set three

category = [
  {id: "animals", parent: null}
  {id: "mammals", parent: "animals"}
  {id: "cats", parent: "mammals"}
  {id: "dogs", parent: "mammals"}
  {id: "alliance", parent: null}
  {id: "labrador", parent: "dogs"}
  {id: "chihuahua", parent: "dogs"}
  {id: "siamese", parent: "cats"}
  {id: "persian", parent: "cats"}
  {id: "ee", parent: "dare"}
  {id: "sdw", parent: "ee"}
  {id: "dare", parent: null}
  {id: "animals1", parent: null}
  {id: "animals2", parent: "animals1"}
  {id: "animals3", parent: "animals2"}
  {id: "animals4", parent: "animals3"}
  {id: "animals5", parent: "animals4"}
  {id: "animals6", parent: "animals5"}
  {id: "animals7", parent: "animals6"}
  {id: "animals8", parent: "animals7"}
  {id: "animals9", parent: "animals8"}
  {id: "animals10", parent: "animals9"}
  {id: "animals11", parent: "animals10"}
  {id: "animals12", parent: "animals11"}
  {id: "animals13", parent: "animals12"}
  {id: "animals14", parent: "animals13"}
  {id: "animals15", parent: "animals14"}
]

###
EXPECT result
{
  "animals": {
    "mammals": {
      "cats": {
        "siamese": {},
        "persian": {}
      },
      "dogs": {
        "labrador": {},
        "chihuahua": {}
      }
    }
  },
  "alliance": {},
  "dare": {},
  "animals1": {
    "animals2": {
      "animals3": {
        "animals4": {
          "animals5": {
            "animals6": {
              "animals7": {
                "animals8": {
                  "animals9": {
                    "animals10": {
                      "animals11": {
                        "animals12": {
                          "animals13": {
                            "animals14": {
                              "animals15": {}
                            }
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

###

makeTree1 = (categories, parent) ->
  obj = {}
  categories.forEach (item) ->
    if item.parent is parent
      obj[item.id] = makeTree1(categories, item.id)

  obj
  
makeTree2 = (categories, parent) ->
  node = {}
  categories
  .filter (item) -> parent is item.parent
  .forEach (item) ->
    node[item.id] = makeTree2(categories, item.id)
  return node
  
makeTree3 = (categories) ->
  _nodes = {}
  nodes = {}
  for item in categories
    _item = {}

    if not item.parent
      nodes[item.id] = _item

    if item.parent not of _nodes
      _nodes[item.parent] = {}

    if item.id not of _nodes
      _nodes[item.id] = _nodes[item.parent][item.id] = _item

    else
      _nodes[item.parent][item.id] = _nodes[item.id]

  return nodes
  
JSON.stringify( makeTree1(category, null), null, 2)
JSON.stringify( makeTree2(category, null), null, 2)
JSON.stringify( makeTree3(category), null, 2)