# A lightweight infrastructure for defining and running callbacks.
# Callbacks are defined using \{#define\_callback\} at the class level,
# and called using `run_#{name}` at the instance level.
#
# Clients can add callbacks by calling the generated `on_#{name}` method,
# and passing in a block that's run when the callback is activated.
#
# @example Define a callback
# class Munger
#   extend Sass::Callbacks
#   define_callback :string_munged
#
#   def munge(str)
#     res = str.gsub(/[a-z]/, '\1\1')
#     run_string_munged str, res
#     res
#   end
# end
#
# @example Use a callback
# m = Munger.new
# m.on_string_munged {|str, res| puts "#{str} was munged into #{res}!"}
# m.munge "bar" #=> bar was munged into bbaarr!
module Sass::Callbacks
  protected

  # Define a callback with the given name.
  # This will define an `on_#{name}` method
  # that registers a block,
  # and a `run_#{name}` method that runs that block
  # (optionall with some arguments).
  #
  # @param name [Symbol] The name of the callback
  # @return [void]
  def define_callback(name)
    class_eval <<RUBY
def on_#{name}(&block)
  @_sass_callbacks ||= {}
  (@_sass_callbacks[#{name.inspect}] ||= []) << block
end

def run_#{name}(*args)
  return unless @_sass_callbacks
  return unless @_sass_callbacks[#{name.inspect}]
  @_sass_callbacks[#{name.inspect}].each {|c| c[*args]}
end
private :run_#{name}
RUBY
  end
end
