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

public class GerstnerWave : MonoBehaviour
{
    public float waveLength = 0.1f;
    public float amplitude = 0.1f;
    public float speed = 1f;
    public Vector2 direction = new Vector2(1.0f, 0.0f);

    void Update()
    {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Vector3[] vertices = mesh.vertices;
        Vector3[] normals = mesh.normals;

        float waveNumber = 2.0f * Mathf.PI / waveLength;
        float phaseConstant = speed * waveNumber;

        for (int i = 0; i < vertices.Length; i++)
        {
            Vector3 vertex = vertices[i];
            float dotProduct = Vector2.Dot(new Vector2(vertex.x, vertex.z), direction);
            float wavePhase = waveNumber * dotProduct + phaseConstant * Time.time;
            vertex.y = amplitude * Mathf.Sin(wavePhase);
            vertices[i] = vertex;

            // Calculate the normal at the vertex
            float cosPhase = Mathf.Cos(wavePhase);
            float dx = -waveNumber * amplitude * direction.x * cosPhase;
            float dz = -waveNumber * amplitude * direction.y * cosPhase;
            normals[i] = new Vector3(dx, 1.0f, dz).normalized;
        }

        mesh.vertices = vertices;
        mesh.normals = normals;
    }

    public Vector3 GetWaveNormal(Vector3 position)
    {
        float waveNumber = 2.0f * Mathf.PI / waveLength;
        float phaseConstant = speed * waveNumber;
        float dotProduct = Vector2.Dot(new Vector2(position.x + transform.position.x, position.z + transform.position.z), direction);
        float wavePhase = waveNumber * dotProduct + phaseConstant * Time.time;

        float cosPhase = Mathf.Cos(wavePhase);

        // We differentiate the wave function to get the slope at the current point
        float dx = -waveNumber * amplitude * direction.x * cosPhase;
        float dz = -waveNumber * amplitude * direction.y * cosPhase;

        Vector3 normal = new Vector3(dx, 1.0f, dz).normalized;
        return normal;
    }
}