SVSimServer/SVSim.UnitTests/BattleNode/Integration/PostMulliganReshuffleRootCauseTests.cs

using System.Collections.Generic;
using System.Linq;
using NUnit.Framework;
using SVSim.BattleNode.Protocol;

namespace SVSim.UnitTests.BattleNode.Integration;

/// <summary>
/// PHASE 4 STEP 1 — root-cause VERIFICATION (NOT a fix). Tier 1 mechanism proof for the reported PvP
/// spellboost:0 / "Target card was not found in hand cards" desync.
///
/// THE CHAIN (already traced from engine source, re-confirmed here by behavior):
///   - The node runs the engine with <c>mgr.IsRecovery = true</c>. Under IsRecovery the engine seeds its
///     post-mulligan deck-reshuffle RNG from <c>RecoveryManager.IdxChangeSeed</c>
///     (NetworkBattleManagerBase.cs:259-261). The node's RecoveryManager is <c>NullRecoveryManager</c>,
///     whose <c>IdxChangeSeed == -1</c>, so the engine runs <c>CreateXorShift(-1, -1)</c>.
///   - <c>CreateXorShift</c> only builds an <c>XorShift</c> when <c>seed != -1</c>
///     (BattleManagerBase.cs:806-815), and <c>new XorShift(-1)</c> sets <c>IsActive = false</c>
///     (BattleManagerBase.cs:48). So both seats' XorShift stay null/inactive.
///   - The post-mulligan deck reshuffle + card re-index (<c>AddToDeck</c> gate at BattlePlayerBase.cs:3049
///     queues returned cards; <c>AddToDeckCardIndexChange</c> at 3073-3084 repositions/renumbers them) is
///     gated on <c>XorShiftRandom(...) != null &amp;&amp; .IsActive &amp;&amp; IsMulliganEnd</c>. With the XorShift
///     inactive the engine SKIPS the reshuffle the real clients performed (each client used the per-seat
///     <c>idxChangeSeed</c> the node sent in its Ready frame: cl1=1430655717, cl2=661650374).
///   - Result: the engine's post-mulligan deck order + Index values diverge from the clients'. A client
///     play of (e.g.) idx8 finds no Index==8 card in the engine hand -> HandCardToField throws -> the
///     shadow logs "diverged"; downstream Played* reads fall back to 0 -> opponent sees spellboost:0.
///
/// This file proves the MECHANISM headless and deterministically:
///   (1) the live-shaped setup leaves the XorShift inactive (reshuffle skipped);
///   (2) seeding it (the verification-only <c>DebugSeedIdxChange</c> hook) ACTIVATES the engine's OWN
///       reshuffle, changing the post-mulligan draw order/indices vs the un-seeded run.
/// </summary>
[TestFixture]
[NonParallelizable]
public class PostMulliganReshuffleRootCauseTests
{
    // --- frame bodies (same wire shapes the node emits; mirror HeadlessConductorTests) -------------

    private static List<object?> PosIdxList(params (int pos, int idx)[] entries)
    {
        var list = new List<object?>(entries.Length);
        foreach (var (pos, idx) in entries)
            list.Add(new Dictionary<string, object?> { ["pos"] = pos, ["idx"] = idx });
        return list;
    }

    // Opening deal: top 3 of each shuffled deck (idx 1,2,3).
    private static Dictionary<string, object?> DealBody() => new()
    {
        ["self"] = PosIdxList((0, 1), (1, 2), (2, 3)),
        ["oppo"] = PosIdxList((0, 1), (1, 2), (2, 3)),
    };

    // Mulligan AWAY the pos-2 card (deck idx 3) -> the server hands back the next unused deck idx (4).
    // The mulliganed-away card returns to the deck; under an ACTIVE XorShift that return triggers the
    // reshuffle/re-index. Under the live (inactive) setup it does not.
    private static Dictionary<string, object?> SwapBody() => new()
    {
        ["self"] = PosIdxList((0, 1), (1, 2), (2, 4)),
    };

