<?php
/**
 * Date helpers.
 *
 * @package Recast\WCS
 */

namespace Recast\WCS\Support;

defined( 'ABSPATH' ) || exit;

/**
 * Timezone-safe date arithmetic for subscription schedules. Never adds raw seconds across days.
 */
final class Dates {

	/**
	 * Site timezone.
	 *
	 * @return \DateTimeZone
	 */
	public static function site_tz() {
		return wp_timezone();
	}

	/**
	 * Parses a GMT 'Y-m-d H:i:s' string (or '0') into a site-timezone DateTimeImmutable.
	 *
	 * @param string $gmt GMT string.
	 * @return \DateTimeImmutable|null Null for '0' / empty.
	 */
	public static function from_gmt( $gmt ) {
		if ( ! $gmt ) {
			return null; // Covers '' and '0' (no date).
		}
		$utc = \DateTimeImmutable::createFromFormat( 'Y-m-d H:i:s', $gmt, new \DateTimeZone( 'UTC' ) );
		return $utc ? $utc->setTimezone( self::site_tz() ) : null;
	}

	/**
	 * Formats a DateTimeImmutable as a GMT 'Y-m-d H:i:s' string.
	 *
	 * @param \DateTimeImmutable $date Date.
	 * @return string
	 */
	public static function to_gmt( \DateTimeImmutable $date ) {
		return $date->setTimezone( new \DateTimeZone( 'UTC' ) )->format( 'Y-m-d H:i:s' );
	}

	/**
	 * Parses a site-timezone 'Y-m-d H:i' string.
	 *
	 * @param string $local Local string.
	 * @return \DateTimeImmutable|null
	 */
	public static function from_site( $local ) {
		$date = \DateTimeImmutable::createFromFormat( 'Y-m-d H:i', $local, self::site_tz() );
		return $date ? $date : null;
	}

	/**
	 * Shifts by days and calendar months (month arithmetic clamps to the month's last day).
	 *
	 * @param \DateTimeImmutable $date   Date.
	 * @param int                $days   Days (signed).
	 * @param int                $months Months (signed).
	 * @return \DateTimeImmutable
	 */
	public static function shift( \DateTimeImmutable $date, $days = 0, $months = 0 ) {
		if ( 0 !== (int) $months ) {
			$day   = (int) $date->format( 'j' );
			$first = $date->setDate( (int) $date->format( 'Y' ), (int) $date->format( 'n' ), 1 );
			$moved = $first->modify( sprintf( '%+d months', (int) $months ) );
			$last  = (int) $moved->format( 't' );
			$date  = $moved->setDate( (int) $moved->format( 'Y' ), (int) $moved->format( 'n' ), min( $day, $last ) );
		}
		if ( 0 !== (int) $days ) {
			$date = $date->modify( sprintf( '%+d days', (int) $days ) );
		}
		return $date;
	}

	/**
	 * Moves a date to a given day of the month, keeping (or zeroing) the time of day, and rolling
	 * forward month by month until it is at least $lead_hours after $now.
	 *
	 * @param \DateTimeImmutable $current       Current date (site tz).
	 * @param int|string         $day           1..31 or 'last'.
	 * @param \DateTimeImmutable $now           Now (site tz).
	 * @param bool               $preserve_time Keep the time of day.
	 * @param int                $lead_hours    Minimum lead.
	 * @return \DateTimeImmutable
	 */
	public static function anchor_to_day( \DateTimeImmutable $current, $day, \DateTimeImmutable $now, $preserve_time = true, $lead_hours = 24 ) {
		$candidate = $preserve_time ? $current : $current->setTime( 0, 0, 0 );
		$candidate = self::set_day( $candidate, $day );
		$floor     = $now->modify( sprintf( '+%d hours', max( 0, (int) $lead_hours ) ) );
		$guard     = 0;
		while ( $candidate < $floor && $guard++ < 24 ) {
			$candidate = self::set_day( self::shift( $candidate->setDate( (int) $candidate->format( 'Y' ), (int) $candidate->format( 'n' ), 1 ), 0, 1 ), $day );
			if ( ! $preserve_time ) {
				$candidate = $candidate->setTime( 0, 0, 0 );
			} else {
				$candidate = $candidate->setTime( (int) $current->format( 'G' ), (int) $current->format( 'i' ), (int) $current->format( 's' ) );
			}
		}
		return $candidate;
	}

	/**
	 * Sets the day of month with clamping.
	 *
	 * @param \DateTimeImmutable $date Date.
	 * @param int|string         $day  1..31 or 'last'.
	 * @return \DateTimeImmutable
	 */
	public static function set_day( \DateTimeImmutable $date, $day ) {
		$last = (int) $date->format( 't' );
		$d    = 'last' === $day ? $last : min( max( 1, (int) $day ), $last );
		return $date->setDate( (int) $date->format( 'Y' ), (int) $date->format( 'n' ), $d );
	}

	/**
	 * Validates subscription date ordering. Returns an error code or null.
	 *
	 * @param array<string, int> $ts start, trial_end, next_payment, end as timestamps (0 = none).
	 * @return string|null
	 */
	public static function validate_order( array $ts ) {
		$start = isset( $ts['start'] ) ? (int) $ts['start'] : 0;
		$trial = isset( $ts['trial_end'] ) ? (int) $ts['trial_end'] : 0;
		$next  = isset( $ts['next_payment'] ) ? (int) $ts['next_payment'] : 0;
		$end   = isset( $ts['end'] ) ? (int) $ts['end'] : 0;
		if ( $trial && $start && $trial < $start ) {
			return 'trial_before_start';
		}
		if ( $next && $trial && $next < $trial ) {
			return 'next_payment_before_trial_end';
		}
		if ( $next && $start && $next < $start ) {
			return 'next_payment_before_start';
		}
		if ( $end && $next && $end <= $next ) {
			return 'end_not_after_next_payment';
		}
		if ( $end && $trial && $end <= $trial ) {
			return 'end_not_after_trial_end';
		}
		return null;
	}

	/**
	 * Human message for a validate_order() code.
	 *
	 * @param string $code Code.
	 * @return string
	 */
	public static function order_message( $code ) {
		$messages = array(
			'trial_before_start'            => __( 'The trial end is before the start date.', 'recast-subscriptions' ),
			'next_payment_before_trial_end' => __( 'The next payment is before the trial end.', 'recast-subscriptions' ),
			'next_payment_before_start'     => __( 'The next payment is before the start date.', 'recast-subscriptions' ),
			'end_not_after_next_payment'    => __( 'The end date must be after the next payment.', 'recast-subscriptions' ),
			'end_not_after_trial_end'       => __( 'The end date must be after the trial end.', 'recast-subscriptions' ),
		);
		return isset( $messages[ $code ] ) ? $messages[ $code ] : $code;
	}
}