mg4/app/src/main/java/com/evsuite/abrp/MusicTap.java

package com.evsuite.abrp;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.media.audiofx.Visualizer;

/**
 * Listens to what the head unit plays for the Halloween pumpkin's light: Android's audio analyser
 * on the output mix, its kick-drum band read 25 times a second on a thread of its own, made into a
 * {@link MusicPulse}. Runs only while MainActivity says so (the style on screen, the app in
 * front, and "Pumpkin light follows the music" on). Levels only: no sound is kept and no microphone used. Where the analyser hears nothing
 * (the radio) or is not available, the pulse stays 0 and the pumpkin burns as usual.
 */
final class MusicTap {

    private static final int READ_MS = 40, GIVE_UP_AFTER_FAILURES = 50;

    private final Context app;
    private volatile Thread worker;
    private volatile float pulse;

    MusicTap(Context context) {
        app = context.getApplicationContext();
    }

    /** From 0 to 1; safe to read from any thread. */
    float pulse() {
        return pulse;
    }

    void setRunning(boolean run) {
        if (run == (worker != null)) return;
        if (!run) {
            Thread stopping = worker;
            worker = null;
            pulse = 0f;
            stopping.interrupt();
            return;
        }
        if (app.checkSelfPermission(Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED) return;
        Thread thread = new Thread(this::listen, "music-tap");
        thread.setDaemon(true);
        worker = thread;
        thread.start();
    }

    /** All analyser calls live here, off the main thread; it is always let go. */
    private void listen() {
        Thread me = Thread.currentThread();
        Visualizer analyser = null;
        try {
            analyser = new Visualizer(0);
            analyser.setCaptureSize(Visualizer.getCaptureSizeRange()[1]);
            analyser.setScalingMode(Visualizer.SCALING_MODE_NORMALIZED);
            if (analyser.setEnabled(true) != Visualizer.SUCCESS) return;
            int rateHz = analyser.getSamplingRate() / 1000;
            byte[] fft = new byte[analyser.getCaptureSize()];
            MusicPulse music = new MusicPulse();
            long last = System.nanoTime();
            int failures = 0;
            while (worker == me && failures < GIVE_UP_AFTER_FAILURES) {
                Thread.sleep(READ_MS);
                boolean read = analyser.getFft(fft) == Visualizer.SUCCESS;
                failures = read ? 0 : failures + 1;
                long now = System.nanoTime();
                float value = music.update(read ? SoundLevels.band(fft, rateHz, MusicPulse.FROM_HZ, MusicPulse.TO_HZ) : null, (now - last) / 1e9f);
                last = now;
                if (worker == me) pulse = value;
            }
        } catch (InterruptedException e) {
            // Told to stop.
        } catch (RuntimeException e) {
            // No analyser here: the pumpkin burns as usual.
        } finally {
            if (worker == me) pulse = 0f;
            if (analyser != null) {
                try {
                    analyser.setEnabled(false);
                } catch (RuntimeException ignored) {
                    // Released next either way.
                }
                try {
                    analyser.release();
                } catch (RuntimeException ignored) {
                    // Nothing more can be done from here.
                }
            }
        }
    }
}