using System.Collections;
    using System.Collections.Generic;
    using UnityEngine;
    using UnityEngine.AI;

    public class TerrainGeneration : MonoBehaviour
    {
        Mesh mesh;

        Vector3 offsetPosition;
        Vector3[] vertices;

        public int xSize;
        public int zSize;
        public int seed;

        [Range(1,10)]public int octaves;
        public float frequencyMultiplier;
        public float amplitudeMultiplier;
        public float heightMultiplier;
        public float center;
        public float fallOff;
        float fallOffX;
        float fallOffZ;
        float fallOffXZ;
        int[] triangles;

        public GameObject gameEvents;

        public NavMeshSurface[] surfaces;

        // Start is called before the first frame update
        public void Start()
        {
            if (seed == 0)
            {
                seed = Random.Range(0, 99999);
            }
            mesh = new Mesh();
            GetComponent<MeshFilter>().mesh = mesh;
            CreateShape();
            UpdateMesh();
        }

        //generates a random terrain using a seed
        void CreateShape()
        {
            vertices = new Vector3[(xSize + 1) * (zSize + 1)];

            int i = 0;
            for (int z = 0; z <= zSize; z++)
            {
                for (int x = 0; x <= xSize; x++)
                {
                    float freq = 1;
                    float amp = 1;

                    float noieHeight = 0;
                    for (int j = 0; j < octaves; j++)
                    {
                        fallOffX = (center * center - 2 * center * x + 4 * heightMultiplier 
                        * fallOff + x * x) / 4 * fallOff;
                        fallOffZ = (center * center - 2 * center * z + 4 * heightMultiplier 
                        * fallOff + z * z) / 4 * fallOff;
                        fallOffXZ = (fallOffX + fallOffZ) / 2;
                        noieHeight += (Mathf.PerlinNoise((x * .03f * freq) + seed, 
                        (z * .03f * freq) + seed) * heightMultiplier * amp) - fallOffXZ;
                        amp *= amplitudeMultiplier;
                        freq *= frequencyMultiplier;
                    }
                    float y = noieHeight;
                    if (y < 8.4f)
                    {
                        y = 8.4f;
                    }
                    vertices[i] = new Vector3(x, y, z);
                    i++;
                }
            }

            triangles = new int[xSize * zSize * 6];
            int vert = 0;
            int tris = 0;
            for (int z = 0; z < zSize; z++)
            {
                for (int x = 0; x < xSize; x++)
                {
                    triangles[tris + 0] = vert + 0;
                    triangles[tris + 1] = vert + xSize + 1;
                    triangles[tris + 2] = vert + 1;
                    triangles[tris + 3] = vert + 1;
                    triangles[tris + 4] = vert + xSize + 1;
                    triangles[tris + 5] = vert + xSize + 2;

                    vert++;
                    tris += 6;
                }
                vert++;
            }
        }

        void UpdateMesh()
        {
            mesh.Clear();

            mesh.vertices = vertices;
            mesh.triangles = triangles;

            mesh.RecalculateNormals();

            GetComponent<MeshCollider>().sharedMesh = mesh;

            for (int i = 0; i < surfaces.Length; i++)
            {
                surfaces[i].BuildNavMesh();
            }
        }
    }