using System.Collections.Concurrent;
using System.Text.Json;
using DorkNet.Server.Controllers.Match;
using Microsoft.Extensions.Logging;
using StackExchange.Redis;

namespace DorkNet.Server.Services;

/// <summary>
/// Cross-replica tracker for which RoomInstance each authenticated
/// player most recently went to via /goto. The presence heartbeat
/// reads this back so the client's local state matches what the
/// server says, and is the only passive path that extends the room
/// TTL.
///
/// Why this exists: every ~5s the client POSTs /player/heartbeat,
/// expecting a PlayerPresence response that mirrors its own cached
/// presence. If the server returns roomInstance:null but the client
/// knows it's in DormRoom, RecNet.Matchmaking.OnPresenceHeartbeatResponse
/// logs "presence heartbeat response indicates local presence is
/// out-of-sync" repeatedly, the client gives up after a few rounds,
/// and shows the "Error: -2 / We lost the connection to Rec Room"
/// UI even though no network connection actually dropped.
///
/// **Multi-replica**: when <see cref="IConnectionMultiplexer"/> is
/// available, presence lives in Redis as <c>presence:{playerId}</c>
/// (JSON-serialised <see cref="RoomInstanceDto"/>). EXPIRE is set to
/// <see cref="PresenceTtl"/> so a player who silently drops
/// (uninstall, kill -9) ages out automatically; their next /goto
/// refreshes the value and heartbeat refreshes the TTL. Read-only
/// presence queries intentionally do not refresh it, otherwise admin
/// pages and friends-list polls keep stale rooms alive forever. When
/// no Redis is configured, falls back to a process-local
/// <see cref="ConcurrentDictionary"/>
/// — identical to pre-PR-2 behaviour and fine for single-instance
/// dev workflows.
///
/// State is intentionally non-persistent — a server restart drops
/// every presence record, and clients re-establish via their next
/// /goto call. Method signatures stay sync because the call sites
/// (heartbeat, /goto, room-state queries) are too numerous to pay
/// the cost of an async cascade. Sync StackExchange.Redis ops are
/// sub-millisecond on the same network at our QPS.
/// </summary>
public class PlayerPresenceService
{
    private readonly ConcurrentDictionary<long, RoomInstanceDto> _local = new();
    private readonly ConcurrentDictionary<long, DateTimeOffset> _localRoomExpires = new();
    private readonly ConcurrentDictionary<long, DateTimeOffset> _localActiveExpires = new();
    private readonly ConcurrentDictionary<long, DateTimeOffset> _localBootDormGraceExpires = new();
    private readonly ConcurrentDictionary<long, DateTimeOffset> _localNoRoomExpires = new();
    private readonly IConnectionMultiplexer? _redis;
    private readonly ILogger<PlayerPresenceService>? _log;

    /// <summary>
    /// Presence must survive long room loads. The 2020 client can go
    /// quiet for ~45 seconds while downloading/deserializing large
    /// uploaded rooms; a 45s Redis TTL expires right before the next
    /// heartbeat, making the server synthesize dorm fallback presence
    /// and effectively bouncing the player back to dorm. Ten minutes
    /// still ages out abandoned sessions, but does not punish slow
    /// room loads or temporary network stalls.
    /// </summary>
    public static TimeSpan PresenceTtl { get; } = TimeSpan.FromMinutes(10);

    /// <summary>
    /// Short online-status marker refreshed by heartbeat/join activity.
    /// This smooths over flaky SignalR notify sockets without letting a
    /// stale room presence make someone look online for the full room TTL.
    /// </summary>
    public static TimeSpan ActivityTtl { get; } = TimeSpan.FromSeconds(90);

