discourse/app/services/push_notification_pusher.rb

require_dependency 'webpush'

class PushNotificationPusher
  def self.push(user, payload)
    subscriptions(user).each do |subscription|
      subscription = JSON.parse(subscription.data)

      message = {
        title: I18n.t(
          "discourse_push_notifications.popup.#{Notification.types[payload[:notification_type]]}",
          site_title: SiteSetting.title,
          topic: payload[:topic_title],
          username: payload[:username]
        ),
        body: payload[:excerpt],
        badge: get_badge,
        icon: ActionController::Base.helpers.image_url("push-notifications/#{Notification.types[payload[:notification_type]]}.png"),
        tag: "#{Discourse.current_hostname}-#{payload[:topic_id]}",
        base_url: Discourse.base_url,
        url: payload[:post_url],
        hide_when_active: true
      }
      send_notification user, subscription, message
    end
  end

  def self.subscriptions(user)
    user.push_subscriptions
  end

  def self.clear_subscriptions(user)
    user.push_subscriptions.clear
  end

  def self.subscribe(user, subscription, send_confirmation)
    subscriptions = PushSubscription.where(user: user, data: subscription.to_json)
    if subscriptions.length > 1
      subscriptions.destroy_all
      PushSubscription.create user: user, data: subscription.to_json
    elsif subscriptions.length == 0
      PushSubscription.create user: user, data: subscription.to_json
    end
    if send_confirmation == "true"
      message = {
        title: I18n.t("discourse_push_notifications.popup.confirm_title",
                      site_title: SiteSetting.title),
        body: I18n.t("discourse_push_notifications.popup.confirm_body"),
        icon:  ActionController::Base.helpers.image_url("push-notifications/check.png"),
        badge: get_badge,
        tag: "#{Discourse.current_hostname}-subscription"
      }

      send_notification user, subscription, message
    end
  end

  def self.unsubscribe(user, subscription)
    PushSubscription.find_by(user: user, data: subscription.to_json)&.destroy
  end

  protected

  def self.get_badge
    return !SiteSetting.push_notifications_icon_url.blank? ?
             SiteSetting.push_notifications_icon_url :
             ActionController::Base.helpers.image_url("push-notifications/discourse.png")
  end

  def self.send_notification(user, subscription, message)
    begin
      response = Webpush.payload_send(
        endpoint: subscription["endpoint"],
        message: message.to_json,
        p256dh: subscription.dig("keys", "p256dh"),
        auth: subscription.dig("keys", "auth"),
        vapid: {
          subject: Discourse.base_url,
          public_key: SiteSetting.vapid_public_key,
          private_key: SiteSetting.vapid_private_key
        }
      )
    rescue Webpush::InvalidSubscription => e
      unsubscribe user, subscription
    end
  end
end