fix: allow booking the free part of a partly booked day

tests/Booking/TimeRangeTest.php

@@ -83,6 +83,57 @@ class TimeRangeTest extends TestCase
         yield 'out of range is rejected' => ['25:00', '26:00', null];
     }
 
+    public function testRemainingIsTheWholeSpanWhenNothingIsTaken(): void
+    {
+        $free = TimeRange::remaining(TimeRange::wholeDay(), []);
+
+        self::assertSame(['00:00–24:00'], self::render($free));
+    }
+
+    public function testRemainingSplitsAroundABookingInTheMiddle(): void
+    {
+        $free = TimeRange::remaining(TimeRange::wholeDay(), [TimeRange::fromMinutes(540, 780)]);
+
+        self::assertSame(['00:00–09:00', '13:00–24:00'], self::render($free));
+    }
+
+    public function testRemainingIsEmptyWhenTheSpanIsFullyCovered(): void
+    {
+        self::assertSame([], TimeRange::remaining(TimeRange::wholeDay(), [TimeRange::wholeDay()]));
+    }
+
+    public function testRemainingHandlesOverlappingAndUnsortedInput(): void
+    {
+        // Bookings on one resource cannot overlap, but the span may be covered by several that
+        // touch, and nothing guarantees the order they arrive in.
+        $free = TimeRange::remaining(TimeRange::wholeDay(), [
+            TimeRange::fromMinutes(780, 1020),
+            TimeRange::fromMinutes(540, 900),
+        ]);
+
+        self::assertSame(['00:00–09:00', '17:00–24:00'], self::render($free));
+    }
+
+    public function testRemainingIgnoresWhatFallsOutsideTheSpan(): void
+    {
+        $free = TimeRange::remaining(TimeRange::fromMinutes(780, 1020), [TimeRange::fromMinutes(0, 540)]);
+
+        self::assertSame(['13:00–17:00'], self::render($free));
+    }
+
+    public function testRemainingClipsABookingThatOverhangsTheSpan(): void
+    {
+        $free = TimeRange::remaining(TimeRange::fromMinutes(480, 1080), [TimeRange::fromMinutes(0, 600)]);
+
+        self::assertSame(['10:00–18:00'], self::render($free));
+    }
+
+    public function testDurationIsInMinutes(): void
+    {
+        self::assertSame(240, TimeRange::fromMinutes(540, 780)->durationInMinutes());
+        self::assertSame(1440, TimeRange::wholeDay()->durationInMinutes());
+    }
+
     /**
      * Regression guard for a trap that cost real debugging time: Twig resolves `range.allDay` by
      * looking for a method literally named `allDay` BEFORE it tries `isAllDay()`, and it happily
@@ -97,4 +148,14 @@ class TimeRangeTest extends TestCase
         self::assertSame('no', $twig->render('t', ['range' => TimeRange::fromMinutes(9 * 60, 13 * 60)]));
         self::assertSame('yes', $twig->render('t', ['range' => TimeRange::wholeDay()]));
     }
+
+    /**
+     * @param list<TimeRange> $ranges
+     *
+     * @return list<string>
+     */
+    private static function render(array $ranges): array
+    {
+        return array_map(static fn (TimeRange $range): string => $range->start().'–'.$range->end(), $ranges);
+    }
 }