    /// <summary>
    /// Right after login the 2023 watch may boot into its cached offline
    /// DormRoom before the live Photon join finishes. During that window
    /// a null roomInstance is safer than returning stale/live presence:
    /// the client treats the offline placeholder as invalid and accepts
    /// null, but a live private dorm forces a resync.
    /// </summary>
    public static TimeSpan BootDormGraceTtl { get; } = TimeSpan.FromSeconds(45);

    private static readonly JsonSerializerOptions JsonOpts = new()
    {
        // Match the wire format used by the matchmaking response so
        // the round-trip is lossless. Properties are already tagged
        // with [JsonPropertyName] for camelCase wire keys.
        PropertyNamingPolicy = null,
    };

    public PlayerPresenceService(
        IConnectionMultiplexer? redis = null,
        ILogger<PlayerPresenceService>? log = null)
    {
        _redis = redis;
        _log = log;
    }

    public void SetRoom(long playerId, RoomInstanceDto room)
    {
        if (_redis is { } mux)
        {
            try
            {
                var json = JsonSerializer.Serialize(room, JsonOpts);
                var db = mux.GetDatabase();
                db.StringSet(Key(playerId), json, PresenceTtl);
                db.KeyDelete(NoRoomKey(playerId));
                // Per-room membership index for the instance browser
                // (EnumerateActiveInstances). Members are validated against
                // the player's live presence on read, so a player who moved
                // on is pruned lazily instead of needing the old room here.
                if (room is not null && room.RoomId > 0)
                {
                    db.SetAdd(RoomIndexKey(room.RoomId), playerId);
                    db.KeyExpire(RoomIndexKey(room.RoomId), PresenceTtl + PresenceTtl);
                }
                _log?.LogDebug("[presence] set redis player={PlayerId} room={Room} bytes={Bytes}",
                    playerId, room?.Name ?? "<null>", json.Length);
            }
            catch (Exception ex)
            {
                // Don't let a Redis blip take down the goto handler — log
                // and fall through. Heartbeat will see no presence and the
                // watch will resync via its next /goto.
                _log?.LogWarning(ex, "[presence] redis SET failed for player={PlayerId}", playerId);
            }
        }
        else
        {
            _local[playerId] = room;
            _localRoomExpires[playerId] = DateTimeOffset.UtcNow.Add(PresenceTtl);
            _localNoRoomExpires.TryRemove(playerId, out _);
            _log?.LogDebug("[presence] set local player={PlayerId} room={Room}",
                playerId, room?.Name ?? "<null>");
        }
    }

    public void TouchRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                db.KeyExpire(Key(playerId), PresenceTtl);
                // Keep the room's membership index alive as long as its
                // members are: a player refreshed only through here would
                // otherwise outlive the set (SetRoom's 2 × TTL) and drop out
                // of the instance browser and room pushes.
                var json = db.StringGet(Key(playerId));
                if (json.HasValue &&
                    JsonSerializer.Deserialize<RoomInstanceDto>(json.ToString(), JsonOpts) is { RoomId: > 0 } room)
                {
                    db.SetAdd(RoomIndexKey(room.RoomId), playerId);
                    db.KeyExpire(RoomIndexKey(room.RoomId), PresenceTtl + PresenceTtl);
                }
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis EXPIRE failed for player={PlayerId}", playerId);
            }
            return;
        }

        if (_local.ContainsKey(playerId))
            _localRoomExpires[playerId] = DateTimeOffset.UtcNow.Add(PresenceTtl);
    }

    public void MarkActive(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                mux.GetDatabase().StringSet(ActiveKey(playerId), "1", ActivityTtl);
                mux.GetDatabase().SetAdd(ActiveSetKey, playerId);
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis active SET failed for player={PlayerId}", playerId);
            }
            return;
        }

        _localActiveExpires[playerId] = DateTimeOffset.UtcNow.Add(ActivityTtl);
    }

    public void BeginBootDormGrace(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                mux.GetDatabase().StringSet(BootDormGraceKey(playerId), "1", BootDormGraceTtl);
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis boot grace SET failed for player={PlayerId}", playerId);
            }
            return;
        }

