From 7e64b8a990eb3c5c64ffedd96983677bc36906a5 Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Mon, 7 Aug 2023 19:00:34 +0200
Subject: [PATCH] Added GetRandomEntry and GetRandomWeightedEntry to
 SingleRandom

---
 CHANGELOG.md                        |  1 +
 MLEM/Extensions/RandomExtensions.cs | 50 +++++++++++++++++------------
 MLEM/Misc/SingleRandom.cs           | 36 ++++++++++++++++++++-
 3 files changed, 66 insertions(+), 21 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f21f58a..fea90c7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ Jump to version:
 Additions
 - Added GraphicsExtensions.WithRenderTargets, a multi-target version of WithRenderTarget
 - Added Zero, One, Linear and Clamp to Easings
+- Added GetRandomEntry and GetRandomWeightedEntry to SingleRandom
 
 Fixes
 - Fixed TextInput not working correctly when using surrogate pairs
diff --git a/MLEM/Extensions/RandomExtensions.cs b/MLEM/Extensions/RandomExtensions.cs
index 250e50c..b171c8c 100644
--- a/MLEM/Extensions/RandomExtensions.cs
+++ b/MLEM/Extensions/RandomExtensions.cs
@@ -16,8 +16,7 @@ namespace MLEM.Extensions {
         /// <typeparam name="T">The entries' type</typeparam>
         /// <returns>A random entry</returns>
         public static T GetRandomEntry<T>(this Random random, ICollection<T> entries) {
-            // ElementAt internally optimizes for IList access so we don't have to here
-            return entries.ElementAt(random.Next(entries.Count));
+            return RandomExtensions.GetRandomEntry(entries, random.NextSingle());
         }
 
         /// <summary>
@@ -31,28 +30,12 @@ namespace MLEM.Extensions {
         /// <returns>A random entry, based on the entries' weight</returns>
         /// <exception cref="IndexOutOfRangeException">If the weight function returns different weights for the same entry</exception>
         public static T GetRandomWeightedEntry<T>(this Random random, ICollection<T> entries, Func<T, int> weightFunc) {
-            var totalWeight = entries.Sum(weightFunc);
-            var goalWeight = random.Next(totalWeight);
-            var currWeight = 0;
-            foreach (var entry in entries) {
-                currWeight += weightFunc(entry);
-                if (currWeight > goalWeight)
-                    return entry;
-            }
-            throw new IndexOutOfRangeException();
+            return RandomExtensions.GetRandomWeightedEntry(entries, weightFunc, random.NextSingle());
         }
 
         /// <inheritdoc cref="GetRandomWeightedEntry{T}(System.Random,System.Collections.Generic.ICollection{T},System.Func{T,int})"/>
         public static T GetRandomWeightedEntry<T>(this Random random, ICollection<T> entries, Func<T, float> weightFunc) {
-            var totalWeight = entries.Sum(weightFunc);
-            var goalWeight = random.NextDouble() * totalWeight;
-            var currWeight = 0F;
-            foreach (var entry in entries) {
-                currWeight += weightFunc(entry);
-                if (currWeight > goalWeight)
-                    return entry;
-            }
-            throw new IndexOutOfRangeException();
+            return RandomExtensions.GetRandomWeightedEntry(entries, weightFunc, random.NextSingle());
         }
 
         /// <summary>
@@ -87,5 +70,32 @@ namespace MLEM.Extensions {
         }
 #endif
 
+        internal static T GetRandomEntry<T>(ICollection<T> entries, float randomValue) {
+            // ElementAt internally optimizes for IList access so we don't have to here
+            return entries.ElementAt((int) (randomValue * entries.Count));
+        }
+
+        internal static T GetRandomWeightedEntry<T>(ICollection<T> entries, Func<T, int> weightFunc, float randomValue) {
+            var goalWeight = randomValue * entries.Sum(weightFunc);
+            var currWeight = 0;
+            foreach (var entry in entries) {
+                currWeight += weightFunc(entry);
+                if (currWeight > goalWeight)
+                    return entry;
+            }
+            throw new IndexOutOfRangeException();
+        }
+
+        internal static T GetRandomWeightedEntry<T>(ICollection<T> entries, Func<T, float> weightFunc, float randomValue) {
+            var goalWeight = randomValue * entries.Sum(weightFunc);
+            var currWeight = 0F;
+            foreach (var entry in entries) {
+                currWeight += weightFunc(entry);
+                if (currWeight > goalWeight)
+                    return entry;
+            }
+            throw new IndexOutOfRangeException();
+        }
+
     }
 }
diff --git a/MLEM/Misc/SingleRandom.cs b/MLEM/Misc/SingleRandom.cs
index 73f7299..dc3d861 100644
--- a/MLEM/Misc/SingleRandom.cs
+++ b/MLEM/Misc/SingleRandom.cs
@@ -1,4 +1,8 @@
-namespace MLEM.Misc {
+using System;
+using System.Collections.Generic;
+using MLEM.Extensions;
+
+namespace MLEM.Misc {
     /// <summary>
     /// The SingleRandom class allows generating single, one-off pseudorandom numbers based on a seed or a <see cref="SeedSource"/>.
     /// The types of numbers that can be generated are <see cref="int"/> and <see cref="float"/>, both of which can be generated with specific minimum and maximum values if desired.
@@ -138,5 +142,35 @@
             return (maxValue - minValue) * SingleRandom.Single(source) + minValue;
         }
 
+        /// <summary>
+        /// Gets a random entry from the given collection with uniform chance.
+        /// </summary>
+        /// <param name="entries">The entries to choose from</param>
+        /// <param name="source">The <see cref="SeedSource"/> to use.</param>
+        /// <typeparam name="T">The entries' type</typeparam>
+        /// <returns>A random entry</returns>
+        public static T GetRandomEntry<T>(ICollection<T> entries, SeedSource source) {
+            return RandomExtensions.GetRandomEntry(entries, SingleRandom.Single(source));
+        }
+
+        /// <summary>
+        /// Returns a random entry from the given collection based on the specified weight function.
+        /// A higher weight for an entry increases its likeliness of being picked.
+        /// </summary>
+        /// <param name="entries">The entries to choose from</param>
+        /// <param name="weightFunc">A function that applies weight to each entry</param>
+        /// <param name="source">The <see cref="SeedSource"/> to use.</param>
+        /// <typeparam name="T">The entries' type</typeparam>
+        /// <returns>A random entry, based on the entries' weight</returns>
+        /// <exception cref="IndexOutOfRangeException">If the weight function returns different weights for the same entry</exception>
+        public static T GetRandomWeightedEntry<T>(ICollection<T> entries, Func<T, int> weightFunc, SeedSource source) {
+            return RandomExtensions.GetRandomWeightedEntry(entries, weightFunc, SingleRandom.Single(source));
+        }
+
+        /// <inheritdoc cref="GetRandomWeightedEntry{T}(System.Collections.Generic.ICollection{T},System.Func{T,int},MLEM.Misc.SeedSource)"/>
+        public static T GetRandomWeightedEntry<T>(ICollection<T> entries, Func<T, float> weightFunc, SeedSource source) {
+            return RandomExtensions.GetRandomWeightedEntry(entries, weightFunc, SingleRandom.Single(source));
+        }
+
     }
 }