using UnityEngine;

public class CameraControl : MonoBehaviour
{
    public float m_DampTime = 0.2f;                 // Approximate time for the camera to refocus.
    public float m_ScreenEdgeBuffer = 4f;           // Space between the top/bottom most target and the screen edge.
    public float m_MinSize = 6.5f;                  // The smallest orthographic size the camera can be.
    [HideInInspector] public Transform[] m_Targets; // All the targets the camera needs to encompass.


    private Camera m_Camera;                        // Used for referencing the camera.
    private float m_ZoomSpeed;                      // Reference speed for the smooth damping of the orthographic size.
    private Vector3 m_MoveVelocity;                 // Reference velocity for the smooth damping of the position.
    private Vector3 m_DesiredPosition;              // The position the camera is moving towards.


    private void Awake ()
    {
        m_Camera = GetComponentInChildren<Camera> ();
    }


    private void FixedUpdate ()
    {
        // Move the camera towards a desired position.
        Move ();

        // Change the size of the camera based.
        Zoom ();
    }


    private void Move ()
    {
        // Find the average position of the targets.
        FindAveragePosition ();

        // Smoothly transition to that position.
        transform.position = Vector3.SmoothDamp(transform.position, m_DesiredPosition, ref m_MoveVelocity, m_DampTime);
    }


    private void FindAveragePosition ()
    {
        Vector3 averagePos = new Vector3 ();
        int numTargets = 0;

        // Go through all the targets and add their positions together.
        for (int i = 0; i < m_Targets.Length; i++)
        {
            // If the target isn't active, go on to the next one.
            if (!m_Targets[i].gameObject.activeSelf)
                continue;

            // Add to the average and increment the number of targets in the average.
            averagePos += m_Targets[i].position;
            numTargets++;
        }

        // If there are targets divide the sum of the positions by the number of them to find the average.
        if (numTargets > 0)
            averagePos /= numTargets;

        // Keep the same y value.
        averagePos.y = transform.position.y;

        // The desired position is the average position;
        m_DesiredPosition = averagePos;
    }


    private void Zoom ()
    {
        // Find the required size based on the desired position and smoothly transition to that size.
        float requiredSize = FindRequiredSize();
        m_Camera.orthographicSize = Mathf.SmoothDamp (m_Camera.orthographicSize, requiredSize, ref m_ZoomSpeed, m_DampTime);
    }


    private float FindRequiredSize ()
    {
        // Find the position the camera rig is moving towards in its local space.
        Vector3 desiredLocalPos = transform.InverseTransformPoint(m_DesiredPosition);

        // Start the camera's size calculation at zero.
        float size = 0f;

        // Go through all the targets...
        for (int i = 0; i < m_Targets.Length; i++)
        {
            // ... and if they aren't active continue on to the next target.
            if (!m_Targets[i].gameObject.activeSelf)
                continue;

            // Otherwise, find the position of the target in the camera's local space.
            Vector3 targetLocalPos = transform.InverseTransformPoint(m_Targets[i].position);

            // Find the position of the target from the desired position of the camera's local space.
            Vector3 desiredPosToTarget = targetLocalPos - desiredLocalPos;

            // Choose the largest out of the current size and the distance of the tank 'up' or 'down' from the camera.
            size = Mathf.Max(size, Mathf.Abs(desiredPosToTarget.y));

            // Choose the largest out of the current size and the calculated size based on the tank being to the left or right of the camera.
            size = Mathf.Max(size, Mathf.Abs(desiredPosToTarget.x) / m_Camera.aspect);
        }

        // Add the edge buffer to the size.
        size += m_ScreenEdgeBuffer;

        // Make sure the camera's size isn't below the minimum.
        size = Mathf.Max (size, m_MinSize);

        return size;
    }


    public void SetStartPositionAndSize ()
    {
        // Find the desired position.
        FindAveragePosition ();

        // Set the camera's position to the desired position without damping.
        transform.position = m_DesiredPosition;

        // Find and set the required size of the camera.
        m_Camera.orthographicSize = FindRequiredSize ();
    }
}