1 files changed, 163 insertions, 0 deletions
diff --git a/src/playlist/source.cpp b/src/playlist/source.cpp
index 18a7887b..d51d97ab 100644
--- a/src/playlist/source.cpp
+++ b/src/playlist/source.cpp
@@ -22,6 +22,17 @@
 
 namespace playlist {
 
+auto CreateSourceFromResults(
+    std::weak_ptr<database::Database> db,
+    std::shared_ptr<database::Result<database::IndexRecord>> results)
+    -> std::shared_ptr<IResetableSource> {
+  if (results->values()[0]->track()) {
+    return std::make_shared<IndexRecordSource>(db, results);
+  } else {
+    return std::make_shared<NestedSource>(db, results);
+  }
+}
+
 IndexRecordSource::IndexRecordSource(
     std::weak_ptr<database::Database> db,
     std::shared_ptr<database::Result<database::IndexRecord>> initial)
@@ -142,4 +153,156 @@ auto IndexRecordSource::Reset() -> void {
   current_item_ = initial_item_;
 }
 
+NestedSource::NestedSource(
+    std::weak_ptr<database::Database> db,
+    std::shared_ptr<database::Result<database::IndexRecord>> initial)
+    : db_(db),
+      initial_page_(initial),
+      initial_item_(0),
+      current_page_(initial_page_),
+      current_item_(initial_item_),
+      current_child_(CreateChild(initial->values()[0])) {}
+
+auto NestedSource::Current() -> std::optional<database::TrackId> {
+  if (current_child_) {
+    return current_child_->Current();
+  }
+  return {};
+}
+
+auto NestedSource::Advance() -> std::optional<database::TrackId> {
+  if (!current_child_) {
+    return {};
+  }
+
+  auto child_next = current_child_->Advance();
+  if (child_next) {
+    return child_next;
+  }
+  // Our current child has run out of tracks. Move on to the next child.
+  current_item_++;
+  current_child_.reset();
+
+  if (current_item_ >= current_page_->values().size()) {
+    // We're even out of items in this page!
+    auto next_page = current_page_->next_page();
+    if (!next_page) {
+      current_item_--;
+      return {};
+    }
+
+    auto db = db_.lock();
+    if (!db) {
+      return {};
+    }
+
+    current_page_.reset(db->GetPage<database::IndexRecord>(&*next_page).get());
+    current_item_ = 0;
+  }
+  current_child_ = CreateChild(current_page_->values()[current_item_]);
+
+  return Current();
+}
+
+auto NestedSource::Previous() -> std::optional<database::TrackId> {
+  if (current_page_ == initial_page_ && current_item_ <= initial_item_) {
+    return {};
+  }
+
+  current_item_--;
+  current_child_.reset();
+
+  if (current_item_ < 0) {
+    auto prev_page = current_page_->prev_page();
+    if (!prev_page) {
+      return {};
+    }
+
+    auto db = db_.lock();
+    if (!db) {
+      return {};
+    }
+
+    current_page_.reset(db->GetPage<database::IndexRecord>(&*prev_page).get());
+    current_item_ = current_page_->values().size() - 1;
+  }
+  current_child_ = CreateChild(current_page_->values()[current_item_]);
+
+  return Current();
+}
+
+auto NestedSource::Peek(std::size_t n, std::vector<database::TrackId>* out)
+    -> std::size_t {
+  if (current_page_->values().size() <= current_item_) {
+    return {};
+  }
+
+  auto db = db_.lock();
+  if (!db) {
+    return 0;
+  }
+
+  std::size_t items_added = 0;
+
+  std::shared_ptr<database::Result<database::IndexRecord>> working_page =
+      current_page_;
+  std::size_t working_item = current_item_;
+  std::shared_ptr<IResetableSource> working_child = current_child_;
+
+  while (working_child) {
+    auto res = working_child->Peek(n, out);
+    n -= res;
+    items_added += res;
+
+    if (n == 0) {
+      break;
+    } else {
+      working_item++;
+      if (working_item < working_page->values().size()) {
+        working_child = CreateChild(working_page->values()[working_item]);
+      } else {
+        auto next_page = current_page_->next_page();
+        if (!next_page) {
+          break;
+        }
+        working_page.reset(
+            db->GetPage<database::IndexRecord>(&*next_page).get());
+        working_item = 0;
+        working_child = CreateChild(working_page->values()[0]);
+      }
+    }
+  }
+
+  return items_added;
+}
+
+auto NestedSource::Reset() -> void {
+  current_page_ = initial_page_;
+  current_item_ = initial_item_;
+  current_child_ = CreateChild(initial_page_->values()[initial_item_]);
+}
+
+auto NestedSource::CreateChild(std::shared_ptr<database::IndexRecord> record)
+    -> std::shared_ptr<IResetableSource> {
+  auto cont = record->Expand(10);
+  if (!cont) {
+    return {};
+  }
+  auto db = db_.lock();
+  if (!db) {
+    return {};
+  }
+  std::shared_ptr<database::Result<database::IndexRecord>> next_level{
+      db->GetPage<database::IndexRecord>(&*cont).get()};
+  if (!next_level) {
+    return {};
+  }
+  auto next_level_record = next_level->values()[0];
+  if (next_level_record->track()) {
+    return std::make_shared<IndexRecordSource>(db_, next_level);
+  } else {
+    return std::make_shared<NestedSource>(db_, next_level);
+  }
+}
+
 }  // namespace playlist