feat: add high-level capsule feature modules

src/_shared/async-queue.ts

@@ -0,0 +1,62 @@
+export class AsyncQueue<T> implements AsyncIterableIterator<T> {
+	private readonly values: T[] = [];
+	private readonly waiters: Array<{
+		reject: (reason?: unknown) => void;
+		resolve: (value: IteratorResult<T>) => void;
+	}> = [];
+	private closed = false;
+	private error: unknown;
+
+	[Symbol.asyncIterator](): AsyncIterableIterator<T> {
+		return this;
+	}
+
+	next(): Promise<IteratorResult<T>> {
+		if (this.values.length) {
+			return Promise.resolve({ done: false, value: this.values.shift() as T });
+		}
+		if (this.error) return Promise.reject(this.error);
+		if (this.closed) return Promise.resolve({ done: true, value: undefined });
+
+		return new Promise((resolve, reject) => {
+			this.waiters.push({ reject, resolve });
+		});
+	}
+
+	return(): Promise<IteratorResult<T>> {
+		this.end();
+		return Promise.resolve({ done: true, value: undefined });
+	}
+
+	throw(error?: unknown): Promise<IteratorResult<T>> {
+		this.fail(error);
+		return Promise.reject(error);
+	}
+
+	push(value: T): void {
+		if (this.closed) return;
+		const waiter = this.waiters.shift();
+		if (waiter) {
+			waiter.resolve({ done: false, value });
+			return;
+		}
+		this.values.push(value);
+	}
+
+	end(): void {
+		if (this.closed) return;
+		this.closed = true;
+		for (const waiter of this.waiters.splice(0)) {
+			waiter.resolve({ done: true, value: undefined });
+		}
+	}
+
+	fail(error: unknown): void {
+		if (this.closed) return;
+		this.closed = true;
+		this.error = error;
+		for (const waiter of this.waiters.splice(0)) {
+			waiter.reject(error);
+		}
+	}
+}