app.py

import gradio as gr
import torch
import joblib
import numpy as np
from itertools import product
import torch.nn as nn
import matplotlib.pyplot as plt
import io
from PIL import Image

###############################################################################
# 1. MODEL DEFINITION
###############################################################################

class VirusClassifier(nn.Module):
    def __init__(self, input_shape: int):
        super(VirusClassifier, self).__init__()
        self.network = nn.Sequential(
            nn.Linear(input_shape, 64),
            nn.GELU(),
            nn.BatchNorm1d(64),
            nn.Dropout(0.3),
            nn.Linear(64, 32),
            nn.GELU(),
            nn.BatchNorm1d(32),
            nn.Dropout(0.3),
            nn.Linear(32, 32),
            nn.GELU(),
            nn.Linear(32, 2)
        )

    def forward(self, x):
        return self.network(x)


###############################################################################
# 2. FASTA PARSING & K-MER FEATURE ENGINEERING
###############################################################################

def parse_fasta(text):
    """Parse FASTA formatted text into a list of (header, sequence)."""
    sequences = []
    current_header = None
    current_sequence = []
    
    for line in text.strip().split('\n'):
        line = line.strip()
        if not line:
            continue
        if line.startswith('>'):
            if current_header:
                sequences.append((current_header, ''.join(current_sequence)))
            current_header = line[1:]
            current_sequence = []
        else:
            current_sequence.append(line.upper())
    if current_header:
        sequences.append((current_header, ''.join(current_sequence)))
    return sequences

def sequence_to_kmer_vector(sequence: str, k: int = 4) -> np.ndarray:
    """Convert a sequence to a k-mer frequency vector."""
    kmers = [''.join(p) for p in product("ACGT", repeat=k)]
    kmer_dict = {km: i for i, km in enumerate(kmers)}
    vec = np.zeros(len(kmers), dtype=np.float32)
    
    for i in range(len(sequence) - k + 1):
        kmer = sequence[i:i+k]
        if kmer in kmer_dict:
            vec[kmer_dict[kmer]] += 1

    total_kmers = len(sequence) - k + 1
    if total_kmers > 0:
        vec = vec / total_kmers

    return vec


###############################################################################
# 3. SHAP-VALUE (ABLATION) CALCULATION
###############################################################################

def calculate_shap_values(model, x_tensor):
    """
    Calculate SHAP values using a simple ablation approach.
    Returns shap values and model prediction.
    """
    model.eval()
    with torch.no_grad():
        # Get baseline prediction
        baseline_output = model(x_tensor)
        baseline_probs = torch.softmax(baseline_output, dim=1)
        baseline_prob = baseline_probs[0, 1].item()  # Probability of 'human' class
        
        # Calculate impact of zeroing each feature
        shap_values = []
        x_zeroed = x_tensor.clone()
        for i in range(x_tensor.shape[1]):
            original_value = x_zeroed[0, i].item()
            x_zeroed[0, i] = 0.0
            output = model(x_zeroed)
            probs = torch.softmax(output, dim=1)
            prob = probs[0, 1].item()
            impact = baseline_prob - prob
            shap_values.append(impact)
            x_zeroed[0, i] = original_value  # restore
    return np.array(shap_values), baseline_prob


###############################################################################
# 4. PER-BASE SHAP AGGREGATION
###############################################################################

def compute_positionwise_scores(sequence, shap_values, k=4):
    """
    Returns an array of per-base SHAP contributions by averaging
    the k-mer SHAP values of all k-mers covering that base.
    """
    # Create the list of k-mers (in lexicographic order)
    kmers = [''.join(p) for p in product("ACGT", repeat=k)]
    kmer_dict = {km: i for i, km in enumerate(kmers)}
    
    seq_len = len(sequence)
    shap_sums = np.zeros(seq_len, dtype=np.float32)
    coverage = np.zeros(seq_len, dtype=np.float32)
    
    for i in range(seq_len - k + 1):
        kmer = sequence[i:i+k]
        if kmer in kmer_dict:
            val = shap_values[kmer_dict[kmer]]
            shap_sums[i : i + k] += val
            coverage[i : i + k] += 1

    with np.errstate(divide='ignore', invalid='ignore'):
        shap_means = np.where(coverage > 0, shap_sums / coverage, 0.0)
        
