1 files changed, 68 insertions, 0 deletions
diff --git a/src/mbgl/tile/tile_loader.hpp b/src/mbgl/tile/tile_loader.hpp
new file mode 100644
index 0000000000..cab1907741
--- /dev/null
+++ b/src/mbgl/tile/tile_loader.hpp
@@ -0,0 +1,68 @@
+#pragma once
+
+#include <mbgl/util/noncopyable.hpp>
+#include <mbgl/storage/resource.hpp>
+
+namespace mbgl {
+
+class FileSource;
+class AsyncRequest;
+class Response;
+class Tileset;
+
+namespace style {
+class UpdateParameters;
+} // namespace style
+
+template <typename T>
+class TileLoader : private util::noncopyable {
+public:
+    // TileSources can have two states: optional or required.
+    // - optional means that only low-cost actions should be taken to obtain the data
+    //   (e.g. load from cache, but accept stale data)
+    // - required means that every effort should be taken to obtain the data (e.g. load
+    //   from internet and keep the data fresh if it expires)
+    enum class Necessity : bool {
+        Optional = false,
+        Required = true,
+    };
+
+    TileLoader(T&,
+               const OverscaledTileID&,
+               const style::UpdateParameters&,
+               const Tileset&);
+
+    void setNecessity(Necessity newNecessity) {
+        if (newNecessity != necessity) {
+            necessity = newNecessity;
+            if (necessity == Necessity::Required) {
+                makeRequired();
+            } else {
+                makeOptional();
+            }
+        }
+    }
+
+private:
+    // called when the tile is one of the ideal tiles that we want to show definitely. the tile source
+    // should try to make every effort (e.g. fetch from internet, or revalidate existing resources).
+    void makeRequired();
+
+    // called when the zoom level no longer corresponds to the displayed one, but
+    // we're still interested in retaining the tile, e.g. for backfill.
+    // subclassed TileSources should cancel actions they are taking to provide
+    // an up-to-date version or load new data
+    void makeOptional();
+
+    void loadOptional();
+    void loadedData(const Response&);
+    void loadRequired();
+
+    T& tile;
+    Necessity necessity;
+    Resource resource;
+    FileSource& fileSource;
+    std::unique_ptr<AsyncRequest> request;
+};
+
+} // namespace mbgl