<?php
/**
 * Optional alert when new critical check results appear.
 *
 * @package Keepwatch
 */

namespace Keepwatch\Mail;

use Keepwatch\Admin\Menu;
use Keepwatch\Checks\Registry;
use Keepwatch\Checks\Result;
use Keepwatch\Settings;

defined( 'ABSPATH' ) || exit;

/**
 * Hourly scan compares the set of critical result IDs to the last notified set.
 */
final class CriticalAlert {

	public const HOOK               = 'keepwatch_scan_alerts';
	public const OPTION_FINGERPRINT = 'keepwatch_critical_fingerprint';

	/**
	 * Register cron callback.
	 */
	public function register(): void {
		add_action( self::HOOK, array( $this, 'scan' ) );
	}

	/**
	 * Schedule hourly scan when missing.
	 */
	public static function schedule(): void {
		if ( ! wp_next_scheduled( self::HOOK ) ) {
			wp_schedule_event( time() + HOUR_IN_SECONDS, 'hourly', self::HOOK );
		}
	}

	/**
	 * Clear schedule.
	 */
	public static function unschedule(): void {
		wp_clear_scheduled_hook( self::HOOK );
	}

	/**
	 * Run checks and mail when the critical set grows with new IDs.
	 */
	public function scan(): void {
		if ( ! Settings::critical_email_enabled() ) {
			return;
		}

		$to = Settings::weekly_email_recipient();
		if ( '' === $to || ! is_email( $to ) ) {
			return;
		}

		$groups  = Registry::run( Registry::checks() );
		$current = self::critical_ids( $groups );
		$prev    = get_option( self::OPTION_FINGERPRINT, array() );
		if ( ! is_array( $prev ) ) {
			$prev = array();
		}

		$new = array_values( array_diff( $current, $prev ) );
		update_option( self::OPTION_FINGERPRINT, $current, false );

		if ( array() === $new ) {
			return;
		}

		$labels  = self::labels_for_ids( $groups, $new );
		$subject = sprintf(
			/* translators: 1: site name, 2: number of new critical issues */
			__( '[Keepwatch] %1$s: %2$d new critical issue(s)', 'keepwatch' ),
			wp_specialchars_decode( get_bloginfo( 'name' ), ENT_QUOTES ),
			count( $new )
		);

		$lines   = array();
		$lines[] = __( 'Keepwatch found new critical issues on this site:', 'keepwatch' );
		$lines[] = '';
		foreach ( $labels as $label ) {
			$lines[] = '[!] ' . $label;
		}
		$lines[] = '';
		$lines[] = sprintf(
			/* translators: %s: dashboard URL */
			__( 'Open Keepwatch: %s', 'keepwatch' ),
			admin_url( 'tools.php?page=' . Menu::SLUG )
		);
		$lines[] = __( 'You can turn critical alerts off under Tools > Keepwatch > Email alerts.', 'keepwatch' );

		wp_mail( $to, $subject, implode( "\n", $lines ) );
	}

	/**
	 * Critical result IDs, sorted.
	 *
	 * @param array<string, Result[]> $groups Grouped results.
	 * @return string[]
	 */
	public static function critical_ids( array $groups ): array {
		$ids = array();
		foreach ( $groups as $results ) {
			foreach ( $results as $result ) {
				if ( Result::CRITICAL === $result->status ) {
					$ids[] = $result->id;
				}
			}
		}
		$ids = array_values( array_unique( $ids ) );
		sort( $ids );
		return $ids;
	}

	/**
	 * Labels for selected IDs.
	 *
	 * @param array<string, Result[]> $groups Grouped results.
	 * @param string[]                $ids    Result IDs.
	 * @return string[]
	 */
	public static function labels_for_ids( array $groups, array $ids ): array {
		$wanted = array_fill_keys( $ids, true );
		$labels = array();
		foreach ( $groups as $results ) {
			foreach ( $results as $result ) {
				if ( isset( $wanted[ $result->id ] ) ) {
					$labels[] = $result->label;
				}
			}
		}
		return $labels;
	}
}