Enemy Spawner

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SpawnEnemies : MonoBehaviour {

    [Range(0,30)]
    public float spawnInterval = 5;
    public int wave = 1;
    public float gameTime;
    public GameObject enemyPrefab;
    public Transform[] spawn_spots;
    private bool canSpawn = true;
    private float currentTime;

    // Use this for initialization
    void Start () {

        StartCoroutine("GameTimer");
    }

    IEnumerator GameTimer ()
    {
        yield return new WaitForSeconds(3.0f);
        canSpawn = true;
        StartCoroutine("Spawn");

        while(currentTime < gameTime)
        {
            currentTime += Time.deltaTime;
            yield return new WaitForEndOfFrame();
        }

        canSpawn = false;
        NewWave ();

    }


    IEnumerator Spawn ()
    {
        while(canSpawn)
        {
             int spawnPointIndex = Random.Range(0, spawn_spots.Length);
             Instantiate(enemyPrefab, spawn_spots[spawnPointIndex].position, spawn_spots[spawnPointIndex].rotation);
             yield return new WaitForSeconds(spawnInterval);
        }

    }

    void NewWave ()
    {
        wave++;
        spawnInterval += 5f;
        currentTime = 0;
        StartCoroutine("GameTimer");
    }

}