Make RandomLevelsCategory use seed from game (#323)

Closes #122

# Why
Previously, we were using a globally shared instance of `Random` when
calculating the random order of levels. This caused levels to appear
multiple times in the list and caused others to get potentially missed
entirely.

By using a consistent seed we can negate both of those problems and
ensure the full list gets hit consistently.

# How
To fix, introduce the client's `seed` parameter as an available
parameter to use in the filter settings. We can then use this to create
a new `Random` object on each call of `GetRandomLevel()` with the new
seed.

# Remarks
This will require a change in `refresh-web` to make the website generate
a random seed, since if we do not find a seed value server-side we
simply use `0`.

Refresh.GameServer/Database/GameDatabaseContext.Levels.cs

@@ -192,12 +192,16 @@ public DatabaseList<GameLevel> GetNewestLevels(int count, int skip, GameUser? us
             .OrderByDescending(l => l.PublishDate), skip, count);
 
     [Pure]
-    public DatabaseList<GameLevel> GetRandomLevels(int count, int skip, GameUser? user, LevelFilterSettings levelFilterSettings) =>
-        new(this.GetLevelsByGameVersion(levelFilterSettings.GameVersion)
+    public DatabaseList<GameLevel> GetRandomLevels(int count, int skip, GameUser? user, LevelFilterSettings levelFilterSettings)
+    {
+        Random random = new(levelFilterSettings.Seed ?? 0);
+
+        return new DatabaseList<GameLevel>(this.GetLevelsByGameVersion(levelFilterSettings.GameVersion)
             .FilterByLevelFilterSettings(user, levelFilterSettings)
             .AsEnumerable()
-            .OrderBy(_ => Random.Shared.Next()), skip, count);
-
+            .OrderBy(_ => random.Next()), skip, count);
+    }
+
     // TODO: reduce code duplication for getting most of x
     [Pure]
     public DatabaseList<GameLevel> GetMostHeartedLevels(int count, int skip, GameUser? user, LevelFilterSettings levelFilterSettings)

Refresh.GameServer/Endpoints/Game/Levels/FilterSettings/LevelFilterSettings.cs

@@ -2,6 +2,7 @@
 using Refresh.GameServer.Authentication;
 using Refresh.GameServer.Extensions;
 using Refresh.GameServer.Services;
+using Refresh.GameServer.Types.Levels.Categories;
 
 namespace Refresh.GameServer.Endpoints.Game.Levels.FilterSettings;
 
@@ -45,6 +46,12 @@ public class LevelFilterSettings
     /// </summary>
     public TokenGame GameVersion;
 
+    /// <summary>
+    /// The seed used for lucky dip/random levels.
+    /// </summary>
+    /// <seealso cref="RandomLevelsCategory"/>
+    public int? Seed;
+
     public LevelFilterSettings(TokenGame game)
     {
         this.GameVersion = game;
@@ -126,5 +133,11 @@ public LevelFilterSettings(RequestContext context, TokenGame game) : this(game)
             this.Labels ??= new string[1];
             this.Labels[0] = labelFilter0;
         }
+
+        string? seedStr = context.QueryString.Get("seed");
+        if (seedStr != null && int.TryParse(seedStr, out int seed))
+        {
+            this.Seed = seed;
+        }
     }
 }

RefreshTests.GameServer/Tests/Levels/LevelTests.cs

@@ -40,16 +40,32 @@ public void SlotsRandom()
     {
         using TestContext context = this.GetServer();
         GameUser user = context.CreateUser();
-        GameLevel level = context.CreateLevel(user);
+
+        // 3 levels to test with
+        GameLevel level1 = context.CreateLevel(user);
+        GameLevel level2 = context.CreateLevel(user);
+        GameLevel level3 = context.CreateLevel(user);
 
         using HttpClient client = context.GetAuthenticatedClient(TokenType.Game, user);
-
-        HttpResponseMessage message = client.GetAsync($"/lbp/slots/lbp2luckydip").Result;
-        Assert.That(message.StatusCode, Is.EqualTo(OK));
 
-        SerializedMinimalLevelList result = message.Content.ReadAsXML<SerializedMinimalLevelList>();
-        Assert.That(result.Items, Has.Count.EqualTo(1));
-        Assert.That(result.Items.First().LevelId, Is.EqualTo(level.LevelId));
+        void TestSeed(GameLevel expectedLevel, int seed)
+        {
+            // Iterate through a bunch of times to ensure it's deterministic
+            for (int i = 0; i < 10; i++)
+            {
+                HttpResponseMessage message = client.GetAsync($"/lbp/slots/lbp2luckydip?seed={seed}").Result;
+                Assert.That(message.StatusCode, Is.EqualTo(OK));
+
+                SerializedMinimalLevelList result = message.Content.ReadAsXML<SerializedMinimalLevelList>();
+                Assert.That(result.Items, Has.Count.EqualTo(3));
+                Assert.That(result.Items.First().LevelId, Is.EqualTo(expectedLevel.LevelId));
+            }
+        }
+
+        TestSeed(level1, 69420);
+        TestSeed(level2, 1);
+        TestSeed(level3, 2);
+        TestSeed(level3, -2);
     }
 
     [Test]