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package scrollmenu
import org.scalajs.dom
import scala.scalajs.js
import scalatags.JsDom.all._
case class Tree[T](value: T, children: Vector[Tree[T]])
case class MenuNode(frag: dom.HTMLElement, id: String, 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(structure: Tree[String],
main: dom.HTMLElement,
var clean: Boolean = false){
val (headers, domTrees) = {
var i = -1
def recurse(t: Tree[String], depth: Int): Tree[MenuNode] = {
val curr =
li(
a(
t.value,
display := (if (i == -1) "none" else "block"),
href:="#"+Controller.munge(t.value),
cls:="menu-item"
)
)
val originalI = i
i += 1
val children = t.children.map(recurse(_, depth + 1))
Tree(
MenuNode(
curr(ul(marginLeft := "15px",children.map(_.value.frag))).render,
Controller.munge(t.value),
originalI,
if (children.length > 0) children.map(_.value.end).max else originalI + 1
),
children
)
}
def offset(el: dom.HTMLElement, parent: dom.HTMLElement): Double = {
if (el == parent) 0
else el.offsetTop + offset(el.offsetParent.asInstanceOf[dom.HTMLElement], parent)
}
val headers = {
val menuItems = {
def rec(current: Tree[String]): Seq[String] = {
current.value +: current.children.flatMap(rec)
}
rec(structure).tail
}
menuItems.map(Controller.munge)
.map(dom.document.getElementById)
.map(offset(_, main))
.toVector
}
val domTrees = recurse(structure, 0)
(headers, domTrees)
}
private[this] var scrolling = false
def apply() = {
if (!scrolling) {
scrolling = true
dom.requestAnimationFrame((d: Double) => start())
}
}
private[this] var previousWin: MenuNode = null
private[this] def start() = {
scrolling = false
def scroll(el: dom.Element) = {
val rect = el.getBoundingClientRect()
if (rect.top <= 0)
el.scrollIntoView(true)
else if (rect.top > dom.innerHeight)
el.scrollIntoView(false)
}
val scrollTop = main.scrollTop
def walkIndex(tree: Tree[MenuNode]): List[Tree[MenuNode]] = {
val t @ Tree(m, children) = tree
val win = if(m.start == -1) true
else {
val before = headers(m.start) <= scrollTop
val after = (m.end >= headers.length) || headers(m.end) > scrollTop
before && after
}
val childIndexes = children.map(walkIndex)
val childWin = childIndexes.indexWhere(_ != null)
if (childWin != -1) t :: childIndexes(childWin)
else if (win) List(t)
else null
}
val winPath = walkIndex(domTrees)
val winItem = winPath.last.value
def walkTree(tree: Tree[MenuNode], indices: List[Tree[MenuNode]]): Unit = {
for(Tree(MenuNode(frag, _, start, end), children) <- indices){
frag.classList.remove("hide")
frag.classList.remove("selected")
frag.children(1).asInstanceOf[dom.HTMLElement].style.maxHeight = (end - start + 1) * 44 + "px"
frag.children(0).classList.add("pure-menu-selected")
for(child <- children if child.value.frag != indices(1).value.frag){
val childFrag = child.value.frag
childFrag.children(0).classList.remove("pure-menu-selected")
childFrag.classList.add("hide")
childFrag.children(1).asInstanceOf[dom.HTMLElement].style.maxHeight = "0px"
if (child.value.start < winItem.start) childFrag.classList.add("selected")
else childFrag.classList.remove("selected")
}
}
}
if (winItem != previousWin){
scroll(winItem.frag.children(0))
dom.history.replaceState(null, null, "#" + winItem.id)
previousWin = winItem
walkTree(domTrees, winPath)
}
}
}
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