module Lotus
  module Helpers
    module HtmlHelper
      # Empty HTML node
      #
      # @since 0.1.0
      # @api private
      class EmptyHtmlNode
        # List of attributes that get special treatment when rendering.
        #
        # @since 0.2.5
        # @api private
        #
        # @see http://www.w3.org/html/wg/drafts/html/master/infrastructure.html#boolean-attribute
        BOOLEAN_ATTRIBUTES = %w{allowfullscreen async autobuffer autofocus
          autoplay checked compact controls declare default defaultchecked
          defaultmuted defaultselected defer disabled draggable enabled
          formnovalidate hidden indeterminate inert ismap itemscope loop
          multiple muted nohref noresize noshade novalidate nowrap open
          pauseonexit pubdate readonly required reversed scoped seamless
          selected sortable spellcheck translate truespeed typemustmatch
          visible
        }.freeze

        # Attributes separator
        #
        # @since 0.1.0
        # @api private
        ATTRIBUTES_SEPARATOR = ' '.freeze

        # Initialize a new empty HTML node
        #
        # @param name [Symbol,String] the name of the tag
        # @param attributes [Hash,NilClass] the optional tag attributes
        #
        # @return [Lotus::Helpers::HtmlHelper::EmptyHtmlNode]
        #
        # @since 0.1.0
        # @api private
        def initialize(name, attributes)
          @name       = name
          @attributes = attributes
        end

        # Resolve and return the output
        #
        # @return [String] the output
        #
        # @since 0.1.0
        # @api private
        def to_s
          %(<#{ @name }#{attributes}>)
        end

        private
        # Resolve the attributes
        #
        # @return [String,NilClass] the tag attributes
        #
        # @since 0.1.0
        # @api private
        def attributes
          return if @attributes.nil?
          result = ''

          @attributes.each do |attribute_name, value|
            if boolean_attribute?(attribute_name)
              result << boolean_attribute(attribute_name, value) if value
            else
              result << attribute(attribute_name, value)
            end
          end

          result
        end

        def boolean_attribute?(attribute_name)
          BOOLEAN_ATTRIBUTES.include?(attribute_name.to_s)
        end

        # Do not render boolean attributes when their value is _false_.
        def boolean_attribute(attribute_name, value)
          %(#{ATTRIBUTES_SEPARATOR}#{ attribute_name }="#{ attribute_name }")
        end

        def attribute(attribute_name, value)
          %(#{ATTRIBUTES_SEPARATOR}#{ attribute_name }="#{ value }")
        end
      end
    end
  end
end