<?php
/**
 * Recurrence rules: sanitizing a submitted rule and turning it into a list of dates. Pure date maths, no database.
 * The free plugin knows one type, "weekly". An add-on adds types through the recurkit_sanitize_rule, recurkit_dates
 * and recurkit_describe_rule filters, and can raise the cap through recurkit_max_occurrences.
 *
 * @package recurkit
 */

defined( 'ABSPATH' ) || exit;

/** Most occurrences one series may have, the event itself included. */
function recurkit_max_occurrences(): int {
	return max( 2, (int) apply_filters( 'recurkit_max_occurrences', 52 ) );
}

/**
 * True for a real calendar date written as Y-m-d.
 *
 * @param mixed $value Candidate.
 */
function recurkit_is_ymd( $value ): bool {
	if ( ! is_string( $value ) || ! preg_match( '/^(\d{4})-(\d{2})-(\d{2})$/', $value, $m ) ) {
		return false;
	}
	return checkdate( (int) $m[2], (int) $m[3], (int) $m[1] );
}

/**
 * A submitted rule (already unslashed) made safe, or null when the box is off or the rule is unusable.
 *
 * @param array $raw Submitted fields.
 * @return array|null
 */
function recurkit_sanitize_rule( array $raw ): ?array {
	if ( empty( $raw['enabled'] ) ) {
		return null;
	}
	$type = isset( $raw['type'] ) && is_string( $raw['type'] ) ? sanitize_key( $raw['type'] ) : 'weekly';
	$rule = 'weekly' === $type ? recurkit_sanitize_weekly( $raw ) : null;
	$rule = apply_filters( 'recurkit_sanitize_rule', $rule, $raw );
	return is_array( $rule ) ? $rule : null;
}

/**
 * The weekly part of recurkit_sanitize_rule().
 *
 * @param array $raw Submitted fields.
 * @return array|null
 */
function recurkit_sanitize_weekly( array $raw ): ?array {
	if ( ! isset( $raw['days'] ) || ! is_array( $raw['days'] ) ) {
		return null;
	}
	$days = array();
	foreach ( $raw['days'] as $day ) {
		$day = is_scalar( $day ) && ctype_digit( (string) $day ) ? (int) $day : 0;
		if ( $day >= 1 && $day <= 7 ) {
			$days[ $day ] = $day;
		}
	}
	if ( ! $days ) {
		return null;
	}
	ksort( $days );
	return recurkit_sanitize_end(
		$raw,
		array(
			'type' => 'weekly',
			'days' => array_values( $days ),
		)
	);
}

/**
 * Adds a valid end (count or until) to $rule, or returns null. Shared with add-on rule types.
 *
 * @param array $raw  Submitted fields.
 * @param array $rule Rule so far.
 * @return array|null
 */
function recurkit_sanitize_end( array $raw, array $rule ): ?array {
	$end = isset( $raw['end'] ) && is_string( $raw['end'] ) ? $raw['end'] : '';
	if ( 'until' === $end ) {
		$until = isset( $raw['until'] ) && is_string( $raw['until'] ) ? $raw['until'] : '';
		if ( ! recurkit_is_ymd( $until ) ) {
			return null;
		}
		$rule['end']   = 'until';
		$rule['until'] = $until;
		return $rule;
	}
	if ( 'count' === $end ) {
		$count = isset( $raw['count'] ) && is_scalar( $raw['count'] ) ? absint( $raw['count'] ) : 0;
		if ( $count < 2 ) {
			return null;
		}
		$rule['end']   = 'count';
		$rule['count'] = min( $count, recurkit_max_occurrences() );
		return $rule;
	}
	return null;
}

