v10/dist/dev/playback/actors/text-track-segment-loader.js

import { peek } from "../../core/signals/primitives.js";
import { SerialRunner, Task } from "../../core/tasks/task.js";
import { createMachineActor } from "../../core/actors/create-machine-actor.js";
import { DEFAULT_FORWARD_BUFFER_CONFIG, getSegmentsToLoad } from "../../media/buffer/forward-buffer.js";
import { DEFAULT_TEXT_MESSAGE_PIPELINES } from "../primitives/text-segment-load-pipeline.js";
//#region src/playback/actors/text-track-segment-loader.ts
/**
* Loads text-track segments for a track and delegates cue management
* to a TextTracksActor. Mirrors the v/a `SegmentLoaderActor` shape (FSM
* with `idle` / `loading` and `inFlight*` context for continue-vs-preempt),
* adapted to text:
*
* - No init segment, no flush ops (text cues don't need eviction — they're
*   small and the playhead-relative window is enforced by the runtime).
* - Single in-flight identity (`inFlightSegmentId`) — text has only the
*   media-segment path, no init-segment path.
*
* Planning is done in the load handler on every incoming message:
* `getSegmentsToLoad` filters to the forward window, then the segments
* not already in `TextTracksActor`'s context are scheduled. When a new
* `load` arrives mid-run, the handler replans and either:
*
* - **Continues**: the in-flight segment is still in the new plan →
*   `abortPending` only, schedule the rest of the plan (minus the
*   in-flight item, which covers its slot).
* - **Preempts**: in-flight segment is no longer wanted (track switch,
*   large seek out of window) → `abortAll`, schedule the new plan
*   from scratch.
*
* The cue parser is injected so this factory is host-agnostic. A DOM
* host supplies a VTT parser backed by `<track>`/`TextTrack` APIs; a
* non-DOM host (worker, test fake, alternate runtime) supplies its own.
*/
function createTextTrackSegmentLoaderActor(textTracksActor, resolveSegment, config = {}, compositionDeps = {
	state: {},
	context: {},
	config: {}
}) {
	const forwardBufferConfig = {
		...DEFAULT_FORWARD_BUFFER_CONFIG,
		...config.forwardBuffer
	};
	const deps = {
		state: compositionDeps.state,
		context: compositionDeps.context,
		config: {
			...compositionDeps.config,
			textTracksActor,
			resolveSegment
		}
	};
	const pipeline = (config.messagePipelines ?? DEFAULT_TEXT_MESSAGE_PIPELINES)();
	/**
	* Translate a load message into an ordered TextLoadTask list based on
	* committed actor state. In-flight awareness is handled separately in
	* the `loading` state's load handler.
	*
	* Metadata mode (no `range`) is a no-op for text — text tracks have
	* no init-segment concept, so there's nothing to load until a range
	* arrives via `'full-range'` dispatch.
	*/
	const planTasks = (message) => {
		const { track, range } = message;
		if (!range) return [];
		const trackId = track.id;
		const bufferedSegments = peek(textTracksActor.snapshot).context.segments[trackId] ?? [];
		return getSegmentsToLoad(track.segments, bufferedSegments, range.start, forwardBufferConfig).map((segment) => ({
			segment,
			trackId
		}));
	};
	/**
	* Wraps a TextLoadTask into a Task that runs the op's step pipeline
	* (resolve/relocate/dispatch, per the composition's `messagePipelines`).
	* Updates `inFlightSegmentId` around the async region so the load handler can
	* make accurate continue/preempt decisions, and checks the abort signal before
	* each step.
	*
	* Text degrades gracefully: a step throwing (e.g. a failed segment fetch) is
	* logged and swallowed so the runner continues to the next segment — unlike the
	* v/a loader, where a failed init must abort the remaining tasks.
	*/
	const makeLoadTask = (op, { getContext, setContext }) => {
		return new Task(async (signal) => {
			if (signal.aborted) return;
			const frame = { op };
			setContext({
				...getContext(),
				inFlightTrackId: op.trackId,
				inFlightSegmentId: op.segment.id
			});
			try {
				for (const step of pipeline) {
					if (signal.aborted) return;
					await step(frame, signal, deps);
				}
			} catch (error) {
				console.error("Failed to load text-track segment:", error);
			} finally {
				setContext({
					...getContext(),
					inFlightTrackId: null,
					inFlightSegmentId: null
				});
			}
		});
	};
	const scheduleAll = (tasks, ctx) => {
		for (const op of tasks) ctx.runner.schedule(makeLoadTask(op, ctx)).then(void 0, (e) => {
			if (e instanceof Error && e.name === "AbortError") return;
			console.error("Unexpected error in text-track segment loader:", e);
			ctx.runner.abortPending();
		});
	};
	return createMachineActor({
		runner: () => new SerialRunner(),
		initial: "idle",
		context: {
			inFlightTrackId: null,
			inFlightSegmentId: null
		},
		states: {
			idle: { on: { load: (msg, ctx) => {
				const tasks = planTasks(msg);
				if (tasks.length === 0) return;
				ctx.transition("loading");
				scheduleAll(tasks, ctx);
			} } },
			loading: {
				onSettled: "idle",
				on: { load: (msg, ctx) => {
					const { context, runner } = ctx;
					const tasks = planTasks(msg);
					if (context.inFlightTrackId !== null && context.inFlightSegmentId !== null && tasks.some((t) => t.trackId === context.inFlightTrackId && t.segment.id === context.inFlightSegmentId)) {
						runner.abortPending();
						scheduleAll(tasks.filter((t) => !(t.trackId === context.inFlightTrackId && t.segment.id === context.inFlightSegmentId)), ctx);
					} else {
						runner.abortAll();
						scheduleAll(tasks, ctx);
					}
				} }
			}
		}
	});
}
//#endregion
export { createTextTrackSegmentLoaderActor };

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