Add cached renderer

app/src/tiles/renderers/cachedRenderer.ts

@@ -0,0 +1,32 @@
+import { Image } from "mapnik";
+
+import { TileParams, TileRenderer } from "../types";
+import { TileCache } from "../tileCache";
+import { formatParams } from "../util";
+
+class CachedRenderer implements TileRenderer {
+    constructor(
+        /** Cache to use for tiles */
+        public tileCache: TileCache,
+
+        /** Renderer to use when tile hasn't been cached yet */
+        public tileRenderer: TileRenderer
+    ) {}
+
+    async getTile(tileParams: TileParams, dataParams: any): Promise<Image> {
+        try {
+            const tile = await this.tileCache.get(tileParams);
+            return tile;
+        } catch(err) {
+            const im = await this.tileRenderer.getTile(tileParams, dataParams);
+            try {
+                await this.tileCache.put(im, tileParams);
+            } catch (err) {}
+            return im;
+        }
+    }
+}
+
+export {
+    CachedRenderer
+};