Draw Controller - Version 2

DrawControllerV2.cs

public class DrawController : MonoBehaviour
{
    public DrawMode Mode = DrawMode.Rectangle;

    public DrawShape RectanglePrefab;
    public DrawShape CirclePrefab;
    public DrawShape TrianglePrefab;

    // Associates a draw mode to the prefab to instantiate
    private Dictionary<DrawMode, DrawShape> _drawModeToPrefab;

    private readonly List<DrawShape> _allShapes = new List<DrawShape>();

    private DrawShape CurrentShapeToDraw { get; set; }
    private bool IsDrawingShape { get; set; }
    
    private void Awake()
    {
        _drawModeToPrefab = new Dictionary<DrawMode, DrawShape> {
            {DrawMode.Rectangle, RectanglePrefab},
            {DrawMode.Circle, CirclePrefab},
            {DrawMode.Triangle, TrianglePrefab}
        };
    }

    private void Update()
    {
        // ...
    }

    private void AddShapeVertex(Vector2 position)
    {
        if (CurrentShapeToDraw == null) {
            // No current shape -> instantiate a new shape and add two vertices:
            // one for the initial position, and the other for the current cursor
            var prefab = _drawModeToPrefab[Mode];
            CurrentShapeToDraw = Instantiate(prefab);
            CurrentShapeToDraw.name = "Shape " + _allShapes.Count;
            // ...
            _allShapes.Add(CurrentShapeToDraw);
        } else {
            // ...
        }
    }

    private void UpdateShapeVertex(Vector2 position)
    {
        // ...
    }

    /// <summary>
    /// Controlled via Unity GUI button
    /// </summary>
    public void SetDrawMode(string mode)
    {
        Mode = (DrawMode) Enum.Parse(typeof(DrawMode), mode);
    }

    /// <summary>
    /// The types of shapes that can be drawn, useful for
    /// selecting shapes to draw
    /// </summary>
    public enum DrawMode
    {
        Rectangle,
        Circle,
        Triangle
    }
}