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



[ExecuteInEditMode]
[RequireComponent(typeof(MeshRenderer))]
[RequireComponent(typeof(MeshFilter))]
class TerrainScript : MonoBehaviour {

    int m_SegmentCount_x;
    int m_SegmentCount_z;
    float m_Size = 0.001f;
    MeshFilter filter;
    Transform controllerTarget;
    Texture2D m_HeightMap;

    
 



    void Start() {

        filter = GetComponent<MeshFilter>();
        controllerTarget = GameObject.Find("ControllerTarget").transform;
        m_HeightMap = Resources.Load("mars_height") as Texture2D;

    }


    public float GetY(float x, float z, float heightScale)
    {
        Color mapColour = m_HeightMap.GetPixelBilinear(x, z);
        return sinh((mapColour.grayscale-0.5f)*heightScale);
    }

    private float sinh(float x) {
        return ((1 - Mathf.Exp(-2*x))/(2*(Mathf.Exp(-x))));
    }

    void Update() {

        m_SegmentCount_x = Mathf.FloorToInt(controllerTarget.position.x / m_Size);
        m_SegmentCount_z = Mathf.FloorToInt(controllerTarget.position.z / m_Size);


        MeshBuilder meshBuilder = new MeshBuilder();

        float heightScale = ((controllerTarget.rotation.eulerAngles.y)/360.0f)*0.1f;

        for (int i = 0; i <= m_SegmentCount_z; i++)
        {
            float z = m_Size * i;
            float v = (1.0f / m_SegmentCount_z) * i;

            for (int j = 0; j <= m_SegmentCount_x; j++)
            {
                float x = m_Size * j;
                float u = (1.0f / m_SegmentCount_x) * j;
                
                Vector3 offset = new Vector3(x, GetY(x,z, heightScale), z);

                Vector2 uv = new Vector2(u, v);
                bool buildTriangles = i > 0 && j > 0;

                BuildQuadForGrid(meshBuilder, offset, uv, buildTriangles, m_SegmentCount_x + 1);
            }
        }
        
        filter.sharedMesh = meshBuilder.CreateMesh();

    }

    void BuildQuadForGrid(MeshBuilder meshBuilder, Vector3 position, Vector2 uv, 
	bool buildTriangles, int vertsPerRow)
    {
        meshBuilder.Vertices.Add(position);
        meshBuilder.UVs.Add(uv);

        if (buildTriangles)
        {
            int baseIndex = meshBuilder.Vertices.Count - 1;

            int index0 = baseIndex;
            int index1 = baseIndex - 1;
            int index2 = baseIndex - vertsPerRow;
            int index3 = baseIndex - vertsPerRow - 1;

            meshBuilder.AddTriangle(index0, index2, index1);
            meshBuilder.AddTriangle(index2, index3, index1);
        }
    }


}

public class MeshBuilder
{
	private List<Vector3> m_Vertices = new List<Vector3>();
	public List<Vector3> Vertices { get { return m_Vertices; } }

	private List<Vector3> m_Normals = new List<Vector3>();
	public List<Vector3> Normals { get { return m_Normals; } }

	private List<Vector2> m_UVs = new List<Vector2>();
	public List<Vector2> UVs { get { return m_UVs; } }

	private List<int> m_Indices = new List<int>();

	public void AddTriangle(int index0, int index1, int index2)
	{
		m_Indices.Add(index0);
		m_Indices.Add(index1);
		m_Indices.Add(index2);
	}

	public Mesh CreateMesh()
	{
		Mesh mesh = new Mesh();

		mesh.vertices = m_Vertices.ToArray();
		mesh.triangles = m_Indices.ToArray();

		//Normals are optional. Only use them if we have the correct amount:
		if (m_Normals.Count == m_Vertices.Count)
			mesh.normals = m_Normals.ToArray();

		
		mesh.uv = m_UVs.ToArray();

		mesh.RecalculateBounds();

		return mesh;
	}
}