/**
 * Every occurrence date of a series, the event's own date first, sorted, unique, capped.
 *
 * @param array  $rule  Sanitized rule.
 * @param string $start The event's start date, Y-m-d.
 * @return string[]
 */
function recurkit_occurrence_dates( array $rule, string $start ): array {
	if ( ! recurkit_is_ymd( $start ) ) {
		return array();
	}
	$dates = ( isset( $rule['type'] ) && 'weekly' === $rule['type'] ) ? recurkit_weekly_dates( $rule, $start ) : array( $start );
	$dates = (array) apply_filters( 'recurkit_dates', $dates, $rule, $start );
	$dates = array_values( array_unique( array_filter( $dates, 'recurkit_is_ymd' ) ) );
	sort( $dates );
	return array_slice( $dates, 0, recurkit_max_occurrences() );
}

/**
 * Dates of a weekly rule. Walks day by day from the start; stops at the count, the until date or the cap.
 *
 * @param array  $rule  Weekly rule.
 * @param string $start Y-m-d.
 * @return string[]
 */
function recurkit_weekly_dates( array $rule, string $start ): array {
	$max   = recurkit_end_count( $rule );
	$until = 'until' === ( $rule['end'] ?? '' ) ? (string) $rule['until'] : '';
	$days  = array_map( 'intval', (array) ( $rule['days'] ?? array() ) );
	$day   = new DateTimeImmutable( $start . ' 00:00:00', new DateTimeZone( 'UTC' ) );
	$dates = array( $start );
	// 7 * cap days is the furthest a series of `cap` weekly dates can reach.
	for ( $i = 1; $i <= 7 * recurkit_max_occurrences() && count( $dates ) < $max; $i++ ) {
		$day = $day->modify( '+1 day' );
		$ymd = $day->format( 'Y-m-d' );
		if ( '' !== $until && $ymd > $until ) {
			break;
		}
		if ( in_array( (int) $day->format( 'N' ), $days, true ) ) {
			$dates[] = $ymd;
		}
	}
	return $dates;
}

/**
 * How many occurrences a rule allows: its count, else the cap.
 *
 * @param array $rule Rule.
 */
function recurkit_end_count( array $rule ): int {
	$cap = recurkit_max_occurrences();
	return 'count' === ( $rule['end'] ?? '' ) ? min( $cap, max( 1, (int) $rule['count'] ) ) : $cap;
}

/**
 * Short human summary of a rule for the Series screen.
 *
 * @param array $rule Rule.
 */
function recurkit_describe_rule( array $rule ): string {
	$text = '';
	if ( 'weekly' === ( $rule['type'] ?? '' ) ) {
		$names = recurkit_weekday_names();
		$days  = array();
		foreach ( (array) $rule['days'] as $d ) {
			$days[] = $names[ (int) $d ] ?? '';
		}
		/* translators: %s: comma-separated weekday names. */
		$text = sprintf( __( 'Weekly on %s', 'recurkit' ), implode( ', ', array_filter( $days ) ) );
	}
	$text = (string) apply_filters( 'recurkit_describe_rule', $text, $rule );
	if ( '' === $text ) {
		$text = __( 'Custom rule', 'recurkit' );
	}
	if ( 'count' === ( $rule['end'] ?? '' ) ) {
		$n = (int) $rule['count'];
		/* translators: 1: rule summary, 2: number of occurrences. */
		return sprintf( _n( '%1$s, %2$d time', '%1$s, %2$d times', $n, 'recurkit' ), $text, $n );
	}
	if ( 'until' === ( $rule['end'] ?? '' ) ) {
		/* translators: 1: rule summary, 2: end date (Y-m-d). */
		return sprintf( __( '%1$s, until %2$s', 'recurkit' ), $text, (string) $rule['until'] );
	}
	return $text;
}

/**
 * Short weekday names keyed by ISO number (1 = Monday).
 *
 * @return string[]
 */
function recurkit_weekday_names(): array {
	return array(
		1 => __( 'Mon', 'recurkit' ),
		2 => __( 'Tue', 'recurkit' ),
		3 => __( 'Wed', 'recurkit' ),
		4 => __( 'Thu', 'recurkit' ),
		5 => __( 'Fri', 'recurkit' ),
		6 => __( 'Sat', 'recurkit' ),
		7 => __( 'Sun', 'recurkit' ),
	);
}