/**
 * Get index with specific start index one by one. e.g.
 * min: 3, max: 9, start: 6
 *
 * Return index is:
 * [0]: 6
 * [1]: 7
 * [2]: 5
 * [3]: 8
 * [4]: 4
 * [5]: 9
 * [6]: 3
 */
export function getIndexByStartLoc(min, max, start, index) {
  const beforeCount = start - min
  const afterCount = max - start
  const balanceCount = Math.min(beforeCount, afterCount) * 2

  // Balance
  if (index <= balanceCount) {
    const stepIndex = Math.floor(index / 2)
    if (index % 2) {
      return start + stepIndex + 1
    }
    return start - stepIndex
  }

  // One is out of range
  if (beforeCount > afterCount) {
    return start - (index - afterCount)
  }
  return start + (index - beforeCount)
}

/**
 * We assume that 2 list has only 1 item diff and others keeping the order.
 * So we can use dichotomy algorithm to find changed one.
 */
export function findListDiffIndex(originList, targetList, getKey) {
  const originLen = originList.length
  const targetLen = targetList.length

  let shortList
  let longList

  if (originLen === 0 && targetLen === 0) {
    return null
  }

  if (originLen < targetLen) {
    shortList = originList
    longList = targetList
  } else {
    shortList = targetList
    longList = originList
  }

  const notExistKey = { __EMPTY_ITEM__: true }
  function getItemKey(item) {
    if (item !== undefined) {
      return getKey(item)
    }
    return notExistKey
  }

  // Loop to find diff one
  let diffIndex = null
  let multiple = Math.abs(originLen - targetLen) !== 1
  for (let i = 0; i < longList.length; i += 1) {
    const shortKey = getItemKey(shortList[i])
    const longKey = getItemKey(longList[i])

    if (shortKey !== longKey) {
      diffIndex = i
      multiple = multiple || shortKey !== getItemKey(longList[i + 1])
      break
    }
  }

  return diffIndex === null ? null : { index: diffIndex, multiple }
}
