Basic playlists for upcoming

Beware under-testing and bugs. Just getting something barebones in so
that I can do rN+1 bringup

1 files changed, 68 insertions, 0 deletions

diff --git a/src/playlist/include/shuffler.hpp b/src/playlist/include/shuffler.hpp
new file mode 100644
index 00000000..affc6301
--- /dev/null
+++ b/src/playlist/include/shuffler.hpp
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+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <deque>
+#include <memory>
+#include <mutex>
+#include <variant>
+#include <vector>
+
+#include "bloom_filter.hpp"
+#include "database.hpp"
+#include "future_fetcher.hpp"
+#include "random.hpp"
+#include "source.hpp"
+#include "track.hpp"
+
+namespace playlist {
+
+/*
+ * A source composes of other sources and/or specific extra tracks. Supports
+ * iteration over its contents in a random order.
+ */
+class Shuffler : public ISource {
+ public:
+  static auto Create() -> Shuffler*;
+
+  explicit Shuffler(
+      util::IRandom* random,
+      std::unique_ptr<util::BloomFilter<database::TrackId>> filter);
+
+  auto Current() -> std::optional<database::TrackId> override;
+  auto Advance() -> std::optional<database::TrackId> override;
+  auto Peek(std::size_t, std::vector<database::TrackId>*)
+      -> std::size_t override;
+
+  typedef std::variant<database::TrackId, std::shared_ptr<IResetableSource>>
+      Item;
+  auto Add(Item) -> void;
+
+  /*
+   * Returns the enqueued items, starting from the current item, in their
+   * original insertion order.
+   */
+  auto Unshuffle() -> std::vector<Item>;
+
+  // Not copyable or movable.
+
+  Shuffler(const Shuffler&) = delete;
+  Shuffler& operator=(const Shuffler&) = delete;
+
+ private:
+  auto RefillBuffer() -> void;
+
+  util::IRandom* random_;
+
+  std::unique_ptr<util::BloomFilter<database::TrackId>> already_played_;
+  bool out_of_items_;
+
+  std::deque<Item> ordered_items_;
+  std::deque<database::TrackId> shuffled_items_buffer_;
+};
+
+}  // namespace playlist