using System.Collections.Concurrent;

namespace NeonSprawl.Server.Game.Npc;

/// <summary>Thread-safe in-memory NPC runtime state for prototype instances (NEO-93).</summary>
public sealed class InMemoryNpcRuntimeStateStore : INpcRuntimeStateStore
{
    private readonly ConcurrentDictionary<string, NpcRuntimeRow> rowsByNpcId = new(StringComparer.Ordinal);

    private readonly ConcurrentDictionary<string, object> idLocks = new(StringComparer.Ordinal);

    /// <inheritdoc />
    public DateTimeOffset LastAdvancedUtc { get; set; } = DateTimeOffset.MinValue;

    /// <inheritdoc />
    public bool TryGet(string? npcInstanceId, out NpcRuntimeStateSnapshot snapshot)
    {
        var key = NormalizeNpcInstanceId(npcInstanceId);
        if (key.Length == 0 || !PrototypeNpcRegistry.TryGet(key, out _))
        {
            snapshot = default;
            return false;
        }

        lock (idLocks.GetOrAdd(key, _ => new object()))
        {
            var row = rowsByNpcId.GetOrAdd(key, static id => NpcRuntimeRow.CreateIdle(id));
            snapshot = row.ToSnapshot();
            return true;
        }
    }

    /// <inheritdoc />
    public bool TryWrite(string? npcInstanceId, in NpcRuntimeStateSnapshot snapshot)
    {
        var key = NormalizeNpcInstanceId(npcInstanceId);
        if (key.Length == 0 || !PrototypeNpcRegistry.TryGet(key, out _))
        {
            return false;
        }

        lock (idLocks.GetOrAdd(key, _ => new object()))
        {
            rowsByNpcId[key] = NpcRuntimeRow.FromSnapshot(snapshot with { NpcInstanceId = key });
            return true;
        }
    }

    /// <inheritdoc />
    public bool TryResetPrototypeRow(string? npcInstanceId)
    {
        var key = NormalizeNpcInstanceId(npcInstanceId);
        if (key.Length == 0 || !PrototypeNpcRegistry.TryGet(key, out _))
        {
            return false;
        }

        lock (idLocks.GetOrAdd(key, _ => new object()))
        {
            rowsByNpcId[key] = NpcRuntimeRow.CreateIdle(key);
            return true;
        }
    }

    /// <inheritdoc />
    public void ResetAllPrototypeRows()
    {
        foreach (var npcInstanceId in PrototypeNpcRegistry.GetInstanceIdsInOrder())
        {
            _ = TryResetPrototypeRow(npcInstanceId);
        }

        LastAdvancedUtc = DateTimeOffset.MinValue;
    }

    private static string NormalizeNpcInstanceId(string? npcInstanceId) =>
        npcInstanceId?.Trim().ToLowerInvariant() ?? string.Empty;

    private sealed class NpcRuntimeRow
    {
        public required string NpcInstanceId { get; init; }

        public NpcBehaviorState BehaviorState { get; init; }

        public DateTimeOffset PhaseStartedUtc { get; init; }

        public ActiveTelegraphSnapshot? ActiveTelegraph { get; init; }

        public static NpcRuntimeRow CreateIdle(string npcInstanceId) =>
            new()
            {
                NpcInstanceId = npcInstanceId,
                BehaviorState = NpcBehaviorState.Idle,
                PhaseStartedUtc = DateTimeOffset.MinValue,
                ActiveTelegraph = null,
            };

        public NpcRuntimeStateSnapshot ToSnapshot() =>
            new(NpcInstanceId, BehaviorState, PhaseStartedUtc, ActiveTelegraph);

        public static NpcRuntimeRow FromSnapshot(NpcRuntimeStateSnapshot snapshot) =>
            new()
            {
                NpcInstanceId = snapshot.NpcInstanceId,
                BehaviorState = snapshot.BehaviorState,
                PhaseStartedUtc = snapshot.PhaseStartedUtc,
                ActiveTelegraph = snapshot.ActiveTelegraph,
            };
    }
}