require 'strscan'

class Pyrosoma
  class Template
    def initialize(source, filename=nil)
      @source = source
      @filename = filename
      compile
    end
    
    def expand(data, output="", escape=nil, &block)
      escape ||= lambda { |v|
        v.to_s.gsub("&", "&").
               gsub("<", "&lt;").
               gsub(">", "&gt;").
               gsub("'", "&#39;").
               gsub('"', "&quot;")
      }
      @code.call(output, data, block, escape)
      output
    end
    
    def compile
      code = "lambda { |output, data, block, __escape| data.instance_eval {\n"
      
      scanner = StringScanner.new(@source)

      until scanner.eos?
        if scanner.bol? and scanner.scan(/\s*\$ (.*\n)/)
                                             # raw line of code, $ if bla
          code << scanner[1]
        elsif scanner.scan(/\$(:?)(\{(.*?)\}|(@?[\w.!?]+))/)
                                             # expression, ${foo} or $foo.bar
          expr = scanner[3] || scanner[4]
          
          if scanner[1] == ":"               # disable escaping?
            code << %Q{output << (#{expr}).to_s;}
          else
            code << %Q{output << __escape[#{expr}];}
          end
        elsif scanner.scan(/\$\$/)           # plain $
          code << %Q{output << '$';}
        elsif scanner.scan(/\$#.*?(?:#\$|$\n?)/)  # comment $#...#$ or $#...
          # nothing
        elsif scanner.scan(/([^\n$]+\n?)|([^\n$]*\n)/)   # text
          if scanner.matched =~ /\\$/ && scanner.bol?
            code << %Q{output << #{scanner.matched.chop.chop.dump};}
          else
            code << %Q{output << #{scanner.matched.dump};}
          end
          
          code << "\n"  if scanner.bol?
        else
          raise "can't parse template: #{scanner.rest[0..20].dump}"
        end
      end
      
      code << "}}"

      @code = eval(code, nil, @filename || '(template)', 1)
    end
  end
end