<?php
/**
 * Emails in the background: while a form is being sent, its emails (marked
 * with the X-Mammoth-Form header) are put aside and the visitor gets the
 * answer at once. WordPress's scheduled tasks (WP-Cron) send them a moment
 * later; a failed email is tried twice more before it is given up.
 *
 * @package MammothForms
 */

defined( 'ABSPATH' ) || exit;

class Mammoth_Mail_Queue {

	const HOOK     = 'mammoth_send_queued_mail';
	const SWEEP    = 'mammoth_mail_queue_sweep';
	const PREFIX   = 'mammoth_mailq_';
	const FAILED   = 'mammoth_mail_queue_failed';
	const DIR      = 'mammoth-mail';
	const ATTEMPTS = 3;

	/** @var bool Emails are being put aside right now. */
	private static $deferring = false;

	/** @var bool Something was put aside in this request. */
	private static $queued = false;

	public static function init() {
		add_filter( 'pre_wp_mail', array( __CLASS__, 'hold' ), 5, 2 );
		add_action( self::HOOK, array( __CLASS__, 'send' ) );
		add_action( self::SWEEP, array( __CLASS__, 'sweep' ) );
		add_action( 'mammoth_daily_cleanup', array( __CLASS__, 'sweep' ) );
		add_action( 'shutdown', array( __CLASS__, 'kick' ) );
	}

	/** Whether this form's emails go out in the background. */
	public static function wanted( $form ) {
		$mode = isset( $form['config']['settings']['email_sending'] ) ? (string) $form['config']['settings']['email_sending'] : '';
		if ( 'now' === $mode ) {
			return false;
		}
		if ( 'background' === $mode ) {
			return true;
		}
		$smtp = Mammoth_Mail::settings();
		return isset( $smtp['background'] ) && 'yes' === $smtp['background'];
	}

	/** From here until stop(), this form's emails wait for the background. */
	public static function start( $form ) {
		self::$deferring = self::wanted( $form );
	}

	public static function stop() {
		self::$deferring = false;
	}

	/**
	 * pre_wp_mail: keeps a form's email for later.
	 *
	 * @param null|bool $short Another plugin's answer, if any.
	 * @param array     $atts  to, subject, message, headers, attachments.
	 */
	public static function hold( $short, $atts ) {
		if ( null !== $short || ! self::$deferring ) {
			return $short;
		}
		$headers = isset( $atts['headers'] ) ? $atts['headers'] : array();
		$headers = is_array( $headers ) ? implode( "\n", $headers ) : (string) $headers;
		if ( false === stripos( $headers, Mammoth_Mail::HEADER . ':' ) ) {
			return $short;
		}

		$id    = strtolower( wp_generate_password( 24, false ) );
		$files = array();
		$given = isset( $atts['attachments'] ) ? (array) $atts['attachments'] : array();
		if ( $given ) {
			// The caller may delete its files right after wp_mail(): keep copies.
			$dir = self::folder( $id );
			if ( ! $dir ) {
				return $short; // Cannot keep them: send now instead.
			}
			foreach ( $given as $file ) {
				if ( is_string( $file ) && is_readable( $file ) ) {
					$copy = $dir . '/' . wp_unique_filename( $dir, wp_basename( $file ) );
					if ( ! copy( $file, $copy ) ) {
						return $short;
					}
					$files[] = $copy;
				}
			}
		}

		$saved = add_option(
			self::PREFIX . $id,
			array(
				'to'          => $atts['to'],
				'subject'     => $atts['subject'],
				'message'     => $atts['message'],
				'headers'     => isset( $atts['headers'] ) ? $atts['headers'] : '',
				'attachments' => $files,
				'attempts'    => 0,
				'created'     => time(),
			),
			'',
			false
		);
		if ( ! $saved ) {
			self::remove_files( $files );
			return $short;
		}
		wp_schedule_single_event( time(), self::HOOK, array( $id ) );
		// A safety net: two requests writing WP-Cron's list at once can lose an event.
		if ( ! wp_next_scheduled( self::SWEEP ) ) {
			wp_schedule_single_event( time() + 2 * MINUTE_IN_SECONDS, self::SWEEP );
		}
		self::$queued = true;
		return true;
	}

	/**
	 * For a form sent with JavaScript: the address the visitor's browser
	 * calls once it shows the answer, so the emails leave at once without
	 * the visitor waiting for them. '' when nothing waits or WP-Cron is off.
	 */
	public static function browser_kick() {
		if ( ! self::$queued || ( defined( 'DISABLE_WP_CRON' ) && DISABLE_WP_CRON ) ) {
			return '';
		}
		self::$queued = false; // The browser takes care of it.
		return site_url( 'wp-cron.php' );
	}

	/** Otherwise WP-Cron is started at the end of the request. */
	public static function kick() {
		if ( self::$queued && function_exists( 'spawn_cron' ) && ! ( defined( 'DISABLE_WP_CRON' ) && DISABLE_WP_CRON ) ) {
			spawn_cron();
		}
	}