        _localBootDormGraceExpires[playerId] = DateTimeOffset.UtcNow.Add(BootDormGraceTtl);
    }

    public bool IsBootDormGraceActive(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                return mux.GetDatabase().KeyExists(BootDormGraceKey(playerId));
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis boot grace GET failed for player={PlayerId}", playerId);
                return false;
            }
        }

        if (!_localBootDormGraceExpires.TryGetValue(playerId, out var expires)) return false;
        if (expires > DateTimeOffset.UtcNow) return true;
        _localBootDormGraceExpires.TryRemove(playerId, out _);
        return false;
    }

    public void EndBootDormGrace(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                mux.GetDatabase().KeyDelete(BootDormGraceKey(playerId));
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis boot grace DEL failed for player={PlayerId}", playerId);
            }
            return;
        }

        _localBootDormGraceExpires.TryRemove(playerId, out _);
    }

    public IReadOnlyCollection<long> RecentlyActivePlayerIds()
    {
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                var members = db.SetMembers(ActiveSetKey);
                if (members.Length == 0) return Array.Empty<long>();

                var activeIds = new List<long>(members.Length);
                var stale = new List<RedisValue>();
                foreach (var member in members)
                {
                    if (!long.TryParse(member.ToString(), out var playerId))
                    {
                        stale.Add(member);
                        continue;
                    }

                    if (db.KeyExists(ActiveKey(playerId)))
                        activeIds.Add(playerId);
                    else
                        stale.Add(member);
                }

                if (stale.Count > 0)
                    db.SetRemove(ActiveSetKey, stale.ToArray());
                return activeIds;
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis active scan failed");
                return Array.Empty<long>();
            }
        }

        var now = DateTimeOffset.UtcNow;
        var active = new List<long>();
        foreach (var kv in _localActiveExpires)
        {
            if (kv.Value > now)
            {
                active.Add(kv.Key);
            }
            else
            {
                _localActiveExpires.TryRemove(kv.Key, out _);
            }
        }
        return active;
    }

    public bool IsRecentlyActive(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                return mux.GetDatabase().KeyExists(ActiveKey(playerId));
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis active GET failed for player={PlayerId}", playerId);
                return false;
            }
        }

        if (!_localActiveExpires.TryGetValue(playerId, out var expires)) return false;
        if (expires > DateTimeOffset.UtcNow) return true;
        _localActiveExpires.TryRemove(playerId, out _);
        return false;
    }

    public RoomInstanceDto? GetRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                var key = Key(playerId);
                var v = db.StringGet(key);
                if (!v.HasValue)
                {
                    _log?.LogDebug("[presence] miss redis player={PlayerId}", playerId);
                    return null;
                }
                return JsonSerializer.Deserialize<RoomInstanceDto>(v.ToString(), JsonOpts);
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis GET failed for player={PlayerId}", playerId);
                return null;
            }
        }
        if (!_local.TryGetValue(playerId, out var room)) return null;
        if (_localRoomExpires.TryGetValue(playerId, out var expires)
            && expires <= DateTimeOffset.UtcNow)
        {
            _local.TryRemove(playerId, out _);
            _localRoomExpires.TryRemove(playerId, out _);
            _localActiveExpires.TryRemove(playerId, out _);
            return null;
        }
        return room;
    }

    public void Clear(long playerId)
    {
        if (_redis is { } mux)
        {
            var db = mux.GetDatabase();
            db.KeyDelete(Key(playerId));
            db.KeyDelete(ActiveKey(playerId));
            db.KeyDelete(BootDormGraceKey(playerId));
            db.KeyDelete(NoRoomKey(playerId));
            db.SetRemove(ActiveSetKey, playerId);
        }
        else
        {
            _local.TryRemove(playerId, out _);
            _localRoomExpires.TryRemove(playerId, out _);
            _localActiveExpires.TryRemove(playerId, out _);
            _localBootDormGraceExpires.TryRemove(playerId, out _);
            _localNoRoomExpires.TryRemove(playerId, out _);
        }
    }

