module Liquid
  
  class Block < Tag
    def parse(tokens)
      @nodelist ||= []
      @nodelist.clear

      while token = tokens.shift 

        case token
        when /^#{TagStart}/                   
          if token =~ /^#{TagStart}\s*(\w+)\s*(.*)?#{TagEnd}$/

            # if we found the proper block delimitor just end parsing here and let the outer block
            # proceed                               
            if block_delimiter == $1
              end_tag
              return
            end

            # fetch the tag from registered blocks
            if tag = Template.tags[$1]
              @nodelist << tag.new($2, tokens)
            else
              # this tag is not registered with the system 
              # pass it to the current block for special handling or error reporting
              unknown_tag($1, $2, tokens)
            end              
          else
            raise SyntaxError, "Tag '#{token}' was not properly terminated with regexp: #{TagEnd.inspect} "
          end
        when /^#{VariableStart}/
          @nodelist << create_variable(token)
        when ''
          # pass
        else
          @nodelist << token
        end
      end       
      
      # Make sure that its ok to end parsing in the current block. 
      # Effectively this method will throw and exception unless the current block is 
      # of type Document 
      assert_missing_delimitation!
    end                     
    
    def end_tag      
    end

    def unknown_tag(tag, params, tokens)
      case tag 
      when 'else'
        raise SyntaxError, "#{block_name} tag does not expect else tag"
      when 'end'
        raise SyntaxError, "'end' is not a valid delimiter for #{block_name} tags. use #{block_delimiter}"
      else
        raise SyntaxError, "Unknown tag '#{tag}'"
      end
    end

    def block_delimiter
      "end#{block_name}"
    end                           

    def block_name
      self.class.name.scan(/\w+$/).first.downcase
    end

    def create_variable(token)
      token.scan(/^#{VariableStart}(.*)#{VariableEnd}$/) do |content|
        return Variable.new(content.first)
      end
      raise SyntaxError.new("Variable '#{token}' was not properly terminated with regexp: #{VariableEnd.inspect} ")
    end

    def render(context)
      render_all(@nodelist, context)
    end

    protected

    def assert_missing_delimitation!
      raise SyntaxError.new("#{block_name} tag was never closed")
    end

    def render_all(list, context)
      list.collect do |token|
        if token.respond_to?(:render)
          token.render(context)
        else
          token.to_s
        end
      end      
    end
  end  
end