117 lines
3.1 KiB
TypeScript
117 lines
3.1 KiB
TypeScript
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import type { View } from "../lib/model";
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export type FrameEntry = {
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view: View;
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instance: number;
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keepAlive: boolean;
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lastUsed: number;
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};
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export type FrameCacheOptions = {
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/**
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* Maximum number of keep-alive documents, including the active document.
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*
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* A non-keep-alive active document may temporarily exist in addition to this
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* limit. The active document is never evicted; inactive entries are removed
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* from least to most recently used.
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*/
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maxKeepAliveEntries: number;
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shouldKeepAlive: (view: View) => boolean;
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};
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export type FrameTransition = {
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entries: FrameEntry[];
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removed: FrameEntry[];
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activated: FrameEntry;
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};
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/**
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* Owns the bounded set of iframe document identities.
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*
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* Entries retain object identity between snapshots so Solid's `<For>` keeps
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* the corresponding iframe DOM node alive. `instance` is never reused, which
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* makes a recreated document observable in its URL and prevents stale browser
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* history or service-worker responses from masquerading as a retained frame.
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*/
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export class FrameCache {
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readonly #options: FrameCacheOptions;
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readonly #entries = new Map<View, FrameEntry>();
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#active: View;
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#nextInstance = 1;
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#clock = 0;
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constructor(initialView: View, options: FrameCacheOptions) {
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if (!Number.isInteger(options.maxKeepAliveEntries) || options.maxKeepAliveEntries < 0) {
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throw new RangeError("maxKeepAliveEntries must be a non-negative integer");
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}
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this.#options = options;
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this.#active = initialView;
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this.#entries.set(initialView, this.#create(initialView));
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}
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get active(): View {
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return this.#active;
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}
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snapshot(): FrameEntry[] {
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return [...this.#entries.values()];
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}
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activate(view: View): FrameTransition {
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const removed: FrameEntry[] = [];
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const previous = this.#entries.get(this.#active);
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if (previous && previous.view !== view && !previous.keepAlive) {
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this.#entries.delete(previous.view);
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removed.push(previous);
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}
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let activated = this.#entries.get(view);
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if (!activated) {
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activated = this.#create(view);
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this.#entries.set(view, activated);
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}
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activated.lastUsed = ++this.#clock;
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this.#active = view;
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while (this.#keepAliveCount() > this.#options.maxKeepAliveEntries) {
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const candidate = this.#oldestInactiveKeepAlive();
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if (!candidate) break;
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this.#entries.delete(candidate.view);
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removed.push(candidate);
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}
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return {
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entries: this.snapshot(),
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removed,
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activated,
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};
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}
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#create(view: View): FrameEntry {
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return {
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view,
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instance: this.#nextInstance++,
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keepAlive: this.#options.shouldKeepAlive(view),
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lastUsed: ++this.#clock,
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};
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}
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#keepAliveCount(): number {
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let count = 0;
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for (const entry of this.#entries.values()) {
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if (entry.keepAlive) count += 1;
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}
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return count;
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}
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#oldestInactiveKeepAlive(): FrameEntry | undefined {
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let oldest: FrameEntry | undefined;
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for (const entry of this.#entries.values()) {
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if (!entry.keepAlive || entry.view === this.#active) continue;
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if (!oldest || entry.lastUsed < oldest.lastUsed) oldest = entry;
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}
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return oldest;
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}
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}
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