Improve the style picker

src/chatbar/styledelegatehelper.cpp

@@ -0,0 +1,88 @@
+// SPDX-FileCopyrightText: 2025 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#include "styledelegatehelper.h"
+
+#include <QQuickTextDocument>
+#include <QTextCursor>
+#include <QTextDocument>
+
+#include "enums/textstyle.h"
+
+StyleDelegateHelper::StyleDelegateHelper(QObject *parent)
+    : QObject(parent)
+{
+}
+
+QQuickItem *StyleDelegateHelper::textItem() const
+{
+    return m_textItem;
+}
+
+void StyleDelegateHelper::setTextItem(QQuickItem *textItem)
+{
+    if (textItem == m_textItem) {
+        return;
+    }
+
+    m_textItem = textItem;
+
+    if (m_textItem) {
+        if (document()) {
+            formatDocument();
+        }
+    }
+
+    Q_EMIT textItemChanged();
+}
+
+QTextDocument *StyleDelegateHelper::document() const
+{
+    if (!m_textItem) {
+        return nullptr;
+    }
+    const auto quickDocument = qvariant_cast<QQuickTextDocument *>(m_textItem->property("textDocument"));
+    return quickDocument ? quickDocument->textDocument() : nullptr;
+}
+
+void StyleDelegateHelper::formatDocument()
+{
+    if (!document()) {
+        return;
+    }
+
+    auto cursor = QTextCursor(document());
+    if (cursor.isNull()) {
+        return;
+    }
+
+    cursor.beginEditBlock();
+    cursor.select(QTextCursor::Document);
+    cursor.removeSelectedText();
+    const auto style = static_cast<TextStyle::Style>(m_textItem->property("index").toInt());
+    const auto string = TextStyle::styleString(style);
+
+    const int headingLevel = style <= 6 ? style : 0;
+    // Apparently, 5 is maximum for FontSizeAdjustment; otherwise level=1 and
+    // level=2 look the same
+    const int sizeAdjustment = headingLevel > 0 ? 5 - headingLevel : 0;
+
+    QTextBlockFormat blkfmt;
+    blkfmt.setHeadingLevel(headingLevel);
+    cursor.mergeBlockFormat(blkfmt);
+
+    QTextCharFormat chrfmt;
+    chrfmt.setFontWeight(headingLevel > 0 ? QFont::Bold : QFont::Normal);
+    chrfmt.setProperty(QTextFormat::FontSizeAdjustment, sizeAdjustment / 2);
+    if (style == TextStyle::Code) {
+        chrfmt.setFontFamilies({u"monospace"_s});
+    } else if (style == TextStyle::Quote) {
+        chrfmt.setFontItalic(true);
+    }
+
+    cursor.mergeBlockCharFormat(chrfmt);
+    cursor.insertText(string);
+    cursor.endEditBlock();
+}
+
+#include "moc_styledelegatehelper.cpp"