Add a wrapper codec source that does readahead

2 files changed, 56 insertions, 1 deletions

diff --git a/src/audio/include/fatfs_audio_input.hpp b/src/audio/include/fatfs_audio_input.hpp
index 08527350..9b516478 100644
--- a/src/audio/include/fatfs_audio_input.hpp
+++ b/src/audio/include/fatfs_audio_input.hpp
@@ -19,6 +19,7 @@
 #include "codec.hpp"
 #include "future_fetcher.hpp"
 #include "tag_parser.hpp"
+#include "tasks.hpp"
 #include "types.hpp"
 
 namespace audio {
@@ -30,7 +31,7 @@ namespace audio {
  */
 class FatfsAudioInput : public IAudioSource {
  public:
-  explicit FatfsAudioInput(database::ITagParser& tag_parser);
+  explicit FatfsAudioInput(database::ITagParser&, tasks::Worker&);
   ~FatfsAudioInput();
 
   /*
@@ -54,6 +55,7 @@ class FatfsAudioInput : public IAudioSource {
       -> std::optional<codecs::StreamType>;
 
   database::ITagParser& tag_parser_;
+  tasks::Worker& bg_worker_;
 
   std::mutex new_stream_mutex_;
   std::shared_ptr<codecs::IStream> new_stream_;
diff --git a/src/audio/include/readahead_source.hpp b/src/audio/include/readahead_source.hpp
new file mode 100644
index 00000000..dea3ff3f
--- /dev/null
+++ b/src/audio/include/readahead_source.hpp
@@ -0,0 +1,53 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+
+#include "freertos/FreeRTOS.h"
+
+#include "ff.h"
+#include "freertos/stream_buffer.h"
+
+#include "audio_source.hpp"
+#include "codec.hpp"
+#include "tasks.hpp"
+
+namespace audio {
+
+/*
+ * Wraps another stream, proactively buffering large chunks of it into memory
+ * at a time.
+ */
+class ReadaheadSource : public codecs::IStream {
+ public:
+  ReadaheadSource(tasks::Worker&, std::unique_ptr<codecs::IStream>);
+  ~ReadaheadSource();
+
+  auto Read(cpp::span<std::byte> dest) -> ssize_t override;
+
+  auto CanSeek() -> bool override;
+
+  auto SeekTo(int64_t destination, SeekFrom from) -> void override;
+
+  auto CurrentPosition() -> int64_t override;
+
+  ReadaheadSource(const ReadaheadSource&) = delete;
+  ReadaheadSource& operator=(const ReadaheadSource&) = delete;
+
+ private:
+  tasks::Worker& worker_;
+  std::unique_ptr<codecs::IStream> wrapped_;
+
+  std::atomic<bool> is_refilling_;
+  StreamBufferHandle_t buffer_;
+  int64_t tell_;
+};
+
+}  // namespace audio
\ No newline at end of file