Remind the user if they're trying to reply to someone who has left

This happens semi-frequently to me and others - we reply to a user who
has left the room. Sometimes this is useful (for example, bringing up a
previous topic) but in most cases this is accidental, and almost
guaranteed to happen if you turned off join/leave events.

So I added a reminder when replying - which manifests as a small label
in the chatbar - that the user has left and can't be notified of your
reply.

src/chatbar/ChatBar.qml

@@ -197,6 +197,22 @@ QQC2.Control {
             visible: root.currentRoom.mainCache.replyId.length > 0
             sourceComponent: replyPane
         }
+        RowLayout {
+            visible: replyLoader.visible && !root.currentRoom.mainCache.relationAuthorIsPresent
+            spacing: Kirigami.Units.smallSpacing
+
+            Kirigami.Icon {
+                source: "help-hint-symbolic"
+                color: Kirigami.Theme.disabledTextColor
+
+                Layout.preferredWidth: Kirigami.Units.iconSizes.small
+                Layout.preferredHeight: Kirigami.Units.iconSizes.small
+            }
+            QQC2.Label {
+                text: i18nc("@info", "The user you're replying to has left the room, and can't be notified.")
+                color: Kirigami.Theme.disabledTextColor
+            }
+        }
         Loader {
             id: attachLoader
 

src/libneochat/chatbarcache.cpp

@@ -15,6 +15,18 @@ using namespace Qt::StringLiterals;
 ChatBarCache::ChatBarCache(QObject *parent)
     : QObject(parent)
 {
+    if (parent == nullptr) {
+        qWarning() << "ChatBarCache created with no parent, a NeoChatRoom must be set as the parent on creation.";
+        return;
+    }
+    auto room = dynamic_cast<NeoChatRoom *>(parent);
+    if (room == nullptr) {
+        qWarning() << "ChatBarCache created with incorrect parent, a NeoChatRoom must be set as the parent on creation.";
+        return;
+    }
+    connect(room, &NeoChatRoom::memberLeft, this, &ChatBarCache::relationAuthorIsPresentChanged);
+    connect(room, &NeoChatRoom::memberJoined, this, &ChatBarCache::relationAuthorIsPresentChanged);
+    connect(this, &ChatBarCache::relationIdChanged, this, &ChatBarCache::relationAuthorIsPresentChanged);
 }
 
 QString ChatBarCache::text() const
@@ -137,6 +149,11 @@ Quotient::RoomMember ChatBarCache::relationAuthor() const
     return room->member((*room->findInTimeline(m_relationId))->senderId());
 }
 
+bool ChatBarCache::relationAuthorIsPresent() const
+{
+    return relationAuthor().membershipState() == Quotient::Membership::Join;
+}
+
 QString ChatBarCache::relationMessage() const
 {
     if (parent() == nullptr) {

src/libneochat/chatbarcache.h

@@ -99,6 +99,13 @@ class ChatBarCache : public QObject
      */
     Q_PROPERTY(Quotient::RoomMember relationAuthor READ relationAuthor NOTIFY relationIdChanged)
 
+    /**
+     * @brief If the author for the message being replied to is still present in the room.
+     *
+     * @sa Quotient::RoomMember
+     */
+    Q_PROPERTY(bool relationAuthorIsPresent READ relationAuthorIsPresent NOTIFY relationAuthorIsPresentChanged)
+
     /**
      * @brief The content of the related message.
      *
@@ -153,6 +160,7 @@ public:
     void setEditId(const QString &editId);
 
     Quotient::RoomMember relationAuthor() const;
+    bool relationAuthorIsPresent() const;
 
     QString relationMessage() const;
 
@@ -196,6 +204,7 @@ Q_SIGNALS:
     void threadIdChanged(const QString &oldThreadId, const QString &newThreadId);
     void attachmentPathChanged();
     void mentionAdded(const QString &mention);
+    void relationAuthorIsPresentChanged();
 
 private:
     QString m_text = QString();