Add weekly and monthly scheduled billing for offerings

Offerings can now bill weekly (a pending payment 24h before each lesson)
or monthly (one payment on the 1st for that month's lessons), alongside
one-time and full-term. Applies to both private lessons and group classes.

- Offering: new `weekly`/`monthly` billing modes + `isScheduledBilling()`
- Booking/enrolment defer payment for scheduled modes; a single lesson
  booked after its due date has passed (e.g. an add-on in an already-billed
  month) is charged at booking instead
- ScheduledBillingRunner: daily WP-Cron scan generates due payments across
  four cases (private/group × weekly/monthly), deduped via lesson.payment_id
  and payments.period_key
- PaymentDueMailer: one consolidated itemised email per student per scan
- Notice batch: payments emailed together share a reference; the admin
  Payments queue groups them with a lump-sum total for e-transfer reconciliation
- Cancellation never voids a scheduled payment (Payment::isScheduled())
- Schema: us_payments gains due_date, period_key, notice_batch; USC_VERSION 1.2.0

composer test, composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/Payment/Payment.php

@@ -44,6 +44,9 @@ class Payment {
 		public readonly string $status = self::STATUS_PENDING,
 		public readonly float $taxRate = 0.0,
 		public readonly float $taxAmount = 0.0,
+		public readonly ?string $dueDate = null,
+		public readonly ?string $periodKey = null,
+		public readonly ?string $noticeBatch = null,
 		public readonly ?string $etransferEmail = null,
 		public readonly ?string $stripePaymentIntentId = null,
 		public readonly ?string $receiptNumber = null,
@@ -65,6 +68,9 @@ class Payment {
 			status:                Val::string( $row->status ),
 			taxRate:               Val::float( $row->tax_rate ),
 			taxAmount:             Val::float( $row->tax_amount ),
+			dueDate:               Val::stringOrNull( $row->due_date ?? null ),
+			periodKey:             Val::stringOrNull( $row->period_key ?? null ),
+			noticeBatch:           Val::stringOrNull( $row->notice_batch ?? null ),
 			etransferEmail:        Val::stringOrNull( $row->etransfer_email ),
 			stripePaymentIntentId: Val::stringOrNull( $row->stripe_payment_intent_id ),
 			receiptNumber:         Val::stringOrNull( $row->receipt_number ),
@@ -79,6 +85,15 @@ class Payment {
 		return self::STATUS_PAID === $this->status;
 	}
 
+	/**
+	 * Whether this payment was generated by the daily billing scan (weekly /
+	 * monthly) rather than taken at registration. Scheduled payments carry a due
+	 * date, can cover several lessons, and are never auto-voided on cancellation.
+	 */
+	public function isScheduled(): bool {
+		return null !== $this->dueDate;
+	}
+
 	/**
 	 * Amount billed including tax.
 	 */
@@ -120,6 +135,9 @@ class Payment {
 			'currency'          => $this->currency,
 			'method'            => $this->method,
 			'status'            => $this->status,
+			'due_date'          => $this->dueDate,
+			'period_key'        => $this->periodKey,
+			'notice_batch'      => $this->noticeBatch,
 			'receipt_number'    => $this->receiptNumber,
 			'paid_at'           => $this->paidAt,
 			'created_at'        => $this->createdAt,

src/Payment/PaymentController.php

@@ -33,22 +33,59 @@ class PaymentController {
 			}
 		}
 
-		$rows = array_map(
-			static function ( Payment $payment ): array {
-				$student = get_userdata( $payment->studentId );
-
-				return [
-					'id'              => (int) $payment->id,
-					'student'         => $student ? $student->display_name : (string) $payment->studentId,
-					'amount'          => number_format( $payment->amount, 2 ) . ' ' . $payment->currency,
-					'method'          => $payment->method,
-					'for'             => $payment->registrationType . ' #' . $payment->registrationId,
-					'etransfer_email' => (string) $payment->etransferEmail,
-				];
-			},
-			$this->payments->findPending()
-		);
+		$groups = $this->groupPending( $this->payments->findPending() );
 
