<?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\Guardian\GuardianService;
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 payer 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,
		private GuardianService $guardians,
	) {}

	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 *payer*, filled as pending payments are created and
		// flushed to a single email at the end, so a payer billed for several
		// lessons on one day is emailed once — never once per lesson, and a guardian
		// gets one notice covering every child rather than one per child. Each entry
		// keeps the created payment and its label; credits are applied across the
		// whole bucket before the notice is built, so the family's account credit
		// offsets the run's charges oldest-first.
		$buckets = [];

		$this->billPrivateLessons( $now, $buckets );
		$this->billGroupEnrollments( $now, $buckets );

		$this->sendNotices( $buckets );
	}

	/**
	 * 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{payment: Payment, label: string}>> $buckets
	 */
	private function billPrivateLessons( \DateTimeImmutable $now, array &$buckets ): 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,
				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 );
	}

	/**
	 * 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{payment: Payment, label: string}>> $buckets
	 */
	private function billMonthlyLessonGroups( string $today, array $monthly, array &$buckets ): 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,
				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{payment: Payment, label: string}>> $buckets
	 */
	private function billGroupEnrollments( \DateTimeImmutable $now, array &$buckets ): 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 );
			} else {
				$this->billGroupWeekly( $now, $enrollment, $offering, $windows, $buckets );
			}
		}
	}

	/**
	 * 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{payment: Payment, label: string}>> $buckets
	 */
	private function billGroupWeekly( \DateTimeImmutable $now, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets ): 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,
				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.
	 *
	 * A monthly group class is priced **per month**, not per session: the fee is
	 * charged once for the month however many times the class meets in it. This is
	 * what the student is quoted and agrees to on the way in ("40.00 CAD monthly"),
	 * and it is the one place the monthly rule differs from private lessons, whose
	 * per-lesson fee is multiplied by the lessons that fall in the month.
	 *
	 * @param list<array{start: string, end: string}> $windows
	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
	 */
	private function billGroupMonthly( \DateTimeImmutable $now, string $today, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets ): void { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
		// Count this enrolment's sessions per calendar month. The count does not
		// price the month — it names it on the student's notice ("3 sessions").
		$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,
				Payment::REG_ENROLLMENT,
				(int) $enrollment->id,
				$enrollment->studentId,
				$enrollment->instructorId,
				$offering->price,
				$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 it to the payer's notice bucket with the label to show on the notice.
	 * Credits are applied later, once the whole bucket is known. Returns the created
	 * payment, or null when there was nothing to charge.
	 *
	 * The charge is bucketed against whoever owes it, so a guardian's notice covers
	 * all their children; the label names the child when that differs from the
	 * payer, or a parent cannot tell whose lesson each line is.
	 *
	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
	 */
	private function bill( array &$buckets, string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $etransferEmail, string $dueDate, string $periodKey, string $label ): ?Payment {
		$payerId = $this->guardians->payerFor( $studentId );
		$payment = $this->payments->createForRegistration( $type, $registrationId, $studentId, $instructorId, $amount, $currency, $etransferEmail, $dueDate, $periodKey, $payerId );

		if ( null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
			$buckets[ $payerId ][] = [
				'payment' => $payment,
				'label'   => $payerId === $studentId ? $label : $this->labelFor( $studentId, $label ),
			];
		}

		return $payment;
	}

	/**
	 * Prefix a notice line with the student it is for — "Ada: Piano Lesson —
	 * Mar 3, 2026" — used only when the payer is not the student.
	 */
	private function labelFor( int $studentId, string $label ): string {
		$name = $this->guardians->studentName( $studentId );

		return '' === $name ? $label : $name . ': ' . $label;
	}

	/**
	 * For each payer, apply any account credit they hold against the run's charges,
	 * tag the payments they still owe with a shared batch reference, and email them
	 * one itemised notice. The notice lists each charge at its full amount, then the
	 * credit applied and the reduced total due; a charge fully covered by credit is
	 * already settled and carries no reference. A lump-sum e-transfer for the balance
	 * reconciles to the reference.
	 *
	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
	 */
	private function sendNotices( array $buckets ): void {
		foreach ( $buckets as $payerId => $entries ) {
			$payments = array_map( static fn( array $entry ): Payment => $entry['payment'], $entries );
			$applied  = $this->payments->applyCredits( $payerId, $payments );

			$items       = [];
			$batchIds    = [];
			$creditTotal = 0.0;

			foreach ( $entries as $entry ) {
				$payment  = $entry['payment'];
				$id       = (int) $payment->id;
				$credited = $applied[ $id ] ?? 0.0;

				$creditTotal += $credited;

				$items[] = [
					'label'           => $entry['label'],
					'amount'          => $payment->total(),
					'currency'        => $payment->currency,
					'due_date'        => $payment->dueDate,
					'etransfer_email' => $payment->etransferEmail,
				];

				// A charge still carrying a balance is what a lump-sum e-transfer covers;
				// one fully settled by credit needs no reconciliation reference.
				if ( round( $payment->total() - $credited, 2 ) > 0.0 ) {
					$batchIds[] = $id;
				}
			}

			$reference = [] !== $batchIds ? $this->reference() : '';
			$this->payments->assignNoticeBatch( $batchIds, $reference );

			$user = get_userdata( $payerId );
			if ( $user instanceof \WP_User ) {
				$this->mailer->send( $user, $items, $reference, round( $creditTotal, 2 ) );
			}
		}
	}

	/**
	 * 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();
	}
}