changed gap strategy to search its largest gap unit

code/backend/Cleanuparr.Infrastructure.Tests/Features/Seeker/SeekerUnitEvaluatorTests.cs

@@ -1211,6 +1211,28 @@ public class SeekerUnitEvaluatorTests : IDisposable
         missingPicks.ShouldBeGreaterThan(600);
     }
 
+    [Fact]
+    public async Task SelectNext_CustomFormatGapWeighted_Sonarr_SearchesTheLargestGapUnit()
+    {
+        // Arrange
+        SetupSonarr([Series(1)], []);
+        await AddSonarrCustomFormatEntryAsync(episodeId: 20, currentScore: 5, cutoffScore: 10);
+        await AddSonarrCustomFormatEntryAsync(episodeId: 21, currentScore: 0, cutoffScore: 30);
+        SeekerEvaluation evaluation = await EvaluateSonarrAsync(InstanceConfig(_sonarr, c =>
+        {
+            c.UseCustomFormatScore = true;
+            c.SonarrSearchMode = SonarrSearchMode.Episode;
+        }));
+
+        // Act
+        List<long> picked = Enumerable.Range(0, 50)
+            .Select(_ => SeekerUnitEvaluator.SelectNext(evaluation, SelectionStrategy.CustomFormatGapWeighted, 1)[0].EpisodeId)
+            .ToList();
+
+        // Assert
+        picked.ShouldAllBe(id => id == 21);
+    }
+
     [Theory]
     [InlineData(SelectionStrategy.CustomFormatGapWeighted, false, SelectionStrategy.BalancedWeighted)]
     [InlineData(SelectionStrategy.CustomFormatGapWeighted, true, SelectionStrategy.CustomFormatGapWeighted)]

code/backend/Cleanuparr.Infrastructure/Features/Seeker/SeekerUnitEvaluator.cs

@@ -135,7 +135,7 @@ public sealed class SeekerUnitEvaluator
 
         return ItemSelectorFactory.Create(strategy)
             .Select([.. selectionCandidates], count)
-            .Select(id => ToCandidate(PickUnit(remainingByItem[id])))
+            .Select(id => ToCandidate(PickUnit(remainingByItem[id], strategy)))
             .ToList();
     }
 
@@ -708,9 +708,20 @@ public sealed class SeekerUnitEvaluator
 
     /// <summary>
     /// Picks a random season of the item, then its earliest airing unit.
+    /// Under <see cref="SelectionStrategy.CustomFormatGapWeighted"/> it picks the missing unit, else the largest gap unit.
     /// </summary>
-    private static SeekerSearchUnit PickUnit(List<SeekerSearchUnit> itemUnits)
+    private static SeekerSearchUnit PickUnit(List<SeekerSearchUnit> itemUnits, SelectionStrategy strategy)
     {
+        if (strategy is SelectionStrategy.CustomFormatGapWeighted)
+        {
+            return itemUnits
+                .OrderByDescending(u => u.Reasons.Contains(SeekerSearchReason.Missing))
+                .ThenByDescending(u => u.CustomFormatGap)
+                .ThenBy(u => u.AirDateUtc ?? DateTimeOffset.MaxValue)
+                .ThenBy(u => u.EpisodeId)
+                .First();
+        }
+
         List<int> seasons = itemUnits.Select(u => u.SeasonNumber).Distinct().ToList();
         int seasonNumber = seasons[Random.Shared.Next(seasons.Count)];