var degrees = 180 / Math.PI;

export var identity = {
  translateX: 0,
  translateY: 0,
  rotate: 0,
  skewX: 0,
  scaleX: 1,
  scaleY: 1
};

export default function(a, b, c, d, e, f) {
  var scaleX, scaleY, skewX;
  if (scaleX = Math.sqrt(a * a + b * b)) a /= scaleX, b /= scaleX;
  if (skewX = a * c + b * d) c -= a * skewX, d -= b * skewX;
  if (scaleY = Math.sqrt(c * c + d * d)) c /= scaleY, d /= scaleY, skewX /= scaleY;
  if (a * d < b * c) a = -a, b = -b, skewX = -skewX, scaleX = -scaleX;
  return {
    translateX: e,
    translateY: f,
    rotate: Math.atan2(b, a) * degrees,
    skewX: Math.atan(skewX) * degrees,
    scaleX: scaleX,
    scaleY: scaleY
  };
}