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package scrollmenu
import org.scalajs.dom
case class Tree[T](value: T, children: Vector[Tree[T]])
case class MenuNode(frag: dom.HTMLElement, start: Int, end: Int)
/**
* High performance scrollspy to work keep the left menu bar in sync.
* Lots of sketchy imperative code in order to maximize performance.
*/
class ScrollSpy(headers: Vector[Double], domTrees: Seq[Tree[MenuNode]]){
var scrolling = false
def apply(threshold: Double) = if (!scrolling){
scrolling = true
dom.requestAnimationFrame((d: Double) => start(threshold))
}
def start(threshold: Double) = {
scrolling = false
def walkTree(tree: Tree[MenuNode]): Boolean = {
val Tree(MenuNode(menuItem, index, next), children) = tree
val before = headers(index) < threshold
val after = (next >= headers.length) || headers(next) > threshold
val win = before && after
if (win){
menuItem.classList.remove("hide")
var winFound = false
for(c <- tree.children){
val newWinFound = walkTree(c)
if (!winFound) c.value.frag.classList.add("selected")
else c.value.frag.classList.remove("selected")
winFound = winFound | newWinFound
}
if (!winFound) {
tree.children.foreach(_.value.frag.classList.remove("selected"))
}
menuItem.children(0).classList.add("pure-menu-selected")
}else{
menuItem.children(0).classList.remove("pure-menu-selected")
menuItem.classList.add("hide")
menuItem.classList.remove("selected")
}
win
}
domTrees.map(walkTree)
}
}
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