using UnityEngine;

namespace EventBossFight
{
    /// <summary>
    /// UI RectTransform 跟随另一 RectTransform（视频 Boss 挂点，替代 Spine BoneFollower）。
    /// 同一 rootCanvas 下直接同步世界坐标；否则经屏幕坐标转换到父 Rect 的局部空间。
    /// </summary>
    [RequireComponent(typeof(RectTransform))]
    [DefaultExecutionOrder(1000)]
    public class EventBossFightRectFollowerGraphic : MonoBehaviour
    {
        [SerializeField]
        private RectTransform target;

        public RectTransform Target => target;

        public void SetTarget(RectTransform t)
        {
            target = t;
        }

        private void OnEnable()
        {
            ApplyFollow();
        }

        private void LateUpdate()
        {
            ApplyFollow();
        }

        private void ApplyFollow()
        {
            if (!target)
                return;
            var self = (RectTransform)transform;
            var parent = self.parent as RectTransform;
            if (!parent)
            {
                self.SetPositionAndRotation(target.position, target.rotation);
                return;
            }

            var canvasSelf = self.GetComponentInParent<Canvas>();
            var canvasTarget = target.GetComponentInParent<Canvas>();
            if (canvasSelf && canvasTarget && canvasSelf.rootCanvas == canvasTarget.rootCanvas)
            {
                self.SetPositionAndRotation(target.position, target.rotation);
                return;
            }

            var camTarget = GetEventCamera(canvasTarget);
            var camSelf = GetEventCamera(canvasSelf);
            // Overlay 下 WorldToScreenPoint 须传 null；Camera 模式用对应 Canvas 的 worldCamera
            Camera camForScreen = null;
            if (canvasTarget != null && canvasTarget.renderMode == RenderMode.ScreenSpaceOverlay)
                camForScreen = null;
            else
                camForScreen = camTarget ?? camSelf ?? Camera.main;

            var screenPoint = RectTransformUtility.WorldToScreenPoint(camForScreen, target.position);
            var camForParent = canvasSelf && canvasSelf.renderMode == RenderMode.ScreenSpaceOverlay
                ? null
                : camSelf ?? camForScreen;

            if (RectTransformUtility.ScreenPointToLocalPointInRectangle(parent, screenPoint, camForParent,
                    out var localPoint))
            {
                self.anchoredPosition = localPoint;
                self.localRotation = Quaternion.Inverse(parent.rotation) * target.rotation;
            }
            else
                self.SetPositionAndRotation(target.position, target.rotation);
        }

        private static Camera GetEventCamera(Canvas canvas)
        {
            if (!canvas || canvas.renderMode == RenderMode.ScreenSpaceOverlay)
                return null;
            return canvas.worldCamera;
        }
    }
}