7 files changed, 317 insertions, 0 deletions
diff --git a/src/audio/include/audio_backend.hpp b/src/audio/include/audio_backend.hpp
new file mode 100644
index 00000000..85985cc2
--- /dev/null
+++ b/src/audio/include/audio_backend.hpp
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <cstdint>
+namespace drivers {
+
+class IAudioBackend {
+ public:
+  virtual ~IAudioBackend() {}
+
+  enum SampleRate {};
+  enum BitDepth {};
+
+  virtual auto Configure(SampleRate sample_rate, BitDepth bit_depth)
+      -> bool = 0;
+  virtual auto WritePcmData(uint8_t* data, size_t length) -> bool = 0;
+
+  virtual auto SetVolume(uint8_t percent) -> void = 0;
+};
+
+}  // namespace drivers
diff --git a/src/audio/include/audio_decoder.hpp b/src/audio/include/audio_decoder.hpp
new file mode 100644
index 00000000..f460f9e9
--- /dev/null
+++ b/src/audio/include/audio_decoder.hpp
@@ -0,0 +1,34 @@
+#pragma once
+
+#include <cstddef>
+#include "ff.h"
+
+namespace audio {
+
+enum SampleRate {};
+enum BitDepth {};
+
+struct PcmStreamHeader {
+  SampleRate sample_rate;
+  BitDepth bit_depth;
+  bool configure_now;
+};
+
+class AudioDecoder {
+ public:
+  AudioDecoder();
+  ~AudioDecoder();
+
+  auto SetSource(RingbufHandle_t& source) -> void;
+
+  enum Status {};
+  auto ProcessChunk() -> Status;
+
+  auto GetOutputStream() const -> RingbufHandle_t;
+
+ private:
+  RingbufHandle_t input_;
+  RingbufHandle_t output_;
+};
+
+}  // namespace audio
diff --git a/src/audio/include/audio_element.hpp b/src/audio/include/audio_element.hpp
new file mode 100644
index 00000000..ea4256ac
--- /dev/null
+++ b/src/audio/include/audio_element.hpp
@@ -0,0 +1,73 @@
+#pragma once
+
+#include <cstdint>
+
+namespace audio {
+
+extern const std::size_t kMaxFrameSize;
+
+class IAudioElement {
+ public:
+  virtual ~IAudioElement();
+
+  enum CommandType {
+    /*
+     * Sets the sequence number of the most recent byte stream. Any commands
+     * received that have a lower sequence number than this will be discarded.
+     */
+    SEQUENCE_NUMBER,
+    /*
+     * Instructs this element to read a specific number of bytes from its
+     * input buffer.
+     */
+    READ_FRAME,
+    /*
+     * Represents an element-specific command. This handling of this is
+     * delegated to element implementations.
+     */
+    ELEMENT,
+    /* Instructs this element to shut down. */
+    QUIT,
+  };
+
+  struct Command {
+    CommandType type;
+    uint8_t sequence_number;
+    union {
+      void* data;
+      std::size_t frame_size;
+    };
+  };
+
+  /*
+   * Returns a queue that should be used for all communication with this
+   * element.
+   */
+  virtual auto InputCommandQueue() -> QueueHandle_t = 0;
+
+  /*
+   * Returns a buffer that will be used to stream input bytes to this element.
+   * This may be NULL, if this element represents a source, e.g. a FATFS
+   * reader.
+   */
+  virtual auto InputBuffer() -> StreamBufferHandle_t = 0;
+
+  /*
+   * Called when an element-specific command has been received.
+   */
+  virtual auto ProcessElementCommand(void* command) -> void = 0;
+
+  virtual auto SkipElementCommand(void* command) -> void = 0;
+
+  /*
+   * Called with the result of a read bytes command.
+   */
+  virtual auto ProcessData(uint8_t* data, uint16_t length) -> void = 0;
+
+  /*
+   * Called periodically when there are no pending commands.
+   */
+  virtual auto ProcessIdle() -> void = 0;
+};
+
+}  // namespace audio
diff --git a/src/audio/include/audio_output.hpp b/src/audio/include/audio_output.hpp
new file mode 100644
index 00000000..82dca82d
--- /dev/null
+++ b/src/audio/include/audio_output.hpp
@@ -0,0 +1,29 @@
+#pragma once
+
+#include <cstdint>
+#include <memory>
+
+#include "audio_common.h"
+#include "audio_element.h"
+
+namespace drivers {
+
+class IAudioOutput {
+ public:
+  IAudioOutput(audio_element_handle_t element) : element_(element) {}
+  virtual ~IAudioOutput() { audio_element_deinit(element_); }
+
+  auto GetAudioElement() -> audio_element_handle_t { return element_; }
+
+  virtual auto SetVolume(uint8_t volume) -> void = 0;
+  virtual auto GetVolume() const -> uint8_t { return volume_; }
+
+  virtual auto Configure(audio_element_info_t& info) -> void = 0;
+  virtual auto SetSoftMute(bool enabled) -> void = 0;
+
+ protected:
+  audio_element_handle_t element_;
+  uint8_t volume_;
+};
+
+}  // namespace drivers
diff --git a/src/audio/include/audio_playback.hpp b/src/audio/include/audio_playback.hpp
new file mode 100644
index 00000000..41ab46d2
--- /dev/null
+++ b/src/audio/include/audio_playback.hpp
@@ -0,0 +1,97 @@
+#pragma once
+
+#include <cstdint>
+#include <memory>
+#include <string>
+
+#include "audio_common.h"
+#include "audio_element.h"
+#include "audio_event_iface.h"
+#include "audio_pipeline.h"
+#include "esp_err.h"
+#include "fatfs_stream.h"
+#include "i2s_stream.h"
+#include "mp3_decoder.h"
+#include "result.hpp"
+
+#include "audio_output.hpp"
+#include "dac.hpp"
+#include "storage.hpp"
+
+namespace drivers {
+
+/*
+ * Sends an I2S audio stream to the DAC. Includes basic controls for pausing
+ * and resuming the stream, as well as support for gapless playback of the next
+ * queued song, but does not implement any kind of sophisticated queing or
+ * playback control; these should be handled at a higher level.
