module Form
  class Tag
    # List which tags don't need to be closed.
    # Did you know that the technical name is "void elements"?
    # http://www.w3.org/TR/html5/syntax.html#void-elements
    #
    VOID_ELEMENTS = [
      :area, :base, :br, :col, :command, :embed,
      :hr, :img, :input, :keygen, :link, :meta,
      :param, :source, :track, :wbr
    ]

    # The tag name.
    #
    attr_accessor :name

    # The tag content. It will be ignored in open tags.
    #
    attr_accessor :content

    # The tag attributes.
    #
    attr_accessor :attributes

    # Escape the value.
    #
    def self.html_escape(string)
      string.to_s.gsub(/&/, "&amp;").gsub(/\"/, "&quot;").gsub(/>/, "&gt;").gsub(/</, "&lt;")
    end

    # Create a new tag.
    #
    #   Form::Tag.new(:p, "Hello World!", class: "greeting").render
    #   #=> <p class="greeting">Hello World!</p>
    #
    def initialize(name, content = "", attributes = {}, &block)
      if content.kind_of?(Hash)
        attributes = content
        content = ""
      end

      @name = name.to_sym
      @content = content
      @attributes = attributes

      yield self if block_given?
    end

    # Detect if this tag omits the closing part.
    #
    def void?
      VOID_ELEMENTS.include?(name)
    end

    # Append the specified HTML to this tag.
    #
    def <<(element)
      @content << element.to_s
    end

    # Create nested tags with ease.
    #
    def tag(name, content = "", attributes = {}, &block)
      @content << self.class.new(name, content, attributes, &block).to_s
    end

    # Build the tag, concating all parts.
    #
    def to_s
      open_tag << (void? ? "" : content.to_s) << close_tag
    end

    def html_escape(string)
      self.class.html_escape(string)
    end

    private
    #
    #
    def render_attributes
      attributes.collect do |name, value|
        next unless value && value != ""
        bool?(value) ? " #{name}" : %[ #{name}="#{html_escape(value)}"]
      end.join("")
    end

    # Check if value is boolean.
    # LolRuby doesn't have a Boolean class or something.
    #
    def bool?(value)
      value.kind_of?(TrueClass) || value.kind_of?(FalseClass)
    end

    # The opening part of the tag.
    #
    def open_tag
      "<#{name}#{render_attributes}>"
    end

    # The closing part of the tag.
    #
    def close_tag
      void? ? "" : "</#{name}>"
    end
  end
end