const {indexOf: iOF} = [];
export const append = (get, parent, children, start, end, before) => {
  const isSelect = 'selectedIndex' in parent;
  let noSelection = isSelect;
  while (start < end) {
    const child = get(children[start], 1);
    parent.insertBefore(child, before);
    if (isSelect && noSelection && child.selected) {
      noSelection = !noSelection;
      let {selectedIndex} = parent;
      parent.selectedIndex = selectedIndex < 0 ?
        start :
        iOF.call(parent.querySelectorAll('option'), child);
    }
    start++;
  }
};

export const eqeq = (a, b) => a == b;

export const identity = O => O;

export const indexOf = (
  moreNodes,
  moreStart,
  moreEnd,
  lessNodes,
  lessStart,
  lessEnd,
  compare
) => {
  const length = lessEnd - lessStart;
  /* istanbul ignore if */
  if (length < 1)
    return -1;
  while ((moreEnd - moreStart) >= length) {
    let m = moreStart;
    let l = lessStart;
    while (
      m < moreEnd &&
      l < lessEnd &&
      compare(moreNodes[m], lessNodes[l])
    ) {
      m++;
      l++;
    }
    if (l === lessEnd)
      return moreStart;
    moreStart = m + 1;
  }
  return -1;
};

export const isReversed = (
  futureNodes,
  futureEnd,
  currentNodes,
  currentStart,
  currentEnd,
  compare
) => {
  while (
    currentStart < currentEnd &&
    compare(
      currentNodes[currentStart],
      futureNodes[futureEnd - 1]
    )) {
      currentStart++;
      futureEnd--;
    };
  return futureEnd === 0;
};

export const next = (get, list, i, length, before) => i < length ?
              get(list[i], 0) :
              (0 < i ?
                get(list[i - 1], -0).nextSibling :
                before);

export const remove = (get, children, start, end) => {
  while (start < end)
    drop(get(children[start++], -1));
};

// - - - - - - - - - - - - - - - - - - -
// diff related constants and utilities
// - - - - - - - - - - - - - - - - - - -

const DELETION = -1;
const INSERTION = 1;
const SKIP = 0;
const SKIP_OND = 50;

const HS = (
  futureNodes,
  futureStart,
  futureEnd,
  futureChanges,
  currentNodes,
  currentStart,
  currentEnd,
  currentChanges
) => {

  let k = 0;
  /* istanbul ignore next */
  let minLen = futureChanges < currentChanges ? futureChanges : currentChanges;
  const link = Array(minLen++);
  const tresh = Array(minLen);
  tresh[0] = -1;

  for (let i = 1; i < minLen; i++)
    tresh[i] = currentEnd;

  const nodes = currentNodes.slice(currentStart, currentEnd);

  for (let i = futureStart; i < futureEnd; i++) {
    const index = nodes.indexOf(futureNodes[i]);
    if (-1 < index) {
      const idxInOld = index + currentStart;
      k = findK(tresh, minLen, idxInOld);
      /* istanbul ignore else */
      if (-1 < k) {
        tresh[k] = idxInOld;
        link[k] = {
          newi: i,
          oldi: idxInOld,
          prev: link[k - 1]
        };
      }
    }
  }

  k = --minLen;
  --currentEnd;
  while (tresh[k] > currentEnd) --k;

  minLen = currentChanges + futureChanges - k;
  const diff = Array(minLen);
  let ptr = link[k];
  --futureEnd;
  while (ptr) {
    const {newi, oldi} = ptr;
    while (futureEnd > newi) {
      diff[--minLen] = INSERTION;
      --futureEnd;
    }
    while (currentEnd > oldi) {
      diff[--minLen] = DELETION;
      --currentEnd;
    }
    diff[--minLen] = SKIP;
    --futureEnd;
    --currentEnd;
    ptr = ptr.prev;
  }
  while (futureEnd >= futureStart) {
    diff[--minLen] = INSERTION;
    --futureEnd;
  }
  while (currentEnd >= currentStart) {
    diff[--minLen] = DELETION;
    --currentEnd;
  }
  return diff;
};

