using System;
using Godot;
using Array = Godot.Collections.Array;

public static class HexMeshBuilder
{
    public static ArrayMesh CreateFlatHexMesh()
    {
        var uvs = new Vector2[19];
        var vertices = new Vector3[19];
        var normals = new Vector3[19];

        const float height = 0.02f;
        vertices[0] = new(0f, height, 0f);
        uvs[0] = new(0.5f, 0.5f);
        normals[0] = Vector3.Up;

        for (var i = 0; i < 18; i++)
        {
            var angleDeg = 60f * i - 30f;
            var angleRad = Mathf.DegToRad(angleDeg);
            var x = MathF.Cos(angleRad);
            var z = MathF.Sin(angleRad);

            var y = i >= 12 ? height : 0.0f;
            var s = 1.0f - y;
            vertices[i + 1] = new(x * s, y, z * s);
            uvs[i + 1] = 
                i < 6 ? new((i % 6), 0.5f) : 
                i >= 12 ? new Vector2(x * 0.5f + 0.5f, z * 0.5f + 0.5f) :
                new((i % 6), 0.5f + height);
            normals[i + 1] = 
                i < 6 ? Vector3.Up : 
                i >= 12 ? new Vector3(x, s, z).Normalized() :
                new Vector3(x, 0.75f, z).Normalized();
        }

        var indices = new int[18 * 3];
        var idx = 0;
        for (var i = 0; i < 6; i++)
        {
            var curr = i + 1;
            var next = (i + 1) % 6 + 1;

            indices[idx++] = 0;
            indices[idx++] = curr + 12;
            indices[idx++] = next + 12;
        }

        for (var j = 0; j < 6; j++)
        {
            var curr = j + 7;
            var next = (j + 1) % 6 + 7;

            indices[idx++] = curr;
            indices[idx++] = next;
            indices[idx++] = next + 6;
            indices[idx++] = curr;
            indices[idx++] = next + 6;
            indices[idx++] = curr + 6;
        }

        var arrays = new Array();
        arrays.Resize((int)Mesh.ArrayType.Max);
        arrays[(int)Mesh.ArrayType.Vertex] = vertices;
        arrays[(int)Mesh.ArrayType.Normal] = normals;
        arrays[(int)Mesh.ArrayType.Index] = indices;
        arrays[(int)Mesh.ArrayType.TexUV] = uvs;

        var mesh = new ArrayMesh();
        mesh.AddSurfaceFromArrays(Mesh.PrimitiveType.Triangles, arrays);

        return mesh;
    }
}