41 lines
1.4 KiB
JavaScript
41 lines
1.4 KiB
JavaScript
/*
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* Keeps the active playlist in memory between player-state requests.
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* State, command and discovery requests share a queue so responses cannot
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* overwrite newer state or reuse tracks from a different playlist version.
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*/
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export class PlayerStateClient {
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#sendRequest;
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#snapshot = null;
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#pending = Promise.resolve();
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// sendRequest performs the application's JSON GET/POST transport.
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constructor(sendRequest) {
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this.#sendRequest = sendRequest;
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}
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// Queues a state-producing request and returns a complete browser snapshot.
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// A failed request does not prevent subsequent requests from being sent.
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request(path, body) {
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const result = this.#pending.then(() => this.#read(path, body));
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this.#pending = result.catch(() => {});
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return result;
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}
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// Sends the cached version and restores omitted tracks from that exact version.
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async #read(path, body) {
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if (this.#snapshot) {
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path += `?playlistVersion=${encodeURIComponent(this.#snapshot.playlistVersion)}`;
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}
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const nextState = await this.#sendRequest(path, body);
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if (nextState.tracks === null) {
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if (!this.#snapshot || nextState.playlistVersion !== this.#snapshot.playlistVersion) {
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this.#snapshot = null;
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throw new Error("Playlist cache does not match the server version.");
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}
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nextState.tracks = this.#snapshot.tracks;
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}
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this.#snapshot = nextState;
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return nextState;
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}
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}
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