    /// <summary>Forget the player's room but keep everything that says they
    /// are still here (activity marker, login lock, boot grace). Used when a
    /// join fails or times out: the player is still online and about to run
    /// the client's fallback chain, so friends must not see them go offline,
    /// they just must not see a room the player never reached.</summary>
    public void ClearRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                mux.GetDatabase().KeyDelete(Key(playerId));
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis room DEL failed for player={PlayerId}", playerId);
            }
            return;
        }

        _local.TryRemove(playerId, out _);
        _localRoomExpires.TryRemove(playerId, out _);
    }

    /// <summary>
    /// Record that the player deliberately left online matchmaking: they are
    /// online, but in no room instance.
    ///
    /// The 2023 client does this in TryGoToOfflineRoom
    /// (RecNet.Runtime/RecNet/Matchmaking.txt:12677, the only caller of
    /// <c>matchmake/none</c> at :13279): it swaps its cached presence to the
    /// local offline instance (RoomInstanceId -1) and posts matchmake/none,
    /// ignoring the reply (<c>&lt;TryGoToOfflineRoom&gt;b__119_0</c> returns a
    /// constant). From then on the heartbeat handler
    /// (Matchmaking.txt:18103, compare at :18415-18467) treats a negative RoomInstanceId like no
    /// room (HCHDEHIGEBE.GIICPDHJOOH = <c>RoomInstanceId &lt; 0</c>) and is
    /// only in sync while the server answers <c>roomInstance: null</c>. Any
    /// room here — the old one, or a synthesised dorm — reads as out-of-sync
    /// and the client cancels its offline load to chase the server's room.
    /// The marker keeps the heartbeat's dorm fallback from firing for this
    /// player until they matchmake somewhere again.
    /// </summary>
    public void SetNoRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                db.KeyDelete(Key(playerId));
                db.StringSet(NoRoomKey(playerId), "1", PresenceTtl);
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis no-room SET failed for player={PlayerId}", playerId);
            }
            return;
        }

        _local.TryRemove(playerId, out _);
        _localRoomExpires.TryRemove(playerId, out _);
        _localNoRoomExpires[playerId] = DateTimeOffset.UtcNow.Add(PresenceTtl);
    }

    /// <summary>True while the player is online with no room after
    /// <see cref="SetNoRoom"/>. Cleared by the next <see cref="SetRoom"/> or
    /// <see cref="Clear"/>.</summary>
    public bool IsInNoRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                return mux.GetDatabase().KeyExists(NoRoomKey(playerId));
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis no-room GET failed for player={PlayerId}", playerId);
                return false;
            }
        }

        if (!_localNoRoomExpires.TryGetValue(playerId, out var expires)) return false;
        if (expires > DateTimeOffset.UtcNow) return true;
        _localNoRoomExpires.TryRemove(playerId, out _);
        return false;
    }

    /// <summary>Keep the no-room marker alive while the player keeps
    /// heartbeating from the offline room.</summary>
    public void TouchNoRoom(long playerId)
    {
        if (_redis is { } mux)
        {
            try
            {
                mux.GetDatabase().KeyExpire(NoRoomKey(playerId), PresenceTtl);
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis no-room EXPIRE failed for player={PlayerId}", playerId);
            }
            return;
        }

        if (_localNoRoomExpires.ContainsKey(playerId))
            _localNoRoomExpires[playerId] = DateTimeOffset.UtcNow.Add(PresenceTtl);
    }

