import { cmp, Pos } from "../line/pos.js"
import { lst } from "../util/misc.js"

import { normalizeSelection, Range, Selection } from "./selection.js"

// Compute the position of the end of a change (its 'to' property
// refers to the pre-change end).
export function changeEnd(change) {
  if (!change.text) return change.to
  return Pos(change.from.line + change.text.length - 1,
             lst(change.text).length + (change.text.length == 1 ? change.from.ch : 0))
}

// Adjust a position to refer to the post-change position of the
// same text, or the end of the change if the change covers it.
function adjustForChange(pos, change) {
  if (cmp(pos, change.from) < 0) return pos
  if (cmp(pos, change.to) <= 0) return changeEnd(change)

  let line = pos.line + change.text.length - (change.to.line - change.from.line) - 1, ch = pos.ch
  if (pos.line == change.to.line) ch += changeEnd(change).ch - change.to.ch
  return Pos(line, ch)
}

export function computeSelAfterChange(doc, change) {
  let out = []
  for (let i = 0; i < doc.sel.ranges.length; i++) {
    let range = doc.sel.ranges[i]
    out.push(new Range(adjustForChange(range.anchor, change),
                       adjustForChange(range.head, change)))
  }
  return normalizeSelection(doc.cm, out, doc.sel.primIndex)
}

function offsetPos(pos, old, nw) {
  if (pos.line == old.line)
    return Pos(nw.line, pos.ch - old.ch + nw.ch)
  else
    return Pos(nw.line + (pos.line - old.line), pos.ch)
}

// Used by replaceSelections to allow moving the selection to the
// start or around the replaced test. Hint may be "start" or "around".
export function computeReplacedSel(doc, changes, hint) {
  let out = []
  let oldPrev = Pos(doc.first, 0), newPrev = oldPrev
  for (let i = 0; i < changes.length; i++) {
    let change = changes[i]
    let from = offsetPos(change.from, oldPrev, newPrev)
    let to = offsetPos(changeEnd(change), oldPrev, newPrev)
    oldPrev = change.to
    newPrev = to
    if (hint == "around") {
      let range = doc.sel.ranges[i], inv = cmp(range.head, range.anchor) < 0
      out[i] = new Range(inv ? to : from, inv ? from : to)
    } else {
      out[i] = new Range(from, from)
    }
  }
  return new Selection(out, doc.sel.primIndex)
}