 		include USC_PLUGIN_DIR . 'templates/admin/payments.php';
 	}
+
+	/**
+	 * Group pending payments by their shared notice batch, so payments the daily
+	 * scan emailed a student together (and which a single lump-sum e-transfer
+	 * covers) are shown as one group with a combined total. Payments with no batch
+	 * — legacy at-registration e-transfers — are each their own single-item group.
+	 *
+	 * @param list<Payment> $pending
+	 * @return list<array{reference: string, is_group: bool, total: string, rows: list<array{id: int, student: string, amount: string, method: string, for: string, etransfer_email: string}>}>
+	 */
+	private function groupPending( array $pending ): array {
+		$groups = [];
+
+		foreach ( $pending as $payment ) {
+			$batch = (string) $payment->noticeBatch;
+			$key   = '' !== $batch ? 'b:' . $batch : 's:' . (string) $payment->id;
+
+			if ( ! isset( $groups[ $key ] ) ) {
+				$groups[ $key ] = [
+					'reference' => $batch,
+					'currency'  => $payment->currency,
+					'total_raw' => 0.0,
+					'rows'      => [],
+				];
+			}
+
+			$student = get_userdata( $payment->studentId );
+
+			$groups[ $key ]['total_raw'] += $payment->total();
+			$groups[ $key ]['rows'][]     = [
+				'id'              => (int) $payment->id,
+				'student'         => $student ? $student->display_name : (string) $payment->studentId,
+				'amount'          => number_format( $payment->amount, 2 ) . ' ' . $payment->currency,
+				'method'          => $payment->method,
+				'for'             => $payment->registrationType . ' #' . $payment->registrationId,
+				'etransfer_email' => (string) $payment->etransferEmail,
+			];
+		}
+
+		return array_values(
+			array_map(
+				static fn( array $group ): array => [
+					'reference' => $group['reference'],
+					'is_group'  => count( $group['rows'] ) > 1,
+					'total'     => number_format( $group['total_raw'], 2 ) . ' ' . $group['currency'],
+					'rows'      => $group['rows'],
+				],
+				$groups
+			)
+		);
+	}
 }

src/Payment/PaymentDueMailer.php

@@ -0,0 +1,92 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+/**
+ * Emails a student a single itemised notice for every payment the daily billing
+ * scan generated for them in one run, so a student billed for several lessons on
+ * the same day receives one email with a line per item and a grand total — never
+ * one email per lesson.
+ */
+class PaymentDueMailer {
+
+	/**
+	 * Send one student their consolidated due-payment notice for the current scan.
+	 * The optional `$reference` is the shared notice-batch code the student can quote
+	 * on a lump-sum e-transfer so the studio can reconcile it to these payments.
+	 *
+	 * @param list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}> $items
+	 * @return bool False when there is no recipient or nothing to bill.
+	 */
+	public function send( \WP_User $student, array $items, string $reference = '' ): bool {
+		if ( '' === (string) $student->user_email || [] === $items ) {
+			return false;
+		}
+
+		$currency = (string) $items[0]['currency'];
+		$total    = 0.0;
+		$lines    = [];
+		$emails   = [];
+
+		foreach ( $items as $item ) {
+			$amount = (float) $item['amount'];
+			$total += $amount;
+
+			$lines[] = sprintf(
+				/* translators: 1: item description, 2: due date, 3: currency, 4: amount */
+				__( '- %1$s (due %2$s): %3$s %4$s', 'unsupervised-schedular' ),
+				(string) $item['label'],
+				$this->formatDate( $item['due_date'] ?? null ),
+				$currency,
+				number_format( $amount, 2 )
+			);
+
+			$etransfer = (string) ( $item['etransfer_email'] ?? '' );
+			if ( '' !== $etransfer ) {
+				$emails[ $etransfer ] = true;
+			}
+		}
+
+		$body = __( 'You have upcoming payments due:', 'unsupervised-schedular' ) . "\n\n"
+			. implode( "\n", $lines ) . "\n\n"
+			. sprintf(
+				/* translators: 1: currency, 2: total amount */
+				__( 'Total due: %1$s %2$s', 'unsupervised-schedular' ),
+				$currency,
+				number_format( $total, 2 )
+			);
+
+		if ( [] !== $emails ) {
+			$body .= "\n\n" . sprintf(
+				/* translators: %s: e-transfer destination email address(es) */
+				__( 'Please send your e-transfer to: %s', 'unsupervised-schedular' ),
+				implode( ', ', array_keys( $emails ) )
+			);
+		}
+
+		if ( '' !== $reference ) {
+			$body .= "\n\n" . sprintf(
+				/* translators: %s: payment reference code */
+				__( 'Please include this reference with your payment: %s', 'unsupervised-schedular' ),
+				$reference
+			);
+		}
+
+		return (bool) wp_mail( $student->user_email, __( 'Payment due', 'unsupervised-schedular' ), $body );
+	}
+
+	/**
+	 * Present a stored `Y-m-d` due date in a friendlier form; falls back to the
+	 * raw value (or an empty string) when it is not a parseable date.
+	 */
+	private function formatDate( ?string $date ): string {
+		if ( null === $date || '' === $date ) {
+			return '';
+		}
+
+		$parsed = \DateTimeImmutable::createFromFormat( '!Y-m-d', $date );
+
+		return false !== $parsed ? $parsed->format( 'M j, Y' ) : $date;
+	}
+}

