module Net; module SSH; module Kerberos; module Common; class Context

  class GeneralError < StandardError; end

  class State < Struct.new(:handle, :result, :token, :timestamp)
    def complete?; result.complete? end
  end

  attr_reader :cred_name, :cred_krb_name, :server_name, :server_krb_name

  def initialize
    raise "Don't create this class directly - use a subclass" if self.class == Context
  end

  def create(user, host)
    dispose if @credentials or @target or @handle

    creds, name = acquire_current_credentials
    begin
      @cred_name = name.to_s.sub(/^[^\\\/]*[\\\/]/, '')
      @cred_krb_name = @cred_name.gsub('@', '/');

      z = (user.include?('@') ? user.gsub('@','/') : user+'/')
      unless z.downcase == @cred_krb_name[0,z.length].downcase
        raise GeneralError, "Credentials mismatch: current is #{@cred_name}, requested is #{user}"
      end
      @credentials = creds
    ensure
      if @credentials.nil?
        release_credentials creds
        @cred_name = @cred_krb_name = nil
      end
    end

    @server_name = Socket.gethostbyname(host)[0]
    @target, @server_krb_name = import_server_name host

    true
  end

  def credentials?; ! @credentials.nil? end
  
  def established?; ! @handle.nil? && (@state.nil? || @state.complete?) end
  
  def init(token=nil); raise NotImplementedError, "subclasses must implement this method" end
  
  def get_mic(token=nil); raise NotImplementedError, "subclasses must implement this method" end
  
  def dispose
    @handle and delete_context @handle
    @credentials and release_credentials @credentials
    @target and release_server_name @target
  ensure
    @credentials = @cred_name = @cred_krb_name = nil
    @target = @server_name = @server_krb_name = nil
    @handle = @state = nil
  end 

private

  def acquire_current_credentials; raise NotImplementedError, "subclasses must implement this method" end

  def release_credentials(creds); raise NotImplementedError, "subclasses must implement this method" end

  def import_server_name(host); raise NotImplementedError, "subclasses must implement this method" end

  def release_server_name(target); raise NotImplementedError, "subclasses must implement this method" end

  def delete_context(handle); raise NotImplementedError, "subclasses must implement this method" end

end; end; end; end; end