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

#if UNITY_EDITOR
using UnityEditor;
#endif

namespace GameWrapper.Curve
{
    /// <summary>
    /// B样条曲线
    /// </summary>
    public sealed class BSplineCurve : MonoBehaviour
    {
        [Header("是否本地坐标")]
        public bool isLocalPos = true;

        [Header("点位索引")]
        public int Index;
        [Header("下一个目标点位")]
        public BSplineCurve NextTarget;

        [Header("控制点设置")]
        public List<Vector3> listControlPoint = new();
        /// <summary>
        /// 实际点位
        /// </summary>
        private List<Vector3> curvePoints = new();

        [Range(2, 7)]
        private int degree = 2; // 曲线阶数（次数+1）
        [Range(0.001f, 0.1f)]
        private float stepSize = 0.01f;

        #region API
        /// <summary>
        /// 获取曲线上特定参数值的点
        /// </summary>
        public Vector3 GetPointOnCurve(float t)
        {
            if (listControlPoint.Count <= degree || curvePoints.Count == 0)
                return Vector3.zero;

            int n = listControlPoint.Count - 1;
            float normalizedT = Mathf.Lerp(degree, n + 1, Mathf.Clamp01(t));

            Vector3 point = Vector3.zero;
            float[] knots = GenerateKnotVector();

            for (int i = 0; i <= n; i++)
            {
                float basis = BasisFunction(i, degree, normalizedT, knots);
                point += GetPos(i) * basis;
            }

            return point;
        }

        /// <summary>
        /// 生成B样条曲线
        /// </summary>
        public void GenerateCurve()
        {
            curvePoints.Clear();

            if (null != NextTarget)
            {
                Vector3 startPos = gameObject.transform.position;
                Vector3 endPos = NextTarget.gameObject.transform.position;

                if (isLocalPos)
                {
                    startPos -= gameObject.transform.position;
                    endPos -= gameObject.transform.position;
                }

                if (listControlPoint.Count <= 0)
                {
                    listControlPoint.Add(startPos);
                    listControlPoint.Add(endPos);
                }
                else if (listControlPoint.Count <= 1)
                {
                    listControlPoint[0] = startPos;
                    listControlPoint.Add(endPos);
                }
                else
                {
                    listControlPoint[0] = startPos;
                    listControlPoint[^1] = endPos;
                }
            }

            if (listControlPoint.Count < 2)
                return;

            int n = listControlPoint.Count - 1; // 控制点索引最大值
            int m = n + degree + 1; // 节点向量最大值

            // 生成均匀节点向量
            float[] knots = new float[m + 1];
            for (int i = 0; i <= m; i++)
            {
                knots[i] = i;
            }

            curvePoints.Add(GetPos(0));
            // 计算曲线点
            for (float t = degree; t <= n + 1; t += stepSize)
            {
                Vector3 point = Vector3.zero;

                for (int i = 0; i <= n; i++)
                {
                    float basis = BasisFunction(i, degree, t, knots);
                    point += GetPos(i) * basis;
                }

                curvePoints.Add(point);
            }
            curvePoints.Add(GetPos(listControlPoint.Count - 1));
        }
        #endregion

        /// <summary>
        /// B样条基函数计算（De Boor递归算法）
        /// </summary>
        private float BasisFunction(int i, int k, float t, float[] knots)
        {
            if (0 == k)
                return (t >= knots[i] && t < knots[i + 1]) ? 1f : 0f;
            else
            {
                float denominator1 = knots[i + k] - knots[i];
                float denominator2 = knots[i + k + 1] - knots[i + 1];

                float term1 = 0f;
                float term2 = 0f;

                if (0 != denominator1)
                    term1 = (t - knots[i]) / denominator1 * BasisFunction(i, k - 1, t, knots);

                if (0 != denominator2)
                    term2 = (knots[i + k + 1] - t) / denominator2 * BasisFunction(i + 1, k - 1, t, knots);

                return term1 + term2;
            }
        }

        /// <summary>
        /// 生成节点向量
        /// </summary>
        private float[] GenerateKnotVector()
        {
            int n = listControlPoint.Count - 1;
            int m = n + degree + 1;
            float[] knots = new float[m + 1];

            for (int i = 0; i <= m; i++)
            {
                knots[i] = i;
            }

            return knots;
        }

        private Vector3 GetPos(int index)
        {
            if (isLocalPos)
                return listControlPoint[index] + gameObject.transform.position;
            else
                return listControlPoint[index];
        }

#if UNITY_EDITOR
        [Header("是否显示控制点")]
        public bool isShowControlPoints = true;
        [Header("是否显示曲线")]
        public bool isShowCurve = true;
        [Header("控制点颜色")]
        public Color controlPointColor = new(1f, 0f, 0f, 0.8f);
        [Header("曲线颜色")]
        public Color curveColor = Color.blue;

        void OnDrawGizmos()
        {
            if (Selection.activeGameObject != gameObject)
                return;

            GenerateCurve();

            // 绘制曲线
            if (isShowCurve && curvePoints.Count > 1)
            {
                Gizmos.color = curveColor;
                for (int i = 0; i < curvePoints.Count - 1; ++i)
                {
                    Gizmos.DrawLine(curvePoints[i], curvePoints[i + 1]);
                }
            }

            // 绘制控制点
            if (isShowControlPoints)
            {
                Gizmos.color = controlPointColor;
                for (int i = 0; i < listControlPoint.Count; ++i)
                {
                    Vector3 point = GetPos(i);
                    Gizmos.DrawSphere(point, 0.2f);
                    Gizmos.DrawIcon(point, i.ToString());
                }

                // 绘制控制多边形
                for (int i = 0; i < listControlPoint.Count - 1; ++i)
                {
                    Gizmos.DrawLine(GetPos(i), GetPos(i + 1));
                }
            }
        }
#endif
    }
}