src/Payment/PaymentRepository.php

@@ -25,6 +25,9 @@ class PaymentRepository {
 				'status'                   => $payment->status,
 				'tax_rate'                 => $payment->taxRate,
 				'tax_amount'               => $payment->taxAmount,
+				'due_date'                 => $payment->dueDate,
+				'period_key'               => $payment->periodKey,
+				'notice_batch'             => $payment->noticeBatch,
 				'etransfer_email'          => $payment->etransferEmail,
 				'stripe_payment_intent_id' => $payment->stripePaymentIntentId,
 				'receipt_number'           => $payment->receiptNumber,
@@ -32,7 +35,7 @@ class PaymentRepository {
 				'paid_at'                  => $payment->paidAt,
 				'created_at'               => current_time( 'mysql' ),
 			],
-			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s' ]
+			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s' ]
 		);
 
 		return $this->db->insert_id;
@@ -119,6 +122,51 @@ class PaymentRepository {
 		return $row ? Payment::fromRow( $row ) : null;
 	}
 
+	/**
+	 * Tag a set of payments with a shared notice-batch reference — the payments the
+	 * daily scan emailed a student together, so the admin can see which pending
+	 * payments a single lump-sum e-transfer covers. No-op for an empty id list.
+	 *
+	 * @param list<int> $ids
+	 */
+	public function assignNoticeBatch( array $ids, string $batch ): void {
+		if ( [] === $ids ) {
+			return;
+		}
+
+		$placeholders = implode( ', ', array_fill( 0, count( $ids ), '%d' ) );
+		$sql          = $this->db->prepare(
+			"UPDATE %i SET notice_batch = %s WHERE id IN ( {$placeholders} )",
+			$this->table,
+			$batch,
+			...$ids
+		);
+
+		if ( null !== $sql ) {
+			$this->db->query( $sql );
+		}
+	}
+
+	/**
+	 * Whether a scheduled payment already exists for a registration and billing
+	 * period. The daily billing scan uses this to avoid double-billing an
+	 * enrolment for the same session (weekly) or month (monthly). A voided
+	 * (`failed`) row still counts so a cancelled charge is not silently re-created.
+	 */
+	public function existsForPeriod( string $registrationType, int $registrationId, string $periodKey ): bool {
+		$found = $this->db->get_var(
+			$this->db->prepare(
+				'SELECT id FROM %i WHERE registration_type = %s AND registration_id = %d AND period_key = %s LIMIT 1',
+				$this->table,
+				$registrationType,
+				$registrationId,
+				$periodKey
+			)
+		);
+
+		return null !== $found;
+	}
+
 	public function findByRegistration( string $registrationType, int $registrationId ): ?Payment {
 		$row = $this->db->get_row(
 			$this->db->prepare(

