pvbemu/app/Bundle.java

import java.awt.image.*;
import java.io.*;
import java.nio.charset.*;
import java.util.*;
import javax.imageio.*;

public class Bundle {

    // File loaded from disk
    static class File2 implements Comparable<File2> {

        // Instance fields
        byte[] data;     // Contents
        String filename; // Full path relative to root

        // Comparator
        public int compareTo(File2 o) {
            if (filename.equals("app/_boot.js"))
                return -1;
            if (o.filename.equals("app/_boot.js"))
                return 1;
            return filename.compareTo(o.filename);
        }

    }

    // Load all files in directory tree into memory
    static HashMap<String, File2> readFiles(String bundleTitle) {
        var dirs  = new ArrayDeque<File>();
        var root  = new File(".");
        var subs  = new ArrayDeque<String>();
        var files = new HashMap<String, File2>();

        // Process all subdirectories
        dirs.add(root);
        while (!dirs.isEmpty()) {
            var dir = dirs.remove();

            // Add all subdirectories
            for (var sub : dir.listFiles(f->f.isDirectory())) {

                // Exclusions
                if (dir == root && sub.getName().equals(".git"))
                    continue;

                // Add the directory for bundling
                dirs.add(sub);
            }

            // Add all files
            for (var file : dir.listFiles(f->f.isFile())) {
                var file2 = new File2();

                // Read the file into memory
                try {
                    var stream = new FileInputStream(file);
                    file2.data = stream.readAllBytes();
                    stream.close();
                } catch (Exception e) {
                    throw new RuntimeException(e.getMessage());
                }

                // Determine the file's full pathname
                subs.clear();
                subs.addFirst(file.getName());
                for (;;) {
                    file = file.getParentFile();
                    if (file.equals(root))
                        break;
                    subs.addFirst(file.getName());
                }
                file2.filename = String.join("/", subs);

                // Exclusions
                if (
                    file2.filename.startsWith(".git"           ) ||
                    file2.filename.startsWith(bundleTitle + "_") &&
                    file2.filename.endsWith  (".html"          )
                ) continue;

                // Add the file to the output
                files.put(file2.filename, file2);
            }

        }

        return files;
    }

    // Prepend manifest object to _boot.js
    static void manifest(HashMap<String, File2> files, String bundleName) {

        // Produce a sorted list of files
        var values = files.values().toArray(new File2[files.size()]);
        Arrays.sort(values);

        // Build a file manifest
        var manifest = new StringBuilder();
        manifest.append("\"use strict\";\nlet manifest=[");
        for (var file : values) {
            manifest.append(
                "[\"" + file.filename + "\"," + file.data.length + "]");
            if (file != values[values.length - 1])
                manifest.append(",");
        }
        manifest.append("],bundleName=\"" + bundleName + "\";");

        // Prepend the manifest to _boot.js
        var boot = files.get("app/_boot.js");
        boot.data = (
            manifest.toString() +
            new String(boot.data, StandardCharsets.UTF_8) +
            "\u0000"
        ).getBytes(StandardCharsets.UTF_8);
    }

    // Construct bundled blob
    static byte[] blob(HashMap<String, File2> files) {

        // Produce a sorted list of files
        var values = files.values().toArray(new File2[files.size()]);
        Arrays.sort(values);

        // Build the blob
        var blob = new ByteArrayOutputStream();
        for (var file : values) try {
            blob.write(file.data);
        } catch (Exception e) { }

        return blob.toByteArray();
    }

    // Encode bundled blob as a .png
    static byte[] png(byte[] blob) {

        // Calculate the dimensions of the image
        int width  = (int) Math.ceil(Math.sqrt(blob.length));
        int height = (int) Math.ceil((double) blob.length / width);

        // Prepare the pixel data
        var pixels = new int[width * height];
        for (int x = 0; x < blob.length; x++) {
            int l = blob[x] & 0xFF;
            pixels[x] = 0xFF000000 | l << 16 | l << 8 | l;
        }

        // Produce a BufferedImage containing the pixels
        var img = new BufferedImage(width, height,
            BufferedImage.TYPE_BYTE_GRAY);
        img.getRaster().setPixels(0, 0, width, height, pixels);

        // Encode the image as a PNG byte array
        var png = new ByteArrayOutputStream();
        try { ImageIO.write(img, "png", png); }
        catch (Exception e) { }
        return png.toByteArray();
    }

    // Embed bundle .png into template.html as a data URL
    static void template(byte[] png, String bundleName) {

        // Encode the PNG as a data URL
        String url = "data:image/png;base64," +
            Base64.getMimeEncoder().encodeToString(png)
            .replaceAll("\\r\\n", "");

        try {

            // Read template.html into memory
            var inStream = new FileInputStream("app/template.html");
            String template =
                new String(inStream.readAllBytes(), StandardCharsets.UTF_8)
                .replace("src=\"\"", "src=\"" + url + "\"")
            ;
            inStream.close();

            // Write the output HTML file
            var outStream = new FileOutputStream(bundleName + ".html");
            outStream.write(template.getBytes(StandardCharsets.UTF_8));
            outStream.close();
        } catch (Exception e) { throw new RuntimeException(e.getMessage()); }

    }

    // Determine the filename of the bundle
    static String bundleName(String name) {
        var calendar = Calendar.getInstance();
        return String.format("%s_%04d%02d%02d",
            name,
            calendar.get(Calendar.YEAR),
            calendar.get(Calendar.MONTH) + 1,
            calendar.get(Calendar.DAY_OF_MONTH)
        );
    }

    // Program entry point
    public static void main(String[] args) {

        // Error checking
        if (args.length != 1) {
            System.err.println("Usage: Bundle <name>");
            return;
        }

        // Program tasks
        String bundleName = bundleName(args[0]);
        var files = readFiles(args[0]);
        manifest(files, bundleName);
        var blob = blob(files);
        var png = png(blob);
        template(png, bundleName);
    }

}