using UnityEngine;

[DisallowMultipleComponent]
[RequireComponent(typeof(Rigidbody))]
[RequireComponent(typeof(CapsuleCollider))]
public class BobberBuoyancyStable : MonoBehaviour
{
    [Header("Water")]
    public float waterLevelY = 0f;

    [Tooltip("必须至少浸入这么深才开始产生浮力（防止还没入水就被顶）")]
    public float enterWaterDepth = 0.003f; // 3mm（按你的尺度改）

    [Tooltip("在这个深度范围内做平滑过渡（越大越软）")]
    public float smoothDepth = 0.02f;

    [Header("Buoyancy Spring")]
    public float buoyancySpring = 30f;
    public float buoyancyDamping = 8f;

    [Tooltip("最大上浮加速度限制(0=不限制)")]
    public float maxUpAcceleration = 0f;

    [Header("Water Drag")]
    public float extraLinearDampingInWater = 2f;
    public float extraAngularDampingInWater = 2f;

    [Header("Center Of Mass")]
    public bool driveCenterOfMassFromCapsule = true;
    public Vector3 extraCenterOfMassOffset = new Vector3(0f, -0.01f, 0f);

    [Header("Righting")]
    public float rightingTorque = 1.5f;
    public float rightingDamping = 0.5f;

    Rigidbody rb;
    CapsuleCollider cap;

    float airLinearDamping;
    float airAngularDamping;

    void Awake()
    {
        rb = GetComponent<Rigidbody>();
        cap = GetComponent<CapsuleCollider>();
        rb.useGravity = true;

        airLinearDamping = rb.linearDamping;
        airAngularDamping = rb.angularDamping;

        ApplyCenterOfMass();
        rb.maxAngularVelocity = 50f;
    }

    void FixedUpdate()
    {
        ApplyCenterOfMass();

        Bounds b = cap.bounds;
        float bottomY = b.min.y;
        float topY = b.max.y;

        // 用“底部点”判定是否真正入水（必须超过阈值）
        float bottomSubmersion = waterLevelY - bottomY; // >0 表示底部在水下
        if (bottomSubmersion <= enterWaterDepth)
        {
            // 认为未入水：不施加浮力，恢复空气阻尼
            rb.linearDamping = airLinearDamping;
            rb.angularDamping = airAngularDamping;
            return;
        }

        // 进入水中：阻尼随浸入增强
        // 这里用一个0~1的平滑权重，避免刚入水就“猛顶”
        float w = Smooth01((bottomSubmersion - enterWaterDepth) / Mathf.Max(1e-4f, smoothDepth));

        rb.linearDamping = airLinearDamping + extraLinearDampingInWater * w;
        rb.angularDamping = airAngularDamping + extraAngularDampingInWater * w;

        // 垂直速度（用刚体自身速度就够稳定）
        float vY = rb.linearVelocity.y;

        // 弹簧+阻尼浮力（仅向上）
        float forceY = buoyancySpring * bottomSubmersion - buoyancyDamping * vY;
        if (forceY < 0f) forceY = 0f;

        // 平滑权重：刚入水时逐渐接管
        forceY *= w;

        // 限制最大上浮加速度（可选）
        if (maxUpAcceleration > 0f)
        {
            float maxForce = rb.mass * maxUpAcceleration;
            if (forceY > maxForce) forceY = maxForce;
        }

        // 浮力作用点：必须放在水面下（否则会出现奇怪力矩）
        float buoyY = Mathf.Min(waterLevelY - 0.001f, topY); // 强制在水面下1mm
        buoyY = Mathf.Max(buoyY, bottomY);                  // 不低于底部
        Vector3 buoyPoint = new Vector3(b.center.x, buoyY, b.center.z);

        rb.AddForceAtPosition(Vector3.up * forceY, buoyPoint, ForceMode.Force);

        // 归正扭矩（只在水里生效）
        Vector3 up = transform.up;
        Vector3 axis = Vector3.Cross(up, Vector3.up);
        float mag = axis.magnitude;
        if (mag > 1e-4f)
        {
            axis /= mag;
            float angle = Mathf.Asin(Mathf.Clamp(mag, -1f, 1f));
            float angVelOnAxis = Vector3.Dot(rb.angularVelocity, axis);
            float torque = (rightingTorque * angle - rightingDamping * angVelOnAxis) * w;
            rb.AddTorque(axis * torque, ForceMode.Acceleration);
        }
    }

    void ApplyCenterOfMass()
    {
        if (!driveCenterOfMassFromCapsule) return;
        rb.centerOfMass = cap.center + extraCenterOfMassOffset;
    }

    static float Smooth01(float t)
    {
        t = Mathf.Clamp01(t);
        // smoothstep
        return t * t * (3f - 2f * t);
    }
}