<?php
declare(strict_types=1);

namespace WebCalendar\WP;

defined( 'ABSPATH' ) || exit;

/**
 * The page a visitor should go "Back to Calendar" to.
 *
 * An event page's back link went to the home page (wordpress.org support).
 * Visitors who arrive from the calendar are sent back to it by a small script
 * on the event page; this answers for everyone else (search, social, the
 * sitemap), and is the link's href before that script runs.
 *
 * In order: the page chosen under Settings > Calendar Page; a published page
 * (or else post) that holds the WebCalendar block or [webcalendar] shortcode;
 * the home page. The `webcal_calendar_page_url` filter has the last word.
 */
final class CalendarPageLocator {

	/** Settings > Calendar Page: a page ID, 0 for automatic. */
	public const OPTION = 'webcal_calendar_page';

	/** The detected page ID, 0 when none was found. Cleared on any post save. */
	public const DETECTED_TRANSIENT = 'webcal_calendar_page_detected';

	/**
	 * The URL "Back to Calendar" should link to.
	 */
	public function url(): string {
		$url = $this->chosen() ?? $this->detected() ?? home_url( '/' );

		/**
		 * Filters where "Back to Calendar" on an event page leads.
		 *
		 * @param string $url The chosen or detected calendar page, or the home page.
		 */
		$filtered = apply_filters( 'webcal_calendar_page_url', $url );
		return '' !== $filtered ? $filtered : $url;
	}

	/**
	 * Forget the detected page, so the next lookup sees a page just added,
	 * edited or removed. Hooked to save_post and deleted_post.
	 */
	public function forget_detected(): void {
		delete_transient( self::DETECTED_TRANSIENT );
	}

	/**
	 * The page chosen in Settings, if it is still published.
	 */
	private function chosen(): ?string {
		$raw = get_option( self::OPTION, 0 );
		$id  = is_scalar( $raw ) ? absint( $raw ) : 0;
		if ( $id <= 0 || 'publish' !== get_post_status( $id ) ) {
			return null;
		}
		$url = get_permalink( $id );
		return is_string( $url ) && '' !== $url ? $url : null;
	}

	/**
	 * A published page, or failing that post, that shows the calendar.
	 *
	 * Matches the block and the shortcode with or without attributes, but
	 * not [webcalendar-submit] or [webcalendar-rsvp], which share its prefix.
	 * Cached, including "none found", since every event page asks.
	 */
	private function detected(): ?string {
		global $wpdb;

		$cached = get_transient( self::DETECTED_TRANSIENT );
		if ( is_numeric( $cached ) ) {
			$id = (int) $cached;
		} else {
			$sql = $wpdb->prepare(
				"SELECT ID FROM {$wpdb->posts}
				WHERE post_status = 'publish' AND post_password = ''
				AND post_type IN ('page', 'post')
				AND ( post_content LIKE %s OR post_content LIKE %s OR post_content LIKE %s )
				ORDER BY ( post_type = 'page' ) DESC, menu_order ASC, ID ASC
				LIMIT 1",
				'%' . $wpdb->esc_like( '[webcalendar]' ) . '%',
				'%' . $wpdb->esc_like( '[webcalendar ' ) . '%',
				'%' . $wpdb->esc_like( '<!-- wp:webcalendar/main' ) . '%'
			);
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching, WordPress.DB.PreparedSQL.NotPrepared -- $sql is from $wpdb->prepare() above; cached in a transient.
			$found = is_string( $sql ) ? $wpdb->get_var( $sql ) : null;
			$id    = is_numeric( $found ) ? (int) $found : 0;
			set_transient( self::DETECTED_TRANSIENT, $id, DAY_IN_SECONDS );
		}

		if ( $id <= 0 ) {
			return null;
		}
		$url = get_permalink( $id );
		return is_string( $url ) && '' !== $url ? $url : null;
	}
}