using NeonSprawl.Server.Game.Items;

namespace NeonSprawl.Server.Game.Encounters;

/// <summary>
/// Applies encounter reward-table grants and marks completion idempotently (NEO-105).
/// Combat defeat wiring: <see cref="AbilityInput.AbilityCastApi"/> (NEO-106).
/// </summary>
public static class EncounterCompletionOperations
{
    private static readonly EncounterGrantApplied[] EmptyGrants = [];

    /// <summary>
    /// When all required targets are defeated and the encounter is not yet completed, applies
    /// <paramref name="encounterId"/>'s reward-table fixed grants then marks completion.
    /// </summary>
    public static EncounterCompletionResult TryCompleteAndGrant(
        string playerId,
        string encounterId,
        IEncounterDefinitionRegistry encounterRegistry,
        IRewardTableDefinitionRegistry rewardTableRegistry,
        IEncounterProgressStore progressStore,
        IEncounterCompletionStore completionStore,
        IItemDefinitionRegistry itemRegistry,
        IPlayerInventoryStore inventoryStore,
        TimeProvider timeProvider)
    {
        if (!encounterRegistry.TryNormalizeKnown(encounterId, out var normalizedEncounterId) ||
            !encounterRegistry.TryGetDefinition(normalizedEncounterId, out var encounterDefinition))
        {
            return Deny(EncounterCompletionReasonCodes.UnknownEncounter);
        }

        if (completionStore.IsCompleted(playerId, normalizedEncounterId))
        {
            return Deny(EncounterCompletionReasonCodes.AlreadyCompleted);
        }

        if (!EncounterProgressOperations.IsAllRequiredTargetsDefeated(
                playerId,
                normalizedEncounterId,
                encounterRegistry,
                progressStore))
        {
            return Deny(EncounterCompletionReasonCodes.NotReady);
        }

        if (!rewardTableRegistry.TryGetDefinition(encounterDefinition.RewardTableId, out var rewardTable))
        {
            return Deny(EncounterCompletionReasonCodes.UnknownRewardTable);
        }

        var grants = rewardTable.FixedGrants;
        if (grants.Count == 0)
        {
            return Deny(EncounterCompletionReasonCodes.UnknownRewardTable);
        }

        if (!inventoryStore.TryGetSnapshot(playerId, out var snapshot))
        {
            return Deny(EncounterCompletionReasonCodes.InventoryStoreMissing);
        }

        var simulated = CloneSnapshot(snapshot);
        foreach (var grant in grants)
        {
            if (!PlayerInventoryOperations.TrySimulateAddStack(
                    ref simulated,
                    grant.ItemId,
                    grant.Quantity,
                    itemRegistry))
            {
                return Deny(EncounterCompletionReasonCodes.InventoryFull);
            }
        }

        var applied = new List<EncounterGrantApplied>(grants.Count);
        foreach (var grant in grants)
        {
            var addOutcome = PlayerInventoryOperations.TryAddStack(
                playerId,
                grant.ItemId,
                grant.Quantity,
                itemRegistry,
                inventoryStore);

            if (addOutcome.Kind == PlayerInventoryMutationKind.StoreMissing)
            {
                CompensatingRemoveGrants(playerId, applied, itemRegistry, inventoryStore);
                return Deny(EncounterCompletionReasonCodes.InventoryStoreMissing);
            }

            if (addOutcome.Kind == PlayerInventoryMutationKind.Denied)
            {
                CompensatingRemoveGrants(playerId, applied, itemRegistry, inventoryStore);
                return Deny(MapInventoryReason(addOutcome.ReasonCode));
            }

            applied.Add(new EncounterGrantApplied(grant.ItemId, grant.Quantity));
        }

        var completedAt = timeProvider.GetUtcNow();
        if (!completionStore.TryMarkCompleted(playerId, normalizedEncounterId, completedAt))
        {
            CompensatingRemoveGrants(playerId, applied, itemRegistry, inventoryStore);
            return Deny(EncounterCompletionReasonCodes.AlreadyCompleted);
        }

        // TODO(E7.M2): quest-credit router consumes EncounterCompleteEvent (NEO-107 expands persistence + hook).

        var normalizedPlayerId = EncounterProgressIds.NormalizePlayerId(playerId);
        var completeEvent = new EncounterCompleteEvent(
            normalizedPlayerId,
            normalizedEncounterId,
            rewardTable.Id,
            applied,
            completedAt,
            MakeIdempotencyKey(normalizedPlayerId, normalizedEncounterId));

        return new EncounterCompletionResult(
            Success: true,
            ReasonCode: null,
            GrantsApplied: applied,
            CompleteEvent: completeEvent,
            CompletedAt: completedAt);
    }

    private static string MapInventoryReason(string? reasonCode) =>
        reasonCode switch
        {
            PlayerInventoryReasonCodes.InventoryFull => EncounterCompletionReasonCodes.InventoryFull,
            PlayerInventoryReasonCodes.InvalidItem => EncounterCompletionReasonCodes.InvalidItem,
            PlayerInventoryReasonCodes.InvalidQuantity => EncounterCompletionReasonCodes.InvalidQuantity,
            _ => reasonCode ?? EncounterCompletionReasonCodes.InventoryFull,
        };

    private static string MakeIdempotencyKey(string normalizedPlayerId, string normalizedEncounterId) =>
        $"{normalizedPlayerId}:{normalizedEncounterId}";

    private static PlayerInventorySnapshot CloneSnapshot(PlayerInventorySnapshot snapshot) =>
        new()
        {
            BagSlots = PlayerInventorySnapshot.CloneSlots(snapshot.BagSlots),
            EquipmentSlots = PlayerInventorySnapshot.CloneSlots(snapshot.EquipmentSlots),
        };

    private static void CompensatingRemoveGrants(
        string playerId,
        IReadOnlyList<EncounterGrantApplied> grants,
        IItemDefinitionRegistry itemRegistry,
        IPlayerInventoryStore inventoryStore)
    {
        for (var i = grants.Count - 1; i >= 0; i--)
        {
            var grant = grants[i];
            _ = PlayerInventoryOperations.TryRemoveStack(
                playerId,
                grant.ItemId,
                grant.Quantity,
                itemRegistry,
                inventoryStore);
        }
    }

    private static EncounterCompletionResult Deny(string reasonCode) =>
        new(
            Success: false,
            ReasonCode: reasonCode,
            GrantsApplied: EmptyGrants,
            CompleteEvent: null,
            CompletedAt: null);
}