// this is pretty much the same petit-dom code without the delete map part
// https://github.com/yelouafi/petit-dom/blob/bd6f5c919b5ae5297be01612c524c40be45f14a7/src/vdom.js#L556-L561
const OND = (
  futureNodes,
  futureStart,
  rows,
  currentNodes,
  currentStart,
  cols,
  compare
) => {
  const length = rows + cols;
  const v = [];
  let d, k, r, c, pv, cv, pd;
  outer: for (d = 0; d <= length; d++) {
    /* istanbul ignore if */
    if (d > SKIP_OND)
      return null;
    pd = d - 1;
    /* istanbul ignore next */
    pv = d ? v[d - 1] : [0, 0];
    cv = v[d] = [];
    for (k = -d; k <= d; k += 2) {
      if (k === -d || (k !== d && pv[pd + k - 1] < pv[pd + k + 1])) {
        c = pv[pd + k + 1];
      } else {
        c = pv[pd + k - 1] + 1;
      }
      r = c - k;
      while (
        c < cols &&
        r < rows &&
        compare(
          currentNodes[currentStart + c],
          futureNodes[futureStart + r]
        )
      ) {
        c++;
        r++;
      }
      if (c === cols && r === rows) {
        break outer;
      }
      cv[d + k] = c;
    }
  }

  const diff = Array(d / 2 + length / 2);
  let diffIdx = diff.length - 1;
  for (d = v.length - 1; d >= 0; d--) {
    while (
      c > 0 &&
      r > 0 &&
      compare(
        currentNodes[currentStart + c - 1],
        futureNodes[futureStart + r - 1]
      )
    ) {
      // diagonal edge = equality
      diff[diffIdx--] = SKIP;
      c--;
      r--;
    }
    if (!d)
      break;
    pd = d - 1;
    /* istanbul ignore next */
    pv = d ? v[d - 1] : [0, 0];
    k = c - r;
    if (k === -d || (k !== d && pv[pd + k - 1] < pv[pd + k + 1])) {
      // vertical edge = insertion
      r--;
      diff[diffIdx--] = INSERTION;
    } else {
      // horizontal edge = deletion
      c--;
      diff[diffIdx--] = DELETION;
    }
  }
  return diff;
};

const applyDiff = (
  diff,
  get,
  parentNode,
  futureNodes,
  futureStart,
  currentNodes,
  currentStart,
  currentLength,
  before
) => {
  const live = [];
  const length = diff.length;
  let currentIndex = currentStart;
  let i = 0;
  while (i < length) {
    switch (diff[i++]) {
      case SKIP:
        futureStart++;
        currentIndex++;
        break;
      case INSERTION:
        // TODO: bulk appends for sequential nodes
        live.push(futureNodes[futureStart]);
        append(
          get,
          parentNode,
          futureNodes,
          futureStart++,
          futureStart,
          currentIndex < currentLength ?
            get(currentNodes[currentIndex], 0) :
            before
        );
        break;
      case DELETION:
        currentIndex++;
        break;
    }
  }
  i = 0;
  while (i < length) {
    switch (diff[i++]) {
      case SKIP:
        currentStart++;
        break;
      case DELETION:
        // TODO: bulk removes for sequential nodes
        if (-1 < live.indexOf(currentNodes[currentStart]))
          currentStart++;
        else
          remove(
            get,
            currentNodes,
            currentStart++,
            currentStart
          );
        break;
    }
  }
};

const findK = (ktr, length, j) => {
  let lo = 1;
  let hi = length;
  while (lo < hi) {
    const mid = ((lo + hi) / 2) >>> 0;
    if (j < ktr[mid])
      hi = mid;
    else
      lo = mid + 1;
  }
  return lo;
}

export const smartDiff = (
  get,
  parentNode,
  futureNodes,
  futureStart,
  futureEnd,
  futureChanges,
  currentNodes,
  currentStart,
  currentEnd,
  currentChanges,
  currentLength,
  compare,
  before
) => {
  applyDiff(
    OND(
      futureNodes,
      futureStart,
      futureChanges,
      currentNodes,
      currentStart,
      currentChanges,
      compare
    ) ||
    HS(
      futureNodes,
      futureStart,
      futureEnd,
      futureChanges,
      currentNodes,
      currentStart,
      currentEnd,
      currentChanges
    ),
    get,
    parentNode,
    futureNodes,
    futureStart,
    currentNodes,
    currentStart,
    currentLength,
    before
  );
};

const drop = node => (node.remove || dropChild).call(node);

function dropChild() {
  const {parentNode} = this;
  /* istanbul ignore else */
  if (parentNode)
    parentNode.removeChild(this);
}