Jon Staab
142 lines
3.5 KiB
TypeScript
142 lines
3.5 KiB
TypeScript
import {readable, derived, writable, Readable, Subscriber} from "svelte/store"
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import {batch, indexBy, remove, assoc, now} from "@welshman/lib"
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import {withGetter, ReadableWithGetter} from "./getter.js"
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// Collection utility
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export type FreshnessUpdate = {
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ns: string
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key: string
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ts: number
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}
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export const freshness = withGetter(writable<Record<string, number>>({}))
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export const getFreshnessKey = (ns: string, key: string) => `${ns}:${key}`
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export const getFreshness = (ns: string, key: string) =>
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freshness.get()[getFreshnessKey(ns, key)] || 0
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export const setFreshnessImmediate = ({ns, key, ts}: FreshnessUpdate) =>
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freshness.update(assoc(getFreshnessKey(ns, key), ts))
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export const setFreshnessThrottled = batch(100, (updates: FreshnessUpdate[]) =>
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freshness.update($freshness => {
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for (const {ns, key, ts} of updates) {
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$freshness[getFreshnessKey(ns, key)] = ts
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}
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return $freshness
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}),
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)
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export type CachedLoaderOptions<T> = {
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name: string
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indexStore: ReadableWithGetter<Map<string, T>>
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load: (key: string, relays: string[]) => Promise<any>
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subscribers?: Subscriber<T>[]
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}
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export const makeCachedLoader = <T>({
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name,
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load,
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indexStore,
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subscribers = [],
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}: CachedLoaderOptions<T>) => {
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const pending = new Map<string, Promise<T | void>>()
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const loadAttempts = new Map<string, number>()
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return async (key: string, relays: string[] = []) => {
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const stale = indexStore.get().get(key)
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// If we have no loader function, nothing we can do
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if (!load) {
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return stale
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}
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const freshness = getFreshness(name, key)
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// If we have an item, reload if it's stale
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if (stale && freshness > now() - 3600) {
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return stale
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}
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// If we already are loading, await and return
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if (pending.has(key)) {
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return pending.get(key)!.then(() => indexStore.get().get(key))
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}
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const attempt = loadAttempts.get(key) || 0
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// Use exponential backoff to throttle attempts
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if (freshness > now() - Math.pow(2, attempt)) {
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return stale
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}
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loadAttempts.set(key, attempt + 1)
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setFreshnessThrottled({ns: name, key, ts: now()})
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const promise = load(key, relays)
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pending.set(key, promise)
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try {
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await promise
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} catch (e) {
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console.warn(`Failed to load ${name} item ${key}`, e)
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} finally {
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pending.delete(key)
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}
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const fresh = indexStore.get().get(key)
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if (fresh) {
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loadAttempts.delete(key)
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for (const subscriber of subscribers) {
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subscriber(fresh)
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}
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}
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return fresh
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}
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}
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export type CollectionOptions<T> = {
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name: string
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store: Readable<T[]>
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getKey: (item: T) => string
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load: (key: string, relays: string[]) => Promise<any>
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}
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export const collection = <T>({name, store, getKey, load}: CollectionOptions<T>) => {
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const indexStore = withGetter(derived(store, $items => indexBy(getKey, $items)))
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let subscribers: Subscriber<T>[] = []
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const loadItem = makeCachedLoader({name, load, indexStore, subscribers})
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const deriveItem = (key: string | undefined, relays: string[] = []) => {
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if (!key) {
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return readable(undefined)
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}
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// If we don't yet have the item, or it's stale, trigger a request for it. The derived
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// store will update when it arrives
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loadItem(key, relays)
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return derived(indexStore, $index => $index.get(key))
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}
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const onItem = (cb: Subscriber<T>) => {
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subscribers.push(cb)
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return () => {
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subscribers = remove(cb, subscribers)
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}
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}
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return {indexStore, deriveItem, loadItem, onItem}
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}
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