# frozen_string_literal: true

# rubocop:disable Layout/LineLength
module ActionMailbox
  # Ingests inbound emails from Amazon SES/SNS and confirms subscriptions.
  #
  # Subscription requests must provide the following parameters in a JSON body:
  # - +Message+: Notification content
  # - +MessagId+: Notification unique identifier
  # - +Timestamp+: iso8601 timestamp
  # - +TopicArn+: Topic identifier
  # - +Type+: Type of event ("Subscription")
  #
  # Inbound email events must provide the following parameters in a JSON body:
  # - +Message+: Notification content
  # - +MessagId+: Notification unique identifier
  # - +Timestamp+: iso8601 timestamp
  # - +SubscribeURL+: Topic identifier
  # - +TopicArn+: Topic identifier
  # - +Type+: Type of event ("SubscriptionConfirmation")
  #
  # All requests are authenticated by validating the provided AWS signature.
  #
  # Returns:
  #
  # - <tt>204 No Content</tt> if a request is successfully processed
  # - <tt>401 Unauthorized</tt> if a request does not contain a valid signature
  # - <tt>404 Not Found</tt> if the Amazon ingress has not been configured
  # - <tt>422 Unprocessable Entity</tt> if a request provides invalid parameters
  #
  # == Usage
  #
  # 1. Tell Action Mailbox to accept emails from Amazon SES:
  #
  #        # config/environments/production.rb
  #        config.action_mailbox.ingress = :amazon
  #
  # 2. Configure which SNS topics will be accepted:
  #
  #        config.action_mailbox.amazon.subscribed_topics = %w(
  #          arn:aws:sns:eu-west-1:123456789001:example-topic-1
  #          arn:aws:sns:us-east-1:123456789002:example-topic-2
  #        )
  #
  # 3. {Configure SES}[https://docs.aws.amazon.com/ses/latest/DeveloperGuide/receiving-email-notifications.html]
  #    to route emails through SNS.
  #
  #    Configure SNS to send emails to +/rails/action_mailbox/amazon/inbound_emails+.
  #
  #    If your application is found at <tt>https://example.com</tt> you would
  #    specify the fully-qualified URL <tt>https://example.com/rails/action_mailbox/amazon/inbound_emails</tt>.
  #
  # rubocop:enable Layout/LineLength
  module Ingresses
    module Amazon
      class InboundEmailsController < ActionMailbox::BaseController
        before_action :verify_authenticity
        before_action :validate_topic
        before_action :confirm_subscription

        def create
          head :bad_request unless mail.present?

          ActionMailbox::InboundEmail.create_and_extract_message_id!(mail)
          head :no_content
        end

        private

        def verify_authenticity
          head :bad_request unless notification.present?
          head :unauthorized unless verified?
        end

        def confirm_subscription
          return unless notification['Type'] == 'SubscriptionConfirmation'
          return head :ok if confirmation_response_code&.start_with?('2')

          Rails.logger.error('SNS subscription confirmation request rejected.')
          head :unprocessable_entity
        end

        def validate_topic
          return if valid_topics.include?(topic)

          Rails.logger.warn("Ignoring unknown topic: #{topic}")
          head :unauthorized
        end

        def confirmation_response_code
          @confirmation_response_code ||= begin
            Net::HTTP.get_response(URI(notification['SubscribeURL'])).code
          end
        end

        def notification
          @notification ||= JSON.parse(request.body.read)
        rescue JSON::ParserError => e
          Rails.logger.warn("Unable to parse SNS notification: #{e}")
          nil
        end

        def verified?
          verifier.authentic?(@notification.to_json)
        end

        def verifier
          Aws::SNS::MessageVerifier.new
        end

        def message
          @message ||= JSON.parse(notification['Message'])
        end

        def mail
          return nil unless notification['Type'] == 'Notification'
          return nil unless message['notificationType'] == 'Received'

          message['content']
        end

        def topic
          return nil unless notification.present?

          notification['TopicArn']
        end

        def valid_topics
          ::Rails.configuration.action_mailbox.amazon.subscribed_topics
        end
      end
    end
  end
end