    /// <summary>List the live instances of a given room, grouped by
    /// PhotonRoomId (or RoomInstanceId when a row has none), with the player
    /// ids currently presenced in each. Drives the room instance browser
    /// (<c>GET match.*/room/{id}/instances</c>) and the event instance list.
    ///
    /// <para>Only players whose presence is still live count: an expired
    /// room presence (<see cref="PresenceTtl"/>) is dropped, and so is a
    /// player whose activity marker (<see cref="ActivityTtl"/>, refreshed by
    /// every heartbeat and join) has lapsed. A client that crashed keeps its
    /// room presence for up to ten minutes, but it is not in the instance and
    /// must not inflate the player count or keep an empty instance listed.</para>
    ///
    /// <para><b>Redis.</b> <see cref="SetRoom"/> records each player in a
    /// per-room set (<c>presence-room:{roomId}</c>); this reads that set and
    /// validates every member against their current presence, pruning the
    /// ones that have moved on or expired. Without the index the Redis path
    /// had nothing to enumerate and returned an empty list on every
    /// multi-replica deployment.</para>
    ///
    /// <para>Private instances are skipped unless
    /// <paramref name="includePrivate"/> is set; callers that include them
    /// must apply their own visibility rule.</para></summary>
    public IEnumerable<(RoomInstanceDto Room, List<long> PlayerIds)> EnumerateActiveInstances(
        long roomId, bool includePrivate = false)
    {
        var members = new List<(long PlayerId, RoomInstanceDto Room)>();
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                var stale = new List<RedisValue>();
                foreach (var member in db.SetMembers(RoomIndexKey(roomId)))
                {
                    if (!long.TryParse(member.ToString(), out var playerId))
                    {
                        stale.Add(member);
                        continue;
                    }
                    var room = GetRoom(playerId);
                    if (room is null || room.RoomId != roomId)
                    {
                        stale.Add(member);
                        continue;
                    }
                    members.Add((playerId, room));
                }
                if (stale.Count > 0)
                    db.SetRemove(RoomIndexKey(roomId), stale.ToArray());
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[presence] redis room index scan failed room={RoomId}", roomId);
                return Array.Empty<(RoomInstanceDto, List<long>)>();
            }
        }
        else
        {
            foreach (var playerId in _local.Keys.ToList())
            {
                var room = GetRoom(playerId); // honours the room TTL
                if (room is not null && room.RoomId == roomId)
                    members.Add((playerId, room));
            }
        }

        var groups = new Dictionary<string, (RoomInstanceDto Room, List<long> PlayerIds)>(StringComparer.Ordinal);
        foreach (var (playerId, room) in members)
        {
            if (room.IsPrivate && !includePrivate) continue;
            if (!IsRecentlyActive(playerId)) continue;
            var key = InstanceKey(room);
            if (!groups.TryGetValue(key, out var entry))
            {
                entry = (room, new List<long>());
                groups[key] = entry;
            }
            entry.PlayerIds.Add(playerId);
        }
        return groups.Values;
    }

    /// <summary>The identity two presence rows share when they are in the
    /// same live instance: the Photon room, else the instance id.</summary>
    public static string InstanceKey(RoomInstanceDto room)
        => string.IsNullOrEmpty(room.PhotonRoomId)
            ? "<" + room.RoomInstanceId + ">"
            : room.PhotonRoomId;

    private static string RoomIndexKey(long roomId) => "presence-room:" + roomId;

    private static string Key(long playerId) => $"presence:{playerId}";
    private static string ActiveKey(long playerId) => $"presence-active:{playerId}";
    private static string BootDormGraceKey(long playerId) => $"presence-boot-dorm-grace:{playerId}";
    private static string NoRoomKey(long playerId) => $"presence-noroom:{playerId}";
    private const string ActiveSetKey = "presence-active";

    // ── LoginLock single-session enforcement ─────────────────────────
    // The 2020 watch generates a fresh GUID per session and sends it
    // in the `LoginLock` form field on every match.* request. Real
    // Rec Room rejects heartbeats whose lock doesn't match the
    // most-recent /player/login — that's how a second login on the
    // same account kicks the first session. We mirror that by storing
    // the most-recent lock in Redis (or the in-process fallback)
    // keyed by player id, with the same 45-s TTL as presence.
    //
    // SetLock OVERWRITES regardless of prior value — newest login
    // wins. ValidateLock returns false when the caller's lock is stale
    // or absent, which the heartbeat handler maps to a
    // session-terminated response so the watch logs out.

