<?php
namespace Advently\Calendar;

defined( 'ABSPATH' ) || exit;

/**
 * When each door opens, and whether a given door may be opened right now.
 *
 * Every door unlocks at 00:00 of its day in the site's timezone. "Now" is
 * always converted into that timezone first, so the visitor's clock and the
 * server's default zone never decide anything.
 */
final class Schedule {

	/** @var \DateTimeImmutable */
	private $start;

	/** @var int */
	private $doors;

	/** @var \DateTimeZone */
	private $tz;

	public function __construct( string $start, int $doors, \DateTimeZone $tz ) {
		$this->tz    = $tz;
		$this->doors = max( 1, $doors );
		$this->start = new \DateTimeImmutable( $start . ' 00:00:00', $tz );
	}

	public function doors(): int {
		return $this->doors;
	}

	public function dateOf( int $n ): \DateTimeImmutable {
		if ( ! $this->valid( $n ) ) {
			throw new \OutOfRangeException( 'Door out of range.' );
		}
		// Calendar-day arithmetic in the local zone keeps 00:00 across DST changes.
		return $this->start->modify( '+' . ( $n - 1 ) . ' days' );
	}

	/**
	 * First moment after the last door's day.
	 */
	public function end(): \DateTimeImmutable {
		return $this->start->modify( '+' . $this->doors . ' days' );
	}

	/**
	 * @return string locked|today|past|ended|invalid
	 */
	public function status( int $n, \DateTimeImmutable $now ): string {
		if ( ! $this->valid( $n ) ) {
			return 'invalid';
		}
		$now = $now->setTimezone( $this->tz );
		if ( $now >= $this->end() ) {
			return 'ended';
		}
		$opens = $this->dateOf( $n );
		if ( $now < $opens ) {
			return 'locked';
		}
		return $now < $opens->modify( '+1 day' ) ? 'today' : 'past';
	}

	/**
	 * @return array<int,string> Door number => status.
	 */
	public function statuses( \DateTimeImmutable $now ): array {
		$all = [];
		for ( $n = 1; $n <= $this->doors; $n++ ) {
			$all[ $n ] = $this->status( $n, $now );
		}
		return $all;
	}

	/**
	 * Whether door $n may be opened now, and whether it still carries its coupon.
	 *
	 * @param string $missedPolicy open|locked|open_no_coupon — anything else is treated as locked.
	 * @return array{allowed:bool, coupon:bool, reason:string}
	 */
	public function decide( int $n, \DateTimeImmutable $now, string $missedPolicy ): array {
		$status = $this->status( $n, $now );

		switch ( $status ) {
			case 'today':
				return self::verdict( true, true, 'today' );
			case 'past':
				if ( 'open' === $missedPolicy ) {
					return self::verdict( true, true, 'past' );
				}
				if ( 'open_no_coupon' === $missedPolicy ) {
					return self::verdict( true, false, 'past' );
				}
				return self::verdict( false, false, 'missed' );
			default:
				return self::verdict( false, false, $status );
		}
	}

	public function nextUnlock( \DateTimeImmutable $now ): ?\DateTimeImmutable {
		$now = $now->setTimezone( $this->tz );
		for ( $n = 1; $n <= $this->doors; $n++ ) {
			$opens = $this->dateOf( $n );
			if ( $opens > $now ) {
				return $opens;
			}
		}
		return null;
	}

	private function valid( int $n ): bool {
		return $n >= 1 && $n <= $this->doors;
	}

	private static function verdict( bool $allowed, bool $coupon, string $reason ): array {
		return [
			'allowed' => $allowed,
			'coupon'  => $coupon,
			'reason'  => $reason,
		];
	}
}