using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// 贝塞尔曲线
/// </summary>
[Serializable]
public class BezierCurve
{
    /// <summary>
    /// 段数
    /// </summary>
    [Range(1, 100)] public int segments = 10;

    /// <summary>
    /// 是否循环
    /// </summary>
    public bool loop;

    /// <summary>
    /// 点集合
    /// </summary>
    public List<BezierCurvePoint> points = new List<BezierCurvePoint>(2)
        {
            new BezierCurvePoint() { position = Vector3.back * 5f, tangent = Vector3.back * 5f + Vector3.left * 3f },
            new BezierCurvePoint() { position = Vector3.forward * 5f, tangent = Vector3.forward * 5f + Vector3.right * 3f }
        };

    /// <summary>
    /// 根据归一化位置值获取对应的贝塞尔曲线上的点
    /// </summary>
    /// <param name="t">归一化位置值 [0,1]</param>
    /// <returns></returns>
    public Vector3 EvaluatePosition(float t)
    {
        Vector3 retVal = Vector3.zero;
        if (points.Count > 0)
        {
            float max = points.Count - 1 < 1 ? 0 : (loop ? points.Count : points.Count - 1);
            float standardized = (loop && max > 0) ? ((t %= max) + (t < 0 ? max : 0)) : Mathf.Clamp(t, 0, max);
            int rounded = Mathf.RoundToInt(standardized);
            int i1, i2;
            if (Mathf.Abs(standardized - rounded) < Mathf.Epsilon)
                i1 = i2 = (rounded == points.Count) ? 0 : rounded;
            else
            {
                i1 = Mathf.FloorToInt(standardized);
                if (i1 >= points.Count)
                {
                    standardized -= max;
                    i1 = 0;
                }
                i2 = Mathf.CeilToInt(standardized);
                i2 = i2 >= points.Count ? 0 : i2;
            }
            retVal = i1 == i2 ? points[i1].position : BezierCurveUtility.Bezier3(points[i1].position,
                points[i1].position + points[i1].tangent, points[i2].position
                - points[i2].tangent, points[i2].position, standardized - i1);
        }
        return retVal;
    }
}

[Serializable]
public struct BezierCurvePoint
{
    /// <summary>
    /// 坐标点
    /// </summary>
    public Vector3 position;

    /// <summary>
    /// 控制点 与坐标点形成切线
    /// </summary>
    public Vector3 tangent;
}

public class BezierCurveUtility
{
    /// <summary>
    /// 三阶贝塞尔曲线
    /// </summary>
    /// <param name="p0">起点</param>
    /// <param name="p1">控制点1</param>
    /// <param name="p2">控制点2</param>
    /// <param name="p3">终点</param>
    /// <param name="t">[0,1]</param>
    /// <returns></returns>
    public static Vector3 Bezier3(Vector3 p0, Vector3 p1, Vector3 p2, Vector3 p3, float t)
    {
        Vector3 p0p1 = (1 - t) * p0 + t * p1;
        Vector3 p1p2 = (1 - t) * p1 + t * p2;
        Vector3 p2p3 = (1 - t) * p2 + t * p3;
        Vector3 p0p1p2 = (1 - t) * p0p1 + t * p1p2;
        Vector3 p1p2p3 = (1 - t) * p1p2 + t * p2p3;
        return (1 - t) * p0p1p2 + t * p1p2p3;
    }
}