61 lines
1.9 KiB
TypeScript
61 lines
1.9 KiB
TypeScript
export type VideoCanvasSaveStatus = "saved" | "pending" | "saving" | "error";
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/** Keep edits made during a request; never retry a stale revision as an overwrite. */
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export class VideoCanvasSaveQueue {
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private latest: string;
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private saved: string;
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private running: Promise<void> | null = null;
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private blocked = false;
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private status: VideoCanvasSaveStatus = "saved";
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constructor(
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baseline: string,
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private revision: string,
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private readonly write: (snapshot: string, revision: string) => Promise<string>,
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private readonly changed: (status: VideoCanvasSaveStatus, message?: string) => void,
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) {
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this.latest = baseline;
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this.saved = baseline;
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}
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get failed() { return this.status === "error"; }
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get dirty() { return this.latest !== this.saved || this.running !== null; }
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update(snapshot: string) {
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this.latest = snapshot;
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if (!this.running && this.status !== "error") {
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this.setStatus(this.dirty ? "pending" : "saved");
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}
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}
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private setStatus(status: VideoCanvasSaveStatus, message?: string) {
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this.status = status;
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this.changed(status, message);
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}
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flush(): Promise<void> {
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if (this.running) return this.running;
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if (this.blocked || !this.dirty) return Promise.resolve();
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this.running = this.drain().finally(() => { this.running = null; });
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return this.running;
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}
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private async drain() {
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this.setStatus("saving");
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try {
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while (this.latest !== this.saved) {
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const snapshot = this.latest;
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this.revision = await this.write(snapshot, this.revision);
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this.saved = snapshot;
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}
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this.setStatus("saved");
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} catch (error) {
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this.blocked = error instanceof CanvasRevisionConflict;
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this.setStatus("error", error instanceof Error ? error.message : "保存失败，请重试");
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}
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}
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}
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export class CanvasRevisionConflict extends Error {}
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