import { Observable } from '../Observable';
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import { isArray } from '../util/isArray';
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import { isFunction } from '../util/isFunction';
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import { NodeEventHandler } from './fromEvent';
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import { map } from '../operators/map';
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/* tslint:disable:max-line-length */
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export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any, removeHandler?: (handler: NodeEventHandler, signal?: any) => void): Observable<T>;
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/** @deprecated resultSelector no longer supported, pipe to map instead */
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export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any, removeHandler?: (handler: NodeEventHandler, signal?: any) => void, resultSelector?: (...args: any[]) => T): Observable<T>;
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/* tslint:enable:max-line-length */
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/**
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* Creates an Observable from an arbitrary API for registering event handlers.
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*
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* <span class="informal">When that method for adding event handler was something {@link fromEvent}
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* was not prepared for.</span>
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*
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* 
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*
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* `fromEventPattern` allows you to convert into an Observable any API that supports registering handler functions
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* for events. It is similar to {@link fromEvent}, but far
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* more flexible. In fact, all use cases of {@link fromEvent} could be easily handled by
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* `fromEventPattern` (although in slightly more verbose way).
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*
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* This operator accepts as a first argument an `addHandler` function, which will be injected with
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* handler parameter. That handler is actually an event handler function that you now can pass
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* to API expecting it. `addHandler` will be called whenever Observable
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* returned by the operator is subscribed, so registering handler in API will not
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* necessarily happen when `fromEventPattern` is called.
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*
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* After registration, every time an event that we listen to happens,
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* Observable returned by `fromEventPattern` will emit value that event handler
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* function was called with. Note that if event handler was called with more
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* then one argument, second and following arguments will not appear in the Observable.
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*
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* If API you are using allows to unregister event handlers as well, you can pass to `fromEventPattern`
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* another function - `removeHandler` - as a second parameter. It will be injected
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* with the same handler function as before, which now you can use to unregister
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* it from the API. `removeHandler` will be called when consumer of resulting Observable
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* unsubscribes from it.
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*
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* In some APIs unregistering is actually handled differently. Method registering an event handler
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* returns some kind of token, which is later used to identify which function should
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* be unregistered or it itself has method that unregisters event handler.
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* If that is the case with your API, make sure token returned
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* by registering method is returned by `addHandler`. Then it will be passed
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* as a second argument to `removeHandler`, where you will be able to use it.
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*
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* If you need access to all event handler parameters (not only the first one),
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* or you need to transform them in any way, you can call `fromEventPattern` with optional
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* third parameter - project function which will accept all arguments passed to
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* event handler when it is called. Whatever is returned from project function will appear on
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* resulting stream instead of usual event handlers first argument. This means
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* that default project can be thought of as function that takes its first parameter
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* and ignores the rest.
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*
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* ## Example
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* ### Emits clicks happening on the DOM document
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*
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* ```ts
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* import { fromEventPattern } from 'rxjs';
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*
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* function addClickHandler(handler) {
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* document.addEventListener('click', handler);
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* }
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*
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* function removeClickHandler(handler) {
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* document.removeEventListener('click', handler);
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* }
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*
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* const clicks = fromEventPattern(
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* addClickHandler,
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* removeClickHandler
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* );
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* clicks.subscribe(x => console.log(x));
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*
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* // Whenever you click anywhere in the browser, DOM MouseEvent
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* // object will be logged.
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* ```
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*
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* ## Example
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* ### Use with API that returns cancellation token
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*
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* ```ts
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* import { fromEventPattern } from 'rxjs';
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*
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* const token = someAPI.registerEventHandler(function() {});
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* someAPI.unregisterEventHandler(token); // this APIs cancellation method accepts
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* // not handler itself, but special token.
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*
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* const someAPIObservable = fromEventPattern(
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* function(handler) { return someAPI.registerEventHandler(handler); }, // Note that we return the token here...
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* function(handler, token) { someAPI.unregisterEventHandler(token); } // ...to then use it here.
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* );
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* ```
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*
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* ## Example
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* ### Use with project function
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*
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* ```ts
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* import { fromEventPattern } from 'rxjs';
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*
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* someAPI.registerEventHandler((eventType, eventMessage) => {
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* console.log(eventType, eventMessage); // Logs "EVENT_TYPE" "EVENT_MESSAGE" to console.
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* });
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*
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* const someAPIObservable = fromEventPattern(
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* handler => someAPI.registerEventHandler(handler),
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* handler => someAPI.unregisterEventHandler(handler)
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* (eventType, eventMessage) => eventType + " --- " + eventMessage // without that function only "EVENT_TYPE"
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* ); // would be emitted by the Observable
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*
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* someAPIObservable.subscribe(value => console.log(value));
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*
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* // Logs:
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* // "EVENT_TYPE --- EVENT_MESSAGE"
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* ```
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*
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* @see {@link fromEvent}
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* @see {@link bindCallback}
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* @see {@link bindNodeCallback}
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*
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* @param {function(handler: Function): any} addHandler A function that takes
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* a `handler` function as argument and attaches it somehow to the actual
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* source of events.
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* @param {function(handler: Function, token?: any): void} [removeHandler] A function that
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* takes a `handler` function as an argument and removes it from the event source. If `addHandler`
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* returns some kind of token, `removeHandler` function will have it as a second parameter.
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* @param {function(...args: any): T} [project] A function to
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* transform results. It takes the arguments from the event handler and
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* should return a single value.
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* @return {Observable<T>} Observable which, when an event happens, emits first parameter
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* passed to registered event handler. Alternatively it emits whatever project function returns
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* at that moment.
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* @static true
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* @name fromEventPattern
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* @owner Observable
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*/
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export function fromEventPattern<T>(addHandler: (handler: NodeEventHandler) => any,
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removeHandler?: (handler: NodeEventHandler, signal?: any) => void,
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resultSelector?: (...args: any[]) => T): Observable<T | T[]> {
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if (resultSelector) {
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// DEPRECATED PATH
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return fromEventPattern<T>(addHandler, removeHandler).pipe(
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map(args => isArray(args) ? resultSelector(...args) : resultSelector(args))
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);
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}
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return new Observable<T | T[]>(subscriber => {
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const handler = (...e: T[]) => subscriber.next(e.length === 1 ? e[0] : e);
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let retValue: any;
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try {
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retValue = addHandler(handler);
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} catch (err) {
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subscriber.error(err);
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return undefined;
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}
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if (!isFunction(removeHandler)) {
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return undefined;
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}
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return () => removeHandler(handler, retValue) ;
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});
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}
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