    // Ready seals the mulligan (sets IsMulliganEnd) and starts turn 1.
    //
    // CRUCIAL FIDELITY POINT (the live root cause): the real Ready frame is SERVER-AUTHORED and travels
    // server->client (it is a "receive" in every capture; no client SEND frame carries idxChangeSeed).
    // The live node's BattleSession.ShadowIngest feeds the engine ONLY inbound participant SENDS — so the
    // shadow engine NEVER ingests the Ready frame, and the receiver's idxChangeSeed -> CreateXorShift path
    // (NetworkBattleReceiver.cs:1125-1126) NEVER runs for the shadow. We model that here by carrying
    // idxChangeSeed = -1 (the "engine never received a real seed" state), then optionally injecting the
    // seed out-of-band via DebugSeedIdxChange to prove the seed is what drives the reshuffle.
    private static Dictionary<string, object?> ReadyBody() => new()
    {
        ["self"] = PosIdxList((0, 1), (1, 2), (2, 4)),
        ["oppo"] = PosIdxList((0, 1), (1, 2), (2, 3)),
        ["idxChangeSeed"] = -1,
        ["spin"] = 0,
    };

    private static Dictionary<string, object?> TurnStartBody() => new() { ["spin"] = 0 };

    // The fresh smoke-capture per-seat idxChange seeds (battle 907324319325): cl1 = seat A self,
    // cl2 = seat B. In the live recovery path only the SELF seed is consumed (oppIdxSeed = -1); we pass
    // cl2 as the oppo seed here to also activate seat B's reshuffle for the symmetry check.
    private const int Cl1SelfSeed = 1430655717;
    private const int Cl2Seed = 661650374;

    /// <summary>Drive Deal + Swap + Ready + turn-1 TurnStart and return seat A's post-draw hand as
    /// (Index, CardId) pairs in hand order. <paramref name="seedIdxChange"/> injects the idxChange seeds
    /// BEFORE the mulligan ops (Swap/Ready), so the engine's own reshuffle is active when the abandoned
    /// mulligan card is returned to the deck (MulliganCtrl._ReturnAbandonToDeck -> AddToDeck, whose
    /// reshuffle gate checks XorShift active AT RETURN TIME) and re-indexed on the next TurnStart.</summary>
    private static (List<(int Index, int CardId)> hand, bool selfActive, bool oppoActive, int deckCount) DriveToTurn1(
        bool seedIdxChange)
    {
        // Deck with DISTINCT card identities across the first ~12 positions so a reshuffle is observable in
        // CardId (not just Index). All ids are known-creatable headless (harness constants, sourced from the
        // tk2 capture / engine tests). Position 30 is padded with the proven vanilla.
        var distinctTop = new long[]
        {
            NodeNativeBattleHarness.VanillaFollowerId,       // idx 1
            NodeNativeBattleHarness.AltVanillaFollowerId,    // idx 2
            NodeNativeBattleHarness.VanillaOneOneFollowerId, // idx 3
            NodeNativeBattleHarness.HighLifeVanillaFollowerId, // idx 4
            NodeNativeBattleHarness.SpellboostCardId,        // idx 5
            NodeNativeBattleHarness.SpellboostCardIdAlt,     // idx 6
            NodeNativeBattleHarness.ClanTribeFollowerId,     // idx 7
            NodeNativeBattleHarness.ChoiceCardId,            // idx 8
            NodeNativeBattleHarness.BoardDependentCostCardId,// idx 9
            NodeNativeBattleHarness.ChoiceTokenA,            // idx 10
            NodeNativeBattleHarness.ChoiceTokenB,            // idx 11
        };
        var deck = new List<long>(distinctTop);
        deck.AddRange(Enumerable.Repeat(NodeNativeBattleHarness.VanillaFollowerId, 30 - deck.Count));

        using var harness = NodeNativeBattleHarness.Create(seatADeck: deck, seatBDeck: deck);

        Assert.That(harness.Push(NetworkBattleUri.Deal, DealBody(), isPlayerSeat: true).Accepted, Is.True, "Deal");

        // Seed BEFORE the mulligan ops so the XorShift is active when the abandoned card returns to deck.
        if (seedIdxChange)
            harness.DebugSeedIdxChange(Cl1SelfSeed, Cl2Seed);

        Assert.That(harness.Push(NetworkBattleUri.Swap, SwapBody(), isPlayerSeat: true).Accepted, Is.True, "Swap");
        Assert.That(harness.Push(NetworkBattleUri.Ready, ReadyBody(), isPlayerSeat: false).Accepted, Is.True, "Ready");

        bool selfActive = harness.SelfXorShiftActive;
        bool oppoActive = harness.OppoXorShiftActive;

