47 lines
1.2 KiB
TypeScript
47 lines
1.2 KiB
TypeScript
import { Observable, of } from 'rxjs';
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const cacheAgeLimitInMilliseconds = 1000 * 60 * 60;
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export function isDataOutdated(name: string): boolean {
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const lastUpdated: number = +localStorage.getItem(name + '-timestamp');
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const now: number = Date.now();
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const elapsedTime: number = now - lastUpdated;
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return elapsedTime > cacheAgeLimitInMilliseconds;
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}
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export function storeInCache<T>(
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data: Observable<T>,
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name: string
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): Observable<T> {
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data.subscribe({
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next: (response: T) => {
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localStorage.setItem(name, JSON.stringify(response));
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localStorage.setItem(name + '-timestamp', `${Date.now()}`);
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},
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});
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return data;
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}
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export function readFromCache<T>(
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name: string,
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callback: () => Observable<T>
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): Observable<T> {
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let data: Observable<T>;
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if (isDataOutdated(name)) {
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data = storeInCache<T>(callback(), name);
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} else {
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let dataFromCache = localStorage.getItem(name);
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try {
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data = of(JSON.parse(dataFromCache));
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} catch (err) {
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console.error(
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`Could not parse ${JSON.stringify(
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dataFromCache
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)}: ${err}. Fetching again data from callback function.`
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);
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data = storeInCache<T>(callback(), name);
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}
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}
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return data;
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}
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