using UnityEngine;
using UnityEngine.Serialization;

/// <summary>
/// 统一物理线缆（移植自 Assets/Prototype/2D线缆物理交互 原型）：
/// 固定粒子数 + 可变总长度的 Verlet 绳，一条线覆盖旧 Cable（拖拽）/ PhysicCable（闲置）两套状态。
/// 拖拽时按需送线、松手自动回收到最短长度、插入插孔时末端钉住。
/// </summary>
[RequireComponent(typeof(LineRenderer))]
public class PhysicCable : MonoBehaviour
{
    public enum CableState
    {
        Hidden,   // 收起，不渲染不模拟
        Free,     // 闲置下垂，自动回收到最短长度
        Dragging, // 末端钉在拖拽目标上，按需送线
        Plugged   // 末端钉在插孔上
    }

    [FormerlySerializedAs("StartTranform")] public Transform startTransform; // 出线口

    [Header("绳体")]
    [SerializeField] private int pointCount = 40;
    [SerializeField] private float minLength = 2f;          // 闲置时的自然下垂长度
    [SerializeField, Range(0.05f, 1f)] private float idleLengthScale = 0.08f;
    [SerializeField] private float maxStretch = 8f;         // 最大拉出长度（相对 minLength 的倍数）
    [SerializeField] private float gravity = 100f;          // 世界单位/s²，向下
    [SerializeField, Range(0.8f, 1f)] private float damping = 0.965f;
    [SerializeField] private int constraintIterations = 24;
    [SerializeField, Range(0f, 1f)] private float bendSmooth = 0.3f; // 弯曲刚度（中点平滑）
    [SerializeField] private float endGravityBoost = 1.8f;  // 末端几个点的重力加成，让插头端垂坠

    [Header("收放")]
    [SerializeField] private float feedRate = 0.45f;    // 送线速度
    [SerializeField] private float holdRate = 0.06f;    // 拖拽/插接中回收速度
    [SerializeField] private float retractRate = 0.09f; // 松手后回收速度
    [SerializeField] private float lengthMargin = 0.45f; // 需求长度余量

    [Header("出线口保护段")]
    [SerializeField] private float stubMinOffset = 0.12f; // 出线口处沿出线方向至少伸出的距离

    [Header("插头朝向")]
    [SerializeField] private float plugRefArcLength = 0.6f; // 取角度参考点时向回走的弧长
    [SerializeField] private float plugTurnRate = 0.18f;
    [SerializeField] private float plugMaxTurnStep = 0.11f; // 每步最大转角（弧度）

    [Header("可选")]
    [SerializeField] private Transform reelCenter; // 出线方向参考中心，空则用 startTransform.parent
    [SerializeField] private Transform floorLimit; // 地面高度参考，空则不启用地面碰撞

    [Header("外观(单 Mesh 分带,对应原型 pixel 预设)")]
    [SerializeField] private Material cableMaterial;   // 空则运行时回退 Sprite-Unlit-Default / Sprites-Default
    // Tools 层整层高于 FixTop(屏幕 UI Canvas 在 FixTop/100),插头历来在 Tools 上未被遮挡;
    // 线缆与插头(Tools/48)成对相邻,剪线等演出覆盖物(Tools/50+)仍可整体盖住两者
    [SerializeField] private string sortingLayerName = "Tools";
    [SerializeField] private int sortingOrder = 47;
    // 三档色阶(描边/主体/顶光),压暗去饱和贴合场景像素环境;原型的第四档高光去掉
    [SerializeField] private Color shadowColor = new(0.05f, 0.05f, 0.07f, 0.2f);
    [SerializeField] private float shadowWidth = 0.295f;
    [SerializeField] private float shadowDrop = 0.12f;      // 原型:向下平移 7px
    [SerializeField] private Color darkColor = new(0.09f, 0.11f, 0.18f, 1f);   // 深色描边
    [SerializeField] private float darkWidth = 0.33f;       // 原型:w+4
    [SerializeField] private Color bodyColor = new(0.24f, 0.30f, 0.44f, 1f);   // 主体(低饱和板岩蓝)
    [SerializeField] private float bodyWidth = 0.26f;       // 原型:w=15px ≈ 0.26wu
    [SerializeField] private Color midColor = new(0.38f, 0.45f, 0.60f, 1f);    // 顶光
    [SerializeField] private float midWidth = 0.143f;       // 原型:0.55w
    [SerializeField] private float midLift = 0.036f;        // 原型:上移 0.14w

