output/Interface: convert to abstract class

Yet another C-style vtable replaced with C++.

1 files changed, 101 insertions, 9 deletions

diff --git a/src/output/Interface.hxx b/src/output/Interface.hxx
index 645a94b2e..83737df5b 100644
--- a/src/output/Interface.hxx
+++ b/src/output/Interface.hxx
@@ -20,22 +20,33 @@
 #ifndef MPD_AUDIO_OUTPUT_INTERFACE_HXX
 #define MPD_AUDIO_OUTPUT_INTERFACE_HXX
 
-struct AudioOutputPlugin;
+#include <chrono>
+
+struct AudioFormat;
+struct Tag;
 
 class AudioOutput {
-	/**
-	 * The plugin which implements this output device.
-	 */
-	const AudioOutputPlugin &plugin;
+	const unsigned flags;
 
 	bool need_fully_defined_audio_format = false;
 
+protected:
+	static constexpr unsigned FLAG_ENABLE_DISABLE = 0x1;
+	static constexpr unsigned FLAG_PAUSE = 0x2;
+
 public:
-	AudioOutput(const AudioOutputPlugin &_plugin)
-		:plugin(_plugin) {}
+	explicit AudioOutput(unsigned _flags):flags(_flags) {}
+	virtual ~AudioOutput() = default;
+
+	AudioOutput(const AudioOutput &) = delete;
+	AudioOutput &operator=(const AudioOutput &) = delete;
 
-	const AudioOutputPlugin &GetPlugin() const {
-		return plugin;
+	bool SupportsEnableDisable() const {
+		return flags & FLAG_ENABLE_DISABLE;
+	}
+
+	bool SupportsPause() const {
+		return flags & FLAG_PAUSE;
 	}
 
 	bool GetNeedFullyDefinedAudioFormat() const {
@@ -50,6 +61,87 @@ public:
 	void NeedFullyDefinedAudioFormat() {
 		need_fully_defined_audio_format = true;
 	}
+
+	/**
+	 * Enable the device.  This may allocate resources, preparing
+	 * for the device to be opened.
+	 *
+	 * Throws #std::runtime_error on error.
+	 */
+	virtual void Enable() {}
+
+	/**
+	 * Disables the device.  It is closed before this method is
+	 * called.
+	 */
+	virtual void Disable() noexcept {}
+
+	/**
+	 * Really open the device.
+	 *
+	 * Throws #std::runtime_error on error.
+	 *
+	 * @param audio_format the audio format in which data is going
+	 * to be delivered; may be modified by the plugin
+	 */
+	virtual void Open(AudioFormat &audio_format) = 0;
+
+	/**
+	 * Close the device.
+	 */
+	virtual void Close() noexcept = 0;
+
+	/**
+	 * Returns a positive number if the output thread shall further
+	 * delay the next call to Play() or Pause(), which will happen
+	 * until this function returns 0.  This should be implemented
+	 * instead of doing a sleep inside the plugin, because this
+	 * allows MPD to listen to commands meanwhile.
+	 *
+	 * @return the duration to wait
+	 */
+	virtual std::chrono::steady_clock::duration Delay() const noexcept {
+		return std::chrono::steady_clock::duration::zero();
+	}
+
+	/**
+	 * Display metadata for the next chunk.  Optional method,
+	 * because not all devices can display metadata.
+	 */
+	virtual void SendTag(const Tag &) {}
+
+	/**
+	 * Play a chunk of audio data.
+	 *
+	 * Throws #std::runtime_error on error.
+	 *
+	 * @return the number of bytes played
+	 */
+	virtual size_t Play(const void *chunk, size_t size) = 0;
+
+	/**
+	 * Wait until the device has finished playing.
+	 */
+	virtual void Drain() {}
+
+	/**
+	 * Try to cancel data which may still be in the device's
+	 * buffers.
+	 */
+	virtual void Cancel() noexcept {}
+
+	/**
+	 * Pause the device.  If supported, it may perform a special
+	 * action, which keeps the device open, but does not play
+	 * anything.  Output plugins like "shout" might want to play
+	 * silence during pause, so their clients won't be
+	 * disconnected.  Plugins which do not support pausing will
+	 * simply be closed, and have to be reopened when unpaused.
+	 *
+	 * @return false on error (output will be closed by caller),
+	 * true for continue to pause
+	 */
+	virtual bool Pause() noexcept { return true; }
 };
 
 #endif