src/Payment/PaymentService.php

@@ -29,8 +29,12 @@ class PaymentService {
 	 * (card via Stripe — coming soon; e-transfer confirmed manually). The
 	 * e-transfer destination is frozen now from the offering override or the studio
 	 * default. Returns null when the registration has no price to charge.
+	 *
+	 * A `$dueDate`/`$periodKey` mark a payment generated later by the daily billing
+	 * scan (weekly / monthly) rather than taken at registration; both stay null for
+	 * the pay-now flow.
 	 */
-	public function createForRegistration( string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $offeringEtransferEmail = null ): ?Payment {
+	public function createForRegistration( string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $offeringEtransferEmail = null, ?string $dueDate = null, ?string $periodKey = null ): ?Payment {
 		if ( $amount <= 0.0 ) {
 			return null;
 		}
@@ -58,6 +62,8 @@ class PaymentService {
 				status:           $status,
 				taxRate:          $taxRate,
 				taxAmount:        $taxAmount,
+				dueDate:          $dueDate,
+				periodKey:        $periodKey,
 				etransferEmail:   $etransferEmail,
 			)
 		);
@@ -71,6 +77,26 @@ class PaymentService {
 		return $this->payments->findById( $id );
 	}
 
+	/**
+	 * Whether a scheduled payment already exists for a registration and billing
+	 * period — the daily billing scan's dedup check for group enrolments (whose one
+	 * row maps to many periodic charges). Delegates to the ledger.
+	 */
+	public function scheduledPaymentExists( string $type, int $registrationId, string $periodKey ): bool {
+		return $this->payments->existsForPeriod( $type, $registrationId, $periodKey );
+	}
+
+	/**
+	 * Tag the payments the daily scan emailed a student together with a shared
+	 * notice-batch reference, so a lump-sum e-transfer can be reconciled to the
+	 * pending payments it covers. Delegates to the ledger.
+	 *
+	 * @param list<int> $ids
+	 */
+	public function assignNoticeBatch( array $ids, string $batch ): void {
+		$this->payments->assignNoticeBatch( $ids, $batch );
+	}
+
 	/**
 	 * Studio-admin confirmation that a pending payment (e-transfer) was received.
 	 * Marks it paid, confirms the registration, and emails the receipt.
@@ -92,7 +118,10 @@ class PaymentService {
 	/**
 	 * Void the still-pending payment of a cancelled registration so it drops
 	 * out of the confirmation queue. Paid payments are left alone — refunds
-	 * are a manual, admin-side decision.
+	 * are a manual, admin-side decision. Scheduled payments (weekly / monthly)
+	 * are also left alone: a monthly charge can cover several lessons and may
+	 * already be collected, so cancelling one lesson must never void it or
+	 * trigger a rebill.
 	 */
 	public function voidPending( ?int $paymentId ): void {
 		if ( null === $paymentId ) {
@@ -100,7 +129,7 @@ class PaymentService {
 		}
 
 		$payment = $this->payments->findById( $paymentId );
-		if ( null !== $payment && Payment::STATUS_PENDING === $payment->status ) {
+		if ( null !== $payment && ! $payment->isScheduled() && Payment::STATUS_PENDING === $payment->status ) {
 			$this->payments->updateStatus( $paymentId, Payment::STATUS_FAILED );
 		}
 	}

