type Position = {
  top: string
  left: string
}

/**
 * Returns position of cursor on the page.
 * @param toStart Position of beginning of selection or end of selection.
 */
export function cursorPosition(toStart = true): Position | undefined {
  const s = window.getSelection()!
  if (s.rangeCount > 0) {
    const cursor = document.createElement("span")
    cursor.textContent = "|"

    const r = s.getRangeAt(0).cloneRange()
    r.collapse(toStart)
    r.insertNode(cursor)

    const {x, y, height} = cursor.getBoundingClientRect()
    const top = (window.scrollY + y + height) + "px"
    const left = (window.scrollX + x) + "px"
    cursor.parentNode!.removeChild(cursor)

    return {top, left}
  }
  return undefined
}

/**
 * Returns selected text.
 */
export function selectedText() {
  const s = window.getSelection()!
  if (s.rangeCount === 0) return ''
  return s.getRangeAt(0).toString()
}

/**
 * Returns text before the cursor.
 * @param editor Editor DOM node.
 */
export function textBeforeCursor(editor: Node) {
  const s = window.getSelection()!
  if (s.rangeCount === 0) return ''

  const r0 = s.getRangeAt(0)
  const r = document.createRange()
  r.selectNodeContents(editor)
  r.setEnd(r0.startContainer, r0.startOffset)
  return r.toString()
}

/**
 * Returns text after the cursor.
 * @param editor Editor DOM node.
 */
export function textAfterCursor(editor: Node) {
  const s = window.getSelection()!
  if (s.rangeCount === 0) return ''

  const r0 = s.getRangeAt(0)
  const r = document.createRange()
  r.selectNodeContents(editor)
  r.setStart(r0.endContainer, r0.endOffset)
  return r.toString()
}