using JetBrains.Annotations;
using UnityEngine;

public static class MeshGenerator
{
    public static MeshData GenerateTerrainMesh(float[,] heightMap, float heightMultiplier, AnimationCurve _heightCurve, int levelOfDetail)
    {
        AnimationCurve heightCurve = new AnimationCurve(_heightCurve.keys);
        
        int width = heightMap.GetLength(0);
        int height = heightMap.GetLength(1);
        float topLeftX = (width - 1) / -2f;
        float topLeftZ = (height - 1) / 2f;

        int meshSimplficationIncrement = (levelOfDetail == 0) ? 1 : levelOfDetail * 2;
        int verticesPerLine = (width - 1) / meshSimplficationIncrement + 1;

        MeshData meshData = new(verticesPerLine, verticesPerLine);
        int vertexIndex = 0;

        for(int y=0; y<height; y += meshSimplficationIncrement)
        {
            for(int x=0; x<width; x += meshSimplficationIncrement)
            {
                meshData.vertices[vertexIndex] = new Vector3(topLeftX + x, heightCurve.Evaluate(heightMap[x, y]) * heightMultiplier, topLeftZ - y);
                meshData.uvs[vertexIndex] = new Vector2(x/(float)width, y/(float)height);

                if (x < width - 1 && y < height - 1)
                {
                    meshData.AddTriangle(vertexIndex, vertexIndex + verticesPerLine + 1, vertexIndex + verticesPerLine);
                    meshData.AddTriangle(vertexIndex + verticesPerLine + 1, vertexIndex, vertexIndex + 1);
                }

                vertexIndex++;
            }
        }

        return meshData;
    }
}

public class MeshData
{
    public Vector3[] vertices;
    public int[] triangles;
    public Vector2[] uvs;

    int triangleIndex;

    public MeshData(int meshWidth, int meshHeight)
    {
        vertices = new Vector3[meshWidth * meshHeight];
        uvs = new Vector2[meshWidth * meshHeight];
        triangles = new int[(meshWidth - 1) * (meshHeight - 1) * 6];
    }

    public void AddTriangle(int a, int b, int c)
    {
        triangles[triangleIndex] = a;
        triangles[triangleIndex+1] = b;
        triangles[triangleIndex+2] = c;

        triangleIndex += 3;
    }

    public Mesh CreateMesh()
    {
        Mesh mesh = new();
        mesh.vertices = vertices;
        mesh.triangles = triangles;
        mesh.uv = uvs;
        mesh.RecalculateNormals();

        return mesh;
    }
}