#!/usr/bin/env ruby

require 'pp'
require 'rubygems'
require_gem 'multi'
require 'amulti'
require_gem 'sexp'
require 'sexp'

class Logo
  def initialize
    @x, @y  = 100, 100
    @angle  = 0
    @buffer = ""
    @pen    = true

    amulti(:run, :right,   Numeric) {|sym, r, rest| turn(r)  ; run(rest) }
    amulti(:run, :left,    Numeric) {|sym, l, rest| turn(-l) ; run(rest) }
    amulti(:run, :forward, Numeric) {|sym, f, rest| move(f)  ; run(rest) }
    amulti(:run, :penup)   {|sym, rest| @pen = true  ; run(rest) }
    amulti(:run, :pendown) {|sym, rest| @pen = false ; run(rest) }
    amulti(:run, :repeat,  Numeric, Array) do |sym, i, code, rest|
      i.to_i.times{ run(code) }
      run(rest)
    end
    amulti(:run) {}
  end

  def turn(num)
    @angle = (@angle + num) % 360
  end

  def move(distance)
    oldx, oldy = @x, @y
    radians = @angle * Math::PI / 180
    @x += distance * Math.cos(radians)
    @y += distance * Math.sin(radians)
    return unless @pen
    @buffer += <<-END
<line x1="#{oldx}" y1="#{oldy}" x2="#{@x}" y2="#{@y}"/>
    END
  end

  def eval(string)
    run("(#{string})".parse_sexp)
  end

  def render
    return <<-END
<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
"http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
<svg width="100%" height="100%" xmlns="http://www.w3.org/2000/svg">
<g stroke="black" stroke-width="1">
#{@buffer}</g>
</svg>
    END
  end
end

logo = Logo.new
logo.eval %q{
  repeat 4 (forward 100 right 90)
  forward 50 right 90 forward 100
}
puts logo.render