using System.Globalization;

namespace AcDream.App.Streaming;

internal enum WorldRevealKind
{
    Login,
    Portal,
}

internal readonly record struct WorldRevealLifecycleSnapshot(
    long Generation,
    WorldRevealKind Kind,
    WorldRevealReadinessSnapshot Readiness,
    bool Materialized,
    bool Completed,
    bool Cancelled,
    bool WorldViewportObserved,
    int InvariantFailureCount)
{
    public bool IsActive => Generation != 0 && !Cancelled;
    public bool IsReady => Readiness.IsReady;
}

/// <summary>
/// Observes logical login/portal reveal generations without owning rendering or
/// changing gameplay state. The owner turns the canonical readiness decision
/// into deterministic lifecycle markers for connected automation and records a
/// hard diagnostic failure if normal world geometry becomes visible early.
/// </summary>
internal sealed class WorldRevealLifecycleTelemetry
{
    private readonly Action<string> _log;
    private WorldRevealLifecycleSnapshot _snapshot;
    private long _nextGeneration;
    private int _portalMaterializationCount;

    public WorldRevealLifecycleTelemetry(Action<string>? log = null)
    {
        _log = log ?? (_ => { });
    }

    public WorldRevealLifecycleSnapshot Snapshot => _snapshot;
    public int PortalMaterializationCount => _portalMaterializationCount;

    public long Begin(WorldRevealKind kind)
    {
        if (_snapshot.Generation != 0
            && !_snapshot.Cancelled
            && !_snapshot.WorldViewportObserved)
        {
            Log("superseded", _snapshot);
        }

        long generation = checked(++_nextGeneration);
        _snapshot = new WorldRevealLifecycleSnapshot(
            generation,
            kind,
            default,
            Materialized: false,
            Completed: false,
            Cancelled: false,
            WorldViewportObserved: false,
            InvariantFailureCount: _snapshot.InvariantFailureCount);
        Log("begin", _snapshot);
        return generation;
    }

    public void ObserveReadiness(WorldRevealReadinessSnapshot readiness)
    {
        if (_snapshot.Generation == 0 || _snapshot.Cancelled)
            return;

        if (_snapshot.Readiness == readiness)
            return;

        if (_snapshot.Readiness.DestinationCell != 0u
            && readiness.DestinationCell != 0u
            && _snapshot.Readiness.DestinationCell != readiness.DestinationCell)
        {
            FailInvariant(
                "destination-changed",
                $"from=0x{_snapshot.Readiness.DestinationCell:X8} to=0x{readiness.DestinationCell:X8}");
        }

        _snapshot = _snapshot with { Readiness = readiness };
        Log("readiness", _snapshot);
    }

    public void ObserveMaterialized()
    {
        if (_snapshot.Generation == 0 || _snapshot.Cancelled || _snapshot.Materialized)
            return;

        _snapshot = _snapshot with { Materialized = true };
        if (_snapshot.Kind == WorldRevealKind.Portal)
            _portalMaterializationCount++;
        Log("materialized", _snapshot);
    }

    public void ObserveWorldViewportVisible()
    {
        if (_snapshot.Generation == 0 || _snapshot.Cancelled || _snapshot.WorldViewportObserved)
            return;

        if (!_snapshot.Readiness.IsReady)
            FailInvariant("viewport-before-ready", null);

        _snapshot = _snapshot with { WorldViewportObserved = true };
        Log("world-visible", _snapshot);
    }

    public void Complete()
    {
        if (_snapshot.Generation == 0 || _snapshot.Cancelled || _snapshot.Completed)
            return;

        _snapshot = _snapshot with { Completed = true };
        Log("complete", _snapshot);
    }

    public void Cancel()
    {
        if (_snapshot.Generation == 0 || _snapshot.Cancelled)
            return;

        _snapshot = _snapshot with { Cancelled = true };
        Log("cancel", _snapshot);
    }

    private void FailInvariant(string reason, string? detail)
    {
        _snapshot = _snapshot with
        {
            InvariantFailureCount = checked(_snapshot.InvariantFailureCount + 1),
        };
        string suffix = string.IsNullOrWhiteSpace(detail) ? string.Empty : $" {detail}";
        _log($"[world-reveal] event=invariant-failure reason={reason}{suffix} {Describe(_snapshot)}");
    }

    private void Log(string eventName, WorldRevealLifecycleSnapshot snapshot) =>
        _log($"[world-reveal] event={eventName} {Describe(snapshot)}");

    private static string Describe(WorldRevealLifecycleSnapshot snapshot)
    {
        WorldRevealReadinessSnapshot ready = snapshot.Readiness;
        return string.Create(
            CultureInfo.InvariantCulture,
            $"generation={snapshot.Generation} kind={snapshot.Kind} " +
            $"cell=0x{ready.DestinationCell:X8} indoor={ready.IsIndoor} " +
            $"radius={ready.RequiredRenderRadius} unhydratable={ready.IsUnhydratable} " +
            $"render={ready.IsRenderNeighborhoodReady} composites={ready.AreCompositeTexturesReady} " +
            $"collision={ready.IsCollisionReady} ready={ready.IsReady} " +
            $"materialized={snapshot.Materialized} completed={snapshot.Completed} " +
            $"cancelled={snapshot.Cancelled} visible={snapshot.WorldViewportObserved} " +
            $"failures={snapshot.InvariantFailureCount}");
    }
}