src/Payment/ScheduledBillingRunner.php

@@ -0,0 +1,365 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+use Unsupervised\Schedular\Booking\BookingRepository;
+use Unsupervised\Schedular\GroupClass\Enrollment;
+use Unsupervised\Schedular\GroupClass\EnrollmentRepository;
+use Unsupervised\Schedular\Offering\Offering;
+use Unsupervised\Schedular\Offering\OfferingRepository;
+use Unsupervised\Schedular\Val;
+
+/**
+ * Generates the pending payments that scheduled-billing offerings (weekly /
+ * monthly) owe as they come due, then emails each student one itemised notice.
+ *
+ * Runs from the daily WP-Cron action `us_generate_due_payments`. It is
+ * self-healing: every run re-scans from the current ledger state, so a missed
+ * day is simply picked up the next time. Dedup keeps a second run from
+ * double-billing — private lessons via `us_lessons.payment_id`, group enrolments
+ * via `us_payments.period_key`.
+ */
+class ScheduledBillingRunner {
+
+	public const HOOK = 'us_generate_due_payments';
+
+	public function __construct(
+		private PaymentService $payments,
+		private BookingRepository $bookings,
+		private EnrollmentRepository $enrollments,
+		private OfferingRepository $offerings,
+		private PaymentDueMailer $mailer,
+	) {}
+
+	public function register(): void {
+		add_action( self::HOOK, [ $this, 'run' ] );
+	}
+
+	/**
+	 * Generate every payment now due and send the consolidated notices.
+	 */
+	public function run(): void {
+		$now = $this->now();
+
+		// One notice bucket per student, filled as pending payments are created and
+		// flushed to a single email at the end, so a student billed for several
+		// lessons on one day is emailed once — never once per lesson. $batchIds
+		// tracks the payment ids behind each student's bucket so they can be tagged
+		// with a shared reference for lump-sum e-transfer reconciliation.
+		$buckets  = [];
+		$batchIds = [];
+
+		$this->billPrivateLessons( $now, $buckets, $batchIds );
+		$this->billGroupEnrollments( $now, $buckets, $batchIds );
+
+		$this->sendNotices( $buckets, $batchIds );
+	}
+
+	/**
+	 * Private-lesson billing. Weekly lessons are billed one payment each once they
+	 * are within 24 hours; monthly lessons are grouped per calendar month and billed
+	 * one payment for the month once its 1st has arrived.
+	 *
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function billPrivateLessons( \DateTimeImmutable $now, array &$buckets, array &$batchIds ): void {
+		$today   = $now->format( 'Y-m-d' );
+		$monthly = [];
+
+		foreach ( $this->bookings->findUnbilledScheduledLessons() as $row ) {
+			$price = Val::float( $row->price ?? 0 );
+			if ( $price <= 0.0 ) {
+				continue;
+			}
+
+			$startRaw = Val::string( $row->start_dt ?? '' );
+			$start    = false !== strtotime( $startRaw ) ? new \DateTimeImmutable( $startRaw ) : null;
+			if ( null === $start ) {
+				continue;
+			}
+
+			$lessonId     = Val::int( $row->id );
+			$studentId    = Val::int( $row->student_id );
+			$instructorId = Val::int( $row->instructor_id );
+			$currency     = Val::string( $row->currency ?? 'CAD' );
+			$etransfer    = Val::stringOrNull( $row->etransfer_email ?? null );
+			$title        = Val::string( $row->title ?? '' );
+
+			if ( Offering::BILLING_MONTHLY === Val::string( $row->billing_mode ?? '' ) ) {
+				$monthly[ $studentId . ':' . Val::int( $row->offering_id ) . ':' . $start->format( 'Y-m' ) ][] = [
+					'lesson_id'     => $lessonId,
+					'student_id'    => $studentId,
+					'instructor_id' => $instructorId,
+					'currency'      => $currency,
+					'etransfer'     => $etransfer,
+					'title'         => $title,
+					'price'         => $price,
+					'start'         => $start,
+				];
+				continue;
+			}
+
+			// Weekly: due 24 hours before the lesson.
+			$due = $start->modify( '-1 day' );
+			if ( $due->format( 'Y-m-d H:i:s' ) > $now->format( 'Y-m-d H:i:s' ) ) {
+				continue;
+			}
+
+			$this->bill(
+				$buckets,
+				$batchIds,
+				Payment::REG_LESSON,
+				$lessonId,
+				$studentId,
+				$instructorId,
+				$price,
+				$currency,
+				$etransfer,
+				$due->format( 'Y-m-d' ),
+				$start->format( 'Y-m-d' ),
+				$title . ' — ' . $start->format( 'M j, Y' )
+			);
+		}
+
