EnemySpawner.cs

Public class EnemySpawner : MonoBehaviour
{
    public GameObject enemyPrefab;
    public float width = 10;
    public float height = 5;
    public float speed = 10f;

    private bool movingRight = true;
    private float maxX;
    private float minX;

    // Use this for initialization
    void Start ()
    {
        // Calculate the Boundary of the screen
        float distanceToCamera = transform.position.z - Camera.main.transform.position.z;
        Vector3 leftBoundary = Camera.main.ViewportToWorldPoint(new Vector3(0, 0, distanceToCamera));
        Vector3 rightBoundary = Camera.main.ViewportToWorldPoint(new Vector3(1, 0, distanceToCamera));
        maxX = rightBoundary.x;
        minX = leftBoundary.x;

        // Loop through every item in the collection to create an enemy on the positions.
        foreach (Transform child in transform)
        {
            GameObject enemy = Instantiate(enemyPrefab, child.transform.position, Quaternion.identity) as GameObject;
            enemy.transform.parent = child;
        }
    }

    public void OnDrawGizmos()
    {
        Gizmos.DrawWireCube(transform.position, new Vector3(width, height, 0));
    }

    // Update is called once per frame
    void Update()
    {
        // Check if the formation is going outside of the play space.
        float rightEdgeOfFormation = transform.position.x + (0.5f * width);
        float leftEdgeOfFormation = transform.position.x - (0.5f * width);

        // Set the formation to move left or right between the limits of the edges
        if (movingRight)
        {
            transform.position += Vector3.right * speed * Time.deltaTime;
        }
        else
        {
            transform.position += Vector3.left * speed * Time.deltaTime;
        }

        // Switch the direction of the formation
        if (leftEdgeOfFormation < minX)
        {
            movingRight = true;
        }
        else if (rightEdgeOfFormation > maxX)
        {
            movingRight = false;
        }

        if (AllMembersDead())
        {
            Debug.Log("Empty formation!");
        }
    }

    bool AllMembersDead()
    {
        foreach (Transform childPositionGameObject in transform)
        {
            if (childPositionGameObject.childCount > 0)
            {
                return false;
            }
        }
        return true;
    }
}