1 files changed, 105 insertions, 0 deletions
diff --git a/src/playlist/include/source.hpp b/src/playlist/include/source.hpp
new file mode 100644
index 00000000..069c1e93
--- /dev/null
+++ b/src/playlist/include/source.hpp
@@ -0,0 +1,105 @@
+/*
+ * 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 "track.hpp"
+
+namespace playlist {
+
+/*
+ * Stateful interface for iterating over a collection of tracks by id.
+ */
+class ISource {
+ public:
+  virtual ~ISource() {}
+
+  virtual auto Current() -> std::optional<database::TrackId> = 0;
+
+  /*
+   * Discards the current track id and continues to the next in this source.
+   * Returns the new current track id.
+   */
+  virtual auto Advance() -> std::optional<database::TrackId> = 0;
+
+  /*
+   * Repeatedly advances until a track with the given id is the current track.
+   * Returns false if this source ran out of tracks before the requested id
+   * was encounted, true otherwise.
+   */
+  virtual auto AdvanceTo(database::TrackId id) -> bool {
+    for (auto t = Current(); t.has_value(); t = Advance()) {
+      if (*t == id) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /*
+   * Places the next n tracks into the given vector, in order. Does not change
+   * the value returned by Current().
+   */
+  virtual auto Peek(std::size_t n, std::vector<database::TrackId>*)
+      -> std::size_t = 0;
+};
+
+/*
+ * A Source that supports restarting iteration from its original initial
+ * value.
+ */
+class IResetableSource : public ISource {
+ public:
+  virtual ~IResetableSource() {}
+
+  virtual auto Previous() -> std::optional<database::TrackId> = 0;
+
+  /*
+   * Restarts iteration from this source's initial value.
+   */
+  virtual auto Reset() -> void = 0;
+};
+
+class IndexRecordSource : public IResetableSource {
+ public:
+  IndexRecordSource(std::weak_ptr<database::Database> db,
+                    std::shared_ptr<database::Result<database::IndexRecord>>);
+
+  IndexRecordSource(std::weak_ptr<database::Database> db,
+                    std::shared_ptr<database::Result<database::IndexRecord>>,
+                    std::size_t,
+                    std::shared_ptr<database::Result<database::IndexRecord>>,
+                    std::size_t);
+
+  auto Current() -> std::optional<database::TrackId> override;
+  auto Advance() -> std::optional<database::TrackId> override;
+  auto Peek(std::size_t n, std::vector<database::TrackId>*)
+      -> std::size_t override;
+
+  auto Previous() -> std::optional<database::TrackId> override;
+  auto Reset() -> void override;
+
+ private:
+  std::weak_ptr<database::Database> db_;
+
+  std::shared_ptr<database::Result<database::IndexRecord>> initial_page_;
+  ssize_t initial_item_;
+
+  std::shared_ptr<database::Result<database::IndexRecord>> current_page_;
+  ssize_t current_item_;
+};
+
+}  // namespace playlist