require 'gitlab/email/handler/create_note'
require 'gitlab/email/handler/create_issue'

# Inspired in great part by Discourse's Email::Receiver
module Gitlab
  module Email
    class ProcessingError < StandardError; end
    class EmailUnparsableError < ProcessingError; end
    class SentNotificationNotFoundError < ProcessingError; end
    class ProjectNotFound < ProcessingError; end
    class EmptyEmailError < ProcessingError; end
    class AutoGeneratedEmailError < ProcessingError; end
    class UserNotFoundError < ProcessingError; end
    class UserBlockedError < ProcessingError; end
    class UserNotAuthorizedError < ProcessingError; end
    class NoteableNotFoundError < ProcessingError; end
    class InvalidNoteError < ProcessingError; end
    class InvalidIssueError < ProcessingError; end

    class Receiver
      def initialize(raw)
        @raw = raw
      end

      def execute
        raise EmptyEmailError if @raw.blank?

        mail = build_mail
        mail_key = extract_mail_key(mail)

        raise SentNotificationNotFoundError unless mail_key

        if handler = find_handler(mail, mail_key)
          handler.execute
        elsif mail_key =~ %r{/|\+}
          # Sent Notification mail_key would not have / or +
          raise ProjectNotFound
        else
          raise SentNotificationNotFoundError
        end
      end

      def build_mail
        Mail::Message.new(@raw)
      rescue Encoding::UndefinedConversionError,
             Encoding::InvalidByteSequenceError => e
        raise EmailUnparsableError, e
      end

      def extract_mail_key(mail)
        key_from_to_header(mail) || key_from_additional_headers(mail)
      end

      def key_from_to_header(mail)
        mail.to.find do |address|
          key = Gitlab::IncomingEmail.key_from_address(address)
          break key if key
        end
      end

      def key_from_additional_headers(mail)
        Array(mail.references).find do |mail_id|
          key = Gitlab::IncomingEmail.key_from_fallback_message_id(mail_id)
          break key if key
        end
      end

      def find_handler(mail, mail_key)
        [Handler::CreateNote, Handler::CreateIssue].find do |klass|
          handler = klass.new(mail, mail_key)
          break handler if handler.can_handle?
        end
      end
    end
  end
end