How to convert text inside a node into child node using xquery update?

Question

I have a xml document like

<root>
  <first>
    First Level
    <second>
      second level
       <third>
         Third Level
       </third>
    </second>
    <second2>
      another second level
    </second2>
  </first>
</root>

How to convert this document with all nodes, that means if a node contains text and child node convert text into a child node (let's say childtext) using xquery-update

<root>
  <first>
    <childtext>First Level</childtext>
    <second>
      <childtext>second level</childtext>
       <third>
         Third Level
       </third> 
    </second>
    <second2>
      another second level
    </second2>
  </first>
</root>

And here is what I tried:

let $a :=
<root>
  <first>
    First Level
    <second>
      second level
       <third>
         Third Level
       </third>
    </second>
    <second2>
      another second level
    </second2>
  </first>
</root>
return 
copy $i := $a
modify (
  for $x in $i/descendant-or-self::*
  return (
    if($x/text() and exists($x/*)) then (
      insert node <childtext>
        {$x/text()}
       </childtext> as first into $x
        (: here should be some code to delete the text only:)
    ) else ()
  )
)
return $i

I could not delete the text which has sibling node.

Answer 1

As you want to replace an element, you should simply use the replace construct, instead of inserting the new element and deleting the old one. Seems much simpler to me:

copy $i := $a
modify (
  for $x in $i/descendant-or-self::*[exists(*)]/text()
  return replace node $x with <childtext>{$x}</childtext>
)
return $i

Answer 2

The modified solution is from @dirkk here:

copy $i := $a
modify (
  for $x in $i/descendant-or-self::*
  return (
    if($x/text() and exists($x/*)) then (
      if(count($x/text())=1) then (
      replace node $x/text() with <child>    {$x/text()}</child>
      ) else (
        for $j at $pos in 1 to count($x/text())
        return 
       replace node $x/text()[$pos] with <child>{$x/text()[$pos]}</child>

    )


    ) else ()
  )
)
return $i

Thank you Once again.