/**
 * Promise prioritizer for API actions. The prioritizer takes
 * a promise at a time, always prioritizing the latest promise and
 * aborting and ignoring the others.
 *
 * This allows us to send multiple promises in quick successions but
 * trust that we get back only the latest successful request.
 *
 * @class
 *
 * @constructor
 */
mw.echo.api.PromisePrioritizer = function MwEchoApiPromisePrioritizer() {
	this.deferred = $.Deferred();
	this.promise = null;
};

/* Initialization */

OO.initClass( mw.echo.api.PromisePrioritizer );

/**
 * Prioritize a promise
 *
 * @param {jQuery.Promise|Promise} promise Promise
 * @return {jQuery.Promise} The main deferred object that resolves
 *  or rejects when the latest promise is resolved or rejected.
 */
mw.echo.api.PromisePrioritizer.prototype.prioritize = function ( promise ) {
	const previousPromise = this.promise;

	promise
		.then(
			this.setSuccess.bind( this, promise ),
			this.setFailure.bind( this, promise )
		);
	this.promise = promise;

	if ( previousPromise && previousPromise.abort ) {
		previousPromise.abort();
	}

	return this.deferred.promise();
};

/**
 * Set success for the promise. Resolve the main deferred object only
 * if we are dealing with the currently prioritized promise.
 *
 * @param {jQuery.Promise} promise The promise that resolved successfully.
 *  The main deferred object is resolved with the result of the
 *  latest prioritized promise.
 */
mw.echo.api.PromisePrioritizer.prototype.setSuccess = function ( promise ) {
	if ( this.promise === promise ) {
		this.promise.done( ( ...args ) => {
			this.deferred.resolve( ...args );

			this.promise = null;
			this.deferred = $.Deferred();
		} );
	}
};

/**
 * Set failure for the promise. Reject the main deferred object only
 * if we are dealing with the currently prioritized promise.
 *
 * @param {jQuery.Promise} promise The promise that failed.
 *  The main deferred object is rejected with the result of the
 *  latest prioritized promise
 */
mw.echo.api.PromisePrioritizer.prototype.setFailure = function ( promise ) {
	if ( this.promise === promise ) {
		this.promise.fail( ( ...args ) => {
			this.deferred.reject( ...args );

			this.promise = null;
			this.deferred = $.Deferred();
		} );
	}
};
