using UnityEngine;
using System.Collections.Generic;

public struct BezierLineSegment
{
    public Vector3 fromPoint;
    public Vector3 toPoint;
    public Vector3 controlPoint;
    public Quaternion fromDir;
    public Quaternion toDir;

    public void CalculateDir()
    {
        fromDir = Quaternion.FromToRotation(Vector3.forward, controlPoint - fromPoint);
        toDir = Quaternion.FromToRotation(Vector3.forward, toPoint - controlPoint);
    }

    public bool IsStraight()
    {
        return fromDir == toDir;
    }
}

[ExecuteInEditMode]
public class BezierPipe : MonoBehaviour
{

    public float cornerScale = 1f;
    [Range(1, 100)]
    public int cornerStep = 10;
    [Range(2, 100)]
    public int circleStep = 10;

    public float r = 0.1f;

    public Transform point1;
    public Vector3 point1Dir = Vector3.up;
    public Transform point2;
    public Vector3 point2Dir = Vector3.up;

    public bool update = false;

    public Mesh mesh;
    List<Vector3> verts = new List<Vector3>();
    List<int> triangles = new List<int>();
    private MeshCollider mc;

    // Use this for initialization
    void Start()
    {
        mesh = new Mesh();
        mesh.name = "Pipe";
        MeshFilter mf = GetComponent<MeshFilter>();
        if (mf != null)
        {
            mf.sharedMesh = mesh;
        }
        mc = GetComponent<MeshCollider>();
        if (mc != null)
        {
            mc.sharedMesh = mesh;
        }
        BuildMesh();
    }

    // Update is called once per frame
    void Update()
    {
        if (update)
        {
            BuildMesh();
        }
    }

    void GetCirclePoint(Vector3 pos, Quaternion dir, bool draw)
    {
        for (int a = 0; a <= circleStep; a++)
        {
            float p = 2 * Mathf.PI * a / circleStep;
            Vector3 cp = new Vector3(r * Mathf.Cos(p), r * Mathf.Sin(p), 0);
            cp = dir * cp + pos;
            //if(draw)
            //    Gizmos.DrawSphere(cp, 0.0005f);
            cp = transform.worldToLocalMatrix.MultiplyPoint(cp);
            //cp += transform.position;
            verts.Add(cp);
        }
    }

    void SetTriangles()
    {
        triangles.Clear();
        for (int i = 0; i < verts.Count - circleStep - 2; i++)
        {
            triangles.Add(i);
            triangles.Add(i + 1);
            triangles.Add(i + circleStep + 1);
            triangles.Add(i + circleStep + 1);
            triangles.Add(i + 1);
            triangles.Add(i + circleStep + 2);
        }
        mesh.triangles = triangles.ToArray();
    }

    public void BuildMesh()
    {
        if (point1 != null && point2 != null)
        {
            verts.Clear();
            float scale = cornerScale;
            float length = (point1.position - point2.position).magnitude / 4;
            if (scale > length)
            {
                scale = length;
            }
            BezierLineSegment[] segments = new BezierLineSegment[3];
            segments[0].fromPoint = point1.position;
            point1Dir.Normalize();
            segments[0].controlPoint = point1.position + point1.rotation * point1Dir * scale;

            segments[2].toPoint = point2.position;
            point2Dir.Normalize();
            segments[2].controlPoint = point2.position + point2.rotation * point2Dir * scale;

            segments[1].controlPoint = (segments[0].controlPoint + segments[2].controlPoint) / 2;

            segments[0].toPoint = segments[1].fromPoint = segments[0].controlPoint + (segments[1].controlPoint - segments[0].controlPoint).normalized * scale;
            segments[1].toPoint = segments[2].fromPoint = segments[2].controlPoint + (segments[1].controlPoint - segments[2].controlPoint).normalized * scale;

            transform.position = segments[1].controlPoint;
            segments[1].CalculateDir();
            transform.rotation = segments[1].fromDir;
            //            Debug.Log (transform.eulerAngles);

            foreach (var segment in segments)
            {
                segment.CalculateDir();
                if (segment.IsStraight())
                {
                    GetCirclePoint(segment.fromPoint, segment.fromDir, true);
                    GetCirclePoint(segment.controlPoint, segment.fromDir, false);
                    GetCirclePoint(segment.toPoint, segment.toDir, true);
                    //Gizmos.DrawLine(segment.fromPoint, segment.controlPoint);
                    //Gizmos.DrawLine(segment.controlPoint, segment.toPoint);
                }
                else
                {
                    GetCirclePoint(segment.fromPoint, segment.fromDir, true);
                    Vector3 p1 = segment.fromPoint;
                    for (int s = 1; s < cornerStep; s++)
                    {
                        float t = (float)s / cornerStep;
                        Vector3 p2 = GetBezierPoint(t,segment.fromPoint, segment.controlPoint, segment.toPoint);
                        //Quaternion dir = Quaternion.FromToRotation(Vector3.forward, p2 - p1);
                        Quaternion dir = Quaternion.Lerp(segment.fromDir, segment.toDir, t);
                        GetCirclePoint(p2, dir, false);
                        //Gizmos.DrawLine(p1, p2);
                        p1 = p2;
                    }
                    GetCirclePoint(segment.toPoint, segment.toDir, true);
                    //Gizmos.DrawLine(p1,segment.toPoint);
                }
            }
            mesh.Clear();
            mesh.vertices = verts.ToArray();
            SetTriangles();
            mesh.RecalculateNormals();

            if (mc != null)
            {
                mc.sharedMesh = mesh;
            }
        }
    }
    Vector3 GetBezierPoint(float t, Vector3 p0, Vector3 p1, Vector3 p2)
    {
        float u = 1f - t;
        float tt = t * t;
        float uu = u * u;

        // 计算二次贝塞尔曲线公式
        Vector3 p = uu * p0;  // (1 - t)^2 * P0
        p += 2 * u * t * p1;   // 2 * (1 - t) * t * P1
        p += tt * p2;          // t^2 * P2

        return p;
    }
}