Track end of document edit session

src/hooks/use-document-sync-to-firebase.ts

@@ -1,6 +1,7 @@
-import { useEffect, useMemo } from "react";
+import { useEffect, useMemo, useRef } from "react";
 import { throttle as _throttle } from "lodash";
 import { onSnapshot, SnapshotOut } from "mobx-state-tree";
+import { OnDisconnect } from "firebase-admin/database";
 import { useSyncMstNodeToFirebase } from "./use-sync-mst-node-to-firebase";
 import { useSyncMstPropToFirebase } from "./use-sync-mst-prop-to-firebase";
 import { DEBUG_DOCUMENT, DEBUG_SAVE } from "../lib/debug";
@@ -40,6 +41,7 @@ export function useDocumentSyncToFirebase(
 ) {
   const { key, type, uid, contentStatus } = document;
   const { content: contentPath, metadata, typedMetadata } = firebase.getUserDocumentPaths(user, type, key, uid);
+  const disconnectHandler = useRef<OnDisconnect|undefined>(undefined);
 
   // TODO: when running in doc-editor this warning was printed constantly
   // Ideally we'd figure out how to separate the syncing from the document stuff so the doc-editor can use
@@ -62,9 +64,14 @@ export function useDocumentSyncToFirebase(
         if (document.treeMonitor) {
           document.treeMonitor.enabled = false;
         }
+        // If an onDisconnect was set, remove it and set updated timestamp to now.
+        if (disconnectHandler.current) {
+          firebase.setLastEditedNow(user, key, uid, disconnectHandler.current);
+          console.log("Doc closed, setting last modified", key);
+        }
       };
     }
-  }, [readOnly, contentStatus, document.treeMonitor]);
+  }, [readOnly, contentStatus, document.treeMonitor, firebase, user, key, uid]);
 
   if (!readOnly && DEBUG_DOCUMENT) {
     // provide the document to the console so developers can inspect its content
@@ -196,10 +203,13 @@ export function useDocumentSyncToFirebase(
     ({ changeCount: document.incChangeCount(), content: JSON.stringify(snapshot) });
 
   const mutation = useMutation((snapshot: DocumentContentSnapshotType) => {
-    const tileMap = snapshot.tileMap || {};
+    if (!disconnectHandler.current) {
+      disconnectHandler.current = firebase.setLastEditedOnDisconnect(user, key, uid);
+      console.log("Doc modified, tracking disconnect", key);
+    }
 
+    const tileMap = snapshot.tileMap || {};
     const tools: string[] = [];
-
     Object.keys(tileMap).forEach((tileKey) => {
       const tileInfo = tileMap[tileKey] as ITileMapEntry;
       const tileType = tileInfo.content.type;

src/lib/firebase.ts

@@ -180,6 +180,32 @@ export class Firebase {
     return `${this.getUserPath(user, userId)}/documentMetadata${suffix}`;
   }
 
+  public getLastEditedMetadataPath(user: UserModelType, documentKey: string, userId?: string) {
+    return `${this.getUserDocumentMetadataPath(user, documentKey, userId)}/lastEditedAt`;
+  }
+
+  /**
+   * Set up a Firebase onDisconnect handler to update the lastEditedAt timestamp when the user disconnects.
+   */
+  public setLastEditedOnDisconnect(user: UserModelType, documentKey: string, userId?: string) {
+    const ref = this.ref(this.getLastEditedMetadataPath(user, documentKey, userId));
+    const onDisconnect = ref.onDisconnect();
+    onDisconnect.set(firebase.database.ServerValue.TIMESTAMP);
+    return onDisconnect;
+  }
+
+  /**
+   * Set the lastEditedAt timestamp to the current time, optionally cancelling an onDisconnect handler.
+   */
+  public setLastEditedNow(user: UserModelType, documentKey: string, userId: string|undefined,
+      onDisconnect?: firebase.database.OnDisconnect) {
+    if (onDisconnect) {
+      onDisconnect.cancel();
+    }
+    return this.ref(this.getLastEditedMetadataPath(user, documentKey, userId))
+      .set(firebase.database.ServerValue.TIMESTAMP);
+  }
+
   // Unpublished personal document/learning log metadata
   public getOtherDocumentPath(user: UserModelType, documentType: OtherDocumentType, documentKey?: string) {
     const dir = documentType === PersonalDocument ? "personalDocs" : "learningLogs";