import {Observable, Subject} from "rxjs";

/**
 * Usage
 *
 * @Component({
 *   selector: 'todo',
 *   template: ``
 * })
 * class Todo {
 *   @Input() name: string;
 *   @InputChange<Todo, string>('name') nameChange$: Observable<string>;
 * }
 */
export function InputChange<C, T>(inputName: keyof C) {
	return function (target: C, key: string): void {
		let value: T;
		const onChange: Subject<T> = new Subject<T>();
		Object.defineProperty(target, key, {
			get: (): Observable<T> => {
				return onChange.asObservable();
			}
		});
		Object.defineProperty(target, inputName, {
			get: (): T => {
				return value;
			},
			set: (val: T): void => {
				onChange.next(val);
				value = val;
			}
		});
	};
}