Use Proxy store for nested chunks (#85)

* Use Proxy store for nested chunks

Code adapted from gzuidhof/zarr.js#88 (comment)
No Typescript types yet

* Only use nested(store) for correct version of OME-Zarr

* format fixes

* Move nested handling to io.ts

* Revert changes to ome.ts, removing isNested duplication

src/io.ts

@@ -18,6 +18,7 @@ import {
   loadMultiscales,
   MAGENTA_GREEN,
   MAX_CHANNELS,
+  nested,
   open,
   parseMatrix,
   range,
@@ -115,13 +116,30 @@ function loadMultiChannel(config: MultichannelConfig, data: ZarrPixelSource<stri
   };
 }
 
+function isNested(attrs: Ome.Attrs) {
+  let version;
+  if ('plate' in attrs) {
+    version = attrs.plate.version;
+  } else if ('omero' in attrs) {
+    version = attrs.multiscales[0].version;
+  } else if ('well' in attrs) {
+    version = attrs.well.version;
+  }
+  // OME-Zarr uses nested chunks since version 0.2
+  return version && version !== '0.1';
+}
+
 export async function createSourceData(config: ImageLayerConfig): Promise<SourceData> {
   const node = await open(config.source);
   let data: ZarrArray[];
 
   if (node instanceof ZarrGroup) {
     const attrs = (await node.attrs.asObject()) as Ome.Attrs;
 
+    if (isNested(attrs)) {
+      node.store = nested(node.store);
+    }
+
     if ('plate' in attrs) {
       return loadPlate(config, node, attrs.plate);
     }

src/utils.ts

@@ -48,6 +48,24 @@ export async function loadMultiscales(grp: ZarrGroup, multiscales: Ome.Multiscal
   throw Error('Multiscales metadata included a path to a group.');
 }
 
+export function nested(store: ZarrArray['store']) {
+  const get = (target: ZarrArray['store'], key: string | number | symbol) => {
+    if (key === 'getItem' || key === 'containsItem') {
+      return (path: string, ...args: unknown[]) => {
+        if (path.endsWith('.zarray') || path.endsWith('.zattrs') || path.endsWith('.zgroup')) {
+          return target[key](path, ...args);
+        }
+        const prefix = path.split('/');
+        const chunkKey = prefix.pop()!;
+        const newPath = [...prefix, chunkKey.replaceAll('.', '/')].join('/');
+        return target[key](newPath, ...args);
+      };
+    }
+    return Reflect.get(target, key);
+  };
+  return new Proxy(store, { get });
+}
+
 export function hexToRGB(hex: string): number[] {
   if (hex.startsWith('#')) hex = hex.slice(1);
   const r = parseInt(hex.slice(0, 2), 16);