    [Header("端部收窄(默认关闭:整根线宽与插头/孔匹配)")]
    [SerializeField, Range(0f, 0.3f)] private float tipTaperFraction = 0f;  // 末端收窄段占全长比例,0 关闭
    [SerializeField, Range(0.3f, 1f)] private float tipTaperScale = 0.72f;  // 末端最细处宽度比例

    [Header("自遮挡(尾段盖头段)")]
    [SerializeField] private float overlapMargin = 0.1f;    // 原型:m.w + 6px 的余量部分


    public CableState State { get; private set; } = CableState.Hidden;

    public Vector3 EndPosition => _pts != null
        ? _pts[_n - 1].pos
        : (startTransform != null ? startTransform.position : transform.position);

    public float CurrentLength => _length;

    private struct Particle
    {
        public Vector3 pos;
        public Vector3 prev;
    }

    private Particle[] _pts;
    private int _n;
    private float _length;
    private Vector3 _pointer;    // 拖拽指针（世界坐标，驱动送线长度）
    private Vector3 _dragTarget; // 末端钉住目标（重 lerp + 长度钳制，消除拽满时的抖动）
    private Transform _dock;     // 当前插入的插孔
    private Vector3 _plugSnapEnd; // 插接吸附目标:渐进收敛到孔心后末端硬钉,保证完全对齐堵住孔
    private float _plugAngle = -Mathf.PI / 2f; // 插头朝向（弧度，初始朝下）

    private LineRenderer _line; // 遗留组件,仅保持禁用(旧场景/CableSystem 仍会引用)
    private CableMeshRenderer _cableMesh;
    private Vector3[] _renderA;
    private Vector3[] _renderB;
    private const int SmoothIterations = 2; // Chaikin 切角细分次数

    private bool _initialized;

    private void Awake()
    {
        _line = GetComponent<LineRenderer>();
        if (_line != null) _line.enabled = false;
        EnsureMeshRenderer();
    }

    // ------------------------------ 状态 API ------------------------------

    public void Hide()
    {
        State = CableState.Hidden;
        _dock = null;
        SetCableRenderersEnabled(false);
    }

    /// <summary>闲置下垂状态；resetShape 时把绳重置为从出线口自然下垂。</summary>
    public void ShowFree(bool resetShape = false)
    {
        EnsureInit();
        if (resetShape) ResetHangingShape();
        _dock = null;
        State = CableState.Free;
        SetCableRenderersEnabled(true);
    }

    public void BeginDrag(Vector3 pointerWorld)
    {
        EnsureInit();
        if (State == CableState.Hidden) ResetHangingShape();
        _dock = null;
        _pointer = FlattenZ(pointerWorld);
        _dragTarget = _pts[_n - 1].pos;
        State = CableState.Dragging;
        SetCableRenderersEnabled(true);
    }

    public void SetPointer(Vector3 pointerWorld)
    {
        _pointer = FlattenZ(pointerWorld);
    }

    public void EndDrag()
    {
        if (State == CableState.Dragging)
        {
            State = CableState.Free;
        }
    }

    /// <summary>末端钉到插孔；snapStraight 用于读档，把绳直接摆成出线口到插孔的直线。</summary>
    public void PlugInto(Transform dock, bool snapStraight = false)
    {
        EnsureInit();
        _dock = dock;
        State = CableState.Plugged;
        SetCableRenderersEnabled(true);
        if (snapStraight && dock != null)
        {
            ResetStraightTo(FlattenZ(dock.position));
        }
        // 吸附目标从当前末端出发,向孔心渐进收敛(保留吸入动画,最终严格钉在孔心)
        _plugSnapEnd = _pts[_n - 1].pos;
    }

