class Rtml::Widgets::HighlevelVariableProcessing < Rtml::Widget
  affects :screen
  entry_point :terminal_variables, :tvars, :_if, :_elsif, :_else, :_end
  shared :setvars => Rtml::HighLevel::VariableManager.new
  disable_subprocessing!

  # Provides a higher-level conditional construct as an alternative to using next and variant tags to generate
  # a TML branch.
  #
  # Examples:
  #   screen :main do
  #     _if(tvars[:amount] == 0) { goto :amount_too_low }
  #     _elsif(tvars[:amount] > 10000) { goto :amount_too_high }
  #     _else { goto :swipe_card }
  #   end
  #
  def _if(condition, &block)
    scrid = "#{parent.property('id')}_if"
    conditional_goto(scrid, condition, &block)
  end

  # Provides a higher-level conditional construct as an alternative to using next and variant tags to generate
  # a TML branch.
  #
  # Examples:
  #   screen :main do
  #     _if(tvars[:amount] == 0) { goto :amount_too_low }
  #     _elsif(tvars[:amount] > 10000) { goto :amount_too_high }
  #     _else { goto :swipe_card }
  #   end
  #
  def _elsif(condition, &block)
    scrid = "#{parent.property('id')}_elsif"
    conditional_goto(scrid, condition, &block)
  end
  alias _elseif _elsif

  # Provides a higher-level conditional construct as an alternative to using next and variant tags to generate
  # a TML branch.
  #
  # Examples:
  #   screen :main do
  #     _if(tvars[:amount] == 0) { goto :amount_too_low }
  #     _elsif(tvars[:amount] > 10000) { goto :amount_too_high }
  #     _else { goto :swipe_card }
  #   end
  #
  def _else(&block)
    scrid = "#{parent.property('id')}_else"
    conditional_goto(scrid, nil, &block)
  end

  # Returns a handle to the list of TML variables. Follow this with an array operator to access and manipulate
  # the variable assignments for this screen.
  #
  # You can use the alias #tvars for shorthand access to this method.
  #
  # Examples:
  #   screen :init do                                            => <screen id="init">
  #     terminal_variables[:amount] = 0                          =>   <setvar name="amount" lo="0" />
  #     terminal_variables[:first_name] = 'John'                 =>   <setvar name="first_name" lo="John" />
  #     terminal_variables[:last_name] = 'Smith'                 =>   <setvar name="last_name" lo="Smith" />
  #     terminal_variables[:full_name] = tvars[:first_name] +    =>   <setvar name="full_name" lo="tmlvar:first_name"
  #                                      tvars[:last_name]       =>           op="plus"        ro="tmlvar:last_name" />
  #   end                                                        => </screen>
  #
  # You can also use periods instead of array operators to do the same thing:
  #
  # Examples:
  #   screen :init do                                            => <screen id="init">
  #     terminal_variables.amount = 0                            =>   <setvar name="amount" lo="0" />
  #     terminal_variables.first_name = 'John'                   =>   <setvar name="first_name" lo="John" />
  #     terminal_variables.last_name = 'Smith'                   =>   <setvar name="last_name" lo="Smith" />
  #     terminal_variables.full_name = tvars.first_name +        =>   <setvar name="full_name" lo="tmlvar:first_name"
  #                                    tvars.last_name           =>           op="plus"        ro="tmlvar:last_name" />
  #   end                                                        => </screen>
  def terminal_variables
    setvars.screen ||= parent
    setvars
  end

  alias tvars terminal_variables
  alias tml   terminal_variables

  private
  def conditional_goto(scrid, condition, &blk)
    unless (document.root / "screen[id='#{scrid}']").empty?
      scrid = "#{scrid}_#{widget_id}"
    end
    destination = parent.property('next') || ((c = parent / 'next').empty? ? 'assert' : c.first.property('uri'))
    if condition.nil?
      parent.goto scrid
      parent.property('next', nil)
    else
      parent.goto scrid, :if => condition
    end
    r = document.screen(scrid, :next => destination)


    method_name = "method_wrapper_for_#{scrid}"
    block = blk

    (class << r; self; end).instance_eval do
      define_method method_name, &block
      new_method = instance_method(method_name)
      define_method method_name do
        new_method.bind(self).call
      end
    end

    ret = r.send(method_name)
    if r.elements.length == 1 && (nxt = r.elements.first).name == 'next' && nxt.elements.empty?
      # all user did was "goto" -- that should result in a variant in parent, not a whole new screen.
      # This is mostly for TML legibility.
      if condition.blank?
        parent.goto nxt.property('uri')
      else
        parent.goto nxt.property('uri'), :if => condition
      end
      document.remove_screen(r)
    end
    
    ret
#    r
  end

  def document
    @document ||= parent.document
  end
end