feat: lay out the calendar's month grid without a painter

1 files changed, 57 insertions, 0 deletions

diff --git a/src/monthlayout.h b/src/monthlayout.h
new file mode 100644
index 0000000..0aad3fe
--- /dev/null
+++ b/src/monthlayout.h
@@ -0,0 +1,57 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <QDate>
+#include <QPoint>
+#include <QRect>
+
+/// Where everything in the month grid goes, with no painter and no widget.
+///
+/// The CardLayout precedent: a geometric claim is tested as a function call,
+/// because AGENTS.md records how rendering probes lie. Six rows of seven
+/// always, so the grid does not jump in height between months.
+class MonthLayout
+{
+public:
+    static constexpr int kCells = 42;
+
+    MonthLayout(const QRect &area, int year, int month, Qt::DayOfWeek firstDay,
+                int dayNumberHeight, int chipHeight);
+
+    static QDate gridStart(int year, int month, Qt::DayOfWeek firstDay);
+
+    QDate dateAt(int cell) const;
+    int cellOf(const QDate &date) const;  ///< -1 when not on the grid.
+    QRect cellRect(int cell) const;
+    int cellAt(const QPoint &point) const;  ///< -1 outside the grid.
+
+    /// How many chip slots fit under a cell's day number.
+    int capacity() const;
+    /// How many of `total` chips are drawn; when fewer than `total`, the
+    /// next slot holds "+N more".
+    int visibleChips(int total) const;
+    QRect chipRect(int cell, int slot) const;
+
+private:
+    QRect m_area;
+    QDate m_start;
+    int m_dayNumberHeight;
+    int m_chipHeight;
+};