module.exports = function findChildren(root, items = [], opts = {}) {
  const { rootKey, foreignKey, withRoot } = opts
  const bypass = {}
  let children = [root]
  let nextItems = []
  recurse()
  if (!withRoot)
    children.shift()
  return children

  function recurse() {
    for (child of children) {
      if (bypass[child[rootKey]]) continue
      const foundChildren = items.filter(item => child[rootKey] === item[foreignKey])
      if (foundChildren.length) {
        children = children.concat(foundChildren)
        bypass[child[rootKey]] = true
        recurse()
      }
    }
  }
}