feat(tags): hit-test a chip in the tag strip

chipRectAt() is the single source of a chip's geometry, used by paintEvent and
by the hit test, so the drawn chip and the clickable chip cannot drift.

The +N chip yields nothing: it stands for a list of tags rather than one, so
there is no single value a search could be built from.

2 files changed, 73 insertions, 4 deletions

diff --git a/src/tagstrip.cpp b/src/tagstrip.cpp
index bad116a..7e671ce 100644
--- a/src/tagstrip.cpp
+++ b/src/tagstrip.cpp
@@ -18,6 +18,7 @@
 
 #include "tagstrip.h"
 
+#include <QContextMenuEvent>
 #include <QFontMetrics>
 #include <QPainter>
 
@@ -109,6 +110,50 @@ void TagStrip::resizeEvent(QResizeEvent *event)
     relayout();
 }
 
+QRect TagStrip::chipRectAt(int index) const
+{
+    if (index < 0 || index >= m_visible.size())
+        return {};
+
+    const QFontMetrics metrics(font());
+
+    // Reproduces paintEvent's own vertical placement exactly, which is derived
+    // from the font's height rather than from the chip's, so a chip whose text
+    // is shorter than the line still lands on the same baseline.
+    const int top = (height() - (metrics.height() + TagChip::kPaddingY * 2)) / 2;
+
+    int x = 0;
+    for (int i = 0; i < index; ++i)
+        x += TagChip::sizeFor(metrics, m_visible.at(i)).width() + TagChip::kSpacing;
+
+    return QRect(QPoint(x, top), TagChip::sizeFor(metrics, m_visible.at(index)));
+}
+
+QString TagStrip::chipAt(const QPoint &point) const
+{
+    for (int i = 0; i < m_visible.size(); ++i) {
+        if (chipRectAt(i).contains(point))
+            return m_visible.at(i);
+    }
+    // Deliberately nothing for the overflow chip and for empty space: the +N
+    // chip names a list, not a tag.
+    return {};
+}
+
+void TagStrip::contextMenuEvent(QContextMenuEvent *event)
+{
+    const QString tag = chipAt(event->pos());
+    if (tag.isEmpty()) {
+        // Ignored rather than accepted, so a parent that offers its own menu
+        // still gets the chance to show it.
+        event->ignore();
+        return;
+    }
+
+    event->accept();
+    emit tagContextMenuRequested(tag, event->globalPos());
+}
+
 void TagStrip::paintEvent(QPaintEvent *)
 {
     if (m_visible.isEmpty())
@@ -119,12 +164,13 @@ void TagStrip::paintEvent(QPaintEvent *)
     const int top = (height() - (metrics.height() + TagChip::kPaddingY * 2)) / 2;
 
     int x = 0;
-    for (const QString &tag : m_visible) {
-        const QSize size = TagChip::sizeFor(metrics, tag);
+    for (int i = 0; i < m_visible.size(); ++i) {
+        const QString &tag = m_visible.at(i);
+        const QRect rect = chipRectAt(i);
         const QColor colour = m_tagColors ? m_tagColors->colourFor(tag)
                                           : TagColors().colourFor(tag);
-        TagChip::paint(&painter, QRect(QPoint(x, top), size), tag, colour);
-        x += size.width() + TagChip::kSpacing;
+        TagChip::paint(&painter, rect, tag, colour);
+        x = rect.right() + 1 + TagChip::kSpacing;
     }
 
     if (!m_hidden.isEmpty()) {
diff --git a/src/tagstrip.h b/src/tagstrip.h
index 4102bed..f59233b 100644
--- a/src/tagstrip.h
+++ b/src/tagstrip.h
@@ -18,10 +18,12 @@
 
 #pragma once
 
+#include <QRect>
 #include <QStringList>
 #include <QWidget>
 
 class TagColors;
+class QContextMenuEvent;
 
 /// One row of tag chips under the message pane.
 ///
@@ -48,9 +50,30 @@ public:
     QStringList visibleTags() const { return m_visible; }
     QStringList hiddenTags() const { return m_hidden; }
 
+    /// The rect of the visible chip at `index`, empty when out of range.
+    ///
+    /// The SAME function paintEvent lays out from, so what is drawn and what
+    /// is clickable cannot drift. `CardDelegate::expanderRectFor` exists for
+    /// this reason and this follows it.
+    QRect chipRectAt(int index) const;
+
+    /// The tag under `point`, empty when the point is on no chip.
+    ///
+    /// The trailing "+N" chip yields an empty string: it stands for a list of
+    /// tags rather than for one, so there is nothing a search could name.
+    QString chipAt(const QPoint &point) const;
+
+signals:
+    /// A visible chip was right-clicked. `globalPos` is where to pop a menu.
+    ///
+    /// The strip does not build the menu itself: what a tag can do belongs to
+    /// the window, which owns the query bar and the actions.
+    void tagContextMenuRequested(const QString &tag, const QPoint &globalPos);
+
 protected:
     void paintEvent(QPaintEvent *event) override;
     void resizeEvent(QResizeEvent *event) override;
+    void contextMenuEvent(QContextMenuEvent *event) override;
 
 private:
     /// Recomputes the visible/hidden split for the current width.