+		$this->billMonthlyLessonGroups( $today, $monthly, $buckets, $batchIds );
+	}
+
+	/**
+	 * Bill each month's worth of monthly private lessons as one payment (count ×
+	 * fee), once the month's 1st has arrived. The payment links to the earliest
+	 * lesson in the group; the rest are pointed at it so they are not re-billed.
+	 *
+	 * @param array<string, list<array{lesson_id: int, student_id: int, instructor_id: int, currency: string, etransfer: ?string, title: string, price: float, start: \DateTimeImmutable}>> $monthly
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function billMonthlyLessonGroups( string $today, array $monthly, array &$buckets, array &$batchIds ): void {
+		foreach ( $monthly as $group ) {
+			$first      = $group[0]['start'];
+			$monthStart = $first->format( 'Y-m-01' );
+
+			// Not billable until the 1st of the lesson's month has arrived.
+			if ( $monthStart > $today ) {
+				continue;
+			}
+
+			$lessonIds = array_map( static fn( array $l ): int => $l['lesson_id'], $group );
+			$anchorId  = $lessonIds[0];
+			$count     = count( $group );
+
+			$payment = $this->bill(
+				$buckets,
+				$batchIds,
+				Payment::REG_LESSON,
+				$anchorId,
+				$group[0]['student_id'],
+				$group[0]['instructor_id'],
+				$group[0]['price'] * $count,
+				$group[0]['currency'],
+				$group[0]['etransfer'],
+				$monthStart,
+				$first->format( 'Y-m' ),
+				sprintf(
+					/* translators: 1: offering title, 2: month, 3: number of lessons */
+					_n( '%1$s (%2$s): %3$d lesson', '%1$s (%2$s): %3$d lessons', $count, 'unsupervised-schedular' ),
+					$group[0]['title'],
+					$first->format( 'F Y' ),
+					$count
+				)
+			);
+
+			if ( null === $payment ) {
+				continue;
+			}
+
+			// createForRegistration links the anchor; point the rest of the month at
+			// the same payment so the next scan sees them as billed.
+			foreach ( array_slice( $lessonIds, 1 ) as $extraId ) {
+				$this->bookings->setPaymentId( $extraId, (int) $payment->id );
+			}
+		}
+	}
+
+	/**
+	 * Group-class billing off each active enrolment's concrete session windows.
+	 * Weekly bills one payment per session (24h before); monthly bills one payment
+	 * per month (on the 1st) for that month's sessions. Dedup is by `period_key`
+	 * since a single enrolment maps to many periodic charges.
+	 *
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function billGroupEnrollments( \DateTimeImmutable $now, array &$buckets, array &$batchIds ): void {
+		$today     = $now->format( 'Y-m-d' );
+		$offerings = [];
+
+		foreach ( $this->enrollments->findActiveByBillingModes( Offering::SCHEDULED_BILLING_MODES ) as $enrollment ) {
+			$offeringId = $enrollment->offeringId;
+			if ( ! array_key_exists( $offeringId, $offerings ) ) {
+				$offerings[ $offeringId ] = $this->offerings->findById( $offeringId );
+			}
+			$offering = $offerings[ $offeringId ];
+			if ( null === $offering || $offering->price <= 0.0 ) {
+				continue;
+			}
+
+			$windows = $offering->sessionWindows();
+			if ( [] === $windows ) {
+				continue;
+			}
+
+			if ( Offering::BILLING_MONTHLY === $offering->billingMode ) {
+				$this->billGroupMonthly( $now, $today, $enrollment, $offering, $windows, $buckets, $batchIds );
+			} else {
+				$this->billGroupWeekly( $now, $enrollment, $offering, $windows, $buckets, $batchIds );
+			}
+		}
+	}
+
+	/**
+	 * Bill one payment per group-class session that is now within 24 hours.
+	 *
+	 * @param list<array{start: string, end: string}> $windows
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function billGroupWeekly( \DateTimeImmutable $now, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets, array &$batchIds ): void {
+		foreach ( $windows as $window ) {
+			$start = new \DateTimeImmutable( $window['start'] );
+			$due   = $start->modify( '-1 day' );
+			if ( $due->format( 'Y-m-d H:i:s' ) > $now->format( 'Y-m-d H:i:s' ) ) {
+				continue;
+			}
+
+			$periodKey = $start->format( 'Y-m-d' );
+			if ( $this->payments->scheduledPaymentExists( Payment::REG_ENROLLMENT, (int) $enrollment->id, $periodKey ) ) {
+				continue;
+			}
+
+			$this->bill(
+				$buckets,
+				$batchIds,
+				Payment::REG_ENROLLMENT,
+				(int) $enrollment->id,
+				$enrollment->studentId,
