Add leave room warning for last admin

src/components/structures/MatrixChat.tsx

@@ -138,6 +138,7 @@ import { ValidatedServerConfig } from '../../utils/ValidatedServerConfig';
 import { isLocalRoom } from '../../utils/localRoom/isLocalRoom';
 import { SdkContextClass, SDKContext } from '../../contexts/SDKContext';
 import { viewUserDeviceSettings } from '../../actions/handlers/viewUserDeviceSettings';
+import { isNumberArray } from '../../utils/TypeUtils';
 import { VoiceBroadcastResumer } from '../../voice-broadcast';
 
 // legacy export
@@ -1132,6 +1133,29 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 ));
             }
         }
+
+        const client = MatrixClientPeg.get();
+        const plEvent = roomToLeave.currentState.getStateEvents(EventType.RoomPowerLevels, '');
+        const plContent = plEvent ? plEvent.getContent() : {};
+        const userLevels = plContent.users || {};
+        const currentUserLevel = userLevels[client.getUserId()];
+        const userLevelValues = Object.values(userLevels);
+        if (isNumberArray(userLevelValues)) {
+            const maxUserLevel = Math.max(...userLevelValues);
+            // If the user is the only user with highest power level
+            if (maxUserLevel === currentUserLevel &&
+                userLevelValues.lastIndexOf(maxUserLevel) == userLevelValues.indexOf(maxUserLevel)) {
+                warnings.push((
+                    <span className="warning" key="last_admin_warning">
+                        { ' '/* Whitespace, otherwise the sentences get smashed together */ }
+                        { _t("You are the sole person with the highest role in this room. " +
+                        "If you leave, the room could become unmoderable. Consider giving " +
+                        "another user your role.") }
+                    </span>
+                ));
+            }
+        }
+
         return warnings;
     }
 

src/i18n/strings/en_EN.json

@@ -3277,6 +3277,7 @@
     "You are the only person here. If you leave, no one will be able to join in the future, including you.": "You are the only person here. If you leave, no one will be able to join in the future, including you.",
     "This space is not public. You will not be able to rejoin without an invite.": "This space is not public. You will not be able to rejoin without an invite.",
     "This room is not public. You will not be able to rejoin without an invite.": "This room is not public. You will not be able to rejoin without an invite.",
+    "You are the sole person with the highest role in this room. If you leave, the room could become unmoderable. Consider giving another user your role.": "You are the sole person with the highest role in this room. If you leave, the room could become unmoderable. Consider giving another user your role.",
     "Are you sure you want to leave the space '%(spaceName)s'?": "Are you sure you want to leave the space '%(spaceName)s'?",
     "Are you sure you want to leave the room '%(roomName)s'?": "Are you sure you want to leave the room '%(roomName)s'?",
     "Failed to forget room %(errCode)s": "Failed to forget room %(errCode)s",

src/utils/TypeUtils.ts

@@ -28,3 +28,14 @@ export function makeType(Type: any, opts: any) {
     Object.assign(c, opts);
     return c;
 }
+
+/**
+ * Typeguard that checks if an unknown variable is an array of numbers
+ * @param value the variable to check
+ * @returns true if the variable is an array of numbers, false otherwise
+ */
+export function isNumberArray(value: unknown): value is number[] {
+    return (
+        Array.isArray(value) && value.every(element => typeof element === "number")
+    );
+}