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130 lines
3.6 KiB
TypeScript
130 lines
3.6 KiB
TypeScript
const events = require('events');
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export class EventManager {
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private emitter_: any;
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private appStatePrevious_: any;
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private appStateWatchedProps_: string[];
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private appStateListeners_: any;
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constructor() {
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this.reset();
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}
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reset() {
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this.emitter_ = new events.EventEmitter();
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this.appStatePrevious_ = {};
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this.appStateWatchedProps_ = [];
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this.appStateListeners_ = {};
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}
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on(eventName: string, callback: Function) {
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return this.emitter_.on(eventName, callback);
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}
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emit(eventName: string, object: any = null) {
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return this.emitter_.emit(eventName, object);
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}
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removeListener(eventName: string, callback: Function) {
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return this.emitter_.removeListener(eventName, callback);
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}
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off(eventName: string, callback: Function) {
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return this.removeListener(eventName, callback);
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}
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filterOn(filterName: string, callback: Function) {
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return this.emitter_.on(`filter:${filterName}`, callback);
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}
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filterOff(filterName: string, callback: Function) {
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return this.removeListener(`filter:${filterName}`, callback);
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}
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filterEmit(filterName: string, object: any) {
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// We freeze the object we pass to the listeners so that they
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// don't modify it directly. Instead they must return a
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// modified copy (or the input itself).
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let output = Object.freeze(object);
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const listeners = this.emitter_.listeners(`filter:${filterName}`);
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for (const listener of listeners) {
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const newOutput = listener(output);
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if (newOutput === undefined) {
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throw new Error(`Filter "${filterName}": Filter must return a value or the unmodified input. Returning nothing or "undefined" is not supported.`);
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}
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if (newOutput !== output) {
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output = Object.freeze(newOutput);
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}
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}
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return output;
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}
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appStateOn(propName: string, callback: Function) {
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if (!this.appStateListeners_[propName]) {
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this.appStateListeners_[propName] = [];
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this.appStateWatchedProps_.push(propName);
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}
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this.appStateListeners_[propName].push(callback);
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}
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appStateOff(propName: string, callback: Function) {
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if (!this.appStateListeners_[propName]) {
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throw new Error('EventManager: Trying to unregister a state prop watch for a non-watched prop (1)');
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}
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const idx = this.appStateListeners_[propName].indexOf(callback);
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if (idx < 0) throw new Error('EventManager: Trying to unregister a state prop watch for a non-watched prop (2)');
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this.appStateListeners_[propName].splice(idx, 1);
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}
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stateValue_(state: any, propName: string) {
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const parts = propName.split('.');
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let s = state;
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for (const p of parts) {
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if (!(p in s)) throw new Error(`Invalid state property path: ${propName}`);
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s = s[p];
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}
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return s;
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}
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// This function works by keeping a copy of the watched props and, whenever this function
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// is called, comparing the previous and new values and emitting events if they have changed.
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// The appStateEmit function should be called from a middleware.
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appStateEmit(state: any) {
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if (!this.appStateWatchedProps_.length) return;
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for (const propName of this.appStateWatchedProps_) {
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let emit = false;
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const stateValue = this.stateValue_(state, propName);
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if (!(propName in this.appStatePrevious_) || this.appStatePrevious_[propName] !== stateValue) {
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this.appStatePrevious_[propName] = stateValue;
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emit = true;
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}
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if (emit) {
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const listeners = this.appStateListeners_[propName];
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if (!listeners || !listeners.length) continue;
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const eventValue = Object.freeze(stateValue);
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for (const listener of listeners) {
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listener({ value: eventValue });
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}
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}
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}
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}
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}
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const eventManager = new EventManager();
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export default eventManager;
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