    return shap_means


###############################################################################
# 5. HEATMAP PLOTS
###############################################################################

def plot_linear_heatmap(shap_means, title="Per-base SHAP Heatmap"):
    """
    Plots a 1D heatmap of per-base SHAP contributions.
    Negative = push toward Non-Human, Positive = push toward Human.
    """
    heatmap_data = shap_means.reshape(1, -1)  # shape (1, seq_len)
    fig, ax = plt.subplots(figsize=(12, 2))
    
    cax = ax.imshow(heatmap_data, aspect='auto', cmap='RdBu_r')
    cbar = plt.colorbar(cax, orientation='horizontal', pad=0.2)
    cbar.set_label('SHAP Contribution')

    ax.set_yticks([])
    ax.set_xlabel('Position in Sequence')
    ax.set_title(title)
    plt.tight_layout()
    return fig

def get_top_signal_region(shap_means, window_size=500):
    """
    Find the window of length `window_size` that has the highest
    sum of absolute SHAP values. Returns (start_index, end_index).
    """
    seq_len = len(shap_means)
    if window_size >= seq_len:
        return 0, seq_len  # entire sequence if window too large
    
    abs_values = np.abs(shap_means)
    max_sum = -1
    max_start = 0

    # Slide a window over shap_means
    current_sum = np.sum(abs_values[:window_size])
    max_sum = current_sum
    for start in range(1, seq_len - window_size + 1):
        # Remove the leftmost base, add the new rightmost base
        current_sum = current_sum - abs_values[start-1] + abs_values[start + window_size - 1]
        if current_sum > max_sum:
            max_sum = current_sum
            max_start = start
    
    return max_start, max_start + window_size

def plot_zoomed_heatmap(shap_means, window_size=500, title="Zoomed SHAP Region"):
    """
    Finds the region with the largest absolute SHAP sum in a fixed window,
    then plots a 1D heatmap of just that sub-region.
    """
    start, end = get_top_signal_region(shap_means, window_size)
    sub_means = shap_means[start:end].reshape(1, -1)
    
    fig, ax = plt.subplots(figsize=(12, 2))
    cax = ax.imshow(sub_means, aspect='auto', cmap='RdBu_r')
    cbar = plt.colorbar(cax, orientation='horizontal', pad=0.2)
    cbar.set_label('SHAP Contribution')
    
    ax.set_yticks([])
    ax.set_xlabel(f'Position in Sequence (zoomed in {start} - {end})')
    ax.set_title(title)
    
    plt.tight_layout()
    return fig


###############################################################################
# 6. OTHER PLOT: TOP-K K-MER BAR PLOT
###############################################################################

def create_importance_bar_plot(shap_values, kmers, top_k=10):
    """Create a bar plot of the most important k-mers."""
    plt.rcParams.update({'font.size': 10})
    fig = plt.figure(figsize=(10, 5))
    
    # Sort by absolute importance
    indices = np.argsort(np.abs(shap_values))[-top_k:]
    values = shap_values[indices]
    features = [kmers[i] for i in indices]
    
    colors = ['#ff9999' if v > 0 else '#99ccff' for v in values]
    
    plt.barh(range(len(values)), values, color=colors)
    plt.yticks(range(len(values)), features)
    plt.xlabel('SHAP value (impact on model output)')
    plt.title(f'Top {top_k} Most Influential k-mers')
    plt.gca().invert_yaxis()
    return fig

###############################################################################
# 7. HELPER FUNCTION: FIG TO IMAGE
###############################################################################

def fig_to_image(fig):
    """Convert a Matplotlib figure to a PIL Image."""
    import io
    buf = io.BytesIO()
    fig.savefig(buf, format='png', bbox_inches='tight', dpi=150)
    buf.seek(0)
    img = Image.open(buf)
    plt.close(fig)
    return img

###############################################################################
# 8. MAIN PREDICTION FUNCTION
###############################################################################

def predict(file_obj, top_kmers=10, fasta_text="", zoom_window=500):
    """Main prediction function for Gradio interface."""
    # Handle input
    if fasta_text.strip():
        text = fasta_text.strip()
    elif file_obj is not None:
        try:
            with open(file_obj, 'r') as f:
                text = f.read()
        except Exception as e:
            return f"Error reading file: {str(e)}", None, None, None
    else:
        return "Please provide a FASTA sequence.", None, None, None