    private readonly ConcurrentDictionary<long, string> _localLocks = new();

    public bool SetLock(long playerId, string loginLock)
    {
        if (string.IsNullOrWhiteSpace(loginLock)) return false;
        var replacedActiveSession = false;
        if (_redis is { } mux)
        {
            try
            {
                var db = mux.GetDatabase();
                var key = LockKey(playerId);
                var previous = db.StringGet(key);
                replacedActiveSession = previous.HasValue &&
                    !string.Equals(previous.ToString(), loginLock, StringComparison.Ordinal);
                db.StringSet(key, loginLock, PresenceTtl);
            }
            catch (Exception ex) { _log?.LogWarning(ex, "[lock] redis SET failed for player={PlayerId}", playerId); }
        }
        else
        {
            replacedActiveSession = _localLocks.TryGetValue(playerId, out var previous) &&
                !string.Equals(previous, loginLock, StringComparison.Ordinal);
            _localLocks[playerId] = loginLock;
        }

        if (replacedActiveSession)
            _log?.LogWarning("[lock] concurrent login detected for player={PlayerId}; newest LoginLock wins", playerId);
        return replacedActiveSession;
    }

    public bool ValidateLock(long playerId, string? loginLock)
    {
        if (string.IsNullOrWhiteSpace(loginLock)) return false;
        if (_redis is { } mux)
        {
            try
            {
                var v = mux.GetDatabase().StringGet(LockKey(playerId));
                if (!v.HasValue) return false;
                // Refresh TTL on each successful validate so the
                // active session keeps its lock alive across heartbeats.
                if (string.Equals(v.ToString(), loginLock, StringComparison.Ordinal))
                {
                    mux.GetDatabase().KeyExpire(LockKey(playerId), PresenceTtl);
                    return true;
                }
                return false;
            }
            catch (Exception ex)
            {
                _log?.LogWarning(ex, "[lock] redis GET failed for player={PlayerId}", playerId);
                return true; // fail open — better double-session than mass kick on Redis blip
            }
        }
        return _localLocks.TryGetValue(playerId, out var stored)
            && string.Equals(stored, loginLock, StringComparison.Ordinal);
    }

    private static string LockKey(long playerId) => $"loginlock:{playerId}";

    // ── Photon region pings ──────────────────────────────────────────
    // The 2020 watch reports its measured Photon-region latencies in a
    // single POST after the matchmaking init handshake (see
    // MatchPlayerController.PhotonRegionPings). We hold the latest
    // reading per player in process memory only — region preferences
    // change infrequently, lose-on-restart is fine, and pushing this
    // through Redis would just bloat the key space for no gain.

    private readonly ConcurrentDictionary<long, IReadOnlyDictionary<string, int>> _regionPings = new();

    public void SetPhotonRegionPings(long playerId, IReadOnlyDictionary<string, int> pings)
    {
        if (pings.Count == 0) return;
        _regionPings[playerId] = pings;
    }

    /// <summary>Returns the region code with the lowest reported ping,
    /// or <c>null</c> when no pings were ever received for the
    /// player (matchmaking falls back to its default region in that
    /// case).</summary>
    public string? GetPreferredPhotonRegion(long playerId)
    {
        if (!_regionPings.TryGetValue(playerId, out var pings) || pings.Count == 0)
            return null;
        string? best = null;
        var bestMs = int.MaxValue;
        foreach (var kv in pings)
        {
            if (kv.Value < bestMs)
            {
                bestMs = kv.Value;
                best = kv.Key;
            }
        }
        return best;
    }
}