using UnityEngine;

    public class RtsCamera : MonoBehaviour
    {

        public float speed = 2.0f;                  // movement speed when scrolling on the side of the screen
        public float zoom_speed = 2.0f;             // zoom speed
        public float speed_x = 200.0f;              // Rotation speed
        float rotation_y = 0.0f;                    // variable used for rotation function
        private int edge_threshold = 5;             // area before the end of the screen where scrolling activate
        // limits
        public float scroll_limit_x = 5f;                // how much you can scroll from the center of the scene on the X axis.
        public float scroll_limit_z = 5f;                // how much you can scroll from the center of the screen on the Y axis.


        void Start()
        {
            // adapt the limits based on the starting position of the camera.
            // in this way, there will always be an equal amount to the limit value
            // independently from where the starting position is.
            if (transform.position.x > 0)
                scroll_limit_x += transform.position.x;
            else
                scroll_limit_x -= transform.position.x;

            if (transform.position.z > 0)
                scroll_limit_z += transform.position.z;
            else
                scroll_limit_z -= transform.position.z;
        }

        void Update()
        {
            float scrollwheel = Input.GetAxis("Mouse ScrollWheel");
            float mouse_x = Input.mousePosition.x;
            float mouse_y = Input.mousePosition.y;

            //zoom with scroll wheel; forward to zoom in, backward to scroll out.
            transform.Translate(0, -scrollwheel * zoom_speed, scrollwheel * zoom_speed, Space.World);

            // Orbit function using right mouse button pressed.
            if (Input.GetMouseButton(1))
            {
                rotation_y += Input.GetAxis("Mouse X") * speed_x * Time.deltaTime;
                transform.localEulerAngles = new Vector3(0, rotation_y, 0);
            }

            // movement scrolling on the side of the screen; the threshold define how far to the border
            // is the scrolling activating.
            if (mouse_x >= Screen.width - edge_threshold && transform.position.x <= scroll_limit_x)
            {
                transform.Translate((Vector3.right * speed * Time.deltaTime), Space.Self);
            }
            else if (mouse_x < edge_threshold && transform.position.x >= -scroll_limit_x)
            {
                transform.Translate((Vector3.left * speed * Time.deltaTime), Space.Self);
            }
            else if (mouse_y >= Screen.height - edge_threshold && transform.position.z <= scroll_limit_z)
            {
                transform.Translate((Vector3.forward * speed * Time.deltaTime), Space.Self);
            }
            else if (mouse_y < edge_threshold && transform.position.z >= -scroll_limit_z)
            {
                transform.Translate((Vector3.back * speed * Time.deltaTime), Space.Self);
            }

        }
    }