module ContextExposer::BaseController
  extend ActiveSupport::Concern

  included do
    before_filter :configure_exposed_context

    expose_context :context
  end

  def view_context    
    @view_context ||= build_view_context
  end
  alias_method :context, :view_context

  module ClassMethods
    def exposed name, &block
      # puts "store: #{name} in hash storage for class #{self}"
      exposure_storage[name.to_sym] = block
    end

    def view_context_class name
      define_method :view_context_class do
        @view_context_class ||= name.kind_of?(Class) ? name : name.to_s.camelize.constantize
      end
    end

    protected

    def expose_context name
      return if exposed_view_context?
      if ActionController::Base.instance_methods.include?(name.to_sym)
        Kernel.warn "[WARNING] You are exposing the `#{name}` method, " \
          "which overrides an existing ActionController method of the same name. " \
          "Consider a different exposure name\n" \
          "#{caller.first}"
      end    
      helper_method name
      hide_action name
      @exposed_view_context = true
    end

    def exposed_view_context?
      @exposed_view_context ||= false
    end

    def exposure_storage
      exposure_hash[self.to_s] ||= {}
    end

    def exposure_hash
      @exposure_hash ||= {}
    end
  end

  # must be called after Controller is instantiated
  def configure_exposed_context
    return if configured_exposed_context?
    clazz = self.class
    exposed_methods = clazz.send(:exposure_hash)[clazz.to_s] || []
    # puts "exposed_methods for: #{clazz} - #{exposed_methods}"
    exposed_methods.each do |name, procedure|
      view_context.send :define_singleton_method, name do 
        procedure.call
      end
    end
    @configured_exposed_context = true
  end

  def configured_exposed_context?
    @configured_exposed_context == true
  end

  protected

  # returns a ViewContext object 
  # view helpers can be exposed as singleton methods, dynamically be attached (see below)
  def build_view_context
    view_context_class.new self
  end

  def view_context_class
    @view_context_class ||= ContextExposer::ViewContext
  end
end