import { isBrowser } from './isBrowser';
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import { isDocumentVisible } from './isDocumentVisible';
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import { isOnline } from './isOnline';
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type Listener = () => void;
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const listeners: Listener[] = [];
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if (isBrowser) {
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const revalidate = () => {
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if (!isDocumentVisible() || !isOnline()) return;
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for (let i = 0; i < listeners.length; i++) {
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const listener = listeners[i];
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listener();
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}
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};
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window.addEventListener('visibilitychange', revalidate, false);
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window.addEventListener('focus', revalidate, false);
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}
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export default function subscribe(listener: Listener) {
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listeners.push(listener);
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return function unsubscribe() {
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const index = listeners.indexOf(listener);
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if (index > -1) {
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listeners.splice(index, 1);
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}
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};
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}
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