using UnityEngine;

public class CameraBehaviour : MonoBehaviour
{
    public Transform target;

    private const int MouseWheelSensitivity = 1; //滚轮灵敏度设置
    private const int MouseZoomMin = 1; //相机距离最小值
    private const int MouseZoomMax = 20; //相机距离最大值
    private const float XSpeed = 250.0f;
    private const float YSpeed = 120.0f;
    private const int YMinLimit = -360;
    private const int YMaxLimit = 360;

    private float _eulerX; //存储相机的euler角
    private float _eulerY; //存储相机的euler角

    private float _distance = 5; //相机和target之间的距离，因为相机的Z轴总是指向target，也就是相机z轴方向上的距离
    private Vector3 _targetOnScreenPosition; //目标的屏幕坐标，第三个值为z轴距离
    private Quaternion _cameraRotation; //存储相机的姿态四元数
    private Vector3 _targetPosition; //target的位置
    private Vector3 _initPosition; //平移时用于存储平移的起点位置
    private Vector3 _cameraX; //相机的x轴方向向量
    private Vector3 _cameraY; //相机的y轴方向向量
    private Vector3 _initScreenPosition; //中键刚按下时鼠标的屏幕坐标（第三个值其实没什么用）
    private Vector3 _cursorScreenPosition; //当前鼠标的屏幕坐标（第三个值其实没什么用）

    private Camera _mainCamera;

    private void Start()
    {
        //这里就是设置一下初始的相机视角以及一些其他变量，这里的x和y。。。是和下面getAxis的mouse x与mouse y对应
        var angles = transform.eulerAngles;
        _eulerX = angles.y;
        _eulerY = angles.x;
        _targetPosition = target.position;
        _cameraRotation = Quaternion.Euler(_eulerY + 60, _eulerX, 0);
        
        // 引入中间变量 提高代码效率
        var transform1 = transform;
        //设置相机姿态
        transform1.rotation = _cameraRotation;
        //设置相机位置
        transform1.position = _cameraRotation * new Vector3(0, 0, -_distance) + _targetPosition;
        
        // 获得主摄像机
        _mainCamera = Camera.main;
    }

    private void Update()
    {
        //鼠标右键旋转功能
        if (Input.GetMouseButton(1))
        {
            _eulerX += Input.GetAxis("Mouse X") * XSpeed * 0.02f;
            _eulerY -= Input.GetAxis("Mouse Y") * YSpeed * 0.02f;

            _eulerY = ClampAngle(_eulerY, YMinLimit, YMaxLimit);

            _cameraRotation = Quaternion.Euler(_eulerY + 60, _eulerX, 0);
            var position = _cameraRotation * new Vector3(0.0f, 0.0f, -_distance) + _targetPosition;

            // 引入中间变量 提高代码效率
            var transform1 = transform;
            transform1.rotation = _cameraRotation;
            transform1.position = position;
        }
        else if (Input.GetAxis("Mouse ScrollWheel") != 0) //鼠标滚轮缩放功能
        {
            if (_distance is >= MouseZoomMin and <= MouseZoomMax)
            {
                _distance -= Input.GetAxis("Mouse ScrollWheel") * MouseWheelSensitivity;
            }

            if (_distance < MouseZoomMin)
            {
                _distance = MouseZoomMin;
            }

            if (_distance > MouseZoomMax)
            {
                _distance = MouseZoomMax;
            }

            transform.position = _cameraRotation * new Vector3(0.0F, 0.0F, -_distance) + _targetPosition;
        }

        //鼠标中键平移
        if (Input.GetMouseButtonDown(2))
        {
            // 添加中间变量
            // 提高代码效率
            var transform1 = transform;
            _cameraX = transform1.right;
            _cameraY = transform1.up;

            _initScreenPosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, _targetOnScreenPosition.z);

            //targetOnScreenPosition.z为目标物体到相机平面的法线距离
            _targetOnScreenPosition = _mainCamera.WorldToScreenPoint(_targetPosition);
            _initPosition = _targetPosition;
        }

        if (Input.GetMouseButton(2))
        {
            _cursorScreenPosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, _targetOnScreenPosition.z);
            //0.01这个系数是控制平移的速度，要根据相机和目标物体的distance来灵活选择
            target.position = _initPosition - 0.01f * ((_cursorScreenPosition.x - _initScreenPosition.x) * _cameraX +
                                                      (_cursorScreenPosition.y - _initScreenPosition.y) * _cameraY);

            //重新计算位置
            var mPosition = _cameraRotation * new Vector3(0.0F, 0.0F, -_distance) + target.position;
            transform.position = mPosition;

            // //用这个会让相机的平移变得更平滑，但是可能在你ButtonUp时未使相机移动到应到的位置，导致再进行旋转与缩放操作时出现短暂抖动
            //transform.position=Vector3.Lerp(transform.position,mPosition,Time.deltaTime*moveSpeed);
        }

        if (Input.GetMouseButtonUp(2))
        {
            //平移结束把cameraTargetPosition的位置更新一下，不然会影响缩放与旋转功能
            _targetPosition = target.position;
        }
    }

    //将angle限制在min~max之间
    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);
    }

    /*void testScreenToWorldPoint()
    {
        //第三个坐标指的是在相机z轴指向方向上的距离
        Vector3 screenPoint = Camera.main.WorldToScreenPoint(_targetPosition);
        Debug.Log("ScreenPoint: " + screenPoint);

        // var worldPosition = Camera.main.ScreenToWorldPoint(new Vector3(1,1,10));
        // Debug.Log("worldPosition: "+worldPosition);
    }*/
}