using UnityEngine;

public class CustomScrollView : MonoBehaviour
{
    public RectTransform rectStopUp;
    public RectTransform rectStopDown;
    public RectTransform rectTitle;
    public RectTransform rectCenter;

    public RectTransform rectCenterLimitUp;
    public RectTransform rectCenterLimitDown;
    public RectTransform rectCenterSubUp;
    public RectTransform rectCenterSubDown;

    // 缓冲效果参数
    private float damping = 0.9f; // 阻尼系数，值越小缓冲越快
    private float minVelocity = 0.1f; // 最小速度阈值

    private Vector3 vecStart;
    private Vector3 vecStartCenter;
    private Vector3 vecStartTitle;
    private Vector3 velocity = Vector3.zero; // 当前速度
    private bool isDragging = false;
    private float lastMouseY;
    private bool shouldStopScrollUp = false; // 是否应该停止向上滑动
    private bool shouldStopScrollDown = false; // 是否应该停止向下滑动

    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            StartDragging();
        }

        if (Input.GetMouseButtonUp(0))
        {
            StopDragging();
        }

        if (Input.GetMouseButton(0))
        {
            HandleDragging();
        }

        // 应用缓冲效果
        ApplyInertia();
    }

    private void StartDragging()
    {
        vecStart = Input.mousePosition;
        vecStartCenter = rectCenter.position;
        vecStartTitle = rectTitle.position;
        lastMouseY = Input.mousePosition.y;
        velocity = Vector3.zero;
        isDragging = true;
        shouldStopScrollUp = false;
        shouldStopScrollDown = false;
    }

    private void StopDragging()
    {
        isDragging = false;
    }

    private void HandleDragging()
    {
        if (!isDragging) return;

        Vector3 currentMousePos = Input.mousePosition;

        // 计算基于鼠标Y值移动量的滑动
        float deltaY = currentMousePos.y - vecStart.y;
        Vector3 newPosition = vecStartCenter + new Vector3(0, deltaY, 0);

        // 检查边界限制
        CheckScrollLimits(deltaY);

        // 根据边界限制决定是否更新rectCenter位置
        if (!(deltaY > 0 && shouldStopScrollDown) && !(deltaY < 0 && shouldStopScrollUp))
        {
            // 直接设置rectCenter的位置
            rectCenter.position = newPosition;

            // 计算rectTitle应该移动到的位置
            Vector3 newTitlePosition = vecStartTitle + new Vector3(0, deltaY, 0);

            // 限制rectTitle的位置，不能超过上下边界
            float minY = rectStopDown.position.y;
            float maxY = rectStopUp.position.y;
            newTitlePosition.y = Mathf.Clamp(newTitlePosition.y, minY, maxY);

            // 设置rectTitle的位置
            rectTitle.position = newTitlePosition;
        }

        // 计算当前速度（用于缓冲效果）
        float currentDeltaY = currentMousePos.y - lastMouseY;
        velocity = new Vector3(0, currentDeltaY / Time.deltaTime, 0);
        lastMouseY = currentMousePos.y;
    }

    private void ApplyInertia()
    {
        if (!isDragging && velocity.magnitude > minVelocity)
        {
            // 检查边界限制
            CheckScrollLimits(velocity.y * Time.deltaTime);

            // 检查是否应该停止惯性滑动
            bool shouldStopInertia = (velocity.y > 0 && shouldStopScrollDown) || (velocity.y < 0 && shouldStopScrollUp);

            if (!shouldStopInertia)
            {
                // 使用指数衰减的缓冲
                float deceleration = Mathf.Pow(damping, Time.deltaTime * 60f);
                velocity *= deceleration;

                // rectCenter继续移动
                rectCenter.position += velocity * Time.deltaTime;

                // rectTitle跟随rectCenter移动，但受边界限制
                Vector3 newTitlePosition = rectTitle.position + velocity * Time.deltaTime;
                float minY = rectStopDown.position.y;
                float maxY = rectStopUp.position.y;
                newTitlePosition.y = Mathf.Clamp(newTitlePosition.y, minY, maxY);
                rectTitle.position = newTitlePosition;
            }
            else
            {
                // 如果应该停止，则快速减速
                velocity *= 0.5f;
            }

            if (velocity.magnitude <= minVelocity)
            {
                velocity = Vector3.zero;
            }
        }
        else if (!isDragging && velocity.magnitude <= minVelocity)
        {
            // 当速度很小时，确保rectTitle仍在边界内
            Vector3 currentTitlePos = rectTitle.position;
            float minY = rectStopDown.position.y;
            float maxY = rectStopUp.position.y;
            currentTitlePos.y = Mathf.Clamp(currentTitlePos.y, minY, maxY);
            rectTitle.position = currentTitlePos;
        }
    }

    // 检查滑动边界限制
    private void CheckScrollLimits(float deltaY)
    {
        // 重置标志
        shouldStopScrollUp = false;
        shouldStopScrollDown = false;

        // 检查向下滑动时rectCenterSubUp不能低于rectCenterLimitUp
        if (deltaY < 0) // 向上滑动（rectCenter向下移动）
        {
            if (rectCenterSubUp != null && rectCenterLimitUp != null)
            {
                // 检查rectCenterSubUp的底部是否低于rectCenterLimitUp的顶部
                float subUpBottom = rectCenterSubUp.position.y - rectCenterSubUp.rect.height / 2;
                float limitUpTop = rectCenterLimitUp.position.y + rectCenterLimitUp.rect.height / 2;

                if (subUpBottom < limitUpTop)
                {
                    shouldStopScrollUp = true;
                }
            }
        }

        // 检查向上滑动时rectCenterSubDown不能高于rectCenterLimitDown
        if (deltaY > 0) // 向下滑动（rectCenter向上移动）
        {
            if (rectCenterSubDown != null && rectCenterLimitDown != null)
            {
                // 检查rectCenterSubDown的顶部是否高于rectCenterLimitDown的底部
                float subDownTop = rectCenterSubDown.position.y + rectCenterSubDown.rect.height / 2;
                float limitDownBottom = rectCenterLimitDown.position.y - rectCenterLimitDown.rect.height / 2;

                if (subDownTop > limitDownBottom)
                {
                    shouldStopScrollDown = true;
                }
            }
        }
    }

    // 外部可以调用这个方法来添加额外的速度（例如反弹效果）
    public void AddVelocity(Vector3 additionalVelocity)
    {
        velocity += additionalVelocity;
    }

    // 设置缓冲参数
    public void SetDamping(float newDamping)
    {
        damping = Mathf.Clamp(newDamping, 0.1f, 0.99f);
    }

    // 获取当前速度
    public Vector3 GetCurrentVelocity()
    {
        return velocity;
    }

    // 新增：强制更新rectTitle位置到边界内（可以在必要时调用）
    public void ClampTitlePosition()
    {
        Vector3 currentTitlePos = rectTitle.position;
        float minY = rectStopDown.position.y;
        float maxY = rectStopUp.position.y;
        currentTitlePos.y = Mathf.Clamp(currentTitlePos.y, minY, maxY);
        rectTitle.position = currentTitlePos;
    }
}