using UnityEngine;

[RequireComponent(typeof(Rigidbody))]
[RequireComponent(typeof(CapsuleCollider))]
public class CapsuleBuoyancy : MonoBehaviour
{
    [Header("Water Settings")]
    public float waterHeight = 0f;          // 水面高度
    public float waterDensity = 1000f;      // 水密度

    [Header("Buoyancy Settings")]
    public int samplePoints = 8;            // 采样点数量
    public float buoyancyMultiplier = 1.0f; // 浮力强度调节
    public float waterDrag = 1.5f;          // 水阻力
    public float waterAngularDrag = 1.5f;   // 水角阻力

    private Rigidbody rb;
    private CapsuleCollider capsule;

    private float capsuleVolume;
    private float gravity;

    void Start()
    {
        rb = GetComponent<Rigidbody>();
        capsule = GetComponent<CapsuleCollider>();

        gravity = Physics.gravity.magnitude;

        CalculateCapsuleVolume();
    }

    void FixedUpdate()
    {
        ApplyBuoyancy();
    }

    void CalculateCapsuleVolume()
    {
        float radius = capsule.radius * Mathf.Max(transform.localScale.x, transform.localScale.z);
        float height = Mathf.Max(0, capsule.height * transform.localScale.y - 2f * radius);

        float cylinderVolume = Mathf.PI * radius * radius * height;
        float sphereVolume = (4f / 3f) * Mathf.PI * radius * radius * radius;

        capsuleVolume = cylinderVolume + sphereVolume;
    }

    void ApplyBuoyancy()
    {
        float submergedRatioTotal = 0f;

        for (int i = 0; i < samplePoints; i++)
        {
            float t = (float)i / (samplePoints - 1);
            Vector3 localPoint = Vector3.up * Mathf.Lerp(
                -capsule.height * 0.5f + capsule.radius,
                capsule.height * 0.5f - capsule.radius,
                t);

            Vector3 worldPoint = transform.TransformPoint(localPoint);

            float depth = waterHeight - worldPoint.y;

            if (depth > 0f)
            {
                float normalizedDepth = Mathf.Clamp01(depth / (capsule.height / samplePoints));
                submergedRatioTotal += normalizedDepth;

                float forceMagnitude =
                    waterDensity *
                    gravity *
                    (capsuleVolume / samplePoints) *
                    normalizedDepth *
                    buoyancyMultiplier;

                Vector3 buoyancyForce = Vector3.up * forceMagnitude;

                rb.AddForceAtPosition(buoyancyForce, worldPoint, ForceMode.Force);
            }
        }

        // 如果在水中，加阻力
        if (submergedRatioTotal > 0f)
        {
            rb.linearDamping = waterDrag;
            rb.angularDamping = waterAngularDrag;
        }
        else
        {
            rb.linearDamping = 0f;
            rb.angularDamping = 0.05f;
        }
    }
}