Split availability windows into bookable lesson-length slots with weekly calendar views

Availability windows were stored and served as a single bookable row, so a
9:00 AM-4:00 PM window showed to students as one giant slot and booking it
consumed the whole day; past and multi-day windows also leaked into the
booking page as nonsense entries.

- Split windows into consecutive lesson-length slots on save (REST and admin
  form); each chunk is independently bookable and weekly recurrence creates a
  series per chunk so "reserve this time weekly" holds the same hour each week
- Reject windows spanning multiple days or shorter than the lesson length
  (400 invalid_window)
- Never return slots whose start has passed from GET /availability
- Migrate pre-split rows: Plugin::boot re-runs the Installer on version change
  and AvailabilityRepository::splitOversizedWindows() rewrites unbooked
  same-day oversized windows in place
- Display all times in 12-hour AM/PM form (booking page, wp-admin lists,
  editor previews)
- Add a List | Week view toggle to the student booking page and the
  instructor availability page, with previous/next-week navigation honouring
  the site's start_of_week option (new WeekCalendar helper)

Co-Authored-By: Claude Fable 5 <[email protected]>

tests/Unit/Availability/AvailabilityRepositoryTest.php

@@ -147,11 +147,16 @@ class AvailabilityRepositoryTest extends TestCase
         self::assertFalse($this->repo->delete(1));
     }
 
-    public function testFindAvailableWithNoFiltersPreparesTableOnly(): void
+    public function testFindAvailableWithNoFiltersExcludesPastSlots(): void
     {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
         $this->db->shouldReceive('prepare')
             ->once()
-            ->with(Mockery::pattern('/WHERE is_booked = 0/'), ['wp_us_availability'])
+            ->with(
+                Mockery::pattern('/WHERE is_booked = 0 AND start_dt >= %s/'),
+                ['wp_us_availability', '2026-07-05 12:00:00']
+            )
             ->andReturn('SELECT ...');
 
         $this->db->shouldReceive('get_results')
@@ -166,6 +171,8 @@ class AvailabilityRepositoryTest extends TestCase
 
     public function testFindAvailableWithInstructorFilterPreparesQuery(): void
     {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
         $this->db->shouldReceive('prepare')
             ->once()
             ->with(Mockery::pattern('/instructor_id = %d/'), Mockery::any())
@@ -178,11 +185,13 @@ class AvailabilityRepositoryTest extends TestCase
 
     public function testFindAvailableWithOfferingAndDurationFilters(): void
     {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
         $this->db->shouldReceive('prepare')
             ->once()
             ->with(
                 Mockery::pattern('/offering_id = %d AND duration_minutes = %d/'),
-                Mockery::on(static fn (array $p): bool => $p === ['wp_us_availability', 8, 30])
+                Mockery::on(static fn (array $p): bool => $p === ['wp_us_availability', '2026-07-05 12:00:00', 8, 30])
             )
             ->andReturn('SELECT ...');
 
@@ -191,6 +200,118 @@ class AvailabilityRepositoryTest extends TestCase
         $this->repo->findAvailable(offeringId: 8, durationMinutes: 30);
     }
 
+    public function testCreateFromWindowInsertsOneRowPerLessonLengthChunk(): void
+    {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
+        $captured = [];
+        $ids      = [21, 22, 23];
+
+        $this->db->shouldReceive('insert')
+            ->times(3)
+            ->andReturnUsing(function (string $table, array $data) use (&$captured, &$ids): void {
+                $captured[] = [$data['start_dt'], $data['end_dt']];
+                $this->db->insert_id = array_shift($ids);
+            });
+
+        $window = new AvailabilitySlot(5, '2026-07-06 09:00:00', '2026-07-06 12:00:00', 60);
+        $result = $this->repo->createFromWindow($window);
+
+        self::assertSame([21, 22, 23], $result);
+        self::assertSame(
+            [
+                ['2026-07-06 09:00:00', '2026-07-06 10:00:00'],
+                ['2026-07-06 10:00:00', '2026-07-06 11:00:00'],
+                ['2026-07-06 11:00:00', '2026-07-06 12:00:00'],
+            ],
+            $captured
+        );
+    }
+
+    public function testCreateFromWindowWeeklyCreatesASeriesPerChunk(): void
+    {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
+        $captured = [];
+        $ids      = [30, 31, 40, 41];
+
+        // Two chunks × two weeks: each chunk becomes its own weekly series.
+        $this->db->shouldReceive('insert')
+            ->times(4)
+            ->andReturnUsing(function (string $table, array $data) use (&$captured, &$ids): void {
+                $captured[] = $data['start_dt'];
+                $this->db->insert_id = array_shift($ids);
+            });
+
+        // Each series back-fills its first row with its own recurrence group.
+        $this->db->shouldReceive('update')
+            ->once()
+            ->with('wp_us_availability', ['recurrence_group' => 30], ['id' => 30], ['%d'], ['%d']);
+        $this->db->shouldReceive('update')
+            ->once()
+            ->with('wp_us_availability', ['recurrence_group' => 40], ['id' => 40], ['%d'], ['%d']);
+
+        $window = new AvailabilitySlot(5, '2026-07-06 09:00:00', '2026-07-06 11:00:00', 60);
+        $result = $this->repo->createFromWindow($window, weekly: true, weeks: 2);
+
+        self::assertSame([30, 31, 40, 41], $result);
+        self::assertSame(
+            [
+                '2026-07-06 09:00:00',
+                '2026-07-13 09:00:00',
+                '2026-07-06 10:00:00',
+                '2026-07-13 10:00:00',
+            ],
+            $captured
+        );
+    }
+
+    public function testSplitOversizedWindowsTrimsRowAndInsertsRemainingChunks(): void
+    {
+        Functions\when('current_time')->justReturn('2026-07-05 12:00:00');
+
+        $row = (object) [
+            'id'               => '9',
+            'instructor_id'    => '5',
+            'offering_id'      => null,
+            'start_dt'         => '2026-07-06 09:00:00',
+            'end_dt'           => '2026-07-06 12:00:00',
+            'duration_minutes' => '60',
+            'is_booked'        => '0',
+            'recurrence_group' => null,
+        ];
+
+        $this->db->shouldReceive('prepare')
+            ->once()
+            ->with(Mockery::pattern('/TIMESTAMPDIFF\(MINUTE, start_dt, end_dt\) > duration_minutes/'), 'wp_us_availability')
+            ->andReturn('SELECT ...');
+        $this->db->shouldReceive('get_results')->once()->with('SELECT ...')->andReturn([$row]);
+
+        // The original row is trimmed to the first lesson-length chunk.
+        $this->db->shouldReceive('update')
+            ->once()
+            ->with('wp_us_availability', ['end_dt' => '2026-07-06 10:00:00'], ['id' => 9], ['%s'], ['%d']);
+
+        // The remaining two chunks become new rows.
+        $inserted = [];
+        $this->db->shouldReceive('insert')
+            ->times(2)
+            ->andReturnUsing(function (string $table, array $data) use (&$inserted): void {
+                $inserted[] = [$data['start_dt'], $data['end_dt']];
+                $this->db->insert_id = 50;
+            });
+
+        $this->repo->splitOversizedWindows();
+
+        self::assertSame(
+            [
+                ['2026-07-06 10:00:00', '2026-07-06 11:00:00'],
+                ['2026-07-06 11:00:00', '2026-07-06 12:00:00'],
+            ],
+            $inserted
+        );
+    }
+
     public function testFindByInstructorReturnsSlots(): void
     {
         $row = (object) [