<?php
/**
 * Email building and sending.
 *
 * @package ReplyPing
 */

namespace PlugWren\ReplyPing;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Mailer.
 */
final class Mailer {

	const RATE_LIMIT = 3;

	/**
	 * Unsubscribe page URL for a subscription.
	 *
	 * @param object $sub Subscription.
	 * @return string
	 */
	public static function unsubscribe_url( $sub ) {
		return add_query_arg(
			array(
				'replyping_action' => 'unsubscribe',
				'sid'              => (int) $sub->id,
				'key'              => Db::unsubscribe_key( $sub ),
			),
			home_url( '/' )
		);
	}

	/**
	 * REST one-click unsubscribe URL (RFC 8058).
	 *
	 * @param object $sub Subscription.
	 * @return string
	 */
	public static function one_click_url( $sub ) {
		return add_query_arg(
			array(
				'sid' => (int) $sub->id,
				'key' => Db::unsubscribe_key( $sub ),
			),
			rest_url( 'replyping/v1/unsubscribe' )
		);
	}

	/**
	 * Normalise an email for rate limiting (lowercase, strip +tag).
	 *
	 * @param string $email Email.
	 * @return string
	 */
	private static function normalise_email( $email ) {
		$email = strtolower( trim( $email ) );
		$parts = explode( '@', $email, 2 );
		if ( 2 === count( $parts ) ) {
			$local = explode( '+', $parts[0], 2 );
			$email = $local[0] . '@' . $parts[1];
		}
		return $email;
	}

	/**
	 * Confirmation rate limits: per email, per IP and global, each per hour.
	 *
	 * @param string $email Email.
	 * @param string $ip    Client IP.
	 * @return bool True when sending is allowed (and counts the attempt).
	 */
	public static function consume_rate_limit( $email, $ip = '' ) {
		$limits = array(
			'replyping_rl_e_' . md5( self::normalise_email( $email ) ) => self::RATE_LIMIT,
			'replyping_rl_global' => (int) apply_filters( 'replyping_confirmation_global_limit', 100 ),
		);
		if ( '' !== $ip ) {
			$limits[ 'replyping_rl_i_' . md5( $ip ) ] = (int) apply_filters( 'replyping_confirmation_ip_limit', 5 );
		}

		foreach ( $limits as $key => $max ) {
			if ( (int) get_transient( $key ) >= $max ) {
				return false;
			}
		}
		foreach ( array_keys( $limits ) as $key ) {
			set_transient( $key, (int) get_transient( $key ) + 1, HOUR_IN_SECONDS );
		}
		return true;
	}

	/**
	 * Send a confirmation email.
	 *
	 * @param object $sub       Subscription.
	 * @param string $raw_token Raw token.
	 * @param string $ip        Client IP for rate limiting.
	 * @return bool
	 */
	public static function send_confirmation( $sub, $raw_token, $ip = '' ) {
		if ( ! self::consume_rate_limit( $sub->email, $ip ) ) {
			return false;
		}
		$post = get_post( (int) $sub->post_id );
		if ( ! $post ) {
			return false;
		}
		$confirm = add_query_arg(
			array(
				'replyping_action' => 'confirm',
				'token'            => $raw_token,
			),
			home_url( '/' )
		);
		$vars    = self::placeholders( $sub, $post, null, array( '{confirm_link}' => $confirm ) );
		return self::send(
			$sub->email,
			Settings::get( 'confirm_subject' ),
			Settings::get( 'confirm_body' ),
			$vars,
			$sub,
			'confirmation',
			null
		);
	}

	/**
	 * Send a comment notification.
	 *
	 * @param object      $sub     Subscription.
	 * @param \WP_Comment $comment Comment.
	 * @param \WP_Post    $post    Post.
	 * @return bool
	 */
	public static function send_notification( $sub, $comment, $post ) {
		$vars = self::placeholders( $sub, $post, $comment );
		return self::send(
			$sub->email,
			Settings::get( 'notify_subject' ),
			Settings::get( 'notify_body' ),
			$vars,
			$sub,
			'notification',
			$comment
		);
	}

