using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

/// <summary>
/// 屏幕虚拟摇杆（移动轮盘）。挂在预制体根节点上，底盘和摇杆头两个引用
/// （background / handle）在 Inspector / 预制体里接好，代码里不按名字查找节点。
///
/// 鼠标按住拖拽或手指触摸都可以操作，对外输出归一化方向 <see cref="Value"/>：
/// x = 左右（右为正），y = 前后（上为正），模长 0~1 表示推杆幅度。
/// 松手后方向归零。
/// </summary>
[DisallowMultipleComponent]
public class VirtualJoystick : MonoBehaviour, IPointerDownHandler, IDragHandler, IPointerUpHandler
{
    [Header("引用（必须在 Inspector / 预制体里指定）")]
    [Tooltip("摇杆底盘（RectTransform）。拖拽位置以它的轴心为圆心换算，必须是捕获点击的那个节点")]
    [SerializeField] private RectTransform background;

    [Tooltip("摇杆头（RectTransform），跟着拖拽移动")]
    [SerializeField] private RectTransform handle;

    [Header("手感（距离单位是 UI 像素，以底盘轴心为圆心）")]
    [Tooltip("摇杆头允许离开中心的最大距离。拖到这个距离就是满值输入（Value 模长 = 1），再往外拖摇杆头也不动。" +
             "底盘 280、摇杆头 120 时，80 ≈ 摇杆头刚好贴到底盘边缘。")]
    [SerializeField] private float maxDragRadius = 80f;

    [Tooltip("死区：拖动距离小于「最大半径 × 该比例」时不输出，避免手抖")]
    [Range(0f, 0.9f)]
    [SerializeField] private float deadZone = 0.12f;

    [Tooltip("松手后摇杆头是否弹回中心")]
    [SerializeField] private bool returnToCenter = true;

    [Tooltip("松手后是否隐藏整个轮盘（移动端常用）")]
    [SerializeField] private bool hideOnRelease = false;

    /// <summary>归一化输入方向，x = 左右，y = 前后，模长 0~1。</summary>
    public Vector2 Value { get; private set; }

    /// <summary>当前是否按住了轮盘。</summary>
    public bool IsPressed { get; private set; }

    private Canvas _canvas;
    private Vector2 _handleHomePosition;

    private void Awake()
    {
        if (background == null)
            Debug.LogError("[VirtualJoystick] 没有指定摇杆底盘（background），请在 Inspector / 预制体里拖入。", this);
        if (handle == null)
            Debug.LogError("[VirtualJoystick] 没有指定摇杆头（handle），请在 Inspector / 预制体里拖入。", this);

        _canvas = GetComponentInParent<Canvas>();
        if (handle != null)
            _handleHomePosition = handle.anchoredPosition;
    }

    private void OnEnable()
    {
        ResetInput();
    }

    public void OnPointerDown(PointerEventData eventData)
    {
        IsPressed = true;
        gameObject.SetActive(true);
        UpdateFromPointer(eventData);
    }

    public void OnDrag(PointerEventData eventData)
    {
        IsPressed = true;
        UpdateFromPointer(eventData);
    }

    public void OnPointerUp(PointerEventData eventData)
    {
        IsPressed = false;

        if (returnToCenter)
            ResetInput();

        if (hideOnRelease)
            gameObject.SetActive(false);
    }

    /// <summary>把摇杆归零，手柄回到初始位置。</summary>
    public void ResetInput()
    {
        Value = Vector2.zero;
        if (handle != null)
            handle.anchoredPosition = _handleHomePosition;
    }

    private void UpdateFromPointer(PointerEventData eventData)
    {
        if (background == null) return;

        Camera cam = _canvas != null && _canvas.renderMode == RenderMode.ScreenSpaceOverlay
            ? null
            : (eventData.pressEventCamera != null ? eventData.pressEventCamera : (_canvas != null ? _canvas.worldCamera : null));

        if (!RectTransformUtility.ScreenPointToLocalPointInRectangle(background, eventData.position, cam, out Vector2 local))
            return;

        // local 是相对底盘轴心的像素偏移，直接按「最大拖动半径」归一化
        float radius = Mathf.Max(1f, maxDragRadius);
        float distance = local.magnitude;
        Vector2 direction = distance > 0.0001f ? local / distance : Vector2.zero;
        float magnitude = Mathf.Clamp01(distance / radius);

        if (magnitude < deadZone)
        {
            Value = Vector2.zero;
        }
        else
        {
            // 死区外的部分重新映射到 0~1，避免刚出死区就一大跳
            float remapped = Mathf.InverseLerp(deadZone, 1f, magnitude);
            Value = direction * Mathf.Clamp01(remapped);
        }

        if (handle != null)
            handle.anchoredPosition = _handleHomePosition + direction * (magnitude * radius);
    }
}