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Observer.ts
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Observer.ts
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// Copyright (c) 2022-2023 Heusala Group <info@hg.fi>. All rights reserved.
// Copyright (c) 2020-2021 Sendanor <info@sendanor.fi>. All rights reserved.
import { filter } from "./functions/filter";
import { forEach } from "./functions/forEach";
import { has } from "./functions/has";
import { Disposable } from "./types/Disposable";
// NOTICE! THIS LIBRARY INTENTIONALLY DOES NOT USE HG LOGGER BECAUSE IT IS USED
// IN LOWER LEVEL CALLS
/**
* A callback function that is registered to be executed when a particular event
* is triggered by an `Observer` instance.
*
* @param event The name of the event that was triggered.
* @param args An array of arguments that were passed to the `triggerEvent`
* method when the event was triggered.
*/
export interface ObserverCallback<EventName extends keyof any, T extends any[] = any[] > {
(event: EventName, ...args : T) : void;
}
/**
* A function that can be used to stop listening to events on an `Observer`
* instance.
*
* When this function is called, it will remove the callback function that was
* registered with the `listenEvent` method
* from the list of callback functions that are triggered when the corresponding
* event is triggered.
*/
export interface ObserverDestructor {
() : void;
}
/**
* An array of `ObserverCallback` functions that are registered to be executed
* when a particular event is triggered by an `Observer` instance.
*/
export type ObserverCallbackArray<EventName extends keyof any> = Array<ObserverCallback<EventName>>;
/**
* A record that maps event names to `ObserverCallbackArray` arrays.
*
* This is used by the `Observer` class to store the callback functions that are
* registered to be executed when particular events are triggered.
*/
export type ObserverRecord<EventName extends keyof any> = Record<EventName, ObserverCallbackArray<EventName> >;
/**
* This is a simple observer implementation for implementing synchronous in-process events for a local service.
*
* You can use it like this:
*
* ```
* enum FooEvent {
* CHANGED = "FooService:changed"
* }
*
* class FooService {
*
* private static _data : any;
* private static _observer : Observer<FooEvent> = new Observer<FooEvent>("FooService");
*
* public static getData () : any {
* return this._data;
* }
*
* public static on (name : FooEvent, callback: ObserverCallback<FooEvent>) : ObserverDestructor {
* return this._observer.listenEvent(name, callback);
* }
*
* public static refreshData () {
* HttpService.doSomething().then((response) => {
* this._data = response.data;
* this._observer.triggerEvent(FooEvent.CHANGED);
* }).catch(err => {
* console.error('Error: ', err);
* });
* }
*
* }
*
* FooService.on(FooEvent.CHANGED, () => {
*
* const currentData = FooService.getData();
* // ...
*
* });
*
* FooService.refreshData();
*
* ```
*
*/
export class Observer<EventName extends keyof any> implements Disposable {
private _name : string;
private _callbacks : ObserverRecord<EventName>;
/**
* Returns the name of this `Observer` instance.
*/
getName () : string {
return this._name;
}
/**
* Creates a new `Observer` instance.
*
* @param name You can name this observer, so that you know where it is used.
*/
public constructor (name: string) {
this._name = name;
this._callbacks = {} as ObserverRecord<EventName>;
}
public static create<EventName extends keyof any> (name : string) : Observer<EventName> {
return new Observer<EventName>(name);
}
/**
* Removes all data associated with this `Observer` instance.
*
* After this method is called, the `Observer` instance should no longer be used.
*/
public destroy () {
// @ts-ignore
this._name = undefined;
// @ts-ignore
this._callbacks = undefined;
}
/**
* Check if eventName has listeners.
*
* @param eventName
*/
public hasCallbacks (eventName : EventName) : boolean {
return has(this._callbacks, eventName);
}
/**
* Trigger an event
*
* @param eventName
* @param args
*/
public triggerEvent (eventName : EventName, ...args : Array<any>) {
if (!this.hasCallbacks(eventName)) {
console.warn(`Warning! The observer for "${this._name}" did not have anything listening "${eventName.toString()}"`);
return;
}
const callbacks = this._callbacks[eventName];
forEach(callbacks, (callback: any) => {
try {
callback(eventName, ...args);
} catch( e ) {
console.error(`Observer "${this._name}" and the event handler for "${eventName.toString()}" returned an exception: `, e);
}
});
}
/**
* Start listening events.
*
* Returns destructor function.
*
* @param eventName
* @param callback
*/
public listenEvent (eventName : EventName, callback : ObserverCallback<EventName> ) : ObserverDestructor {
if (!this.hasCallbacks(eventName)) {
this._callbacks[eventName] = [ callback ];
} else {
this._callbacks[eventName].push( callback );
}
return () => this.removeListener(eventName, callback);
}
/**
* Removes the first found listener callback for eventName
*
* @param eventName
* @param callback
*/
public removeListener (eventName : EventName, callback: ObserverCallback<EventName>) : void {
if (!this.hasCallbacks(eventName)) {
console.warn(`Warning! Could not remove callback since the observer for "${this._name}" did not have anything listening "${eventName.toString()}"`);
return;
}
let removedOnce = false;
this._callbacks[eventName] = filter(this._callbacks[eventName], (item: any) => {
if ( !removedOnce && item === callback ) {
removedOnce = true;
return false;
}
return true;
});
if (this._callbacks[eventName].length === 0) {
delete this._callbacks[eventName];
}
if (!removedOnce) {
console.warn(`Warning! Could not remove the callback since the observer for "${this._name}" did not have that callback`);
return;
}
}
/**
* Returns a Promise that is resolved when the specified event is triggered.
*
* @param eventName The name of the event to wait for.
* @param time The maximum amount of time (in milliseconds) to wait for the
* event before timing out.
* @returns A Promise that is resolved when the specified event is triggered,
* or rejected with a timeout error if the event is not triggered
* within the specified timeout.
*/
public async waitForEvent (
eventName : EventName,
time: number
): Promise<void> {
await new Promise<void>(
(resolve, reject) => {
try {
let timeout: any | undefined = undefined;
let listener: ObserverDestructor | undefined = undefined;
timeout = setTimeout(
() => {
try {
timeout = undefined;
if ( listener ) {
listener();
listener = undefined;
}
resolve();
} catch (err) {
reject(err);
}
},
time
);
listener = this.listenEvent(
eventName,
() => {
try {
if ( timeout ) {
clearTimeout(timeout);
timeout = undefined;
}
if (listener) {
listener();
listener = undefined;
}
resolve();
} catch (err) {
reject(err);
}
}
);
} catch (err) {
reject(err);
}
}
);
}
}