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frontend/node_modules/svelte/src/store/shared/index.js

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+/** @import { Readable, StartStopNotifier, Subscriber, Unsubscriber, Updater, Writable } from '../public.js' */
+/** @import { Stores, StoresValues, SubscribeInvalidateTuple } from '../private.js' */
+import { noop, run_all } from '../../internal/shared/utils.js';
+import { safe_not_equal } from '../../internal/client/reactivity/equality.js';
+import { subscribe_to_store } from '../utils.js';
+
+/**
+ * @type {Array<SubscribeInvalidateTuple<any> | any>}
+ */
+const subscriber_queue = [];
+
+/**
+ * Creates a `Readable` store that allows reading by subscription.
+ *
+ * @template T
+ * @param {T} [value] initial value
+ * @param {StartStopNotifier<T>} [start]
+ * @returns {Readable<T>}
+ */
+export function readable(value, start) {
+	return {
+		subscribe: writable(value, start).subscribe
+	};
+}
+
+/**
+ * Create a `Writable` store that allows both updating and reading by subscription.
+ *
+ * @template T
+ * @param {T} [value] initial value
+ * @param {StartStopNotifier<T>} [start]
+ * @returns {Writable<T>}
+ */
+export function writable(value, start = noop) {
+	/** @type {Unsubscriber | null} */
+	let stop = null;
+
+	/** @type {Set<SubscribeInvalidateTuple<T>>} */
+	const subscribers = new Set();
+
+	/**
+	 * @param {T} new_value
+	 * @returns {void}
+	 */
+	function set(new_value) {
+		if (safe_not_equal(value, new_value)) {
+			value = new_value;
+			if (stop) {
+				// store is ready
+				const run_queue = !subscriber_queue.length;
+				for (const subscriber of subscribers) {
+					subscriber[1]();
+					subscriber_queue.push(subscriber, value);
+				}
+				if (run_queue) {
+					for (let i = 0; i < subscriber_queue.length; i += 2) {
+						subscriber_queue[i][0](subscriber_queue[i + 1]);
+					}
+					subscriber_queue.length = 0;
+				}
+			}
+		}
+	}
+
+	/**
+	 * @param {Updater<T>} fn
+	 * @returns {void}
+	 */
+	function update(fn) {
+		set(fn(/** @type {T} */ (value)));
+	}
+
+	/**
+	 * @param {Subscriber<T>} run
+	 * @param {() => void} [invalidate]
+	 * @returns {Unsubscriber}
+	 */
+	function subscribe(run, invalidate = noop) {
+		/** @type {SubscribeInvalidateTuple<T>} */
+		const subscriber = [run, invalidate];
+		subscribers.add(subscriber);
+		if (subscribers.size === 1) {
+			stop = start(set, update) || noop;
+		}
+		run(/** @type {T} */ (value));
+		return () => {
+			subscribers.delete(subscriber);
+			if (subscribers.size === 0 && stop) {
+				stop();
+				stop = null;
+			}
+		};
+	}
+	return { set, update, subscribe };
+}
+
+/**
+ * Derived value store by synchronizing one or more readable stores and
+ * applying an aggregation function over its input values.
+ *
+ * @template {Stores} S
+ * @template T
+ * @overload
+ * @param {S} stores
+ * @param {(values: StoresValues<S>, set: (value: T) => void, update: (fn: Updater<T>) => void) => Unsubscriber | void} fn
+ * @param {T} [initial_value]
+ * @returns {Readable<T>}
+ */
+/**
+ * Derived value store by synchronizing one or more readable stores and
+ * applying an aggregation function over its input values.
+ *
+ * @template {Stores} S
+ * @template T
+ * @overload
+ * @param {S} stores
+ * @param {(values: StoresValues<S>) => T} fn
+ * @param {T} [initial_value]
+ * @returns {Readable<T>}
+ */
+/**
+ * @template {Stores} S
+ * @template T
+ * @param {S} stores
+ * @param {Function} fn
+ * @param {T} [initial_value]
+ * @returns {Readable<T>}
+ */
+export function derived(stores, fn, initial_value) {
+	const single = !Array.isArray(stores);
+	/** @type {Array<Readable<any>>} */
+	const stores_array = single ? [stores] : stores;
+	if (!stores_array.every(Boolean)) {
+		throw new Error('derived() expects stores as input, got a falsy value');
+	}
+	const auto = fn.length < 2;
+	return readable(initial_value, (set, update) => {
+		let started = false;
+		/** @type {T[]} */
+		const values = [];
+		let pending = 0;
+		let cleanup = noop;
+		const sync = () => {
+			if (pending) {
+				return;
+			}
+			cleanup();
+			const result = fn(single ? values[0] : values, set, update);
+			if (auto) {
+				set(result);
+			} else {
+				cleanup = typeof result === 'function' ? result : noop;
+			}
+		};
+		const unsubscribers = stores_array.map((store, i) =>
+			subscribe_to_store(
+				store,
+				(value) => {
+					values[i] = value;
+					pending &= ~(1 << i);
+					if (started) {
+						sync();
+					}
+				},
+				() => {
+					pending |= 1 << i;
+				}
+			)
+		);
+		started = true;
+		sync();
+		return function stop() {
+			run_all(unsubscribers);
+			cleanup();
+			// We need to set this to false because callbacks can still happen despite having unsubscribed:
+			// Callbacks might already be placed in the queue which doesn't know it should no longer
+			// invoke this derived store.
+			started = false;
+		};
+	});
+}
+
+/**
+ * Takes a store and returns a new one derived from the old one that is readable.
+ *
+ * @template T
+ * @param {Readable<T>} store  - store to make readonly
+ * @returns {Readable<T>}
+ */
+export function readonly(store) {
+	return {
+		// @ts-expect-error TODO i suspect the bind is unnecessary
+		subscribe: store.subscribe.bind(store)
+	};
+}
+
+/**
+ * Get the current value from a store by subscribing and immediately unsubscribing.
+ *
+ * @template T
+ * @param {Readable<T>} store
+ * @returns {T}
+ */
+export function get(store) {
+	let value;
+	subscribe_to_store(store, (_) => (value = _))();
+	// @ts-expect-error
+	return value;
+}