<?php
declare(strict_types=1);

namespace Unsupervised\Schedular\Availability;

use Unsupervised\Schedular\Offering\OfferingRepository;

/**
 * Validates a submitted availability window.
 *
 * The admin form and the REST endpoint both accept the same window, and used to
 * check it independently — the endpoint returning a specific 400 for each
 * failure while the form simply returned, saving nothing and saying nothing. A
 * 30-minute window submitted with the default 60-minute lesson length was the
 * visible symptom: no rows, no error, no clue. Both callers now come through
 * here, so neither can drift from the other again.
 *
 * Every rejection is a `WP_Error` carrying a message written for the person who
 * submitted the form: the endpoint returns it as-is (the `status` data makes it
 * a 400), and the admin screen shows `get_error_message()` in a notice.
 */
class WindowValidator {

	public function __construct( private OfferingRepository $offerings ) {}

	/**
	 * Check a submitted window and return it ready to persist.
	 *
	 * @param int    $instructorId    Instructor the window belongs to.
	 * @param string $rawStart        Submitted start, in any form {@see AvailabilitySlot::normalizeDateTime()} accepts.
	 * @param string $rawEnd          Submitted end, likewise.
	 * @param int    $durationMinutes Lesson length the window is split into; 0 falls back to the 60-minute default.
	 * @param int    $offeringId      Offering the slots are tied to, or 0 for any private lesson.
	 *
	 * @return AvailabilitySlot|\WP_Error The window, or why it was rejected.
	 */
	public function validate( int $instructorId, string $rawStart, string $rawEnd, int $durationMinutes, int $offeringId ): AvailabilitySlot|\WP_Error {
		$startDt = AvailabilitySlot::normalizeDateTime( $rawStart );
		$endDt   = AvailabilitySlot::normalizeDateTime( $rawEnd );

		if ( null === $startDt || null === $endDt ) {
			return new \WP_Error(
				'invalid_datetime',
				__( 'Enter a valid start and end date and time.', 'unsupervised-schedular' ),
				[ 'status' => 400 ]
			);
		}

		if ( $endDt <= $startDt ) {
			return new \WP_Error(
				'invalid_datetime',
				__( 'The end time must be after the start time.', 'unsupervised-schedular' ),
				[ 'status' => 400 ]
			);
		}

		if ( substr( $startDt, 0, 10 ) !== substr( $endDt, 0, 10 ) ) {
			return new \WP_Error(
				'invalid_window',
				__( 'Availability must start and end on the same day. Use the weekly repeat to cover multiple weeks.', 'unsupervised-schedular' ),
				[ 'status' => 400 ]
			);
		}

		// A slot may only be tied to an offering the instructor owns, so it can
		// never inherit another instructor's price or payment routing at booking.
		if ( $offeringId > 0 ) {
			$offering = $this->offerings->findById( $offeringId );

			if ( null === $offering || $offering->instructorId !== $instructorId ) {
				return new \WP_Error(
					'invalid_offering',
					__( 'That offering is not available.', 'unsupervised-schedular' ),
					[ 'status' => 400 ]
				);
			}
		}

		$duration = $durationMinutes > 0 ? $durationMinutes : AvailabilitySlot::DEFAULT_DURATION_MINUTES;

		$window = new AvailabilitySlot(
			instructorId:    $instructorId,
			startDt:         $startDt,
			endDt:           $endDt,
			durationMinutes: $duration,
			offeringId:      $offeringId > 0 ? $offeringId : null,
		);

		// The window is stored as lesson-length slots, so one that cannot fit a
		// single lesson would persist nothing at all.
		if ( [] === $window->splitByDuration() ) {
			return new \WP_Error(
				'invalid_window',
				sprintf(
					/* translators: %d: the selected lesson length, in minutes. */
					__( 'This window is shorter than the %d-minute lesson length, so it holds no bookable slots. Choose a shorter lesson length or a longer window.', 'unsupervised-schedular' ),
					$duration
				),
				[ 'status' => 400 ]
			);
		}

		return $window;
	}
}