5 files changed, 132 insertions, 0 deletions

diff --git a/src/database/database.cpp b/src/database/database.cpp
index 1ac5d729..0d1c43e2 100644
--- a/src/database/database.cpp
+++ b/src/database/database.cpp
@@ -268,6 +268,62 @@ auto Database::GetTrackPath(TrackId id)
       });
 }
 
+auto Database::GetTrack(TrackId id) -> std::future<std::optional<Track>> {
+  return worker_task_->Dispatch<std::optional<Track>>(
+      [=, this]() -> std::optional<Track> {
+        std::optional<TrackData> data = dbGetTrackData(id);
+        if (!data || data->is_tombstoned()) {
+          return {};
+        }
+        TrackTags tags;
+        if (!tag_parser_->ReadAndParseTags(data->filepath(), &tags)) {
+          return {};
+        }
+        return Track(*data, tags);
+      });
+}
+
+auto Database::GetBulkTracks(std::vector<TrackId> ids)
+    -> std::future<std::vector<std::optional<Track>>> {
+  return worker_task_->Dispatch<std::vector<std::optional<Track>>>(
+      [=, this]() -> std::vector<std::optional<Track>> {
+        std::map<TrackId, Track> id_to_track{};
+
+        // Sort the list of ids so that we can retrieve them all in a single
+        // iteration through the database, without re-seeking.
+        std::vector<TrackId> sorted_ids = ids;
+        std::sort(sorted_ids.begin(), sorted_ids.end());
+
+        leveldb::Iterator* it = db_->NewIterator(leveldb::ReadOptions{});
+        for (const TrackId& id : sorted_ids) {
+          OwningSlice key = EncodeDataKey(id);
+          it->Seek(key.slice);
+          if (!it->Valid() || it->key() != key.slice) {
+            // This id wasn't found at all. Skip it.
+            continue;
+          }
+          std::optional<Track> track =
+              ParseRecord<Track>(it->key(), it->value());
+          if (track) {
+            id_to_track.insert({id, *track});
+          }
+        }
+
+        // We've fetched all of the ids in the request, so now just put them
+        // back into the order they were asked for in.
+        std::vector<std::optional<Track>> results;
+        for (const TrackId& id : ids) {
+          if (id_to_track.contains(id)) {
+            results.push_back(id_to_track.at(id));
+          } else {
+            // This lookup failed.
+            results.push_back({});
+          }
+        }
+        return results;
+      });
+}
+
 auto Database::GetIndexes() -> std::vector<IndexInfo> {
   // TODO(jacqueline): This probably needs to be async? When we have runtime
   // configurable indexes, they will need to come from somewhere.
diff --git a/src/database/include/database.hpp b/src/database/include/database.hpp
index 77a17b75..7ffc15b0 100644
--- a/src/database/include/database.hpp
+++ b/src/database/include/database.hpp
@@ -100,6 +100,15 @@ class Database {
 
   auto GetTrackPath(TrackId id) -> std::future<std::optional<std::string>>;
 
+  auto GetTrack(TrackId id) -> std::future<std::optional<Track>>;
+
+  /*
+   * Fetches data for multiple tracks more efficiently than multiple calls to
+   * GetTrack.
+   */
+  auto GetBulkTracks(std::vector<TrackId> id)
+      -> std::future<std::vector<std::optional<Track>>>;
+
   auto GetIndexes() -> std::vector<IndexInfo>;
   auto GetTracksByIndex(const IndexInfo& index, std::size_t page_size)
       -> std::future<Result<IndexRecord>*>;
diff --git a/src/database/include/future_fetcher.hpp b/src/database/include/future_fetcher.hpp
new file mode 100644
index 00000000..e8ce9729
--- /dev/null
+++ b/src/database/include/future_fetcher.hpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <memory>
+#include <utility>
+
+#include "database.hpp"
+
+namespace database {
+
+/*
+ * Utility to simplify waiting for a std::future to complete without blocking.
+ * Each instance is good for a single future, and does not directly own anything
+ * other than the future itself.
+ */
+template <typename T>
+class FutureFetcher {
+ public:
+  explicit FutureFetcher(std::future<T>&& fut)
+      : is_consumed_(false), fut_(std::move(fut)) {}
+
+  /*
+   * Returns whether or not the underlying future is still awaiting async work.
+   */
+  auto Finished() -> bool {
+    if (!fut_.valid()) {
+      return true;
+    }
+    if (fut_.wait_for(std::chrono::seconds(0)) != std::future_status::ready) {
+      return false;
+    }
+    return true;
+  }
+
+  /*
+   * Returns the result of the future, and releases ownership of the underling
+   * resource. Will return an absent value if the future became invalid (e.g.
+   * the promise associated with it was destroyed.)
+   */
+  auto Result() -> std::optional<T> {
+    assert(!is_consumed_);
+    if (is_consumed_) {
+      return {};
+    }
+    is_consumed_ = true;
+    if (!fut_.valid()) {
+      return {};
+    }
+    return fut_.get();
+  }
+
+ private:
+  bool is_consumed_;
+  std::future<T> fut_;
+};
+
+}  // namespace database
diff --git a/src/database/include/track.hpp b/src/database/include/track.hpp
index 87fae9b9..620fc59e 100644
--- a/src/database/include/track.hpp
+++ b/src/database/include/track.hpp
@@ -68,6 +68,8 @@ class TrackTags {
   std::optional<int> sample_rate;
   std::optional<int> bits_per_sample;
 
+  std::optional<int> duration;
+
   auto set(const Tag& key, const std::string& val) -> void;
   auto at(const Tag& key) const -> std::optional<shared_string>;
   auto operator[](const Tag& key) const -> std::optional<shared_string>;
diff --git a/src/database/tag_parser.cpp b/src/database/tag_parser.cpp
index b2d206d2..2b784ea5 100644
--- a/src/database/tag_parser.cpp
+++ b/src/database/tag_parser.cpp
@@ -156,6 +156,9 @@ auto TagParserImpl::ReadAndParseTags(const std::string& path, TrackTags* out)
   if (ctx.bitrate > 0) {
     out->bits_per_sample = ctx.bitrate;
   }
+  if (ctx.duration > 0) {
+    out->duration = ctx.duration;
+  }
 
   return true;
 }