add indexing to the database

idk man i wrote most of this in a fugue state whilst high on the couch
with my cat

1 files changed, 72 insertions, 0 deletions

diff --git a/src/database/include/index.hpp b/src/database/include/index.hpp
new file mode 100644
index 00000000..17229164
--- /dev/null
+++ b/src/database/include/index.hpp
@@ -0,0 +1,72 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include <cstdint>
+#include <string>
+#include <variant>
+#include <vector>
+
+#include "leveldb/db.h"
+#include "leveldb/slice.h"
+
+#include "leveldb/write_batch.h"
+#include "shared_string.h"
+#include "track.hpp"
+
+namespace database {
+
+typedef uint8_t IndexId;
+
+struct IndexInfo {
+  // Unique id for this index
+  IndexId id;
+  // Localised, user-friendly description of this index. e.g. "Albums by Artist"
+  // or "All Tracks".
+  std::string name;
+  // Specifier for how this index breaks down the database.
+  std::vector<Tag> components;
+};
+
+struct IndexKey {
+  struct Header {
+    // The index that this key was created for.
+    IndexId id;
+    // The number of components of IndexInfo that have already been filtered.
+    // For example, if an index consists of { kGenre, kArtist }, and this key
+    // represents an artist, then depth = 1.
+    std::uint8_t depth;
+    // The cumulative hash of all filtered components, in order. For example, if
+    // an index consists of { kArtist, kAlbum, kTitle }, and we are at depth = 2
+    // then this may contain hash(hash("Jacqueline"), "My Cool Album").
+    std::uint64_t components_hash;
+  };
+  Header header;
+
+  // The filterable / selectable item that this key represents. "Jacqueline" for
+  // kArtist, "My Cool Album" for kAlbum, etc.
+  std::optional<std::string> item;
+  // If this is a leaf component, the track id for this record.
+  // This could reasonably be the value for a record, but we keep it as a part
+  // of the key to help with disambiguation.
+  std::optional<TrackId> track;
+};
+
+auto Index(const IndexInfo&, const Track&, leveldb::WriteBatch*) -> bool;
+auto ExpandHeader(const IndexKey::Header&, const std::optional<std::string>&)
+    -> IndexKey::Header;
+
+// Predefined indexes
+// TODO(jacqueline): Make these defined at runtime! :)
+
+extern const IndexInfo kAlbumsByArtist;
+extern const IndexInfo kTracksByGenre;
+extern const IndexInfo kAllTracks;
+
+}  // namespace database