        label="Enter Clinical Note",
        placeholder="Example: Patient reports severe swelling and fever on post-op day 3..."
    )

    btn = gr.Button("Predict Readmission Risk")

    output_pred = gr.Textbox(label="Model Prediction")
    output_shap = gr.HTML(label="SHAP Explanation")

    btn.click(full_pipeline, inputs=input_note, outputs=[output_pred, output_shap])

demo.launch(share=True)