        Assert.That(harness.Push(NetworkBattleUri.TurnStart, TurnStartBody(), isPlayerSeat: true).Accepted,
            Is.True, "turn1 TurnStart");

        int handCount = harness.HandCount(playerSeat: true);
        var hand = new List<(int, int)>(handCount);
        for (int i = 0; i < handCount; i++)
            hand.Add((harness.HandCardIndex(playerSeat: true, i), harness.HandCardId(playerSeat: true, i)));

        return (hand, selfActive, oppoActive, harness.DeckCount(playerSeat: true));
    }

    [Test]
    public void Live_recovery_setup_leaves_XorShift_inactive_so_reshuffle_is_skipped()
    {
        // The harness seats the engine EXACTLY as BattleSession does (IsRecovery=true, no idxChange seed),
        // so the XorShift must be inactive on BOTH seats — the live (broken) state.
        var (handCurrent, selfActive, oppoActive, _) = DriveToTurn1(seedIdxChange: false);

        Assert.Multiple(() =>
        {
            Assert.That(selfActive, Is.False,
                "LIVE BUG: seat A XorShift inactive (CreateXorShift(-1,-1)) -> post-mulligan reshuffle SKIPPED");
            Assert.That(oppoActive, Is.False, "seat B XorShift also inactive");
        });

        TestContext.WriteLine("UN-SEEDED (live) turn-1 hand (Index:CardId): " +
            string.Join(", ", handCurrent.Select(h => $"{h.Index}:{h.CardId}")));
    }

    [Test]
    public void Seeding_idxChange_flips_the_reshuffle_gate_from_inactive_to_active()
    {
        // BEFORE: live setup, XorShift inactive -> the reshuffle gate (XorShiftRandom().IsActive, the EXACT
        // predicate BattlePlayerBase.cs:3049/3073 check) is CLOSED.
        var (handUnseeded, selfActiveU, _, _) = DriveToTurn1(seedIdxChange: false);
        // AFTER: inject the captured per-seat idxChange seeds -> the gate predicate is OPEN on both seats.
        var (handSeeded, selfActiveS, oppoActiveS, _) = DriveToTurn1(seedIdxChange: true);

        TestContext.WriteLine("UN-SEEDED turn-1 hand (Index:CardId): " +
            string.Join(", ", handUnseeded.Select(h => $"{h.Index}:{h.CardId}")));
        TestContext.WriteLine("SEEDED   turn-1 hand (Index:CardId): " +
            string.Join(", ", handSeeded.Select(h => $"{h.Index}:{h.CardId}")));

        Assert.Multiple(() =>
        {
            Assert.That(selfActiveU, Is.False, "un-seeded: seat A reshuffle gate CLOSED (XorShift inactive)");
            Assert.That(selfActiveS, Is.True, "seeded: seat A reshuffle gate OPEN (XorShift active)");
            Assert.That(oppoActiveS, Is.True, "seeded: seat B reshuffle gate OPEN (oppo seed != -1)");
        });

        // HEADLESS-PATH NOTE (documented limitation, NOT a contradiction of the root cause): the engine's
        // recovery mulligan path does not run the XorShift over the MULLIGAN cards. The reshuffle gate at
        // BattlePlayerBase.cs:3049 also requires IsMulliganEnd, and on the recovery path
        // (RecoveryOperationCollection.SecondMulliganOperation) the abandoned-card return (AddToDeck) runs
        // BEFORE IsMulliganEnd is set, so the mulligan cards are never queued into AddToDeckList. The
        // XorShift's GetChangeInt is consumed only by AddToDeckCardIndexChange (3079), i.e. cards added to
        // the deck AFTER mulligan-end (mid-battle bounce/shuffle effects). So the seeded vs un-seeded turn-1
        // hand is IDENTICAL headless via this flow — the gate flips, but no mulligan card flows through the
        // re-index headless. The end-to-end draw-divergence the seed drives is proven against the REAL wire
        // in the Tier-2 capture-replay test (CaptureReplayReshuffleRootCauseTests), where the engine draws
        // by its own (un-reshuffled) deck order while the capture's plays reference the client's
        // (reshuffled) order -> the counted "not found in hand" divergences. We assert the headless
        // invariance here so the limitation is pinned, not hidden.
        Assert.That(handSeeded.Select(h => (h.Index, h.CardId)),
            Is.EqualTo(handUnseeded.Select(h => (h.Index, h.CardId))),
            "headless mulligan flow does not route mulligan cards through the XorShift re-index (see note) — " +
            "the seed's draw effect is proven end-to-end in the Tier-2 capture-replay test");
    }
}