path: root/src/audio/audio.cc

// This file is part of the 64k demo project.
// It manages the low-level audio device and high-level audio state.
// Now uses backend abstraction for testability.

#include "audio.h"
#include "audio_backend.h"
#include "miniaudio_backend.h"
#include "ring_buffer.h"
#include "synth.h"
#include "util/asset_manager.h"

#define MINIAUDIO_IMPLEMENTATION
#include "miniaudio.h"

#include <stdio.h>

// Global ring buffer for audio streaming
static AudioRingBuffer g_ring_buffer;

// Pending write buffer for partially written samples
// Maximum size: one chunk (533 frames @ 60fps = 1066 samples stereo)
#define MAX_PENDING_SAMPLES 2048
static float g_pending_buffer[MAX_PENDING_SAMPLES];
static int g_pending_samples = 0;  // How many samples are waiting to be written

// Global backend pointer for audio abstraction
static AudioBackend* g_audio_backend = nullptr;
static MiniaudioBackend g_default_backend;
static bool g_using_default_backend = false;

#if !defined(STRIP_ALL)
// Allow tests to inject a custom backend
void audio_set_backend(AudioBackend* backend) {
  g_audio_backend = backend;
}

// Get current backend (for tests)
AudioBackend* audio_get_backend() {
  return g_audio_backend;
}
#endif /* !defined(STRIP_ALL) */

int register_spec_asset(AssetId id) {
  size_t size;
  const uint8_t* data = GetAsset(id, &size);
  if (!data || size < sizeof(SpecHeader))
    return -1;

  const SpecHeader* header = (const SpecHeader*)data;
  const float* spectral_data = (const float*)(data + sizeof(SpecHeader));

  Spectrogram spec;
  spec.spectral_data_a = spectral_data;
  spec.spectral_data_b = spectral_data; // No double-buffer for static assets
  spec.num_frames = header->num_frames;

  return synth_register_spectrogram(&spec);
}

void audio_init() {
  synth_init();

  // Clear pending buffer
  g_pending_samples = 0;

  // Use default backend if none set
  if (g_audio_backend == nullptr) {
    g_audio_backend = &g_default_backend;
    g_using_default_backend = true;
  }

  g_audio_backend->init();
}

void audio_start() {
  if (g_audio_backend == nullptr) {
    printf("Cannot start: audio not initialized.\n");
    return;
  }
  g_audio_backend->start();
}

void audio_render_ahead(float music_time, float dt) {
  // Target: maintain look-ahead buffer
  const float target_lookahead =
      (float)RING_BUFFER_LOOKAHEAD_MS / 1000.0f;

  // Render in small chunks to keep synth time synchronized with tracker
  // Chunk size: one frame's worth of audio (~16.6ms @ 60fps)
  const int chunk_frames = (int)(dt * RING_BUFFER_SAMPLE_RATE);
  const int chunk_samples = chunk_frames * RING_BUFFER_CHANNELS;

  if (chunk_frames <= 0) return;

  // Keep rendering small chunks until buffer is full enough
  while (true) {
    // First, try to flush any pending samples from previous partial writes
    if (g_pending_samples > 0) {
      const int written = g_ring_buffer.write(g_pending_buffer, g_pending_samples);

      if (written > 0) {
        // Some or all samples were written
        // Move remaining samples to front of buffer
        const int remaining = g_pending_samples - written;
        if (remaining > 0) {
          for (int i = 0; i < remaining; ++i) {
            g_pending_buffer[i] = g_pending_buffer[written + i];
          }
        }
        g_pending_samples = remaining;

        // Notify backend (for testing/tracking)
#if !defined(STRIP_ALL)
        if (g_audio_backend != nullptr) {
          g_audio_backend->on_frames_rendered(written / RING_BUFFER_CHANNELS);
        }
#endif
      }

      // If still have pending samples, buffer is full - wait for consumption
      if (g_pending_samples > 0) break;
    }

    // Check current buffer state
    const int buffered_samples = g_ring_buffer.available_read();
    const float buffered_time =
        (float)buffered_samples / (RING_BUFFER_SAMPLE_RATE * RING_BUFFER_CHANNELS);

    // Stop if buffer is full enough
    if (buffered_time >= target_lookahead) break;

    // Check available space and render chunk that fits
    const int available_space = g_ring_buffer.available_write();
    if (available_space == 0) {
      // Buffer is completely full, wait for audio callback to consume
      break;
    }

    // Determine how much we can actually render
    // Render the smaller of: desired chunk size OR available space
    const int actual_samples = (available_space < chunk_samples) ? available_space : chunk_samples;
    const int actual_frames = actual_samples / RING_BUFFER_CHANNELS;

    // Allocate temporary buffer (stereo)
    float* temp_buffer = new float[actual_samples];

    // Render audio from synth (advances synth state incrementally)
    synth_render(temp_buffer, actual_frames);

    // Write to ring buffer
    const int written = g_ring_buffer.write(temp_buffer, actual_samples);

    // If partial write, save remaining samples to pending buffer
    if (written < actual_samples) {
      const int remaining = actual_samples - written;
      if (remaining <= MAX_PENDING_SAMPLES) {
        for (int i = 0; i < remaining; ++i) {
          g_pending_buffer[i] = temp_buffer[written + i];
        }
        g_pending_samples = remaining;
      }
    }

    // Notify backend of frames rendered (count frames sent to synth)
#if !defined(STRIP_ALL)
    if (g_audio_backend != nullptr) {
      g_audio_backend->on_frames_rendered(actual_frames);
    }
#endif

    delete[] temp_buffer;

    // If we couldn't write everything, stop and retry next frame
    if (written < actual_samples) break;
  }
}

float audio_get_playback_time() {
  const int64_t total_samples = g_ring_buffer.get_total_read();
  return (float)total_samples /
         (RING_BUFFER_SAMPLE_RATE * RING_BUFFER_CHANNELS);
}

// Expose ring buffer for backends
AudioRingBuffer* audio_get_ring_buffer() {
  return &g_ring_buffer;
}

#if !defined(STRIP_ALL)
void audio_render_silent(float duration_sec) {
  const int sample_rate = 32000;
  const int chunk_size = 512;
  int total_frames = (int)(duration_sec * sample_rate);
  float buffer[chunk_size * 2]; // Stereo

  while (total_frames > 0) {
    int frames_to_render =
        (total_frames > chunk_size) ? chunk_size : total_frames;
    synth_render(buffer, frames_to_render);
    total_frames -= frames_to_render;

    // Notify backend of frames rendered (for mock tracking)
    if (g_audio_backend != nullptr) {
      g_audio_backend->on_frames_rendered(frames_to_render);
    }
  }
}
#endif /* !defined(STRIP_ALL) */

void audio_update() {
}

void audio_shutdown() {
  if (g_audio_backend != nullptr) {
    g_audio_backend->shutdown();
  }
  synth_shutdown();

  // Clear backend pointer if using default
  if (g_using_default_backend) {
    g_audio_backend = nullptr;
    g_using_default_backend = false;
  }
}