function drawGCD(){
  var stack = []

  var a = 960 - Math.floor(Math.random()*100), b = 400 + Math.floor(Math.random()*100)

  function gcd(u, v){
    stack.push({u: u, v: v})
    return v ? gcd(v, u % v) : u
  }

  gcd(a, b)


  var size = 960,
      s    = 960/Math.max(a, b),
      s = 1
      colors = ["#1f77b4", "#ff7f0e", "#2ca02c", "#d62728", "#9467bd", "#8c564b", "#e377c2", "#7f7f7f", "#bcbd22", "#17becf"]

  stack[0].translate = [0, 0]

  stack.forEach(function(d, i){
    d.i = i

    d.us = d.u*s
    d.vs = d.v*s

    d.prev = i ? stack[i - 1] : d

    d.flipped = !(!i || !(i % 2))
    d.x = d.flipped ? d.vs : d.us
    d.y = d.flipped ? d.us : d.vs

    d.num = Math.floor(d.u/d.v)

    d.translate = d.prev.translate.slice()
    if (i) d.translate[+!d.flipped] += d.prev.v*d.prev.num
    console.log(d.flipped, d.translate)
    d.color = colors[i]
  })


  var svg = d3.select('body').html('').append('svg')
      .attr({width: size, height: 500})

  svg.append('rect').attr({width: a, height: b})

  svg.dataAppend(stack, 'g')
    .each(function(d){
      if (!d.v) return

      d3.select(this).dataAppend(d3.range(d.num).map(function(i){ return {i: i, j: d.i, p: d} }), 'rect.step')
          .attr(d.flipped ? 'y' : 'x', function(e){ return e.i*d.v })
          .attr('width',  d.v)
          .attr('height', d.v)
          .style('fill', d.color)
          .style('stroke', d3.rgb(d.color).darker(2))
    })
    .translate(ƒ('translate'))


  svg.selectAll('rect.step').style('opacity', 0)
    .transition().delay(function(d, i){ return d ? (d.j + 1)*700 : 0 })
      .style('opacity', 1)
      .style('stroke-width', 10)
    .transition().duration(500)
      .style('stroke-width', 1)


  svg.append('text')
      .translate([10, 500/2])
    .dataAppend(stack, 'tspan.number')
      .text(function(d){ return ' ' + d.u + ' ' })
      
      .style({fill: function(d, i){ return i ? d.prev.color : 'black' }})
      .style('opacity', 0)
    .transition().delay(function(d){ return d.i*700 })
      .style('opacity', 1)

  window.setTimeout(drawGCD, stack.length*700 + 1000)
}


drawGCD()