using UnityEngine;

namespace Utils {
    public static class MeshGenerator {

        public static MeshData GenerateTerrainMesh(float[,] heightMap, float heightMultiplier, AnimationCurve heightCurve, int levelOfDetail) {
            int width = heightMap.GetLength(0);
            int height = heightMap.GetLength(1);
            float topLeftX = (width - 1) / -2.0f;
            float topLeftZ = (height - 1) / 2.0f;

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

            MeshData data = new MeshData(verticesPerLine, verticesPerLine);
            int vertexIndex = 0;
            
            for (int y = 0; y < height; y += simplificationIncrement)
            for (int x = 0; x < width; x += simplificationIncrement) {

                data.vertices[vertexIndex] = new Vector3(topLeftX + x, heightCurve.Evaluate(heightMap[x, y]) * heightMultiplier, topLeftZ - y);
                data.uvs[vertexIndex] = new Vector2(x / (float)width, y / (float)height);

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

            return data;
        }
        
    }

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

        private int triangleIndex;

        public MeshData(int width, int height) {
            vertices = new Vector3[width * height];
            uvs = new Vector2[vertices.Length];
            triangles = new int[(width - 1) * (height - 1) * 6];
            triangleIndex = 0;
        }

        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();
            mesh.vertices = vertices;
            mesh.triangles = triangles;
            mesh.uv = uvs;
            mesh.RecalculateNormals();
            return mesh;
        }
    }
}