sponsorkit/dist/chunks/index.mjs

Toolkit for generating sponsors images

/*
How it works:
`this.#head` is an instance of `Node` which keeps track of its current value and nests another instance of `Node` that keeps the value that comes after it. When a value is provided to `.enqueue()`, the code needs to iterate through `this.#head`, going deeper and deeper to find the last value. However, iterating through every single item is slow. This problem is solved by saving a reference to the last value as `this.#tail` so that it can reference it to add a new value.
*/

class Node {
	value;
	next;

	constructor(value) {
		this.value = value;
	}
}

class Queue {
	#head;
	#tail;
	#size;

	constructor() {
		this.clear();
	}

	enqueue(value) {
		const node = new Node(value);

		if (this.#head) {
			this.#tail.next = node;
			this.#tail = node;
		} else {
			this.#head = node;
			this.#tail = node;
		}

		this.#size++;
	}

	dequeue() {
		const current = this.#head;
		if (!current) {
			return;
		}

		this.#head = this.#head.next;
		this.#size--;
		return current.value;
	}

	peek() {
		if (!this.#head) {
			return;
		}

		return this.#head.value;

		// TODO: Node.js 18.
		// return this.#head?.value;
	}

	clear() {
		this.#head = undefined;
		this.#tail = undefined;
		this.#size = 0;
	}

	get size() {
		return this.#size;
	}

	* [Symbol.iterator]() {
		let current = this.#head;

		while (current) {
			yield current.value;
			current = current.next;
		}
	}
}

function pLimit(concurrency) {
	validateConcurrency(concurrency);

	const queue = new Queue();
	let activeCount = 0;

	const resumeNext = () => {
		if (activeCount < concurrency && queue.size > 0) {
			queue.dequeue()();
			// Since `pendingCount` has been decreased by one, increase `activeCount` by one.
			activeCount++;
		}
	};

	const next = () => {
		activeCount--;

		resumeNext();
	};

	const run = async (function_, resolve, arguments_) => {
		const result = (async () => function_(...arguments_))();

		resolve(result);

		try {
			await result;
		} catch {}

		next();
	};

	const enqueue = (function_, resolve, arguments_) => {
		// Queue `internalResolve` instead of the `run` function
		// to preserve asynchronous context.
		new Promise(internalResolve => {
			queue.enqueue(internalResolve);
		}).then(
			run.bind(undefined, function_, resolve, arguments_),
		);

		(async () => {
			// This function needs to wait until the next microtask before comparing
			// `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
			// after the `internalResolve` function is dequeued and called. The comparison in the if-statement
			// needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
			await Promise.resolve();

			if (activeCount < concurrency) {
				resumeNext();
			}
		})();
	};

	const generator = (function_, ...arguments_) => new Promise(resolve => {
		enqueue(function_, resolve, arguments_);
	});

	Object.defineProperties(generator, {
		activeCount: {
			get: () => activeCount,
		},
		pendingCount: {
			get: () => queue.size,
		},
		clearQueue: {
			value() {
				queue.clear();
			},
		},
		concurrency: {
			get: () => concurrency,

			set(newConcurrency) {
				validateConcurrency(newConcurrency);
				concurrency = newConcurrency;

				queueMicrotask(() => {
					// eslint-disable-next-line no-unmodified-loop-condition
					while (activeCount < concurrency && queue.size > 0) {
						resumeNext();
					}
				});
			},
		},
	});

	return generator;
}

function limitFunction(function_, option) {
	const {concurrency} = option;
	const limit = pLimit(concurrency);

	return (...arguments_) => limit(() => function_(...arguments_));
}

function validateConcurrency(concurrency) {
	if (!((Number.isInteger(concurrency) || concurrency === Number.POSITIVE_INFINITY) && concurrency > 0)) {
		throw new TypeError('Expected `concurrency` to be a number from 1 and up');
	}
}

export { pLimit as default, limitFunction };