	/** WP-Cron: sends one email that was put aside. */
	public static function send( $id ) {
		$id  = preg_replace( '/[^a-z0-9]/', '', (string) $id );
		$job = get_option( self::PREFIX . $id );
		if ( ! is_array( $job ) ) {
			return;
		}
		// add_option() fails when the row exists: only one run gets past here.
		$lock = self::PREFIX . 'lock_' . $id;
		if ( ! add_option( $lock, time(), '', false ) ) {
			if ( (int) get_option( $lock ) > time() - 10 * MINUTE_IN_SECONDS ) {
				return;
			}
			update_option( $lock, time(), false ); // A run that died half-way: take over.
		}
		self::$deferring = false;
		$sent            = wp_mail( $job['to'], $job['subject'], $job['message'], $job['headers'], $job['attachments'] );
		++$job['attempts'];

		if ( $sent || $job['attempts'] >= self::ATTEMPTS ) {
			delete_option( self::PREFIX . $id );
			delete_option( $lock );
			self::remove_files( $job['attachments'] );
			if ( ! $sent ) {
				$failed = get_option( self::FAILED, array() );
				$failed = is_array( $failed ) ? $failed : array();
				update_option(
					self::FAILED,
					array(
						'count'   => ( isset( $failed['count'] ) ? (int) $failed['count'] : 0 ) + 1,
						'time'    => time(),
						'subject' => (string) $job['subject'],
						'error'   => Mammoth_Mail::last_error(),
					),
					false
				);
			}
			return;
		}
		update_option( self::PREFIX . $id, $job, false );
		delete_option( $lock );
		wp_schedule_single_event( time() + 5 * MINUTE_IN_SECONDS * $job['attempts'], self::HOOK, array( $id ) );
	}

	/** Sends what waits for more than a minute with no sending planned. */
	public static function sweep() {
		global $wpdb;
		$names = $wpdb->get_col( $wpdb->prepare( "SELECT option_name FROM {$wpdb->options} WHERE option_name LIKE %s AND option_name NOT LIKE %s ORDER BY option_id ASC LIMIT 50", $wpdb->esc_like( self::PREFIX ) . '%', $wpdb->esc_like( self::PREFIX . 'lock_' ) . '%' ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- the queue itself.
		$left  = false;
		foreach ( (array) $names as $name ) {
			$id  = substr( $name, strlen( self::PREFIX ) );
			$job = get_option( $name );
			if ( ! is_array( $job ) || wp_next_scheduled( self::HOOK, array( $id ) ) ) {
				$left = $left || is_array( $job );
				continue;
			}
			if ( (int) $job['created'] > time() - MINUTE_IN_SECONDS ) {
				$left = true;
				continue;
			}
			self::send( $id );
		}
		if ( $left && ! wp_next_scheduled( self::SWEEP ) ) {
			wp_schedule_single_event( time() + 5 * MINUTE_IN_SECONDS, self::SWEEP );
		}
	}

	/** Emails waiting right now. */
	public static function waiting() {
		global $wpdb;
		return (int) $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM {$wpdb->options} WHERE option_name LIKE %s AND option_name NOT LIKE %s", $wpdb->esc_like( self::PREFIX ) . '%', $wpdb->esc_like( self::PREFIX . 'lock_' ) . '%' ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- a count for the settings screen.
	}

	public static function failed() {
		$failed = get_option( self::FAILED, array() );
		return is_array( $failed ) ? $failed : array();
	}

	public static function clear_failed() {
		delete_option( self::FAILED );
	}

	/* ---------------------------------------------------------------- files */

	private static function folder( $id ) {
		$upload = wp_upload_dir( null, false );
		$base   = trailingslashit( $upload['basedir'] ) . self::DIR;
		if ( ! is_dir( $base ) && ! wp_mkdir_p( $base ) ) {
			return '';
		}
		// phpcs:disable WordPress.WP.AlternativeFunctions.file_system_operations_file_put_contents -- tiny guard files in our own folder.
		if ( ! file_exists( $base . '/.htaccess' ) && false === file_put_contents( $base . '/.htaccess', "Require all denied\nDeny from all\n" ) ) {
			return '';
		}
		if ( ! file_exists( $base . '/index.php' ) ) {
			file_put_contents( $base . '/index.php', "<?php\n// Silence is golden.\n" );
		}
		// phpcs:enable
		$dir = $base . '/' . $id;
		return wp_mkdir_p( $dir ) ? $dir : '';
	}

	private static function remove_files( $files ) {
		$dirs = array();
		foreach ( (array) $files as $file ) {
			if ( is_string( $file ) && file_exists( $file ) ) {
				$dirs[ dirname( $file ) ] = true;
				wp_delete_file( $file );
			}
		}
		foreach ( array_keys( $dirs ) as $dir ) {
			if ( 0 === strpos( wp_normalize_path( $dir ), wp_normalize_path( trailingslashit( wp_upload_dir( null, false )['basedir'] ) . self::DIR . '/' ) ) ) {
				@rmdir( $dir ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged, WordPress.WP.AlternativeFunctions.file_system_operations_rmdir -- our own, now empty, folder.
			}
		}
	}
}