1 files changed, 73 insertions, 0 deletions
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