import {
  looseEqual
} from 'uni-shared'

function setResult (data, k, v) {
  data[k] = v
}

function diffElmData (newObj, oldObj) {
  let result, key, cur, old
  for (key in newObj) {
    cur = newObj[key]
    old = oldObj[key]
    if (!looseEqual(old, cur)) {
      setResult(result || (result = Object.create(null)), key, cur)
    }
  }
  return result
}

export function diff (newData, oldData, result) {
  let id, cur, old
  for (id in newData) {
    cur = newData[id]
    old = oldData[id]
    if (!old) {
      setResult(result, id, cur)
      continue
    }
    const idObj = diffElmData(cur, old)
    idObj && setResult(result, id, idObj)
  }
  return result
}