lockstep/app/src/main/cpp/PlaybackEngine.cpp

//
// Created by david on 01.02.2026.
//

#define LOG_TAG "PlaybackEngine"

#include "PlaybackEngine.h"
#include "logging.h"
#include "mpg123.h"
#include "mp3file.h"
#include <vector>

static inline int readBuffer2(MP3File* mp3)
{
    size_t done = 0;
    int err = mpg123_read(mp3->handle, mp3->buffer, mp3->buffer_size, &done);
    mp3->leftSamples = done / sizeof(int16_t);
    mp3->offset = 0;
    return err != MPG123_OK ? 0 : done;
}

static bool read_mp3(std::string filename, std::vector<float>& samples) {
    // TODO: assumes 48000 Hz sampling rate of the file
    // note: our resource file is mono (1 channel = 1 samples_per_frame)!

    MP3File *mFile = mp3file_open(filename.c_str(), 0); // MPG123_ENC_FLOAT_32 (but does not seem to work)
    bool ok1 = mFile != nullptr;
    bool ok2 = readBuffer2(mFile) != 0; // once is enough (maybe the other one needs to pre-fill other buffers, in oboe etc.)
    if(ok1 && ok2) {
        // num_frames, num_samples, samples_per_frame
        samples.resize(mFile->num_samples);
        for(int i = 0; i < mFile->num_samples; i++) {
            int16_t *src = ((int16_t *) mFile->buffer) + i;
            samples[i] = (*src) / 32768.0f;
        }
    }
    if(mFile)
        mp3file_delete(mFile);
    return ok1 && ok2;
}

PlaybackEngine::PlaybackEngine(std::string filesDir, int resid): mFilesDir(filesDir) {
    LOGI("PlaybackEngine()");
    LOGI("NDK LOG_LEVEL=%d", LOG_LEVEL);
    // NDK LOG_LEVEL=3  (DEBUG)
    std::vector<float> samples;
    read_mp3(mFilesDir + "/" + std::to_string(resid) + ".mp3", samples);
    mPlayer = new MixingPlayer(samples);
    int32_t res = mPlayer->startAudio();
    LOGI("startAudio() = %d", res);
}

PlaybackEngine::~PlaybackEngine() {
    LOGI("~PlaybackEngine()");
    mPlayer->stopAudio();
    delete mPlayer;
    mPlayer = nullptr;
}