+				$enrollment->instructorId,
+				$offering->price,
+				$offering->currency,
+				$offering->etransferEmail,
+				$due->format( 'Y-m-d' ),
+				$periodKey,
+				$offering->title . ' — ' . $start->format( 'M j, Y' )
+			);
+		}
+	}
+
+	/**
+	 * Bill one payment per calendar month of a group class, once its 1st arrives.
+	 *
+	 * @param list<array{start: string, end: string}> $windows
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function billGroupMonthly( \DateTimeImmutable $now, string $today, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets, array &$batchIds ): void { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
+		// Count this enrolment's sessions per calendar month.
+		$months = [];
+		foreach ( $windows as $window ) {
+			$start                             = new \DateTimeImmutable( $window['start'] );
+			$months[ $start->format( 'Y-m' ) ] = ( $months[ $start->format( 'Y-m' ) ] ?? 0 ) + 1;
+		}
+
+		foreach ( $months as $month => $count ) {
+			$monthStart = ( new \DateTimeImmutable( $month . '-01' ) )->format( 'Y-m-d' );
+			if ( $monthStart > $today ) {
+				continue;
+			}
+
+			if ( $this->payments->scheduledPaymentExists( Payment::REG_ENROLLMENT, (int) $enrollment->id, $month ) ) {
+				continue;
+			}
+
+			$this->bill(
+				$buckets,
+				$batchIds,
+				Payment::REG_ENROLLMENT,
+				(int) $enrollment->id,
+				$enrollment->studentId,
+				$enrollment->instructorId,
+				$offering->price * $count,
+				$offering->currency,
+				$offering->etransferEmail,
+				$monthStart,
+				$month,
+				sprintf(
+					/* translators: 1: offering title, 2: month, 3: number of sessions */
+					_n( '%1$s (%2$s): %3$d session', '%1$s (%2$s): %3$d sessions', $count, 'unsupervised-schedular' ),
+					$offering->title,
+					( new \DateTimeImmutable( $month . '-01' ) )->format( 'F Y' ),
+					$count
+				)
+			);
+		}
+	}
+
+	/**
+	 * Create one scheduled payment and, when it is pending (not a comp auto-pay),
+	 * add an itemised line to the student's notice bucket and record its payment id
+	 * for the shared notice batch. Returns the created payment, or null when there
+	 * was nothing to charge.
+	 *
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function bill( array &$buckets, array &$batchIds, string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $etransferEmail, string $dueDate, string $periodKey, string $label ): ?Payment {
+		$payment = $this->payments->createForRegistration( $type, $registrationId, $studentId, $instructorId, $amount, $currency, $etransferEmail, $dueDate, $periodKey );
+
+		if ( null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
+			$buckets[ $studentId ][]  = [
+				'label'           => $label,
+				'amount'          => $payment->total(),
+				'currency'        => $payment->currency,
+				'due_date'        => $payment->dueDate,
+				'etransfer_email' => $payment->etransferEmail,
+			];
+			$batchIds[ $studentId ][] = $payment->id;
+		}
+
+		return $payment;
+	}
+
+	/**
+	 * Tag each student's payments with a shared batch reference and email them one
+	 * itemised notice quoting it, so a lump-sum e-transfer can be reconciled to the
+	 * exact pending payments it covers.
+	 *
+	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
+	 * @param array<int, list<int>> $batchIds
+	 */
+	private function sendNotices( array $buckets, array $batchIds ): void {
+		foreach ( $buckets as $studentId => $items ) {
+			$reference = $this->reference();
+			$this->payments->assignNoticeBatch( $batchIds[ $studentId ] ?? [], $reference );
+
+			$user = get_userdata( $studentId );
+			if ( $user instanceof \WP_User ) {
+				$this->mailer->send( $user, $items, $reference );
+			}
+		}
+	}
+
+	/**
+	 * A short, human-quotable reference shared by every payment in one student's
+	 * notice, printed on the email and shown in the admin payments queue.
+	 */
+	private function reference(): string {
+		return strtoupper( substr( str_replace( '-', '', Val::string( wp_generate_uuid4() ) ), 0, 10 ) );
+	}
+
+	private function now(): \DateTimeImmutable {
+		$mysql = Val::string( current_time( 'mysql' ) );
+
+		return false !== strtotime( $mysql ) ? new \DateTimeImmutable( $mysql ) : new \DateTimeImmutable();
+	}
+}