	/**
	 * Placeholder map.
	 *
	 * @param object           $sub     Subscription.
	 * @param \WP_Post         $post    Post.
	 * @param \WP_Comment|null $comment Comment.
	 * @param array            $extra   Extra placeholders.
	 * @return array
	 */
	private static function placeholders( $sub, $post, $comment, array $extra = array() ) {
		$vars = array(
			'{post_title}'       => wp_strip_all_tags( get_the_title( $post ) ),
			'{site_name}'        => wp_specialchars_decode( get_bloginfo( 'name' ), ENT_QUOTES ),
			'{unsubscribe_link}' => self::unsubscribe_url( $sub ),
			'{comment_author}'   => '',
			'{comment_excerpt}'  => '',
			'{comment_link}'     => get_permalink( $post ),
			'{confirm_link}'     => '',
		);
		if ( $comment ) {
			$vars['{comment_author}']  = wp_strip_all_tags( $comment->comment_author );
			$vars['{comment_excerpt}'] = wp_trim_words( wp_strip_all_tags( $comment->comment_content ), 40 );
			$vars['{comment_link}']    = get_comment_link( $comment );
		}
		return array_merge( $vars, $extra );
	}

	/**
	 * Build and send one email through the single send path.
	 *
	 * @param string           $to      Recipient.
	 * @param string           $subject Subject template.
	 * @param string           $body    Body template.
	 * @param array            $vars    Placeholder map.
	 * @param object           $sub     Subscription.
	 * @param string           $context 'confirmation' or 'notification'.
	 * @param \WP_Comment|null $comment Comment.
	 * @return bool
	 */
	private static function send( $to, $subject, $body, array $vars, $sub, $context, $comment ) {
		$subject = trim( preg_replace( '/[\r\n]+/', ' ', wp_strip_all_tags( strtr( $subject, $vars ) ) ) );
		$message = strtr( $body, $vars );
		if ( false === strpos( $body, '{unsubscribe_link}' ) ) {
			$message .= "\n\n" . __( 'Unsubscribe:', 'replyping' ) . ' ' . $vars['{unsubscribe_link}'];
		}

		$headers = array( 'Content-Type: text/plain; charset=UTF-8' );

		$headers[] = 'List-Unsubscribe: <' . esc_url_raw( self::one_click_url( $sub ) ) . '>';
		$headers[] = 'List-Unsubscribe-Post: List-Unsubscribe=One-Click';

		$subject = (string) apply_filters( 'replyping_email_subject', $subject, $sub, $comment, $context );
		$message = (string) apply_filters( 'replyping_email_message', $message, $sub, $comment, $context );
		$headers = (array) apply_filters( 'replyping_email_headers', $headers, $sub, $comment, $context );

		// Return non-null to short-circuit (custom transports).
		$pre = apply_filters( 'replyping_pre_send_email', null, $to, $subject, $message, $headers, $sub, $context );
		if ( null !== $pre ) {
			return (bool) $pre;
		}

		// Scope the From overrides to this send only.
		add_filter( 'wp_mail_from', array( __CLASS__, 'mail_from' ) );
		add_filter( 'wp_mail_from_name', array( __CLASS__, 'mail_from_name' ) );
		add_action( 'phpmailer_init', array( __CLASS__, 'maybe_strip_list_headers' ) );
		$sent = wp_mail( $to, $subject, $message, $headers );
		remove_filter( 'wp_mail_from', array( __CLASS__, 'mail_from' ) );
		remove_filter( 'wp_mail_from_name', array( __CLASS__, 'mail_from_name' ) );
		remove_action( 'phpmailer_init', array( __CLASS__, 'maybe_strip_list_headers' ) );

		return (bool) $sent;
	}

	/**
	 * PHPMailer's 'mail' transport Q-encodes long custom headers, which breaks List-Unsubscribe; drop them there.
	 *
	 * @param PHPMailerPHPMailerPHPMailer $phpmailer Mailer instance.
	 */
	public static function maybe_strip_list_headers( $phpmailer ) {
		$enabled = (bool) apply_filters( 'replyping_list_unsubscribe_header_enabled', 'mail' !== $phpmailer->Mailer, $phpmailer );
		if ( $enabled ) {
			return;
		}
		$custom = $phpmailer->getCustomHeaders();
		$phpmailer->clearCustomHeaders();
		foreach ( $custom as $header ) {
			if ( in_array( strtolower( $header[0] ), array( 'list-unsubscribe', 'list-unsubscribe-post' ), true ) ) {
				continue;
			}
			$phpmailer->addCustomHeader( $header[0], $header[1] );
		}
	}

	/**
	 * Configured From address.
	 *
	 * @param string $email Default.
	 * @return string
	 */
	public static function mail_from( $email ) {
		$custom = sanitize_email( Settings::get( 'from_email' ) );
		return is_email( $custom ) ? $custom : $email;
	}

	/**
	 * Configured From name.
	 *
	 * @param string $name Default.
	 * @return string
	 */
	public static function mail_from_name( $name ) {
		$custom = trim( preg_replace( '/[\\\\"\'<>\r\n]+/', '', (string) Settings::get( 'from_name' ) ) );
		return '' !== $custom ? $custom : $name;
	}

}