// an undirected graph
class Graph {
  constructor() {
    // Graph has an adjacencyList attribute set as an object
    this.adjacencyList = {}
  }

  addVertex(vertex) {
    // to avoid overwriting the existing vertex, we need if statement
    if (!this.adjacencyList[vertex]) this.adjacencyList[vertex] = []
  }

  addEdge(vertex1, vertex2) {
    // undirected graph is two way connection
    //we push both vertices to each other's array
    this.adjacencyList[vertex1].push(vertex2)
    this.adjacencyList[vertex2].push(vertex1)
  }

  removeEdge(ver1, ver2) {
    // two way connection, delete from both arrays
    this.adjacencyList[ver1] = this.adjacencyList[ver1].filter(
      v => v !== ver2
    )
    this.adjacencyList[ver2] = this.adjacencyList[ver2].filter(
      v => v !== ver1
    )
  }

  removeVertex(vertex) {
    // first find all the conncetion, and remove all edges from both parties,
    // and then delete the vertex from the adjacency list
    let edges = this.adjacencyList[vertex]

    for (let edge of edges) {
      this.removeEdge(vertex, edge)
    }
    delete this.adjacencyList[vertex]
  }
}

export default Graph