# frozen_string_literal: true

# Ingests inbound emails from Mandrill.
#
# Requires a +mandrill_events+ parameter containing a JSON array of Mandrill inbound email event objects.
# Each event is expected to have a +msg+ object containing a full RFC 822 message in its +raw_msg+ property.
#
# Returns:
#
# - <tt>204 No Content</tt> if an inbound email is successfully recorded and enqueued for routing to the appropriate mailbox
# - <tt>401 Unauthorized</tt> if the request's signature could not be validated
# - <tt>404 Not Found</tt> if Action Mailbox is not configured to accept inbound emails from Mandrill
# - <tt>422 Unprocessable Entity</tt> if the request is missing required parameters
# - <tt>500 Server Error</tt> if the Mandrill API key is missing, or one of the Active Record database,
#   the Active Storage service, or the Active Job backend is misconfigured or unavailable
class ActionMailbox::Ingresses::Mandrill::InboundEmailsController < ActionMailbox::BaseController
  before_action :authenticate

  def create
    raw_emails.each { |raw_email| ActionMailbox::InboundEmail.create_and_extract_message_id! raw_email }
    head :ok
  rescue JSON::ParserError => error
    logger.error error.message
    head :unprocessable_entity
  end

  private
    def raw_emails
      events.select { |event| event["event"] == "inbound" }.collect { |event| event.dig("msg", "raw_msg") }
    end

    def events
      JSON.parse params.require(:mandrill_events)
    end


    def authenticate
      head :unauthorized unless authenticated?
    end

    def authenticated?
      if key.present?
        Authenticator.new(request, key).authenticated?
      else
        raise ArgumentError, <<~MESSAGE.squish
          Missing required Mandrill API key. Set action_mailbox.mandrill_api_key in your application's
          encrypted credentials or provide the MANDRILL_INGRESS_API_KEY environment variable.
        MESSAGE
      end
    end

    def key
      Rails.application.credentials.dig(:action_mailbox, :mandrill_api_key) || ENV["MANDRILL_INGRESS_API_KEY"]
    end

    class Authenticator
      attr_reader :request, :key

      def initialize(request, key)
        @request, @key = request, key
      end

      def authenticated?
        ActiveSupport::SecurityUtils.secure_compare given_signature, expected_signature
      end

      private
        def given_signature
          request.headers["X-Mandrill-Signature"]
        end

        def expected_signature
          Base64.strict_encode64 OpenSSL::HMAC.digest(OpenSSL::Digest::SHA1.new, key, message)
        end

        def message
          request.url + request.POST.sort.flatten.join
        end
    end
end