@pkerschbaum/code-oss-file-service/src/vs/base/common/decorators.ts

VS Code ([microsoft/vscode](https://github.com/microsoft/vscode)) includes a rich "`FileService`" and "`DiskFileSystemProvider`" abstraction built on top of Node.js core modules (`fs`, `path`) and Electron's `shell` module. This package allows to use that

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

export function createDecorator(mapFn: (fn: Function, key: string) => Function): Function {
	return (target: any, key: string, descriptor: any) => {
		let fnKey: string | null = null;
		let fn: Function | null = null;

		if (typeof descriptor.value === 'function') {
			fnKey = 'value';
			fn = descriptor.value;
		} else if (typeof descriptor.get === 'function') {
			fnKey = 'get';
			fn = descriptor.get;
		}

		if (!fn) {
			throw new Error('not supported');
		}

		descriptor[fnKey!] = mapFn(fn, key);
	};
}

export function memoize(_target: any, key: string, descriptor: any) {
	let fnKey: string | null = null;
	let fn: Function | null = null;

	if (typeof descriptor.value === 'function') {
		fnKey = 'value';
		fn = descriptor.value;

		if (fn!.length !== 0) {
			console.warn('Memoize should only be used in functions with zero parameters');
		}
	} else if (typeof descriptor.get === 'function') {
		fnKey = 'get';
		fn = descriptor.get;
	}

	if (!fn) {
		throw new Error('not supported');
	}

	const memoizeKey = `$memoize$${key}`;
	descriptor[fnKey!] = function (...args: any[]) {
		if (!this.hasOwnProperty(memoizeKey)) {
			Object.defineProperty(this, memoizeKey, {
				configurable: false,
				enumerable: false,
				writable: false,
				value: fn!.apply(this, args)
			});
		}

		return this[memoizeKey];
	};
}

export interface IDebounceReducer<T> {
	(previousValue: T, ...args: any[]): T;
}

export function debounce<T>(delay: number, reducer?: IDebounceReducer<T>, initialValueProvider?: () => T): Function {
	return createDecorator((fn, key) => {
		const timerKey = `$debounce$${key}`;
		const resultKey = `$debounce$result$${key}`;

		return function (this: any, ...args: any[]) {
			if (!this[resultKey]) {
				this[resultKey] = initialValueProvider ? initialValueProvider() : undefined;
			}

			clearTimeout(this[timerKey]);

			if (reducer) {
				this[resultKey] = reducer(this[resultKey], ...args);
				args = [this[resultKey]];
			}

			this[timerKey] = setTimeout(() => {
				fn.apply(this, args);
				this[resultKey] = initialValueProvider ? initialValueProvider() : undefined;
			}, delay);
		};
	});
}

export function throttle<T>(delay: number, reducer?: IDebounceReducer<T>, initialValueProvider?: () => T): Function {
	return createDecorator((fn, key) => {
		const timerKey = `$throttle$timer$${key}`;
		const resultKey = `$throttle$result$${key}`;
		const lastRunKey = `$throttle$lastRun$${key}`;
		const pendingKey = `$throttle$pending$${key}`;

		return function (this: any, ...args: any[]) {
			if (!this[resultKey]) {
				this[resultKey] = initialValueProvider ? initialValueProvider() : undefined;
			}
			if (this[lastRunKey] === null || this[lastRunKey] === undefined) {
				this[lastRunKey] = -Number.MAX_VALUE;
			}

			if (reducer) {
				this[resultKey] = reducer(this[resultKey], ...args);
			}

			if (this[pendingKey]) {
				return;
			}

			const nextTime = this[lastRunKey] + delay;
			if (nextTime <= Date.now()) {
				this[lastRunKey] = Date.now();
				fn.apply(this, [this[resultKey]]);
				this[resultKey] = initialValueProvider ? initialValueProvider() : undefined;
			} else {
				this[pendingKey] = true;
				this[timerKey] = setTimeout(() => {
					this[pendingKey] = false;
					this[lastRunKey] = Date.now();
					fn.apply(this, [this[resultKey]]);
					this[resultKey] = initialValueProvider ? initialValueProvider() : undefined;
				}, nextTime - Date.now());
			}
		};
	});
}