Let parents register once and book for their children

A parent registers once and manages lessons for one or more children, who
need no login of their own. A child is a real wp_users row with the student
role but no usable login — so student_id keeps meaning "a WordPress user"
on every table, and booking, credits, policies and enrolments work unchanged.
A us_guardians link table maps guardian to child.

The signup form gains a parent/guardian tick that reveals a block per child,
with the account-signup questions asked per child rather than per guardian
— they describe the student, not the account holder. Signup policies are
recorded once per child with the guardian as the acceptor, which is the
record that actually means something. A family that half-creates is rolled
back entirely rather than leaving a guardian who cannot re-register.

The booking and enrolment forms gain a "Who is this for?" picker listing
children first, so the default selection is never the parent — booking for
the wrong child is correctable, quietly billing a parent for their kid's
lesson is not. POST /bookings and POST /enrollments take an optional
student_id honoured only for that child's guardian; anything else is a 403.
That check is the authorisation boundary of the feature.

Payments and credits gain a payer: the charge names the child it was for and
the guardian who owes it, so per-child reporting is unchanged while notices,
receipts and the payment step reach the parent. Credit is held by the payer,
so one child's cancellation can settle a sibling's charge, and the daily
billing scan sends a guardian one notice covering every child.

Closes #132

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

tests/Unit/Payment/PaymentServiceTest.php

@@ -65,7 +65,7 @@ class PaymentServiceTest extends TestCase
 
     private function payment(string $method, string $status, int $id): Payment
     {
-        return new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, 'CAD', $method, $status, id: $id);
+        return new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, currency: 'CAD', method: $method, status: $status, id: $id);
     }
 
     public function testFreeRegistrationCreatesNoPayment(): void
@@ -85,7 +85,7 @@ class PaymentServiceTest extends TestCase
     {
         // A scheduled (weekly/monthly) payment can cover several lessons and may be
         // collected: cancelling one lesson must never void it or trigger a rebill.
-        $scheduled = new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PENDING, dueDate: '2026-07-14', id: 60);
+        $scheduled = new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, dueDate: '2026-07-14', id: 60);
         $this->payments->shouldReceive('findById')->with(60)->andReturn($scheduled);
         $this->payments->shouldNotReceive('updateStatus');
 
@@ -252,7 +252,7 @@ class PaymentServiceTest extends TestCase
 
     public function testCreateIntentForEtransferReturnsDisplayDataWithoutStripe(): void
     {
-        $payment = new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PENDING, etransferEmail: '[email protected]', id: 91);
+        $payment = new Payment(5, 3, Payment::REG_LESSON, 12, 35.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, etransferEmail: '[email protected]', id: 91);
         $this->payments->shouldReceive('findByRegistration')->with(Payment::REG_LESSON, 12)->andReturn($payment);
 
         $this->stripe->shouldNotReceive('createIntent');
@@ -348,7 +348,7 @@ class PaymentServiceTest extends TestCase
     public function testCreditForCancelledLessonCreditsWholeTotalOfSingleLessonPayment(): void
     {
         // A paid single-lesson payment: the whole total (incl. tax) is credited.
-        $paid = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PAID, taxRate: 10.0, taxAmount: 3.00, id: 12);
+        $paid = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PAID, taxRate: 10.0, taxAmount: 3.00, id: 12);
         $this->payments->shouldReceive('findById')->with(12)->andReturn($paid);
         $this->bookings->shouldReceive('countByPaymentId')->with(12)->andReturn(1);
         $this->credits->shouldReceive('existsForLesson')->with(77)->andReturn(false);
@@ -361,7 +361,7 @@ class PaymentServiceTest extends TestCase
                 && $c->sourceLessonId === 77))
             ->andReturn(300);
         $this->credits->shouldReceive('findById')->with(300)->andReturn(
-            new Credit(5, 33.00, 33.00, 'CAD', 12, 77, id: 300)
+            new Credit(5, 33.00, 33.00, currency: 'CAD', sourcePaymentId: 12, sourceLessonId: 77, id: 300)
         );
 
