require "forwardable"
require "mail"

module Email; end

module Email::Mboxrd
  class Message
    extend Forwardable
    def_delegators :@parsed, :subject

    attr_reader :supplied_body

    def self.clean_serialized(serialized)
      cleaned = serialized.gsub(/^>(>*From)/, "\\1")
      # Serialized messages in this format *should* start with a line
      #   From xxx yy zz
      # rubocop:disable Style/IfUnlessModifier
      if cleaned.start_with?("From ")
        cleaned = cleaned.sub(/^From .*[\r\n]*/, "")
      end
      # rubocop:enable Style/IfUnlessModifier
      cleaned
    end

    def self.from_serialized(serialized)
      new(clean_serialized(serialized))
    end

    def initialize(supplied_body)
      @supplied_body = supplied_body.clone
    end

    def to_serialized
      "From #{from}\n" + mboxrd_body
    end

    def date
      parsed.date
    rescue StandardError
      nil
    end

    def imap_body
      supplied_body.gsub(/(?<!\r)\n/, "\r\n")
    end

    private

    def parsed
      @parsed ||= Mail.new(supplied_body)
    end

    def from
      @from ||=
        begin
          from = best_from.dup
          from << " #{asctime}" if asctime != ""
          from
        end
    end

    def best_from
      return first_from if first_from
      return parsed.sender if parsed.sender
      return parsed.envelope_from if parsed.envelope_from
      return parsed.return_path if parsed.return_path

      ""
    end

    def first_from
      return nil if !parsed.from.is_a?(Enumerable)

      parsed.from.find { |from| from }
    end

    def mboxrd_body
      @mboxrd_body ||=
        begin
          mboxrd_body = add_extra_quote(supplied_body.gsub("\r\n", "\n"))
          mboxrd_body += "\n" if !mboxrd_body.end_with?("\n")
          mboxrd_body += "\n" if !mboxrd_body.end_with?("\n\n")
          mboxrd_body
        end
    end

    def add_extra_quote(body)
      # The mboxrd format requires that lines starting with 'From'
      # be prefixed with a '>' so that any remaining lines which start with
      # 'From ' can be taken as the beginning of messages.
      # http://www.digitalpreservation.gov/formats/fdd/fdd000385.shtml
      # Here we add an extra '>' before any "From" or ">From".
      body.gsub(/\n(>*From)/, "\n>\\1")
    end

    def asctime
      @asctime ||= date ? date.asctime : ""
    end
  end
end