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import { run_all, noop } from './internal.js';
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export function readable(start, value) {
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const subscribers = [];
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let stop;
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function set(newValue) {
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if (newValue === value) return;
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value = newValue;
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subscribers.forEach(s => s[1]());
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subscribers.forEach(s => s[0](value));
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}
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return {
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subscribe(run, invalidate = noop) {
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if (subscribers.length === 0) {
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stop = start(set);
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}
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const subscriber = [run, invalidate];
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subscribers.push(subscriber);
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run(value);
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return function() {
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const index = subscribers.indexOf(subscriber);
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if (index !== -1) subscribers.splice(index, 1);
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if (subscribers.length === 0) {
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stop && stop();
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stop = null;
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}
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};
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}
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};
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}
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export function writable(value) {
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const subscribers = [];
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function set(newValue) {
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if (newValue === value) return;
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value = newValue;
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subscribers.forEach(s => s[1]());
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subscribers.forEach(s => s[0](value));
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}
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function update(fn) {
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set(fn(value));
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}
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function subscribe(run, invalidate = noop) {
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const subscriber = [run, invalidate];
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subscribers.push(subscriber);
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run(value);
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return () => {
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const index = subscribers.indexOf(subscriber);
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if (index !== -1) subscribers.splice(index, 1);
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};
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}
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return { set, update, subscribe };
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}
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export function derive(stores, fn) {
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const single = !Array.isArray(stores);
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if (single) stores = [stores];
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const auto = fn.length === 1;
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let value = {};
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return readable(set => {
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let inited = false;
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const values = [];
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let pending = 0;
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const sync = () => {
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if (pending) return;
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const result = fn(single ? values[0] : values, set);
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if (auto && (value !== (value = result))) set(result);
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}
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const unsubscribers = stores.map((store, i) => store.subscribe(
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value => {
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values[i] = value;
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pending &= ~(1 << i);
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if (inited) sync();
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},
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() => {
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pending |= (1 << i);
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})
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);
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inited = true;
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sync();
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return function stop() {
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run_all(unsubscribers);
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};
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});
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}
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