Use RichText text input to provide real mentions

This use internally now a QTextDocument and a new C++ class to
manipulate the document with QTextCursor.

src/chatdocumenthandler.h

@@ -0,0 +1,86 @@
+/**
+ * SPDX-FileCopyrightText: 2020 Carl Schwan <carl@carlschwan.eu>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#pragma once
+
+#include <QFont>
+#include <QObject>
+#include <QTextCursor>
+#include <QUrl>
+
+class QTextDocument;
+class QQuickTextDocument;
+class NeoChatRoom;
+
+class ChatDocumentHandler : public QObject
+{
+    Q_OBJECT
+    Q_PROPERTY(QQuickTextDocument *document READ document WRITE setDocument NOTIFY documentChanged)
+    Q_PROPERTY(int cursorPosition READ cursorPosition WRITE setCursorPosition NOTIFY cursorPositionChanged)
+    Q_PROPERTY(int selectionStart READ selectionStart WRITE setSelectionStart NOTIFY selectionStartChanged)
+    Q_PROPERTY(int selectionEnd READ selectionEnd WRITE setSelectionEnd NOTIFY selectionEndChanged)
+
+    Q_PROPERTY(NeoChatRoom *room READ room WRITE setRoom NOTIFY roomChanged)
+
+public:
+    enum AutoCompletionType {
+        User,
+        Emoji,
+        None,
+        Ignore,
+    };
+    Q_ENUM(AutoCompletionType)
+
+    explicit ChatDocumentHandler(QObject *object = nullptr);
+
+    QQuickTextDocument *document() const;
+    void setDocument(QQuickTextDocument *document);
+
+    int cursorPosition() const;
+    void setCursorPosition(int position);
+
+    int selectionStart() const;
+    void setSelectionStart(int position);
+
+    int selectionEnd() const;
+    void setSelectionEnd(int position);
+
+    NeoChatRoom *room() const;
+    void setRoom(NeoChatRoom *room);
+
+    Q_INVOKABLE void postMessage(const QString &attachmentPath, const QString &replyEventId) const;
+
+    /// This function will look at the current QTextCursor and determine if there
+    /// is the posibility to autocomplete it.
+    Q_INVOKABLE QVariantMap getAutocompletionInfo();
+    Q_INVOKABLE void replaceAutoComplete(const QString &word);
+
+Q_SIGNALS:
+    void documentChanged();
+    void cursorPositionChanged();
+    void selectionStartChanged();
+    void selectionEndChanged();
+    void roomChanged();
+
+private:
+    QTextCursor textCursor() const;
+    QTextDocument *textDocument() const;
+
+    QQuickTextDocument *m_document;
+
+    NeoChatRoom *m_room;
+
+    int m_cursorPosition;
+    int m_selectionStart;
+    int m_selectionEnd;
+
+    int m_autoCompleteBeginPosition = -1;
+    int m_autoCompleteEndPosition = -1;
+
+    QString m_lastState;
+};
+
+Q_DECLARE_METATYPE(ChatDocumentHandler::AutoCompletionType);