+ */
+class AudioPlayback {
+ public:
+  enum Error { FATFS_INIT, I2S_INIT, PIPELINE_INIT };
+  static auto create(std::unique_ptr<IAudioOutput> output)
+      -> cpp::result<std::unique_ptr<AudioPlayback>, Error>;
+
+  AudioPlayback(std::unique_ptr<IAudioOutput>& output,
+                audio_pipeline_handle_t pipeline,
+                audio_element_handle_t source_element,
+                audio_event_iface_handle_t event_interface);
+  ~AudioPlayback();
+
+  /*
+   * Replaces any currently playing file with the one given, and begins
+   * playback.
+   *
+   * Any value set in `set_next_file` is cleared by this method.
+   */
+  auto Play(const std::string& filename) -> void;
+  /* Toogle between resumed and paused. */
+  auto Toggle() -> void;
+  auto Resume() -> void;
+  auto Pause() -> void;
+
+  enum PlaybackState { PLAYING, PAUSED, STOPPED };
+  auto GetPlaybackState() const -> PlaybackState;
+
+  /*
+   * Handles any pending events from the underlying audio pipeline. This must
+   * be called regularly in order to handle configuring the I2S stream for
+   * different audio types (e.g. sample rate, bit depth), and for gapless
+   * playback.
+   */
+  auto ProcessEvents(uint16_t max_time_ms) -> void;
+
+  /*
+   * Sets the file that should be played immediately after the current file
+   * finishes. This is used for gapless playback
+   */
+  auto SetNextFile(const std::string& filename) -> void;
+
+  auto SetVolume(uint8_t volume) -> void;
+  auto GetVolume() const -> uint8_t;
+
+  // Not copyable or movable.
+  AudioPlayback(const AudioPlayback&) = delete;
+  AudioPlayback& operator=(const AudioPlayback&) = delete;
+
+ private:
+  PlaybackState playback_state_;
+
+  enum Decoder { NONE, MP3, AMR, OPUS, OGG, FLAC, WAV, AAC };
+  auto GetDecoderForFilename(std::string filename) const -> Decoder;
+  auto CreateDecoder(Decoder decoder) const -> audio_element_handle_t;
+  auto ReconfigurePipeline(Decoder decoder) -> void;
+
+  std::unique_ptr<IAudioOutput> output_;
+
+  std::string next_filename_ = "";
+
+  audio_pipeline_handle_t pipeline_;
+  audio_element_handle_t source_element_;
+  audio_event_iface_handle_t event_interface_;
+
+  audio_element_handle_t decoder_ = nullptr;
+  Decoder decoder_type_ = NONE;
+};
+
+}  // namespace drivers
diff --git a/src/audio/include/audio_task.hpp b/src/audio/include/audio_task.hpp
new file mode 100644
index 00000000..79604f33
--- /dev/null
+++ b/src/audio/include/audio_task.hpp
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <memory>
+
+#include "audio_element.hpp"
+
+namespace audio {
+
+struct AudioTaskArgs {
+  std::shared_ptr<IAudioElement>& element;
+};
+
+void audio_task(void* args);
+
+}  // namespace audio
diff --git a/src/audio/include/fatfs_audio_input.hpp b/src/audio/include/fatfs_audio_input.hpp
new file mode 100644
index 00000000..ed4da55e
--- /dev/null
+++ b/src/audio/include/fatfs_audio_input.hpp
@@ -0,0 +1,49 @@
+#pragma once
+
+#include <cstdint>
+#include <memory>
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/queue.h"
+#include "freertos/stream_buffer.h"
+
+#include "audio_element.hpp"
+#include "storage.hpp"
+
+namespace audio {
+
+class FatfsAudioInput : public IAudioElement {
+ public:
+  struct InputCommand {
+    std::string filename;
+  };
+
+  struct OutputCommand {
+    // TODO: does this actually need any special output?
+  };
+
+  FatfsAudioInput(std::shared_ptr<drivers::SdStorage> storage);
+  ~FatfsAudioInput();
+
+  auto OutputCommandQueue() -> QueueHandle_t;
+  auto OutputBuffer() -> StreamBufferHandle_t;
+
+ private:
+  std::shared_ptr<drivers::SdStorage> storage_;
+
+  uint8_t current_sequence = 0;
+
+  uint8_t* input_queue_memory_;
+  StaticQueue_t input_queue_metadata_;
+  QueueHandle_t input_queue_;
+
+  uint8_t* output_queue_memory_;
+  StaticQueue_t output_queue_metadata_;
+  QueueHandle_t output_queue_;
+
+  uint8_t* output_buffer_memory_;
+  StaticStreamBuffer_t output_buffer_metadata_;
+  StreamBufferHandle_t output_buffer_;
+};
+
+}  // namespace audio