Graph

using System.Collections.Generic;

public class Graph
{

    private List<Vertex> vertices;
    private HashSet<Edge> edges;

    public int Order => vertices.Count;
    public int Size => edges.Count;

    public GraphRenderer Renderer;
    public Vertex[] Vertices => vertices.ToArray();

    public Graph()
    {
        vertices = new List<Vertex>();
        edges = new HashSet<Edge>();
        Renderer = new GraphRenderer(this);
    }

    public Vertex AddVertex(Vertex vertex)
    {
        vertices.Add(vertex);
        return vertex;
    }

    public void RemoveVertex(Vertex vertex)
    {
        RemoveAllEdges(vertex);
        vertices.Remove(vertex);
    }

    public void AddEdge(Vertex v1, Vertex v2)
    {
        edges.Add(v1.AddEdge(v2));
        edges.Add(v2.AddEdge(v1));
    }

    public void RemoveEdge(Vertex v1, Vertex v2)
    {
        v1.RemoveEdge(v2);
        v2.RemoveEdge(v1);
    }

    public void RemoveAllEdges(Vertex vertex)
    {
        foreach (Vertex connectedVertex in vertex.GetConnectedVertices())
        {
            RemoveEdge(vertex, connectedVertex);
        }
    }

    public Vertex AddConnectedVertex(Vertex v1, Vertex v2)
    {
        AddVertex(v2);
        AddEdge(v1, v2);
        return v2;
    }
}

public class Edge
{
    private Vertex source;
    private Vertex destination;

    public EdgeRenderer Renderer;

    public Vertex Source => source;
    public Vertex Destination => destination;

    public Edge(Vertex source, Vertex destination)
    {
        this.source = source;
        this.destination = destination;

        Renderer = new EdgeRenderer(this);
    }
}