using System.Collections;
using System.Collections.Generic;
using Sirenix.OdinInspector;
using UnityEngine;

public class GerstnerWave : MonoBehaviour
{
    [InfoBox("파도의 길이를 결정, 값이 클수록 파도 간의 간격이 커짐")]
    public float waveLength = 0.1f;
    [InfoBox("파도의 높이를 결정, 값이 클수록 파도의 높이가 커짐")]
    public float amplitude = 0.1f;
    [InfoBox("파도의 속도를 결정, 값이 클수록 파도의 속도가 오름")]
    public float speed = 1f;
    [InfoBox("파도의 방향을 결정")]
    public Vector2 direction = new Vector2(1.0f, 0.0f);

    private void FixedUpdate()
    {
        var mesh = GetComponent<MeshFilter>().mesh;
        var vertices = mesh.vertices;
        var normals = mesh.normals;

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

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

            // Calculate the normal at the vertex
            var cosPhase = Mathf.Cos(wavePhase);
            var dx = -waveNumber * amplitude * direction.x * cosPhase;
            var 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)
    {
        var waveNumber = 2.0f * Mathf.PI / waveLength;
        var phaseConstant = speed * waveNumber;
        var dotProduct = Vector2.Dot(new Vector2(position.x + transform.position.x, position.z + transform.position.z), direction);
        var wavePhase = waveNumber * dotProduct + phaseConstant * Time.time;

        var cosPhase = Mathf.Cos(wavePhase);

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

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