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

public class Starfield : MonoBehaviour
{

    //This is the object with this script attached (camera)
    private Transform thisTransform;
    //The particles (stars)
    private ParticleSystem.Particle[] points;
    private float starDistanceSqr;
    private float starClipDistanceSqr;

    [Tooltip("The color of the stars")]
    public Color starColor;
    [Tooltip("The max amout of stars occuring in the scene")]
    public int starsMax;
    [Tooltip("The size of the stars")]
    public float starSize;
    [Tooltip("The distance for how far out the stars can appear")]
    public float starDistance;
    [Tooltip("The distance when the stars will disappear near the player")]
    public float starClipDistance;

    void Start()
    {
        thisTransform = GetComponent<Transform>();
        starDistanceSqr = starDistance * starDistance;
        starClipDistanceSqr = starClipDistance * starClipDistance;
    }

    private void CreateStars()
    {
        points = new ParticleSystem.Particle[starsMax];

        for (int i = 0; i < starsMax; i++)
        {
            points[i].position = Random.insideUnitSphere * starDistance + thisTransform.position;
            points[i].startColor = new Color(starColor.r, starColor.g, starColor.b, starColor.a);
            points[i].startSize = starSize;
        }
    }

    void Update()
    {
        //If there is no points(stars) then it will run the create stars script
        if (points == null) CreateStars();

        for (int i = 0; i < starsMax; i++)
        {
            if ((points[i].position - thisTransform.position).sqrMagnitude > starDistanceSqr)
            {
                points[i].position = Random.insideUnitSphere.normalized * starDistance + thisTransform.position;
            }

            if ((points[i].position - thisTransform.position).sqrMagnitude <= starClipDistanceSqr)
            {
                float percentage = (points[i].position - thisTransform.position).sqrMagnitude / starClipDistanceSqr;
                points[i].startColor = new Color(1, 1, 1, percentage);
                points[i].startSize = percentage * starSize;
            }
        }
        GetComponent<ParticleSystem>().SetParticles(points, points.Length);
    }
}