class Graph {
  constructor() {
    this._storage = {};
  }

  addNode(node) {
    this._storage[node] = node;
  }

  contains(node) {
    return !!this._storage[node];
  }

  remove(node) {
    if (this._storage[node]) {
      for (var i = 0; i < this._storage[node].edges.length; i++) {
        if (this._storage[node].edges[i] === node){
          delete this._storage[node].edges[i]
        }
      }
      delete this._storage[node]
    }
  }

  addEdge(fromNode, toNode) {
    if (this._storage[fromNode] && this._storage[toNode]) {
      this._storage[fromNode][edges][toNode] = toNode;
      this._storage[toNode][edges][fromNode] = fromNode;
    }
  }

  hasEdge(fromNode, toNode) {
    if (this._storage[fromNode][edges][toNode]) {
      return !!this._storage[fromNode][edges][toNode];
    }
  }

  removeEdge(fromNode, toNode) {
    if (this._storage[fromNode][edges][toNode] && this._storage[fromNode][edges][toNode]) {
      delete this._storage[fromNode][edges][toNode];
      delete this._storage[toNode][edges][fromNode];
    }
  }
}