export function findDiffStart(a, b, pos) {
  for (let i = 0;; i++) {
    if (i == a.childCount || i == b.childCount)
      return a.childCount == b.childCount ? null : pos

    let childA = a.child(i), childB = b.child(i)
    if (childA == childB) { pos += childA.nodeSize; continue }

    if (!childA.sameMarkup(childB)) return pos

    if (childA.isText && childA.text != childB.text) {
      for (let j = 0; childA.text[j] == childB.text[j]; j++)
        pos++
      return pos
    }
    if (childA.content.size || childB.content.size) {
      let inner = findDiffStart(childA.content, childB.content, pos + 1)
      if (inner != null) return inner
    }
    pos += childA.nodeSize
  }
}

export function findDiffEnd(a, b, posA, posB) {
  for (let iA = a.childCount, iB = b.childCount;;) {
    if (iA == 0 || iB == 0)
      return iA == iB ? null : {a: posA, b: posB}

    let childA = a.child(--iA), childB = b.child(--iB), size = childA.nodeSize
    if (childA == childB) {
      posA -= size; posB -= size
      continue
    }

    if (!childA.sameMarkup(childB)) return {a: posA, b: posB}

    if (childA.isText && childA.text != childB.text) {
      let same = 0, minSize = Math.min(childA.text.length, childB.text.length)
      while (same < minSize && childA.text[childA.text.length - same - 1] == childB.text[childB.text.length - same - 1]) {
        same++; posA--; posB--
      }
      return {a: posA, b: posB}
    }
    if (childA.content.size || childB.content.size) {
      let inner = findDiffEnd(childA.content, childB.content, posA - 1, posB - 1)
      if (inner) return inner
    }
    posA -= size; posB -= size
  }
}