require 'stringio'

class Vooly
  class Pull
    def initialize(io, strip_whitespace=false)
      if io.respond_to? :to_io
        @io = io.to_io
      elsif io.respond_to? :to_str
        @io = StringIO.new io.to_str
      else
        raise TypeError, "Can't pull from #{io.class}, only from String and IO"
      end

      @strip = strip_whitespace

      @next_state = :text
      @state = nil
      @text = nil
      @depths = [2]
    end

    attr_reader :state, :text

    def strip!
      case @strip
      when true                 # Strip everything
        @text.strip!
      when false                # Strip whitespace if only whitespace
        @text.strip!  unless @text =~ /\S/
      when nil                  # Strip nothing
        #
      end
    end

    def next
#      puts @io.string
#      puts " " * @io.pos + "^"

      open = close = 0

      if @next_state
        @state = @next_state
        @state = nil  if @state == 0
        @text = ""
      end

      while c = @io.getc
        @next_state = nil  if @io.eof?

        raise ParseError, "Invalid nesting (underflow)"  if @depths.size < 1

        case @state
        when :text              # Ordinary text
          if c == ?<
            open += 1
            close = 0
          elsif c == ?>
            close += 1
            open = 0
          end

          if c != ?< && open >= @depths.last     # Open is greedy
            @io.ungetc c
            @depths << open
            @next_state = :open
            @text = @text[0...-open]

            strip!
            if @text.empty?
              @state = @next_state
              @next_state = nil
            else
              return true
            end
          elsif close == @depths.last           # Close is not
            @depths.pop
            @next_state = :close

            @text = @text[0..-close]
            @text.sub! /\s$/, ''  if @strip == false

            strip!
            if @text.empty?
              @state = @next_state
              @next_state = nil
            else
              return true
            end
          else
            @text << c
            open = close = 0  if c != ?< and c != ?>
          end

        when :open              # Just after <<...
          if c.chr =~ /\w/
            @text << c
          else
            @io.ungetc c  unless @strip == false && c.chr =~ /\s/
            @text = nil  if @text.empty?
            @next_state = :text
            return true
          end

        when :close             # Just after ...>>
          @io.ungetc c  if @strip != true
          @text = nil
          @next_state = :text
          return true

        when nil                # At EOF
          @text = nil
          return false

        else
          raise "Unhandled state #@state"
        end
      end

      if @state == :text
        strip!
        @state = @text = nil  if @text.empty?
        @next_state = 0
        return true
      else
        raise ParseError, "Invalid nesting (overflow)"  if @depths.size != 1

        @text = nil
        return false
      end
    end
  end
end