    // ------------------------------ 插头姿态 ------------------------------

    /// <summary>把插头摆到绳末端并按绳向旋转（角度经过平滑与限速）。</summary>
    public void ApplyPlugPose(Transform plug, Transform plugRoot)
    {
        if (_pts == null || plug == null) return;

        plug.rotation = Quaternion.Euler(0, 0, _plugAngle * Mathf.Rad2Deg - 90f);

        Vector3 end = _pts[_n - 1].pos;
        if (plugRoot != null)
        {
            Vector3 delta = end - plugRoot.position;
            delta.z = 0;
            plug.position += delta;
        }
        else
        {
            plug.position = new Vector3(end.x, end.y, plug.position.z);
        }
    }

    // ------------------------------ 模拟 ------------------------------

    private void FixedUpdate()
    {
        if (State == CableState.Hidden || _pts == null || startTransform == null) return;

        Simulate(Time.fixedDeltaTime);
    }

    private void LateUpdate()
    {
        // 渲染放 LateUpdate:与插头跟随(CablePanel.LateUpdate)读同一份点位,消除拖拽时线头分离
        if (State == CableState.Hidden || _pts == null) return;

        Render();
    }

    private void EnsureInit()
    {
        if (_initialized) return;
        _initialized = true;

        EnsureMeshRenderer();

        _n = Mathf.Max(8, pointCount);
        _pts = new Particle[_n];
        int renderCount = _n << SmoothIterations;
        _renderA = new Vector3[renderCount];
        _renderB = new Vector3[renderCount];

        ResetHangingShape();
    }

    private void ResetHangingShape()
    {
        Vector3 anchor = startTransform.position;
        float idleLength = GetIdleLength();
        for (int i = 0; i < _n; i++)
        {
            float t = i / (float)(_n - 1);
            Vector3 p = anchor + Vector3.down * (t * idleLength) + Vector3.right * (t * 0.02f);
            _pts[i].pos = p;
            _pts[i].prev = p;
        }
        _length = idleLength;
        _plugAngle = -Mathf.PI / 2f;
    }

    private void ResetStraightTo(Vector3 end)
    {
        Vector3 anchor = startTransform.position;
        float idleLength = GetIdleLength();
        for (int i = 0; i < _n; i++)
        {
            float t = i / (float)(_n - 1);
            Vector3 p = Vector3.Lerp(anchor, end, t);
            _pts[i].pos = p;
            _pts[i].prev = p;
        }
        _length = Mathf.Max(idleLength, Vector3.Distance(anchor, end) * 1.04f + lengthMargin);
    }

    private void Simulate(float dt)
    {
        Vector3 anchor = startTransform.position;
        Vector3 outletDir = GetOutletDirection(anchor);
        float idleLength = GetIdleLength();

        bool dragging = State == CableState.Dragging;
        bool plugged = State == CableState.Plugged && _dock != null;
        bool pinnedEnd = dragging || plugged;
        Vector3 dock = plugged ? FlattenZ(_dock.position) : Vector3.zero;

        float lMax = minLength * maxStretch;
        if (plugged)
        {
            // 保证够得着插孔
            lMax = Mathf.Max(lMax, Vector3.Distance(dock, anchor) * 1.12f);
        }

        // --- 拖拽目标：重 lerp + 按当前绳长钳制（拽满时目标跟着绳长走，消除抖动）
        if (dragging)
        {
            _dragTarget += (_pointer - _dragTarget) * 0.3f;
            Vector3 offset = _dragTarget - anchor;
            float dist = offset.magnitude;
            float maxRadius = Mathf.Min(lMax, _length) * 0.99f;
            if (dist > maxRadius)
            {
                _dragTarget = anchor + offset / dist * maxRadius;
            }
        }

