refactor(fs): Add Switch reader

Author: RandomByte

packages/fs/lib/readers/Switch.js

@@ -0,0 +1,82 @@
+import AbstractReader from "../AbstractReader.js";
+
+/**
+ * Reader allowing to switch its underlying reader at runtime.
+ * If no reader is set, read operations will be halted/paused until a reader is set.
+ */
+export default class Switch extends AbstractReader {
+	#reader;
+	#pendingCalls = [];
+
+	constructor({name, reader}) {
+		super(name);
+		this.#reader = reader;
+	}
+
+	/**
+	 * Sets the underlying reader and processes any pending read operations.
+	 *
+	 * @param {@ui5/fs/AbstractReader} reader The reader to delegate to.
+	 */
+	setReader(reader) {
+		this.#reader = reader;
+		this._processPendingCalls();
+	}
+
+	/**
+	 * Unsets the underlying reader. Future calls will be queued.
+	 */
+	unsetReader() {
+		this.#reader = null;
+	}
+
+	async _byGlob(virPattern, options, trace) {
+		if (this.#reader) {
+			return this.#reader._byGlob(virPattern, options, trace);
+		}
+
+		// No reader set, so we queue the call and return a pending promise
+		return this._enqueueCall("_byGlob", [virPattern, options, trace]);
+	}
+
+
+	async _byPath(virPath, options, trace) {
+		if (this.#reader) {
+			return this.#reader._byPath(virPath, options, trace);
+		}
+
+		// No reader set, so we queue the call and return a pending promise
+		return this._enqueueCall("_byPath", [virPath, options, trace]);
+	}
+
+	/**
+	 * Queues a method call by returning a promise and storing its resolver.
+	 *
+	 * @param {string} methodName The method name to call later.
+	 * @param {Array} args The arguments to pass to the method.
+	 * @returns {Promise} A promise that will be resolved/rejected when the call is processed.
+	 */
+	_enqueueCall(methodName, args) {
+		return new Promise((resolve, reject) => {
+			this.#pendingCalls.push({methodName, args, resolve, reject});
+		});
+	}
+
+	/**
+	 * Processes all pending calls in the queue using the current reader.
+	 *
+	 * @private
+	 */
+	_processPendingCalls() {
+		const callsToProcess = this.#pendingCalls;
+		this.#pendingCalls = []; // Clear queue immediately to prevent race conditions
+
+		for (const call of callsToProcess) {
+			const {methodName, args, resolve, reject} = call;
+			// Execute the pending call with the newly set reader
+			this.#reader[methodName](...args)
+				.then(resolve)
+				.catch(reject);
+		}
+	}
+}

packages/fs/lib/resourceFactory.js

@@ -10,6 +10,7 @@ import WriterCollection from "./WriterCollection.js";
 import Filter from "./readers/Filter.js";
 import Link from "./readers/Link.js";
 import Proxy from "./readers/Proxy.js";
+import Switch from "./readers/Switch.js";
 import MonitoredReader from "./MonitoredReader.js";
 import MonitoredReaderWriter from "./MonitoredReaderWriter.js";
 import {getLogger} from "@ui5/logger";
@@ -277,6 +278,19 @@ export function createFlatReader({name, reader, namespace}) {
 	});
 }
 
+export function createSwitch({name, reader}) {
+	return new Switch({
+		name,
+		reader: reader,
+	});
+}
+
+/**
+ * Creates a monitored reader or reader-writer depending on the provided instance
+ * of the given readerWriter.
+ *
+ * @param {@ui5/fs/AbstractReader|@ui5/fs/AbstractReaderWriter} readerWriter Reader or ReaderWriter to monitor
+ */
 export function createMonitor(readerWriter) {
 	if (readerWriter instanceof DuplexCollection) {
 		return new MonitoredReaderWriter(readerWriter);