Function getScrollTopForVirtualIndex

packages/app-core/src/lib/virtual-list.ts:50–77

({
  index,
  itemCount,
  itemSize,
  currentScrollTop,
  viewportHeight
}: VirtualIndexScrollInput)

}

export function getScrollTopForVirtualIndex({
  index,
  itemCount,
  itemSize,
  currentScrollTop,
  viewportHeight
}: VirtualIndexScrollInput): number {
  const count = Math.max(0, Math.floor(itemCount))
  if (count === 0) return Math.max(0, currentScrollTop)

  const size = Math.max(1, itemSize)
  const safeViewportHeight = Math.max(1, viewportHeight)
  const safeIndex = Math.max(0, Math.min(count - 1, Math.floor(index)))
  const current = Math.max(0, currentScrollTop)
  const itemTop = safeIndex * size
  const itemBottom = itemTop + size
  const viewportBottom = current + safeViewportHeight

  let next = current
  if (itemTop < current) {
    next = itemTop
  } else if (itemBottom > viewportBottom) {
    next = itemBottom - safeViewportHeight
  }

  const maxScrollTop = Math.max(0, count * size - safeViewportHeight)
  return Math.max(0, Math.min(maxScrollTop, next))
}