38 lines
1 KiB
JavaScript
38 lines
1 KiB
JavaScript
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/**
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* @template {Record<string, any>} T
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* @param {string} keyPrefix
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* @param {T} defaultState
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* @returns {T}
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*/
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function State(keyPrefix, defaultState) {
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/** @param {string} key */
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function getFromRegistry(key) {
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try {
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// TODO validate type
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const rawValue = localStorage.getItem(keyPrefix+key);
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if (rawValue == null) return null;
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return JSON.parse(rawValue);
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} catch {
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return null;
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}
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}
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return new Proxy(/**@type T*/(Object.fromEntries(
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Object.entries(defaultState)
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.map(([k, v]) => [k, getFromRegistry(k) ?? v]),
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)), {
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get(cache, key) {
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if (typeof key === 'symbol') return undefined;
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// cache hit
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if (key in cache) return cache[key];
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// cache miss => get from localStorage
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return /**@type{any}*/(cache)[key] = getFromRegistry(key);
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},
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set(cache, key, value) {
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if (typeof key === 'symbol') return false;
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/**@type{any}*/(cache)[key] = value;
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localStorage.setItem(keyPrefix+key, JSON.stringify(value));
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return true;
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},
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});
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};
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