        // --- 送线 / 回收（长度由原始指针驱动，而非被钳制后的目标）
        Vector3 endTarget = dragging ? _pointer : (plugged ? dock : _pts[_n - 1].pos);
        float needed = Vector3.Distance(endTarget, anchor) * 1.04f + lengthMargin;
        float targetLength = pinnedEnd ? Mathf.Clamp(needed, idleLength, lMax) : idleLength;
        float rate = targetLength > _length ? feedRate : (pinnedEnd ? holdRate : retractRate);
        _length += (targetLength - _length) * rate;

        float seg = _length / (_n - 1);
        float g = gravity * dt * dt;

        // --- Verlet 积分
        for (int i = 1; i < _n; i++)
        {
            ref Particle p = ref _pts[i];
            Vector3 v = (p.pos - p.prev) * damping;
            p.prev = p.pos;
            float boost = i > _n - 4 ? endGravityBoost : 1f;
            p.pos += v + Vector3.down * (g * boost);
        }

        _pts[0].pos = anchor;
        _pts[0].prev = anchor;

        if (dragging)
        {
            _pts[_n - 1].pos = _dragTarget;
        }
        else if (plugged)
        {
            // 吸附目标渐进收敛到孔心后,末端硬钉——软拉会被重力/张力持续拽偏,堵不严孔
            _plugSnapEnd += (dock - _plugSnapEnd) * 0.5f;
            if ((_plugSnapEnd - dock).sqrMagnitude < 1e-4f) _plugSnapEnd = dock;
            _pts[_n - 1].pos = _plugSnapEnd;
            _pts[_n - 1].prev = _plugSnapEnd;
        }

        // --- 约束迭代
        for (int k = 0; k < constraintIterations; k++)
        {
            for (int i = 0; i < _n - 1; i++)
            {
                ref Particle a = ref _pts[i];
                ref Particle b = ref _pts[i + 1];
                Vector3 d = b.pos - a.pos;
                float dist = d.magnitude;
                if (dist < 1e-6f) dist = 1e-6f;
                float diff = (dist - seg) / dist;
                bool pinA = i == 0;
                bool pinB = i == _n - 2 && pinnedEnd;
                float wa = pinA ? 0f : (pinB ? 1f : 0.5f);
                float wb = pinB ? 0f : (pinA ? 1f : 0.5f);
                a.pos += d * (diff * wa);
                b.pos -= d * (diff * wb);
            }

            // 出线口保护段：靠近出线口的两个点顺着出线方向、横向收紧，
            // 无论绳的其余部分被拽到哪，出线处都不出现折角或自穿插
            ApplyOutletStub(anchor, outletDir);

            // 插接时把末段摆直指向孔心(移植原型的 plugged e2 约束,方向按来线方向泛化):
            // 倒数第二点拉向"孔心沿来线方向后退一节"的位置,末段直插进孔,不斜搭在孔上
            if (plugged)
            {
                Vector3 approach = dock - _pts[_n - 3].pos;
                approach.z = 0;
                float approachDist = approach.magnitude;
                if (approachDist > 1e-4f)
                {
                    Vector3 straightTarget = dock - approach / approachDist * seg;
                    _pts[_n - 2].pos += (straightTarget - _pts[_n - 2].pos) * 0.4f;
                }
            }

            // 弯曲刚度：中点平滑（每 3 次迭代做一次）
            if (bendSmooth > 0f && k % 3 == 0)
            {
                for (int i = 1; i < _n - 1; i++)
                {
                    if (i == _n - 2 && pinnedEnd) continue;
                    Vector3 mid = (_pts[i - 1].pos + _pts[i + 1].pos) * 0.5f;
                    _pts[i].pos += (mid - _pts[i].pos) * (bendSmooth * 0.5f);
                }
            }
        }

        // --- 地面（被钉住的拖拽末端豁免，避免钉点与地面互相拉扯）
        if (floorLimit != null)
        {
            float floorY = floorLimit.position.y;
            for (int i = 1; i < _n; i++)
            {
                if (i == _n - 1 && dragging) continue;
                if (_pts[i].pos.y < floorY)
                {
                    _pts[i].pos.y = floorY;
                    _pts[i].prev.x += (_pts[i].pos.x - _pts[i].prev.x) * 0.5f; // 摩擦
                }
            }
        }

