feat: show my bookings on a month calendar

src/Model/MonthGrid.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Model;
+
+/**
+ * The six-week skeleton behind a month calendar: always whole weeks, always starting on a Monday.
+ *
+ * Six weeks rather than "as many as the month needs" so the grid never changes height as you page
+ * through it -- a month can span six week rows (a 31-day month starting on a Sunday does), and a
+ * calendar that grows and shrinks under the cursor is worse than one with a trailing empty row.
+ *
+ * This is only the skeleton. Both calendars in this app draw the same grid and then disagree
+ * entirely about what goes in a cell: the board shows everybody's occupancy for one kind of
+ * resource plus the day you picked, "Meine Buchungen" shows one person's own bookings across all
+ * kinds and has no selected day at all. So the payload stays with the caller, which decorates
+ * these days by MonthDay::key(). gridStart and gridEnd are public precisely so that decoration
+ * can be one range query over the visible window instead of 42 per-day ones.
+ */
+final readonly class MonthGrid
+{
+    private const WEEKS = 6;
+
+    /**
+     * @param list<list<MonthDay>> $weeks
+     */
+    private function __construct(
+        public \DateTimeImmutable $monthStart,
+        public \DateTimeImmutable $gridStart,
+        public \DateTimeImmutable $gridEnd,
+        public array $weeks,
+    ) {
+    }
+
+    /**
+     * The grid containing $date, with "today" injectable so the flags can be tested without
+     * waiting for the calendar to roll over. BookingHorizon::latest() takes the same optional
+     * argument for the same reason.
+     */
+    public static function around(\DateTimeImmutable $date, ?\DateTimeImmutable $today = null): self
+    {
+        $today = ($today ?? new \DateTimeImmutable('today'))->setTime(0, 0);
+
+        $monthStart = $date->setTime(0, 0)->modify('first day of this month');
+        // "monday this week" is a no-op when the month already starts on a Monday, so this is the
+        // whole leading-days calculation -- no weekday arithmetic needed.
+        $gridStart = $monthStart->modify('monday this week');
+
+        $weeks = [];
+        $cursor = $gridStart;
+
+        for ($week = 0; $week < self::WEEKS; ++$week) {
+            $days = [];
+
+            for ($weekday = 0; $weekday < 7; ++$weekday) {
+                $days[] = new MonthDay(
+                    date: $cursor,
+                    inMonth: $cursor->format('Y-m') === $monthStart->format('Y-m'),
+                    isToday: $cursor == $today,
+                    isPast: $cursor < $today,
+                    isWeekend: (int) $cursor->format('N') >= 6,
+                );
+
+                $cursor = $cursor->modify('+1 day');
+            }
+
+            $weeks[] = $days;
+        }
+
+        // The cursor has already stepped past the grid, hence the day back.
+        return new self($monthStart, $gridStart, $cursor->modify('-1 day'), $weeks);
+    }
+}