Add a wrapper codec source that does readahead

1 files changed, 53 insertions, 0 deletions

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
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