        UpdatePlugAngle(anchor, dragging, plugged);
    }

    private void ApplyOutletStub(Vector3 anchor, Vector3 dir)
    {
        // P1：横向收紧 0.6，且沿出线方向至少伸出 stubMinOffset
        Vector3 rel = _pts[1].pos - anchor;
        float along = Vector3.Dot(rel, dir);
        Vector3 lateral = (rel - dir * along) * 0.4f;
        if (along < stubMinOffset) along = stubMinOffset;
        _pts[1].pos = anchor + dir * along + lateral;

        // P2：横向收紧 0.2
        rel = _pts[2].pos - anchor;
        along = Vector3.Dot(rel, dir);
        lateral = (rel - dir * along) * 0.8f;
        _pts[2].pos = anchor + dir * along + lateral;
    }

    private void UpdatePlugAngle(Vector3 anchor, bool dragging, bool plugged)
    {
        Vector3 end = _pts[_n - 1].pos;
        float targetAngle;

        if (plugged)
        {
            // 插着时插头精灵隐藏，保持角度即可
            targetAngle = _plugAngle;
        }
        else
        {
            // 拽紧时绳近似出线口到插头的直线，直接沿这条线取向；
            // 局部段方向在高张力下噪声大
            Vector3 toEnd = end - anchor;
            float taut = toEnd.magnitude / Mathf.Max(0.001f, _length);
            if (dragging && taut > 0.92f)
            {
                targetAngle = Mathf.Atan2(toEnd.y, toEnd.x);
            }
            else
            {
                // 角度取自向回走固定弧长的参考点；绳被压缩（末端点堆积）时方向不可靠，
                // 保持上一帧角度而不是乱翻
                int k = _n - 1;
                float arc = 0f;
                while (k > 0 && arc < plugRefArcLength)
                {
                    arc += Vector3.Distance(_pts[k].pos, _pts[k - 1].pos);
                    k--;
                }
                Vector3 refP = _pts[k].pos;
                targetAngle = Vector3.Distance(end, refP) > plugRefArcLength * 0.3f
                    ? Mathf.Atan2(end.y - refP.y, end.x - refP.x)
                    : _plugAngle;
            }
        }

        float da = Mathf.DeltaAngle(_plugAngle * Mathf.Rad2Deg, targetAngle * Mathf.Rad2Deg) * Mathf.Deg2Rad;
        float step = Mathf.Clamp(da * plugTurnRate, -plugMaxTurnStep, plugMaxTurnStep);
        _plugAngle += step;
    }

    private Vector3 GetOutletDirection(Vector3 anchor)
    {
        Transform center = reelCenter != null ? reelCenter : startTransform.parent;
        if (center != null)
        {
            Vector3 radial = anchor - center.position;
            radial.z = 0;
            if (radial.sqrMagnitude > 1e-6f)
            {
                return radial.normalized;
            }
        }
        return Vector3.down;
    }

    private Vector3 FlattenZ(Vector3 worldPos)
    {
        worldPos.z = startTransform != null ? startTransform.position.z : transform.position.z;
        return worldPos;
    }

    // ------------------------------ 渲染 ------------------------------

    private void Render()
    {
        for (int i = 0; i < _n; i++)
        {
            _renderA[i] = _pts[i].pos;
        }

        int count = _n;
        Vector3[] src = _renderA;
        Vector3[] dst = _renderB;
        for (int it = 0; it < SmoothIterations; it++)
        {
            count = Chaikin(src, count, dst);
            (src, dst) = (dst, src);
        }

        // 插接时线缆末端由平头切面改为圆头端帽(线自身的圆头,同旧 LineRenderer),读作"插进孔里"
        _cableMesh.UpdateMesh(src, count, FindTailStart(count), State == CableState.Plugged);
    }

