feat(view): lift a muted account colour for the accent bar

The five real account colours are all mid-tone, because they were chosen as
CHIP fills with legible text on top, and three pixels of a mid-tone colour
barely registers beside a card's own background. The bar now lifts saturation
and lightness to a floor.

A floor, not a repaint: a colour already past it is returned untouched, so a
deliberately vivid choice is preserved and only the muted ones move. Hue is
never altered, because hue is the entire information the bar carries and a
shifted one would stop matching the account's chip and its dropdown swatch.

0.65 and 0.50 were chosen by rendering all five accounts as 3px bars against
both a dark and a light card background and looking at them. Higher pushed the
weakest of them, a green at S 0.33, toward a neon that no longer matched its own
chip; lower left it where it started.

accentLineColour had no test at all until now, which is how two earlier versions
of it shipped wrong: one blended toward Base until it WAS the background, the
other passed a chip colour through unchanged. test_carddelegate covers the lift,
the floor's idempotence, hue preservation across all five accounts, and the
fallback for a thread with no account tag.

1 files changed, 135 insertions, 0 deletions

diff --git a/tests/test_carddelegate.cpp b/tests/test_carddelegate.cpp
new file mode 100644
index 0000000..d5e55b5
--- /dev/null
+++ b/tests/test_carddelegate.cpp
@@ -0,0 +1,135 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "carddelegate.h"
+
+#include "threadlistmodel.h"
+
+#include <QTest>
+
+class TestCardDelegate : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void theAccentLiftsAMutedAccountColour();
+    void theAccentKeepsEachAccountTellableApart();
+    void anAccountWithNoColourFallsBackToTheNeutralLine();
+};
+
+namespace {
+
+/// The user's five configured account colours, as a realistic sample. They are
+/// all mid-tone because they were chosen as CHIP fills, which is the whole
+/// reason the bar has to lift them.
+const QList<QColor> &sampleAccounts()
+{
+    static const QList<QColor> colours{
+        QColor("#2f6fa8"), QColor("#3d7a4a"), QColor("#a83f2f"),
+        QColor("#8a5cb8"), QColor("#b8862f"),
+    };
+    return colours;
+}
+
+float saturationOf(const QColor &c)
+{
+    float h = 0, s = 0, l = 0, a = 0;
+    c.getHslF(&h, &s, &l, &a);
+    return s;
+}
+
+float lightnessOf(const QColor &c)
+{
+    float h = 0, s = 0, l = 0, a = 0;
+    c.getHslF(&h, &s, &l, &a);
+    return l;
+}
+
+float hueOf(const QColor &c)
+{
+    float h = 0, s = 0, l = 0, a = 0;
+    c.getHslF(&h, &s, &l, &a);
+    return h;
+}
+
+}  // namespace
+
+void TestCardDelegate::theAccentLiftsAMutedAccountColour()
+{
+    // An account colour is chosen to be a chip's fill with legible text on top,
+    // so it is mid-tone by construction. Three pixels of a mid-tone colour
+    // beside a card's own background barely register, which is what the user
+    // reported: "the colours could be a little more vivid".
+    //
+    // The green is the weakest of the five (S 0.33, L 0.36) and is the one that
+    // has to move most.
+    const QColor muted("#3d7a4a");
+    const QColor accent = CardDelegate::accentLineColour(muted);
+
+    QVERIFY2(saturationOf(accent) > saturationOf(muted),
+             "the accent is no more saturated than the chip colour it comes "
+             "from, so a muted account stays muted as a 3px bar");
+    QVERIFY2(lightnessOf(accent) > lightnessOf(muted),
+             "the accent is no lighter than the chip colour, so it cannot "
+             "carry on a dark theme");
+
+    // The floor, stated as the numbers that were chosen by rendering all five
+    // against both themes. Higher pushed the green toward a neon that no
+    // longer matched its own chip.
+    QVERIFY(saturationOf(accent) >= 0.65f - 0.01f);
+    QVERIFY(lightnessOf(accent) >= 0.50f - 0.01f);
+
+    // A colour already past the floor is left alone: the lift is a floor, not
+    // a repaint, or a user who picked a vivid colour would have it changed.
+    const QColor alreadyVivid = QColor::fromHslF(0.6f, 0.9f, 0.6f);
+    const QColor untouched = CardDelegate::accentLineColour(alreadyVivid);
+    QCOMPARE(saturationOf(untouched), saturationOf(alreadyVivid));
+    QCOMPARE(lightnessOf(untouched), lightnessOf(alreadyVivid));
+}
+
+void TestCardDelegate::theAccentKeepsEachAccountTellableApart()
+{
+    // The bar's whole job is saying WHICH account, so the lift must not
+    // converge two hues. Asserted across the real five rather than one pair:
+    // a floor applied to saturation and lightness leaves hue untouched, and
+    // this is what proves it stayed that way.
+    for (const QColor &configured : sampleAccounts()) {
+        const QColor accent = CardDelegate::accentLineColour(configured);
+        QVERIFY2(qAbs(hueOf(accent) - hueOf(configured)) < 0.01f,
+                 qPrintable(QStringLiteral("account %1 changed hue to %2, so "
+                                           "it no longer matches its own chip")
+                                .arg(configured.name(), accent.name())));
+    }
+
+    // And no two of them collapse onto each other.
+    QSet<QRgb> seen;
+    for (const QColor &configured : sampleAccounts())
+        seen.insert(CardDelegate::accentLineColour(configured).rgb());
+    QCOMPARE(seen.size(), sampleAccounts().size());
+}
+
+void TestCardDelegate::anAccountWithNoColourFallsBackToTheNeutralLine()
+{
+    // A thread with no account tag has no colour to lift, and must not end up
+    // with a saturated bar invented out of an invalid QColor.
+    QCOMPARE(CardDelegate::accentLineColour(QColor()),
+             ThreadListModel::threadLineColour());
+}
+
+QTEST_MAIN(TestCardDelegate)
+#include "test_carddelegate.moc"