using UnityEngine;


/// <summary>
/// 指令碼掛載新建相機上 —— 
/// </summary>
public class ChinarSmoothUi3DCamera : MonoBehaviour
{
    public  Transform pivot;
    public  Vector3   pivotOffset = Vector3.zero;
    public  Transform target;
    public  float     distance       = 10.0f;
    public  float     minDistance    = 2f;
    public  float     maxDistance    = 15f;
    public  float     zoomSpeed      = 1f;
    public  float     xSpeed         = 250.0f;
    public  float     ySpeed         = 250.0f;
    public  bool      allowYTilt     = true;
    public  float     yMinLimit      = -90f;
    public  float     yMaxLimit      = 90f;
    private float     x              = 0.0f;
    private float     y              = 0.0f;
    private float     targetX        = 0f;
    private float     targetY        = 0f;
    public  float     targetDistance = 0f;
    private float     xVelocity      = 1f;
    private float     yVelocity      = 1f;
    private float     zoomVelocity   = 1f;


    private void Start()
    {
        var angles         = transform.eulerAngles;
        targetX        = x = angles.x;
        targetY        = y = ClampAngle(angles.y, yMinLimit, yMaxLimit);
        targetDistance = distance;
    }


    private void LateUpdate()
    {
        if (!pivot) return;
        var scroll = Input.GetAxis("Mouse ScrollWheel");
        if (scroll      > 0.0f) targetDistance -= zoomSpeed;
        else if (scroll < 0.0f)
            targetDistance += zoomSpeed;
        targetDistance = Mathf.Clamp(targetDistance, minDistance, maxDistance);
        if (Input.GetMouseButton(1) || (Input.GetMouseButton(0) && (Input.GetKey(KeyCode.LeftControl) || Input.GetKey(KeyCode.RightControl))))
        {
            targetX += Input.GetAxis("Mouse X") * xSpeed * 0.02f;
            if (allowYTilt)
            {
                targetY -= Input.GetAxis("Mouse Y") * ySpeed * 0.02f;
                targetY =  ClampAngle(targetY, yMinLimit, yMaxLimit);
            }
        }

        x = Mathf.SmoothDampAngle(x, targetX, ref xVelocity, 0.3f);
        y = allowYTilt ? Mathf.SmoothDampAngle(y, targetY, ref yVelocity, 0.3f) : targetY;
        Quaternion rotation = Quaternion.Euler(y, x, 0);//水平移動相當於繞Y軸，垂直移動相當於繞X軸，所以要置換
        distance = Mathf.SmoothDamp(distance, targetDistance, ref zoomVelocity, 0.5f);
        Vector3 position = rotation * new Vector3(0.0f, 0.0f, -distance) + pivot.position + pivotOffset;
        transform.rotation = rotation;
        transform.position = position;
    }


    private static float ClampAngle(float angle, float min, float max)
    {
        if (angle < -360) angle += 360;
        if (angle > 360) angle  -= 360;
        return Mathf.Clamp(angle, min, max);
    }
}