    /// <summary>
    /// 自遮挡检测(移植自原型):找到下垂最低点 j,若 j 之后的尾段与 j 之前的头段
    /// 空间重叠,返回尾段在平滑点数组里的起始下标(从 j 前两个物理点起),否则 -1。
    /// </summary>
    private int FindTailStart(int smoothedCount)
    {
        int j = 0;
        for (int i = 1; i < _n; i++)
        {
            if (_pts[i].pos.y < _pts[j].pos.y) j = i; // 原型 y 向下,这里取世界最低点
        }
        if (j >= _n - 2) return -1;

        float rr = bodyWidth + overlapMargin;
        float rrSqr = rr * rr;
        bool overlap = false;
        for (int s = j + 2; s < _n && !overlap; s += 2)
        {
            for (int t = 0; t < j - 2 && !overlap; t += 2)
            {
                if (s - t >= 8 && (_pts[s].pos - _pts[t].pos).sqrMagnitude < rrSqr) overlap = true;
            }
        }
        if (!overlap) return -1;

        int j0 = Mathf.Max(0, j - 2);
        return Mathf.Clamp(j0 << SmoothIterations, 0, smoothedCount - 2);
    }

    private float GetIdleLength()
    {
        return Mathf.Max(0.1f, minLength * idleLengthScale);
    }

    private void EnsureMeshRenderer()
    {
        if (_cableMesh != null) return;

        // MeshRenderer 不能与本物体上遗留的 LineRenderer 共存,放到子物体;
        // 顶点直接用世界坐标,子物体世界变换必须归零
        Transform child = transform.Find("Cable Mesh");
        if (child == null)
        {
            child = new GameObject("Cable Mesh").transform;
            child.SetParent(transform, false);
        }
        child.position = Vector3.zero;
        child.rotation = Quaternion.identity;
        // 继承 GameObject layer:后处理/渲染特性按层过滤时,线缆与周围面板行为一致
        child.gameObject.layer = gameObject.layer;

        _cableMesh = child.GetComponent<CableMeshRenderer>();
        if (_cableMesh == null) _cableMesh = child.gameObject.AddComponent<CableMeshRenderer>();

        _cableMesh.Configure(ResolveMaterial(), sortingLayerName, sortingOrder);
        _cableMesh.SetBands(BuildBands());
        _cableMesh.SetTipTaper(tipTaperFraction, tipTaperScale);
        _cableMesh.SetVisible(State != CableState.Hidden);
    }

    private Material ResolveMaterial()
    {
        if (cableMaterial != null) return cableMaterial;

        // 直接共用出线口所在线盘 sprite 的材质:与周围环境的受光行为保证完全一致
        if (startTransform != null)
        {
            var reference = startTransform.GetComponentInParent<SpriteRenderer>();
            if (reference != null && reference.sharedMaterial != null)
            {
                return reference.sharedMaterial;
            }
        }

        Shader shader = Shader.Find("Universal Render Pipeline/2D/Sprite-Lit-Default");
        if (shader == null) shader = Shader.Find("Sprites/Default");
        return new Material(shader);
    }

    private CableMeshRenderer.Band[] BuildBands()
    {
        // 提交顺序即画序(后画的盖前画的);三档色阶,比原型少一档高光,贴合场景像素密度
        return new[]
        {
            new CableMeshRenderer.Band(shadowColor, shadowWidth, -shadowDrop, skipInTail: true),
            new CableMeshRenderer.Band(darkColor, darkWidth, 0f),
            new CableMeshRenderer.Band(bodyColor, bodyWidth, 0f),
            new CableMeshRenderer.Band(midColor, midWidth, midLift),
        };
    }

    private void SetCableRenderersEnabled(bool enabled)
    {
        EnsureMeshRenderer();
        _cableMesh.SetVisible(enabled);
    }

    /// <summary>
    /// 一次 Chaikin 切角细分：保留首尾点，每段取 1/4、3/4 两个切分点，输出点数为 2n。
    /// </summary>
    private static int Chaikin(Vector3[] src, int count, Vector3[] dst)
    {
        int idx = 0;
        dst[idx++] = src[0];
        for (int i = 0; i < count - 1; i++)
        {
            dst[idx++] = Vector3.Lerp(src[i], src[i + 1], 0.25f);
            dst[idx++] = Vector3.Lerp(src[i], src[i + 1], 0.75f);
        }
        dst[idx++] = src[count - 1];
        return idx;
    }
}