#pragma mark - UIScrollViewDelegate
-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
  CGFloat height = -scrollView.contentOffset.y;
  UIBezierPath *path = [UIBezierPath bezierPath];
  [path moveToPoint:CGPointMake(0, 0)];
  [path addLineToPoint:CGPointMake(self.view.width, 0)];
  if (height <= 100) {
    //偏移值小于等于100的时候，底部绘制直线
    [path addLineToPoint:CGPointMake(self.view.width, height)];
    [path addLineToPoint:CGPointMake(0, height)];
  }else{
    //偏移值大于100的时候，底部绘制曲线
    [path addLineToPoint:CGPointMake(self.view.width, 100)];
    [path addQuadCurveToPoint:CGPointMake(0, 100) controlPoint:CGPointMake(self.view.center.x, height)];
  }
  [path closePath];
  self.shapeLayer.path = path.CGPath;
}

#pragma mark - private method
-(void)p_initCircle {
  self.circleLayer.frame = CGRectMake(0, 0, self.view.width, 100);
  self.circleLayer.fillColor = nil;
  self.circleLayer.strokeColor = [UIColor whiteColor].CGColor;
  self.circleLayer.lineWidth = 2.0;

  CGPoint center = CGPointMake(self.view.center.x, 50);
  UIBezierPath *path = [UIBezierPath bezierPath];
  [path moveToPoint:CGPointMake(self.view.center.x, 35)];
  [path addArcWithCenter:center radius:15 startAngle:-M_PI_2 endAngle:M_PI * 1.5 clockwise:YES];
  CGFloat r1 = 17.0;
  CGFloat r2 = 22.0;
  for (int i = 0; i < 8 ; i++) {
    CGPoint pointStart = CGPointMake(center.x + sin((M_PI * 2.0 / 8 * i)) * r1, center.y - cos((M_PI * 2.0 / 8 * i)) * r1);
    CGPoint pointEnd = CGPointMake(center.x + sin((M_PI * 2.0 / 8 * i)) * r2, center.y - cos((M_PI * 2.0 / 8 * i)) * r2);
    [path moveToPoint:pointStart];
    [path addLineToPoint:pointEnd];
  }
  self.circleLayer.path = path.CGPath;
}

#pragma mark - UIScrollViewDelegate
-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
  CGFloat height = -scrollView.contentOffset.y;
  if (height <= 100) {
    //偏移值小于等于100的时候，绘制对应的路径
    self.circleLayer.strokeEnd = height / 100.0;
  }else{
    //偏移值大于100的时候，绘制全路径
    self.circleLayer.strokeEnd = 1.0;
  }
}

#pragma mark - UIScrollViewDelegate
-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
  CGFloat height = -scrollView.contentOffset.y;
  [CATransaction begin];
  [CATransaction setDisableActions:YES];
  if (height <= 100) {
    //偏移值小于等于100的时候，不旋转
    self.circleLayer.affineTransform = CGAffineTransformIdentity;
  }else{
    //偏移值小于等于100的时候，旋转
    self.circleLayer.affineTransform = CGAffineTransformMakeRotation(-(M_PI / 720 * height - 100));
  }
  [CATransaction commit];
}

-(void)p_rise {
  self.tableView.scrollEnabled = NO;
  CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
  anim.duration = 0.15;
  anim.toValue = @(M_PI / 4.0);
  anim.repeatCount = MAXFLOAT;
  [self.circleLayer addAnimation:anim forKey:nil];

}

-(void)p_stop {
  self.tableView.scrollEnabled = YES;
  [self.tableView setContentOffset:CGPointMake(0, 0) animated:YES];
  [self.circleLayer removeAllAnimations];
}