using System.Collections.Generic;
using UnityEngine;

public class DrawShape : MonoBehaviour
{
    // List of Vector3 points that define the shape
    public List<Vector3> points;
    public Material material;

    public void Draw(List<Vector3> list, Vector3 offset)
    {
        Vector3 startPoint = list[0];
        Vector3 endPoint = list[list.Count - 1];

        List<Vector3> newPoints = new List<Vector3>();
        newPoints.Add(startPoint+ offset);
        newPoints.AddRange(list);
        newPoints.Add(endPoint+ offset);

        points = newPoints;
        if (points == null || points.Count < 3)
        {
            Debug.LogError("You need at least 3 points to define a shape.");
            return;
        }

        // Create a new GameObject to hold the mesh
        GameObject shapeObject = new GameObject("Shape");
        shapeObject.transform.parent = transform;
        shapeObject.transform.localPosition = Vector3.zero;

        // Add MeshFilter and MeshRenderer components
        MeshFilter meshFilter = shapeObject.AddComponent<MeshFilter>();
        MeshRenderer meshRenderer = shapeObject.AddComponent<MeshRenderer>();

        // Create the mesh and assign it to the MeshFilter
        Mesh mesh = new Mesh();
        meshFilter.mesh = mesh;

        // Set the vertices from the points list
        mesh.vertices = points.ToArray();

        // Triangulate the points
        int[] triangles = Triangulate(points);

        // Set the triangles
        mesh.triangles = triangles;

        // Recalculate normals and bounds
        mesh.RecalculateNormals();
        mesh.RecalculateBounds();

        // Set a basic material
        meshRenderer.material = material;
    }

    int[] Triangulate(List<Vector3> vertices)
    {
        // Simple ear clipping triangulation algorithm for concave/convex polygons
        // Note: This is a very basic implementation and may not handle all cases.

        List<int> indices = new List<int>();
        int n = vertices.Count;

        if (n < 3)
            return indices.ToArray();

        int[] V = new int[n];
        if (Area(vertices) > 0)
        {
            for (int v = 0; v < n; v++)
                V[v] = v;
        }
        else
        {
            for (int v = 0; v < n; v++)
                V[v] = (n - 1) - v;
        }

        int nv = n;
        int count = 2 * nv;
        for (int m = 0, v = nv - 1; nv > 2;)
        {
            if ((count--) <= 0)
                return indices.ToArray();

            int u = v;
            if (nv <= u)
                u = 0;
            v = u + 1;
            if (nv <= v)
                v = 0;
            int w = v + 1;
            if (nv <= w)
                w = 0;

            if (Snip(vertices, u, v, w, nv, V))
            {
                int a, b, c, s, t;
                a = V[u];
                b = V[v];
                c = V[w];
                indices.Add(a);
                indices.Add(b);
                indices.Add(c);
                m++;
                for (s = v, t = v + 1; t < nv; s++, t++)
                    V[s] = V[t];
                nv--;
                count = 2 * nv;
            }
        }

        return indices.ToArray();
    }

    float Area(List<Vector3> vertices)
    {
        int n = vertices.Count;
        float A = 0.0f;
        for (int p = n - 1, q = 0; q < n; p = q++)
        {
            Vector3 v0 = vertices[p];
            Vector3 v1 = vertices[q];
            A += v0.x * v1.y - v1.x * v0.y;
        }
        return A * 0.5f;
    }

    bool Snip(List<Vector3> vertices, int u, int v, int w, int n, int[] V)
    {
        int p;
        Vector3 A = vertices[V[u]];
        Vector3 B = vertices[V[v]];
        Vector3 C = vertices[V[w]];
        if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x))))
            return false;
        for (p = 0; p < n; p++)
        {
            if ((p == u) || (p == v) || (p == w))
                continue;
            Vector3 P = vertices[V[p]];
            if (InsideTriangle(A, B, C, P))
                return false;
        }
        return true;
    }

    bool InsideTriangle(Vector3 A, Vector3 B, Vector3 C, Vector3 P)
    {
        float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
        float cCROSSap, bCROSScp, aCROSSbp;

        ax = C.x - B.x;
        ay = C.y - B.y;
        bx = A.x - C.x;
        by = A.y - C.y;
        cx = B.x - A.x;
        cy = B.y - A.y;
        apx = P.x - A.x;
        apy = P.y - A.y;
        bpx = P.x - B.x;
        bpy = P.y - B.y;
        cpx = P.x - C.x;
        cpy = P.y - C.y;

        aCROSSbp = ax * bpy - ay * bpx;
        cCROSSap = cx * apy - cy * apx;
        bCROSScp = bx * cpy - by * cpx;

        return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
    }
}