how do i add ammo and reloading to this script

using UnityEngine; using System.Collections;

[RequireComponent (typeof (AudioSource))] public class Gun : MonoBehaviour {

 public enum GunType {Semi,Burst,Auto};

 public LayerMask collisonMask;
 public float gunID;
 public GunType gunType;
 public float rpm;
 public float damage = 1;

 // Components
 public Transform spawn;
 public Transform shellEjectionPoint;
 public Rigidbody shell;
 private LineRenderer tracer;

 // System
 private float secondsBetweenShots;
 private float nextPossibleShootTime;

 void Start() {
     secondsBetweenShots = 60 / rpm;
     if (GetComponent<LineRenderer> ()) {
         tracer = GetComponent<LineRenderer> ();
     }
 }

 public void Shoot () {

     if (CanShoot ()) {
         Ray ray = new Ray (spawn.position, spawn.forward);
         RaycastHit hit;

         float shotDistance = 20;

         if (Physics.Raycast (ray, out hit, shotDistance, collisonMask)) {
             shotDistance = hit.distance;

             if (hit.collider.GetComponent<Entity> ()) {
                 hit.collider.GetComponent<Entity> ().TakeDamage(damage);
             }
         }

         nextPossibleShootTime = Time.time + secondsBetweenShots;

         GetComponent<AudioSource>().Play();

         if (tracer) {
             StartCoroutine ("RenderTracer", ray.direction * shotDistance);
         }

         Rigidbody newShell = Instantiate (shell, shellEjectionPoint.position, Quaternion.identity) as Rigidbody;
         newShell.AddForce (shellEjectionPoint.forward * Random.Range (150f, 200f) + spawn.forward * Random.Range (-10f, 10f));
     }

 }

 public void ShootContinuous() {
     if (gunType == GunType.Auto) {
         Shoot ();
     }
 }
 private bool CanShoot() {
     bool canShoot = true;

     if (Time.time < nextPossibleShootTime) {
         canShoot = false;
     }

     return canShoot;
 }

 IEnumerator RenderTracer(Vector3 hitPoint) {
     tracer.enabled = true;
     tracer.SetPosition (0, spawn.position);
     tracer.SetPosition (1, spawn.position + hitPoint);
     yield return null;
     tracer.enabled = false;
 }

}