RTC: Add session activity notifications

packages/core-data/src/awareness/types.ts

@@ -94,3 +94,9 @@ export type EqualityFieldCheck< State, FieldName extends keyof State > = (
 	value1?: State[ FieldName ],
 	value2?: State[ FieldName ]
 ) => boolean;
+
+export interface PostSaveEvent {
+	savedAt: number;
+	savedByClientId: number;
+	postStatus: string | undefined;
+}

packages/core-data/src/hooks/use-post-editor-awareness-state.ts

@@ -2,13 +2,15 @@
  * External dependencies
  */
 import { useEffect, useState } from '@wordpress/element';
+import type { Y } from '@wordpress/sync';
 
 /**
  * Internal dependencies
  */
 import { getSyncManager } from '../sync';
 import type {
 	PostEditorAwarenessState as ActiveCollaborator,
+	PostSaveEvent,
 	YDocDebugData,
 } from '../awareness/types';
 import type { SelectionState } from '../types';
@@ -156,3 +158,71 @@ export function useIsDisconnected(
 	return usePostEditorAwarenessState( postId, postType )
 		.isCurrentCollaboratorDisconnected;
 }
+
+/**
+ * Hook that subscribes to the CRDT state map and returns the most recent
+ * save event (timestamp + client ID). The state map is updated by
+ * `markEntityAsSaved` in `@wordpress/sync`
+ *
+ * @param postId   The ID of the post.
+ * @param postType The type of the post.
+ */
+export function useLastPostSave(
+	postId: number | null,
+	postType: string | null
+): PostSaveEvent | null {
+	const [ lastSave, setLastSave ] = useState< PostSaveEvent | null >( null );
+
+	useEffect( () => {
+		if ( null === postId || null === postType ) {
+			setLastSave( null );
+			return;
+		}
+
+		const awareness = getSyncManager()?.getAwareness< PostEditorAwareness >(
+			`postType/${ postType }`,
+			postId.toString()
+		);
+
+		if ( ! awareness ) {
+			setLastSave( null );
+			return;
+		}
+
+		awareness.setUp();
+
+		const stateMap = awareness.doc.getMap( 'state' );
+		const recordMap = awareness.doc.getMap( 'document' );
+
+		// Only notify for saves that occur after the observer is
+		// set up. This prevents false notifications when the Y.Doc
+		// syncs historical state on page load or peer reconnect.
+		const setupTime = Date.now();
+
+		const observer = ( event: Y.YMapEvent< unknown > ) => {
+			if ( event.keysChanged.has( 'savedAt' ) ) {
+				const savedAt = stateMap.get( 'savedAt' ) as number;
+				const savedByClientId = stateMap.get( 'savedBy' ) as number;
+
+				if (
+					typeof savedAt === 'number' &&
+					typeof savedByClientId === 'number' &&
+					savedAt > setupTime
+				) {
+					const postStatus = recordMap.get( 'status' ) as
+						| string
+						| undefined;
+					setLastSave( { savedAt, savedByClientId, postStatus } );
+				}
+			}
+		};
+
+		stateMap.observe( observer );
+
+		return () => {
+			stateMap.unobserve( observer );
+		};
+	}, [ postId, postType ] );
+
+	return lastSave;
+}

packages/core-data/src/private-apis.js

@@ -6,6 +6,7 @@ import { RECEIVE_INTERMEDIATE_RESULTS } from './utils';
 import {
 	useActiveCollaborators,
 	useResolvedSelection,
+	useLastPostSave,
 } from './hooks/use-post-editor-awareness-state';
 import { lock } from './lock-unlock';
 import { retrySyncConnection } from './sync';
@@ -17,4 +18,5 @@ lock( privateApis, {
 	retrySyncConnection,
 	useActiveCollaborators,
 	useResolvedSelection,
+	useLastPostSave,
 } );