<?php

declare(strict_types=1);

namespace WebCalendar\WP;

defined( 'ABSPATH' ) || exit;

use WebCalendarDeps\Psr\Log\LoggerInterface;

/**
 * Queues outbound emails for deferred sending via WP-Cron.
 *
 * Instead of sending emails synchronously during REST requests (blocking
 * the response until SMTP completes), emails are stored in a wp_option
 * and processed by a WP-Cron event every 5 minutes.
 */
class EmailQueue {

	private const OPTION_KEY = 'webcal_email_queue';
	private const CRON_HOOK  = 'webcal_process_email_queue';

	/**
	 * @var LoggerInterface
	 */
	private $logger;

	/**
	 * Constructor.
	 *
	 * @param LoggerInterface $logger Logger instance.
	 */
	public function __construct( LoggerInterface $logger ) {
		$this->logger = $logger;
	}

	/**
	 * Register the cron hook and schedule.
	 */
	public function register(): void {
		add_action( self::CRON_HOOK, [ $this, 'process' ] );

		if ( ! wp_next_scheduled( self::CRON_HOOK ) ) {
			wp_schedule_event( time(), 'webcal_five_minutes', self::CRON_HOOK );
		}

		add_filter( 'cron_schedules', [ $this, 'add_cron_schedule' ] );
	}

	/**
	 * Add a 5-minute cron schedule.
	 *
	 * @param array<string, array<string, mixed>> $schedules Existing schedules.
	 * @return array<string, array<string, mixed>>
	 */
	public function add_cron_schedule( array $schedules ): array {
		if ( ! isset( $schedules['webcal_five_minutes'] ) ) {
			$schedules['webcal_five_minutes'] = [
				'interval' => 300,
				'display'  => __( 'Every 5 Minutes', 'agenticdaisy-calendar' ),
			];
		}
		return $schedules;
	}

	/**
	 * Add an email to the queue.
	 *
	 * @param string $to      Recipient email address.
	 * @param string $subject Email subject.
	 * @param string $body    Email body.
	 */
	public function enqueue( string $to, string $subject, string $body ): void {
		$queue   = $this->get_queue();
		$queue[] = [
			'to'       => $to,
			'subject'  => $subject,
			'body'     => $body,
			'queued'   => time(),
			'attempts' => 0,
		];
		update_option( self::OPTION_KEY, $queue, false );
	}

	/**
	 * Process all queued emails.
	 *
	 * Sends each email via wp_mail(). Failed emails are retried up to 3 times
	 * before being discarded.
	 */
	public function process(): void {
		$queue = $this->get_queue();
		if ( empty( $queue ) ) {
			return;
		}

		// Clear the queue immediately to prevent duplicate processing
		// by concurrent cron runs.
		update_option( self::OPTION_KEY, [], false );

		$retry = [];
		foreach ( $queue as $email ) {
			$sent = wp_mail( $email['to'], $email['subject'], $email['body'] );
			if ( ! $sent ) {
				$attempts = $email['attempts'] + 1;
				$this->logger->warning( sprintf( 'Failed to send queued email to %s (Attempt %d)', $email['to'], $attempts ) );
				if ( $attempts < 3 ) {
					$email['attempts'] = $attempts;
					$retry[]           = $email;
				}
				// After 3 attempts, silently discard.
			}
		}

		if ( ! empty( $retry ) ) {
			// Merge retries back with any new emails queued during processing.
			$current = $this->get_queue();
			update_option( self::OPTION_KEY, array_merge( $retry, $current ), false );
		}
	}

	/**
	 * Get the current queue.
	 *
	 * @return array<int, array{to: string, subject: string, body: string, queued: int, attempts: int}>
	 */
	public function get_queue(): array {
		$queue = get_option( self::OPTION_KEY, [] );
		/** @var array<int, array{to: string, subject: string, body: string, queued: int, attempts: int}> */
		return is_array( $queue ) ? $queue : [];
	}

	/**
	 * Get the number of emails in the queue.
	 */
	public function count(): int {
		return count( $this->get_queue() );
	}
}