/**
 * Computes the distance between two points
 *
 * @param  {Point}  p
 * @param  {Point}  q
 *
 * @return {Number}  distance
 */
export function pointDistance(a, b) {
  if (!a || !b) {
    return -1;
  }

  return Math.sqrt(
    Math.pow(a.x - b.x, 2) +
    Math.pow(a.y - b.y, 2)
  );
}


/**
 * Returns true if the point r is on the line between p and q
 *
 * @param  {Point}  p
 * @param  {Point}  q
 * @param  {Point}  r
 * @param  {Number} [accuracy=5] accuracy for points on line check (lower is better)
 *
 * @return {Boolean}
 */
export function pointsOnLine(p, q, r, accuracy) {

  if (typeof accuracy === 'undefined') {
    accuracy = 5;
  }

  if (!p || !q || !r) {
    return false;
  }

  var val = (q.x - p.x) * (r.y - p.y) - (q.y - p.y) * (r.x - p.x),
      dist = pointDistance(p, q);

  // @see http://stackoverflow.com/a/907491/412190
  return Math.abs(val / dist) <= accuracy;
}


var ALIGNED_THRESHOLD = 2;

/**
 * Returns whether two points are in a horizontal or vertical line.
 *
 * @param {Point} a
 * @param {Point} b
 *
 * @return {String|Boolean} returns false if the points are not
 *                          aligned or 'h|v' if they are aligned
 *                          horizontally / vertically.
 */
export function pointsAligned(a, b) {
  if (Math.abs(a.x - b.x) <= ALIGNED_THRESHOLD) {
    return 'h';
  }

  if (Math.abs(a.y - b.y) <= ALIGNED_THRESHOLD) {
    return 'v';
  }

  return false;
}


/**
 * Returns true if the point p is inside the rectangle rect
 *
 * @param  {Point}  p
 * @param  {Rect}   rect
 * @param  {Number} tolerance
 *
 * @return {Boolean}
 */
export function pointInRect(p, rect, tolerance) {
  tolerance = tolerance || 0;

  return p.x > rect.x - tolerance &&
         p.y > rect.y - tolerance &&
         p.x < rect.x + rect.width + tolerance &&
         p.y < rect.y + rect.height + tolerance;
}

/**
 * Returns a point in the middle of points p and q
 *
 * @param  {Point}  p
 * @param  {Point}  q
 *
 * @return {Point} middle point
 */
export function getMidPoint(p, q) {
  return {
    x: Math.round(p.x + ((q.x - p.x) / 2.0)),
    y: Math.round(p.y + ((q.y - p.y) / 2.0))
  };
}