From bf57f44833226511132a5ad2f33feb1816ba8424 Mon Sep 17 00:00:00 2001
From: Trevor Manz <trevor.j.manz@gmail.com>
Date: Thu, 14 Mar 2024 14:13:34 -0400
Subject: [PATCH] feat(storage): Add WebFileSystemStore

---
 packages/storage/src/web-fs.ts | 69 ++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 packages/storage/src/web-fs.ts

diff --git a/packages/storage/src/web-fs.ts b/packages/storage/src/web-fs.ts
new file mode 100644
index 00000000..d0b1886a
--- /dev/null
+++ b/packages/storage/src/web-fs.ts
@@ -0,0 +1,69 @@
+import type { AbsolutePath, AsyncReadable } from "./types.js";
+
+/**
+ * Get a file handle to a file in a directory.
+ *
+ * @param root - A root directory from the Web File System API.
+ * @param path - A key to a file in the root directory.
+ * @returns A file handle to the file.
+ */
+async function resolveFileHandleForPath(
+	root: FileSystemDirectoryHandle,
+	path: string,
+): Promise<FileSystemFileHandle> {
+	const dirs = path.split("/");
+	const fname = dirs.pop();
+	if (!fname) {
+		throw new Error("Invalid path");
+	}
+	for (const dir of dirs) {
+		root = await root.getDirectoryHandle(dir);
+	}
+	return root.getFileHandle(fname);
+}
+
+/**
+ * A store for zarrita based on the Web File System API.
+ *
+ * Note: usage requires prompting the user to select a directory to grant
+ * access to the Web File System API.
+ *
+ * @see {@link https://developer.mozilla.org/en-US/docs/Web/API/File_System_API}
+ *
+ * @example
+ * ```js
+ * import * as zarr from "zarrita";
+ * import WebFileSystemStore from "@zarrita/storage/web-fs";
+ *
+ * let directoryHandle = await globalThis.showDirectoryPicker();
+ * let store = new WebFileSystemStore(directoryHandle);
+ * let root = await zarr.root(store);
+ * let arr = await zarr.open(root.resolve("/foo"), { kind: "array" });
+ * ```
+ */
+class WebFileSystemStore implements AsyncReadable {
+	#root: FileSystemDirectoryHandle;
+
+	constructor(root: FileSystemDirectoryHandle) {
+		this.#root = root;
+	}
+
+	async get(key: AbsolutePath): Promise<Uint8Array | undefined> {
+		let fh = await resolveFileHandleForPath(this.#root, key.slice(1)).catch(
+			() => {
+				// TODO: better error handling
+				// I believe a missing file will trigger an error here, which we should explicitly
+				// catch and return `undefined`
+				return undefined;
+			},
+		);
+		if (!fh) {
+			return undefined;
+		}
+		let file = await fh.getFile();
+		let buffer = await file.arrayBuffer();
+		return new Uint8Array(buffer);
+	}
+}
+
+export default WebFileSystemStore;