         $lesson = new Lesson(slotId: 10, studentId: 5, instructorId: 3, status: Lesson::STATUS_CANCELLED, paymentId: 12, id: 77);
@@ -371,7 +371,7 @@ class PaymentServiceTest extends TestCase
     public function testCreditForCancelledLessonSplitsSharedMonthlyPayment(): void
     {
         // A monthly scheduled charge covering 3 lessons: one cancellation credits a third.
-        $paid = new Payment(5, 3, Payment::REG_LESSON, 201, 90.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PAID, dueDate: '2026-07-01', id: 12);
+        $paid = new Payment(5, 3, Payment::REG_LESSON, 201, 90.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PAID, dueDate: '2026-07-01', id: 12);
         $this->payments->shouldReceive('findById')->with(12)->andReturn($paid);
         $this->bookings->shouldReceive('countByPaymentId')->with(12)->andReturn(3);
         $this->credits->shouldReceive('existsForLesson')->with(202)->andReturn(false);
@@ -380,7 +380,7 @@ class PaymentServiceTest extends TestCase
             ->once()
             ->with(Mockery::on(static fn (Credit $c): bool => $c->amount === 30.00))
             ->andReturn(301);
-        $this->credits->shouldReceive('findById')->with(301)->andReturn(new Credit(5, 30.00, 30.00, 'CAD', 12, 202, id: 301));
+        $this->credits->shouldReceive('findById')->with(301)->andReturn(new Credit(5, 30.00, 30.00, currency: 'CAD', sourcePaymentId: 12, sourceLessonId: 202, id: 301));
 
         $lesson = new Lesson(slotId: 10, studentId: 5, instructorId: 3, status: Lesson::STATUS_CANCELLED, paymentId: 12, id: 202);
         self::assertNotNull($this->service->creditForCancelledLesson($lesson));
@@ -388,7 +388,7 @@ class PaymentServiceTest extends TestCase
 
     public function testCreditForCancelledLessonSkipsUnpaidPayment(): void
     {
-        $pending = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PENDING, id: 12);
+        $pending = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, id: 12);
         $this->payments->shouldReceive('findById')->with(12)->andReturn($pending);
         $this->credits->shouldNotReceive('insert');
 
@@ -406,7 +406,7 @@ class PaymentServiceTest extends TestCase
 
     public function testCreditForCancelledLessonSkipsAlreadyCredited(): void
     {
-        $paid = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PAID, id: 12);
+        $paid = new Payment(5, 3, Payment::REG_LESSON, 77, 30.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PAID, id: 12);
         $this->payments->shouldReceive('findById')->with(12)->andReturn($paid);
         $this->bookings->shouldReceive('countByPaymentId')->with(12)->andReturn(1);
         $this->credits->shouldReceive('existsForLesson')->with(77)->andReturn(true);
@@ -420,7 +420,7 @@ class PaymentServiceTest extends TestCase
     {
         // A non-anchor series lesson has no payment_id of its own; the anchor's
         // upfront (unscheduled) payment covers the whole 4-lesson series.
-        $anchorPayment = new Payment(5, 3, Payment::REG_LESSON, 40, 120.00, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PAID, id: 12);
+        $anchorPayment = new Payment(5, 3, Payment::REG_LESSON, 40, 120.00, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PAID, id: 12);
         $this->payments->shouldReceive('findByRegistration')->with(Payment::REG_LESSON, 40)->andReturn($anchorPayment);
         $this->payments->shouldReceive('findById')->with(12)->andReturn($anchorPayment);
         $this->bookings->shouldReceive('countBySeries')->with(40)->andReturn(4);
@@ -430,7 +430,7 @@ class PaymentServiceTest extends TestCase
             ->once()
             ->with(Mockery::on(static fn (Credit $c): bool => $c->amount === 30.00))
             ->andReturn(302);
-        $this->credits->shouldReceive('findById')->with(302)->andReturn(new Credit(5, 30.00, 30.00, 'CAD', 12, 43, id: 302));
+        $this->credits->shouldReceive('findById')->with(302)->andReturn(new Credit(5, 30.00, 30.00, currency: 'CAD', sourcePaymentId: 12, sourceLessonId: 43, id: 302));
 
         $lesson = new Lesson(slotId: 10, studentId: 5, instructorId: 3, recurrence: Lesson::RECURRENCE_WEEKLY, seriesId: 40, paymentId: null, id: 43);
         self::assertNotNull($this->service->creditForCancelledLesson($lesson));
@@ -487,7 +487,7 @@ class PaymentServiceTest extends TestCase
 
     private function pending(int $id, float $amount): Payment
     {
-        return new Payment(5, 3, Payment::REG_LESSON, 12, $amount, 'CAD', Payment::METHOD_ETRANSFER, Payment::STATUS_PENDING, dueDate: '2026-07-14', id: $id);
+        return new Payment(5, 3, Payment::REG_LESSON, 12, $amount, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, dueDate: '2026-07-14', id: $id);
     }
 
     private function intentEvent(string $type, string $intentId): \Stripe\Event
@@ -496,4 +496,85 @@ class PaymentServiceTest extends TestCase
 
