class AuthorizedKeys
  LINE = %r/^
    (?:
      (?<options> .+?)
    \s+)?
      (?<type>    (?:sk-)?ssh-[a-zA-Z0-9.@-]+)
    \s+
      (?<key>     \S+)
    (?:\s+
      (?<comment> .*)
    )?
    $/x

  def self.parse line
    opts, m = {}, LINE.match( line)
    raise "Invalid authorized keys line: #{line}"  unless m
    if m[:options]
      o = m[:options].dup
      while not o.empty?
        case o

        when /^([a-z0-9_-]+)(.*)$/i
          k, o = $1.to_sym, $2
          case o
          when '' then opts[k] = true
          when /^,(.*)$/ then opts[k], o = true, $1
          when /^="([^"]*)"(.*)$/i, /^=([a-z_0-9:-]*)(.*?)$/i
            opts[k], o = $1, $2
            case o
            when /^,(.*)/ then o = $1
            when '' then o = ''
            else raise "Invalid options-string at: #{o}"
            end
          else raise "Invalid options-string at: #{o}"
          end

        when /^\s*#/
          # comment
        end
      end
    end
    new m[:type], m[:key], m[:comment], **opts
  end

  attr_reader :type, :key, :comment, :options

  def initialize type, key, comment, **options
    @type, @key, @comment, @options = type, key, comment, options
  end

  def to_h() {type: @type, key: @key, comment: @comment, options: @options} end
  def to_a() [@type, @key, @comment, @options] end
  def to_s
    [
      @options.map {|k,v| case v when true then "#{k}" else "#{k}=\"#{v}\"" end }.join( ','),
      @type, @key, @comment
    ].join ' '
  end
end