Cycle checkboxes with the mouse wheel

Scrolling over a checkbox glyph cycles its state
unchecked -> partial -> checked (and back), respecting scroll direction:
wheel up steps forward, wheel down steps in reverse. Left-click still
toggles checked/unchecked.

The shared rewriteCheckbox helper applies a state-mapping function to the
Nth cookie; toggleCheckbox and the new cycleCheckbox are thin callers.

ui/qml/OutlineView.qml

@@ -473,7 +473,8 @@ ListView {
                                             font.pointSize: outline.baseFontSize + 1
                                             font.bold: cb !== ""
 
-                                            // Clickable only for checkbox items; toggles via the model.
+                                            // Checkbox interaction: left-click toggles,
+                                            // mouse wheel cycles ( ) -> (-) -> (X).
                                             MouseArea {
                                                 anchors.fill: parent
                                                 enabled: cbGlyph.cb !== ""
@@ -481,6 +482,15 @@ ListView {
                                                 cursorShape: Qt.PointingHandCursor
                                                 onClicked: docModel.toggleCheckbox(
                                                     del.index, modelData.checkboxOrdinal ?? -1)
+                                                onWheel: (wheel) => {
+                                                    // Scroll up = forward, down = reverse.
+                                                    let forward = wheel.angleDelta.y > 0
+                                                    docModel.cycleCheckbox(
+                                                        del.index,
+                                                        modelData.checkboxOrdinal ?? -1,
+                                                        forward)
+                                                    wheel.accepted = true
+                                                }
                                             }
                                         }
 

ui/src/documentmodel.cpp

@@ -187,7 +187,9 @@ bool DocumentModel::isLanguageSupported(const QString &lang)
     return m_supportedLanguages.contains(lang.trimmed().toLower());
 }
 
-bool DocumentModel::toggleCheckbox(int row, int checkboxOrdinal)
+bool DocumentModel::rewriteCheckbox(
+    int row, int checkboxOrdinal,
+    const std::function<QString(const QString &)> &nextState)
 {
     if (!m_client || row < 0 || row >= m_visibleRows.size())
         return false;
@@ -210,28 +212,24 @@ bool DocumentModel::toggleCheckbox(int row, int checkboxOrdinal)
     out.reserve(lines.size());
 
     int seen = -1;
-    bool toggled = false;
+    bool changed = false;
     for (const QString &line : lines) {
         QRegularExpressionMatch m = cookieRe.match(line);
         if (m.hasMatch()) {
             ++seen;
             if (seen == checkboxOrdinal) {
-                const QString state = m.captured(2);
-                const QString next = (state == QLatin1String("X") ||
-                                      state == QLatin1String("x"))
-                                         ? QStringLiteral(" ")
-                                         : QStringLiteral("X");
+                const QString next = nextState(m.captured(2));
                 QString updated = line;
                 updated.replace(m.capturedStart(2), m.capturedLength(2), next);
                 out.append(updated);
-                toggled = true;
+                changed = true;
                 continue;
             }
         }
         out.append(line);
     }
 
-    if (!toggled)
+    if (!changed)
         return false;
 
     const QString newBody = out.join('\n');
@@ -247,6 +245,37 @@ bool DocumentModel::toggleCheckbox(int row, int checkboxOrdinal)
     return true;
 }
 
+bool DocumentModel::toggleCheckbox(int row, int checkboxOrdinal)
+{
+    // Checked -> unchecked; unchecked/partial -> checked.
+    return rewriteCheckbox(row, checkboxOrdinal, [](const QString &state) {
+        const bool checked = (state == QLatin1String("X") ||
+                              state == QLatin1String("x"));
+        return checked ? QStringLiteral(" ") : QStringLiteral("X");
+    });
+}
+
+bool DocumentModel::cycleCheckbox(int row, int checkboxOrdinal, bool forward)
+{
+    // Cycle order: unchecked ( ) -> partial (-) -> checked (X) -> wrap.
+    return rewriteCheckbox(row, checkboxOrdinal, [forward](const QString &state) {
+        // Normalize current state to an index in the cycle.
+        int cur;
+        if (state == QLatin1String("-"))
+            cur = 1;                                // partial
+        else if (state == QLatin1String("X") || state == QLatin1String("x"))
+            cur = 2;                                // checked
+        else
+            cur = 0;                                // unchecked
+        const int next = forward ? (cur + 1) % 3 : (cur + 2) % 3;
+        switch (next) {
+        case 1:  return QStringLiteral("-");
+        case 2:  return QStringLiteral("X");
+        default: return QStringLiteral(" ");
+        }
+    });
+}
+
 void DocumentModel::loadDocument()
 {
     beginResetModel();

ui/src/documentmodel.h

@@ -15,6 +15,8 @@
 #include <QVector>
 #include <QSet>
 
+#include <functional>
+
 class OrkClient;
 
 class DocumentModel : public QAbstractListModel {
@@ -76,6 +78,11 @@ public:
     // back via /body, and refreshes the row. Returns true on success.
     Q_INVOKABLE bool toggleCheckbox(int row, int checkboxOrdinal);
 
+    // Cycle the Nth checkbox through unchecked -> checked -> partial and back.
+    // `forward` steps unchecked->checked->partial; otherwise the reverse. Writes
+    // the section body back via /body and refreshes the row. Returns success.
+    Q_INVOKABLE bool cycleCheckbox(int row, int checkboxOrdinal, bool forward);
+
 signals:
     void documentChanged();
 
@@ -123,6 +130,12 @@ private:
     // Rebuild the visible row list based on expansion state
     void rebuildVisibleRows();
 
+    // Rewrite the Nth checkbox cookie (document order) in the given row's
+    // section body, mapping the current state char (' '/'x'/'X'/'-') to a new
+    // one via `nextState`. Writes back via /body and refreshes. Returns success.
+    bool rewriteCheckbox(int row, int checkboxOrdinal,
+                         const std::function<QString(const QString &)> &nextState);
+
     OrkClient *m_client = nullptr;
     QString m_document;