         return \Stripe\Event::constructFrom(['type' => $type, 'data' => ['object' => $intent]]);
     }
+
+    /**
+     * The billing method resolves against the payer, so comping or card-billing a
+     * family is one setting on the guardian rather than one per child.
+     */
+    public function testCreateForRegistrationResolvesTheBillingMethodAgainstThePayer(): void
+    {
+        $this->resolver->shouldReceive('resolve')->once()->with(5)->andReturn(Payment::METHOD_ETRANSFER);
+        $this->settings->shouldReceive('etransferEmail')->andReturn('');
+        $this->settings->shouldReceive('hstRate')->andReturn(0.0);
+
+        $this->payments->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Payment $p): bool => $p->studentId === 42 && $p->payerId === 5))
+            ->andReturn(90);
+        $this->bookings->shouldReceive('setPaymentId')->once();
+        $this->payments->shouldReceive('findById')->with(90)->andReturn(
+            new Payment(42, 3, Payment::REG_LESSON, 12, 35.00, payerId: 5, id: 90)
+        );
+
+        $payment = $this->service->createForRegistration(Payment::REG_LESSON, 12, 42, 3, 35.00, 'CAD', payerId: 5);
+
+        self::assertSame(5, $payment?->payerId);
+    }
+
+    /**
+     * A credit earned by a child lands on the guardian's balance, so one child's
+     * cancellation can settle a sibling's next charge.
+     */
+    public function testCancelledChildLessonCreditsTheGuardiansBalance(): void
+    {
+        $lesson = new Lesson(slotId: 10, studentId: 42, instructorId: 3, paymentId: 12, id: 77);
+        $paid   = new Payment(42, 3, Payment::REG_LESSON, 77, 30.00, payerId: 5, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PAID, id: 12);
+
+        $this->payments->shouldReceive('findById')->with(12)->andReturn($paid);
+        $this->credits->shouldReceive('existsForLesson')->with(77)->andReturn(false);
+        $this->bookings->shouldReceive('countByPaymentId')->with(12)->andReturn(1);
+
+        $this->credits->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Credit $c): bool => $c->studentId === 42 && $c->payerId === 5 && $c->amount === 30.0))
+            ->andReturn(300);
+        $this->credits->shouldReceive('findById')->with(300)->andReturn(
+            new Credit(42, 30.00, 30.00, payerId: 5, id: 300)
+        );
+
+        self::assertNotNull($this->service->creditForCancelledLesson($lesson));
+    }
+
+    public function testApplyCreditsDrawsDownThePayersBalanceAcrossChildrensCharges(): void
+    {
+        $this->credits->shouldReceive('availableBalance')->with(5)->andReturn(60.0);
+
+        $adasCharge  = new Payment(42, 3, Payment::REG_LESSON, 12, 30.00, payerId: 5, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, dueDate: '2026-07-14', id: 91);
+        $alansCharge = new Payment(43, 3, Payment::REG_LESSON, 13, 30.00, payerId: 5, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, dueDate: '2026-07-14', id: 92);
+
+        $this->payments->shouldReceive('addCreditApplied')->once()->with(91, 30.0);
+        $this->payments->shouldReceive('addCreditApplied')->once()->with(92, 30.0);
+        $this->payments->shouldReceive('markPaid')->twice();
+        $this->bookings->shouldReceive('findById')->andReturn(null);
+        $this->bookings->shouldReceive('updateStatus')->twice();
+        $this->credits->shouldReceive('consume')->once()->with(5, 60.0);
+
+        $applied = $this->service->applyCredits(5, [$adasCharge, $alansCharge]);
+
+        self::assertSame([91 => 30.0, 92 => 30.0], $applied);
+    }
+
+    /**
+     * A guardian paying for their child's lesson must reach the payment step;
+     * anyone else must not.
+     */
+    public function testCreateIntentIsAllowedForBothTheStudentAndTheirPayer(): void
+    {
+        $payment = new Payment(42, 3, Payment::REG_LESSON, 12, 35.00, payerId: 5, currency: 'CAD', method: Payment::METHOD_ETRANSFER, status: Payment::STATUS_PENDING, id: 91);
+        $this->payments->shouldReceive('findByRegistration')->andReturn($payment);
+
+        self::assertNotNull($this->service->createIntent(Payment::REG_LESSON, 12, 42));
+        self::assertNotNull($this->service->createIntent(Payment::REG_LESSON, 12, 5));
+        self::assertNull($this->service->createIntent(Payment::REG_LESSON, 12, 99));
+    }
 }