import LinkedList from '../linked-list/LinkedList';

export default class GraphVertex {
  constructor(value) {
    if (value === undefined) {
      throw new Error('Graph vertex must have a value');
    }

    // Normally you would store string value like vertex name.
    // But generally it may be any object as well
    this.value = value;
    this.edges = new LinkedList();
  }

  /**
   * @param {GraphEdge} edge
   * @returns {GraphVertex}
   */
  addEdge(edge) {
    this.edges.append(edge);

    return this;
  }

  /**
   * @returns {GraphVertex[]}
   */
  getNeighbors() {
    const edges = this.edges.toArray();

    const neighborsConverter = ({ value }) => {
      return value.startVertex === this ? value.endVertex : value.startVertex;
    };

    // Return either start or end vertex.
    // For undirected graphs it is possible that current vertex will be the end one.
    return edges.map(neighborsConverter);
  }

  /**
   * @param {GraphEdge} requiredEdge
   * @returns {boolean}
   */
  hasEdge(requiredEdge) {
    const edgeNode = this.edges.find({
      callback: edge => edge === requiredEdge,
    });

    return !!edgeNode;
  }

  /**
   * @param {GraphVertex} vertex
   * @returns {boolean}
   */
  hasNeighbor(vertex) {
    const vertexNode = this.edges.find({
      callback: edge => edge.startVertex === vertex || edge.endVertex === vertex,
    });

    return !!vertexNode;
  }

  /**
   * @param {GraphVertex} vertex
   * @returns {(GraphEdge|null)}
   */
  findEdge(vertex) {
    const edgeFinder = (edge) => {
      return edge.startVertex === vertex || edge.endVertex === vertex;
    };

    const edge = this.edges.find({ callback: edgeFinder });

    return edge ? edge.value : null;
  }

  /**
   * @returns {string}
   */
  getKey() {
    return this.value;
  }

  /**
   * @param {function} [callback]
   * @returns {string}
   */
  toString(callback) {
    return callback ? callback(this.value) : `${this.value}`;
  }
}