<?php
/**
 * Notification emails.
 *
 * @package SpaceBay
 */

namespace SpaceBay\Notifications;

use SpaceBay\Core\Settings;
use SpaceBay\Frontend\Portal;

defined( 'ABSPATH' ) || exit;

/**
 * Sends one email per notification, from WP-Cron so posting stays fast.
 */
final class Mailer {

	/**
	 * Sends the email of a notification.
	 *
	 * @param int $notification_id Notification ID.
	 * @return bool Whether an email was sent.
	 */
	public static function send( $notification_id ) {
		$row = Notifications::find( $notification_id );

		if ( ! $row || ! empty( $row['is_read'] ) || ! Settings::get( 'emails_enabled', true ) ) {
			return false;
		}

		$user = get_userdata( (int) $row['user_id'] );

		if ( ! $user || ! is_email( $user->user_email ) || ! Preferences::wants_email( $user->ID, $row['action'] ) ) {
			return false;
		}

		$item      = Notifications::format( $row );
		$community = Settings::get( 'community_name' );
		$subject   = sprintf(
			/* translators: 1: Community name, 2: Notification text. */
			__( '[%1$s] %2$s', 'spacebay' ),
			wp_specialchars_decode( $community, ENT_QUOTES ),
			$item['text']
		);

		$html = self::render(
			array(
				'community_name' => $community,
				'text'           => $item['text'],
				'excerpt'        => $item['excerpt'],
				'url'            => $item['url'],
				'button'         => __( 'Open in the community', 'spacebay' ),
				'settings_url'   => Portal::link( 'account/notifications' ),
				'brand_color'    => self::readable_color( (string) Settings::get( 'brand_color', '#3f22ff' ) ),
				'recipient'      => $user->display_name,
				'logo_url'       => Settings::get( 'logo_id' ) ? (string) wp_get_attachment_image_url( (int) Settings::get( 'logo_id' ), 'medium' ) : '',
			)
		);

		$headers = array( 'Content-Type: text/html; charset=UTF-8' );
		$from    = sanitize_email( (string) Settings::get( 'email_from_address', '' ) );

		if ( $from ) {
			$name      = str_replace( array( "\r", "\n", '"' ), '', (string) Settings::get( 'email_from_name', $community ) );
			$headers[] = sprintf( 'From: "%s" <%s>', $name, $from );
		}

		/**
		 * Filters a notification email before it is sent.
		 *
		 * @since 1.0.0
		 *
		 * @param array $email {
		 *     Email parts.
		 *
		 *     @type string   $to      Recipient address.
		 *     @type string   $subject Subject.
		 *     @type string   $message HTML body.
		 *     @type string[] $headers Headers.
		 * }
		 * @param array $row   Notification row.
		 */
		$email = apply_filters(
			'spacebay_notification_email',
			array(
				'to'      => $user->user_email,
				'subject' => $subject,
				'message' => $html,
				'headers' => $headers,
			),
			$row
		);

		return (bool) wp_mail( $email['to'], $email['subject'], $email['message'], $email['headers'] );
	}

	/**
	 * Darkens a colour until white text on it has a contrast of at least 4.5:1,
	 * so the email button stays readable with a very light brand colour.
	 *
	 * @param string $hex Hex colour.
	 * @return string Hex colour.
	 */
	public static function readable_color( $hex ) {
		$hex = sanitize_hex_color( $hex );

		if ( ! $hex ) {
			return '#3f22ff';
		}

		$value = ltrim( $hex, '#' );

		if ( 3 === strlen( $value ) ) {
			$value = $value[0] . $value[0] . $value[1] . $value[1] . $value[2] . $value[2];
		}

		$rgb = array_map( 'hexdec', str_split( $value, 2 ) );

		$step = 0;

		while ( $step < 20 && self::contrast_with_white( $rgb ) < 4.5 ) {
			++$step;
			$rgb = array_map(
				static function ( $channel ) {
					return (int) round( $channel * 0.94 );
				},
				$rgb
			);
		}

		return sprintf( '#%02x%02x%02x', $rgb[0], $rgb[1], $rgb[2] );
	}

	/**
	 * WCAG contrast ratio of white against a colour.
	 *
	 * @param int[] $rgb Red, green and blue from 0 to 255.
	 * @return float
	 */
	private static function contrast_with_white( array $rgb ) {
		$linear = array_map(
			static function ( $channel ) {
				$c = $channel / 255;
				return $c <= 0.03928 ? $c / 12.92 : pow( ( $c + 0.055 ) / 1.055, 2.4 );
			},
			$rgb
		);

		$luminance = 0.2126 * $linear[0] + 0.7152 * $linear[1] + 0.0722 * $linear[2];

		return 1.05 / ( $luminance + 0.05 );
	}

	/**
	 * Renders the email template. Themes can override it by copying
	 * templates/emails/notification.php to your-theme/spacebay/emails/.
	 *
	 * @param array $vars Template variables.
	 * @return string
	 */
	public static function render( array $vars ) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found -- $vars is used by the included template.
		$template = locate_template( array( 'spacebay/emails/notification.php' ) );
		$template = $template ? $template : SPACEBAY_PATH . 'templates/emails/notification.php';

		ob_start();
		include $template;

		return (string) ob_get_clean();
	}
}