module OverrideHelper
  # Call this method to setup a default content block by name. This content will be rendered into the page
  # unless a content_block with the same name also exists somewhere else in the rendered response. 
  # 
  # === Examples
  # Using a block for complex, or lengthy content
  #   <% content_default(:navigation) do %>
  #     <ul>
  #       <li><%= link "Home" %></li>
  #       <li><%= link "Product Info", "product-info" %></li>
  #     </ul>
  #   <% end %>
  # 
  # Passing content as an argument
  #   <title><%= content_default(:title, "Default Title") %></title>
  def content_default(name, content = nil, &block)
    if override_content[name].blank?
      # default
      content = capture(&block) if block_given?      
    else
      # override
      content = override_content[name]
    end
          
    if block_given?
      concat(content)
    else
      return content
    end
  end
  
  # Call this method to override a call to content_default. If no call to content_default with
  # a matching name exists then this block will not get rendered into the response.
  # 
  # === Examples
  # Using a block for complex, or lengthy content
  #   <% content_block(:navigation) do %>
  #     <ul>
  #       <li><%= link "Super Special Home" %></li>
  #       <li><%= link "Different Product Info", "product-info" %></li>
  #     </ul>
  #   <% end %>
  # 
  # Passing content as an argument
  #   <title><%= content_block(:title, "Custom Title") %></title>
  def content_block(name, content = nil, &block)
    content = capture(&block) if block_given?
    override_content[name] = content
    nil
  end

  private
    def override_content # :nodoc:
      @override_content ||= {}      
    end
end