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