BracerLib/Assets/Scripts/Utility/RandomUtility.cs

using System;
using UnityEngine;
using UnityEngine.TestTools;
using Random = System.Random;
using Vector2 = System.Numerics.Vector2;
using Vector3 = System.Numerics.Vector3;

namespace BracerLib.Utility
{
    [ExcludeFromCoverage]
    public static class RandomUtility
    {
        public static readonly string CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

        [ThreadStatic]
        private static Random unrepeatedRandomThreadInstance;

        private static Random unrepeatedRandom => unrepeatedRandomThreadInstance ??= new Random(DateTime.Now.Millisecond);

        private static int prevSeed = -1;

        public static float NextFloat(this Random prng) => (float)prng.NextDouble();

        public static float Range(this Random prng, float minInclusive, float maxExclusive)
            => minInclusive + (maxExclusive - minInclusive) * prng.NextFloat();

        public static void RandomizeUnityRandom()
        {
            var seed = (int)DateTime.Now.Ticks;
            if (seed != prevSeed)
                return;

            prevSeed = seed;
            UnityEngine.Random.InitState(seed);
        }

        /// <summary> Random between 0.0 inclusive and 1.0 exclusive. </summary>
        public static double NextDouble() => unrepeatedRandom.NextDouble();

        /// <summary> Random between 0f inclusive and 1f exclusive. </summary>
        public static float NextFloat() => unrepeatedRandom.NextFloat();

        /// <summary>
        /// Given a value, return a random number between the negative and positive of the input value.
        /// </summary>
        /// <param name="bookendRangeValue">Non-negative value.</param>
        public static float Range(float bookendRangeValue) => unrepeatedRandom.Range(-bookendRangeValue, bookendRangeValue);

        public static float Range(float minInclusive, float maxExclusive) => unrepeatedRandom.Range(minInclusive, maxExclusive);

        public static int Range(int minInclusive, int maxExclusive) => unrepeatedRandom.Next(minInclusive, maxExclusive);

        /// <summary> Random point uniformly distributed on the surface of a sphere of radius 1. </summary>
        public static Vector3 RandomOnUnitSphere() {
            var theta = MathUtility.TWO_PI * NextDouble();
            var phi = Math.Acos(2.0 * NextDouble() - 1.0);
            var sinPhi = Math.Sin(phi);
            return new Vector3(
                (float)(sinPhi * Math.Cos(theta)),
                (float)(sinPhi * Math.Sin(theta)),
                (float)Math.Cos(phi)
            );
        }

        /// <summary> Random point uniformly distributed inside a sphere of radius 1. </summary>
        public static Vector3 RandomInUnitSphere() => RandomOnUnitSphere() * (float)Math.Pow(NextDouble(), 1.0 / 3.0);

        /// <summary> Random point uniformly distributed on the perimeter of a circle of radius 1. </summary>
        public static Vector2 RandomOnUnitCircle() {
            var angle = MathUtility.TWO_PI * NextDouble();
            return new Vector2((float)Math.Cos(angle), (float)Math.Sin(angle));
        }

        /// <summary> Random point uniformly distributed in a circle of radius 1. </summary>
        public static Vector2 RandomInUnitCircle() => RandomOnUnitCircle() * (float)Math.Sqrt(NextDouble());

        /// <summary> Random point uniformly distributed in a ring starting at radius1 and ending at radius2. </summary>
        public static Vector2 RandomInRing(float r1, float r2) {
            var r2sq = r2 * r2;
            return RandomOnUnitCircle() * (float)Math.Sqrt(NextDouble() * (r1 * r1 - r2sq) + r2sq);
        }

        public static Color RandomColorRGB()
        {
            return new Color(
                unrepeatedRandom.NextFloat(),
                unrepeatedRandom.NextFloat(),
                unrepeatedRandom.NextFloat(),
                1f
            );
        }

        public static Color RandomColorRGBA()
        {
            return new Color(
                unrepeatedRandom.NextFloat(),
                unrepeatedRandom.NextFloat(),
                unrepeatedRandom.NextFloat(),
                unrepeatedRandom.NextFloat()
            );
        }
        public static string GetRandomString(int length)
        {
            var stringChars = new char[length];
            var random = new Random();

            for (var i = 0; i < stringChars.Length; i++)
                stringChars[i] = CHARS[random.Next(CHARS.Length)];

            return new string(stringChars);
        }
    }
}