    # Parse FASTA
    sequences = parse_fasta(text)
    if not sequences:
        return "No valid FASTA sequences found.", None, None, None
    
    header, seq = sequences[0]

    # Load model and scaler
    device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
    try:
        model = VirusClassifier(256).to(device)
        model.load_state_dict(torch.load('model.pt', map_location=device))
        scaler = joblib.load('scaler.pkl')
    except Exception as e:
        return f"Error loading model: {str(e)}", None, None, None

    # Generate features
    freq_vector = sequence_to_kmer_vector(seq)
    scaled_vector = scaler.transform(freq_vector.reshape(1, -1))
    x_tensor = torch.FloatTensor(scaled_vector).to(device)

    # Calculate SHAP values and get prediction
    shap_values, prob_human = calculate_shap_values(model, x_tensor)
    
    # Prediction text
    results = [
        f"Sequence: {header}",
        f"Prediction: {'Human' if prob_human > 0.5 else 'Non-human'} Origin",
        f"Confidence: {max(prob_human, 1 - prob_human):.3f}",
        f"Human Probability: {prob_human:.3f}"
    ]
    
    # Create k-mer list (4-mers in lexicographic order)
    kmers = [''.join(p) for p in product("ACGT", repeat=4)]
    
    # 1) Top-k k-mer bar plot
    importance_fig = create_importance_bar_plot(shap_values, kmers, top_kmers)
    importance_img = fig_to_image(importance_fig)
    
    # 2) Full-genome per-base SHAP heatmap
    shap_means = compute_positionwise_scores(seq, shap_values, k=4)
    heatmap_fig = plot_linear_heatmap(shap_means, title="Genome-wide Per-base SHAP")
    heatmap_img = fig_to_image(heatmap_fig)
    
    # 3) Zoomed region (optional, using the largest absolute SHAP region)
    if zoom_window > 0:
        zoom_fig = plot_zoomed_heatmap(shap_means, window_size=zoom_window,
                                       title=f"Top SHAP Region (window={zoom_window})")
        zoom_img = fig_to_image(zoom_fig)
    else:
        zoom_img = None
    
    return "\n".join(results), importance_img, heatmap_img, zoom_img


###############################################################################
# 9. BUILD GRADIO INTERFACE
###############################################################################

css = """
.gradio-container {
    font-family: 'IBM Plex Sans', sans-serif;
}
"""

with gr.Blocks(css=css) as iface:
    gr.Markdown("""
    # Virus Host Classifier
    Predicts whether a viral sequence is of human or non-human origin using k-mer analysis.
    """)
    
    with gr.Row():
        with gr.Column(scale=1):
            file_input = gr.File(
                label="Upload FASTA file",
                file_types=[".fasta", ".fa", ".txt"],
                type="filepath"
            )
            text_input = gr.Textbox(
                label="Or paste FASTA sequence",
                placeholder=">sequence_name\nACGTACGT...",
                lines=5
            )
            top_k = gr.Slider(
                minimum=5,
                maximum=30,
                value=10,
                step=1,
                label="Number of top k-mers to display"
            )
            zoom_window = gr.Slider(
                minimum=0,
                maximum=5000,
                value=500,
                step=100,
                label="Zoom Window Size (0 to disable zoom plot)"
            )
            submit_btn = gr.Button("Analyze Sequence", variant="primary")
            
        with gr.Column(scale=2):
            results_box = gr.Textbox(label="Analysis Results", lines=5)
            kmer_plot = gr.Image(label="Top k-mer SHAP")
            full_heatmap = gr.Image(label="Genome-wide SHAP Heatmap")
            zoomed_heatmap = gr.Image(label="Zoomed SHAP Region (largest signal)")
    
    submit_btn.click(
        predict,
        inputs=[file_input, top_k, text_input, zoom_window],
        outputs=[results_box, kmer_plot, full_heatmap, zoomed_heatmap]
    )
    
    gr.Markdown("""
    ### Visualization Guide
    - **Top k-mer SHAP**: Shows the most influential k-mers and their SHAP values.
    - **Genome-wide SHAP Heatmap**: Per-base SHAP values across the entire sequence.
      - Red = push toward human
      - Blue = push toward non-human
    - **Zoomed SHAP Region**: Shows the subregion of length 'Zoom Window Size' that has the highest absolute SHAP sum.
    """)

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