Snapshots

Snapshots are immutable read-model projections shared by Legato runtimes and consumers.

PlaybackSnapshot

interface PlaybackSnapshot {
  state: PlaybackState;
  currentTrack: Track | null;
  currentIndex: number | null;
  position: number;
  duration: number | null;
  bufferedPosition?: number | null;
  queue: QueueSnapshot;
}

Observable semantics from the contract:

• duration is nullable. null means unknown or live-like timeline semantics.
• A finite duration value is evidence of finite media length, not a seekability guarantee by itself.
• currentTrack and currentIndex can both be null when no active item exists.
• bufferedPosition is optional and may be null.

Minimal example

import type { PlaybackSnapshot } from '@ddgutierrezc/legato-contract';

const snapshot: PlaybackSnapshot = {
  state: 'ready',
  currentTrack: null,
  currentIndex: null,
  position: 0,
  duration: null,
  queue: {
    items: [],
    currentIndex: null,
  },
};

QueueSnapshot

interface QueueSnapshot {
  items: Track[];
  currentIndex: number | null;
}

Observable semantics from the contract:

• items preserves queue order.
• currentIndex is nullable when no active item exists.

Minimal example

import type { QueueSnapshot } from '@ddgutierrezc/legato-contract';

const queue: QueueSnapshot = {
  items: [],
  currentIndex: null,
};

Related pages

• Track
• Events