<?php
/**
 * Scheduler heartbeat and staleness detection.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Application\Notification;

use Bookline\Domain\Notification\NotificationLogRepository;
use Bookline\Domain\Notification\NotificationStatus;
use Bookline\Domain\Notification\OutboundGuard;
use Bookline\Domain\Shared\Clock;
use Bookline\Infrastructure\Notification\SmtpPluginDetector;
use Bookline\Infrastructure\Scheduling\JobScheduler;
use DateInterval;
use DateTimeImmutable;

/**
 * Records heartbeats and exposes health snapshots for admin + REST.
 *
 * @since 0.1.0
 */
final class HealthMonitor {

	public const HEARTBEAT_HOOK     = 'bookline/heartbeat';
	public const HEARTBEAT_OPTION   = 'bookline_heartbeat_at';
	public const STALE_AFTER_SECONDS = 900;

	/**
	 * Constructor.
	 *
	 * @param JobScheduler              $jobs  Jobs.
	 * @param NotificationLogRepository $logs  Logs.
	 * @param Clock                     $clock Clock.
	 * @param SmtpPluginDetector|null   $smtp  SMTP plugin detector.
	 */
	public function __construct(
		private readonly JobScheduler $jobs,
		private readonly NotificationLogRepository $logs,
		private readonly Clock $clock,
		private readonly ?SmtpPluginDetector $smtp = null,
	) {}

	/**
	 * Ensure the recurring heartbeat action exists.
	 *
	 * @since 0.1.0
	 */
	public function ensure_scheduled(): void {
		$this->jobs->schedule_recurring( self::HEARTBEAT_HOOK, 5 * 60, 'bookline' );
	}

	/**
	 * Record a heartbeat timestamp.
	 *
	 * @since 0.1.0
	 */
	public function beat(): void {
		$now = $this->clock->now()->setTimezone( new \DateTimeZone( 'UTC' ) )->format( DATE_ATOM );
		if ( function_exists( 'update_option' ) ) {
			update_option( self::HEARTBEAT_OPTION, $now, false );
			return;
		}
		$GLOBALS['bookline_heartbeat_at'] = $now;
	}

	/**
	 * Last heartbeat instant, if any.
	 *
	 * @since 0.1.0
	 */
	public function last_heartbeat(): ?DateTimeImmutable {
		$raw = function_exists( 'get_option' )
			? get_option( self::HEARTBEAT_OPTION, null )
			: ( $GLOBALS['bookline_heartbeat_at'] ?? null );
		if ( ! is_string( $raw ) || '' === $raw ) {
			return null;
		}
		$dt = DateTimeImmutable::createFromFormat( DATE_ATOM, $raw );
		return false === $dt ? null : $dt;
	}

	/**
	 * Whether the heartbeat is stale (>15 minutes).
	 *
	 * @since 0.1.0
	 */
	public function is_stale(): bool {
		$last = $this->last_heartbeat();
		if ( null === $last ) {
			return true;
		}
		$threshold = $this->clock->now()->sub( new DateInterval( 'PT' . self::STALE_AFTER_SECONDS . 'S' ) );
		return $last < $threshold;
	}

	/**
	 * Health payload for GET /admin/health.
	 *
	 * @return array<string, mixed>
	 *
	 * @since 0.1.0
	 */
	public function snapshot(): array {
		$last           = $this->last_heartbeat();
		$stale          = $this->is_stale();
		$scheduler_ok   = $this->jobs->is_available();
		$queue_depth    = $this->jobs->pending_count( 'bookline' );
		$failed_recent = $this->logs->count_by_status( NotificationStatus::Failed );
		$outbound_live = OutboundGuard::allows_outbound();
		$smtp_label    = null !== $this->smtp ? $this->smtp->active_label() : null;

		$fix = null;
		if ( $stale ) {
			$fix = 'Bookline’s scheduler heartbeat is more than 15 minutes old. Ensure WP-Cron is running, or add `*/5 * * * * cd ' . ( defined( 'ABSPATH' ) ? ABSPATH : '/path/to/wordpress' ) . ' && wp cron event run --due-now` to system crontab. If DISABLE_WP_CRON is true, you must trigger cron externally.';
		} elseif ( ! $outbound_live ) {
			$fix = 'Outbound mail is drafted, not sent. Release zips send by default. Add define( \'BOOKLINE_ALLOW_OUTBOUND\', false ); to wp-config.php only when you want draft-first, or define it as true if a previous install turned it off. Bookline uses wp_mail — install an SMTP plugin for reliable delivery.';
		}

		return [
			'status'          => $stale ? 'degraded' : 'ok',
			'heartbeat'       => null === $last ? null : $last->format( DATE_ATOM ),
			'heartbeat_stale' => $stale,
			'scheduler'       => [
				'available' => $scheduler_ok,
				'pending'   => $queue_depth,
				'failed'    => $this->jobs->failed_count( 'bookline' ),
			],
			'notifications'   => [
				'drafted' => $this->logs->count_by_status( NotificationStatus::Drafted ),
				'queued'  => $this->logs->count_by_status( NotificationStatus::Queued ),
				'failed'  => $failed_recent,
				'sent'    => $this->logs->count_by_status( NotificationStatus::Sent ),
			],
			// Admin SPA aliases (docs/08 §2.2, §2.13).
			'cron_healthy'    => ! $stale && $scheduler_ok,
			'db_healthy'      => true,
			'email_healthy'   => true,
			'outbound_live'   => $outbound_live,
			'smtp_plugin'     => $smtp_label,
			'queue_depth'     => $queue_depth,
			'failed_recent'   => $failed_recent,
			'fix_guidance'    => $fix,
		];
	}
}