feat(svc): ArenaTwoPickCardPoolService (rarity-weighted, class+neutral)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Program.cs

@@ -104,6 +104,7 @@ public class Program
         builder.Services.AddScoped<IStoryMasterRepository, StoryMasterRepository>();
         builder.Services.AddScoped<IViewerStoryProgressRepository, ViewerStoryProgressRepository>();
         builder.Services.AddScoped<IArenaTwoPickRunRepository, ArenaTwoPickRunRepository>();
+        builder.Services.AddScoped<IArenaTwoPickCardPoolService, ArenaTwoPickCardPoolService>();
         builder.Services.AddScoped<IStoryService, StoryService>();
         builder.Services.AddScoped<IDeckListBuilder, DeckListBuilder>();
         builder.Services.AddSingleton<IRandom, SystemRandom>();

SVSim.EmulatedEntrypoint/Services/ArenaTwoPickCardPoolService.cs

@@ -0,0 +1,117 @@
+using Microsoft.EntityFrameworkCore;
+using SVSim.Database;
+using SVSim.Database.Enums;
+using SVSim.Database.Models;
+using SVSim.Database.Models.Config;
+using SVSim.Database.Services;
+
+namespace SVSim.EmulatedEntrypoint.Services;
+
+public class ArenaTwoPickCardPoolService : IArenaTwoPickCardPoolService
+{
+    private readonly SVSimDbContext _db;
+    private readonly IGameConfigService _config;
+
+    public ArenaTwoPickCardPoolService(SVSimDbContext db, IGameConfigService config)
+    {
+        _db = db; _config = config;
+    }
+
+    public List<CandidatePair> GeneratePickSetsForTurn(int classId, int turn, long startingPairId, IRandom rng)
+    {
+        var aCfg = _config.Get<ArenaTwoPickConfig>();
+        var cCfg = _config.Get<ChallengeConfig>();
+
+        var setIds = cCfg.PoolCardSetIds is { Count: > 0 } ids
+            ? ids
+            : _config.Get<RotationConfig>().RotationCardSetIds ?? new List<int>();
+
+        var setIdsArr = setIds.ToArray();
+
+        // Cards belong to sets via the ShadowverseCardSetEntry.Cards collection.
+        // Class membership uses the Class navigation property: null = neutral (classId 0).
+        // Collectible = CollectionInfo != null.
+        var pool = _db.CardSets
+            .Where(s => setIdsArr.Contains(s.Id))
+            .SelectMany(s => s.Cards)
+            .Include(c => c.Class)
+            .Include(c => c.CollectionInfo)
+            .Where(c => c.CollectionInfo != null)
+            .Where(c => c.Class == null || c.Class.Id == classId)
+            .ToList();
+
+        // Group by (isNeutral, Rarity) for O(1) bucket lookup.
+        var byBucket = pool
+            .GroupBy(c => (c.Class == null, c.Rarity))
+            .ToDictionary(g => g.Key, g => g.ToList());
+
+        var pairs = new List<CandidatePair>(2);
+        for (int setNum = 1; setNum <= 2; setNum++)
+        {
+            pairs.Add(new CandidatePair
+            {
+                Id = startingPairId + (setNum - 1),
+                Turn = turn,
+                SetNum = setNum,
+                CardId1 = DrawOne(byBucket, aCfg, rng),
+                CardId2 = DrawOne(byBucket, aCfg, rng),
+                IsSelected = false,
+            });
+        }
+        return pairs;
+    }
+
+    private static long DrawOne(
+        Dictionary<(bool isNeutral, Rarity rarity), List<ShadowverseCardEntry>> byBucket,
+        ArenaTwoPickConfig cfg,
+        IRandom rng)
+    {
+        var rarity = PickRarity(cfg, rng);
+        var isNeutral = rng.NextDouble() < cfg.NeutralMixRate;
+
+        var candidates =
+            TryBucket(byBucket, isNeutral, rarity)
+            ?? TryBucket(byBucket, !isNeutral, rarity)
+            ?? FallbackByRarity(byBucket, isNeutral, rarity)
+            ?? byBucket.Values.SelectMany(v => v).ToList();
+
+        if (candidates.Count == 0)
+            throw new InvalidOperationException(
+                "ArenaTwoPickCardPoolService: card pool is empty for the configured class/set scope");
+
+        var pick = candidates[rng.Next(candidates.Count)];
+        return pick.Id;
+    }
+
+    private static List<ShadowverseCardEntry>? TryBucket(
+        Dictionary<(bool, Rarity), List<ShadowverseCardEntry>> b,
+        bool neutral,
+        Rarity r) =>
+        b.TryGetValue((neutral, r), out var v) && v.Count > 0 ? v : null;
+
+    private static List<ShadowverseCardEntry>? FallbackByRarity(
+        Dictionary<(bool, Rarity), List<ShadowverseCardEntry>> b,
+        bool neutral,
+        Rarity r)
+    {
+        Rarity[] order = { Rarity.Legendary, Rarity.Gold, Rarity.Silver, Rarity.Bronze };
+        int idx = Array.IndexOf(order, r);
+        for (int i = idx + 1; i < order.Length; i++)
+        {
+            if (TryBucket(b, neutral, order[i]) is { } v)  return v;
+            if (TryBucket(b, !neutral, order[i]) is { } w) return w;
+        }
+        return null;
+    }
+
+    private static Rarity PickRarity(ArenaTwoPickConfig cfg, IRandom rng)
+    {
+        var roll = rng.NextDouble();
+        if (roll < cfg.LegendaryRate) return Rarity.Legendary;
+        roll -= cfg.LegendaryRate;
+        if (roll < cfg.GoldRate)      return Rarity.Gold;
+        roll -= cfg.GoldRate;
+        if (roll < cfg.SilverRate)    return Rarity.Silver;
+        return Rarity.Bronze;
+    }
+}

SVSim.EmulatedEntrypoint/Services/IArenaTwoPickCardPoolService.cs

@@ -0,0 +1,12 @@
+using SVSim.Database.Models;
+
+namespace SVSim.EmulatedEntrypoint.Services;
+
+public interface IArenaTwoPickCardPoolService
+{
+    /// <summary>
+    /// Returns exactly 2 candidate pairs for the requested turn. Ids assigned monotonically
+    /// (startingPairId, startingPairId+1); set_num = 1, 2; isSelected = false.
+    /// </summary>
+    List<CandidatePair> GeneratePickSetsForTurn(int classId, int turn, long startingPairId, IRandom rng);
+}