using System;
using System.Collections.Generic;

using Server.Mobiles;

namespace Server.Custom.Bridge
{
    /// <summary>
    ///     The presence stream (https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/PROTOCOL_2.md §11 #1/#2): who is online and where. Two parts:
    ///
    ///       presence.online - a periodic population snapshot (total, per-facet, per-region), emitted
    ///                         on a sweep but only when it changes, so the site has a live "N online"
    ///                         plus a change history without a firehose of identical frames.
    ///       region.enter    - a real-time location transition from EventSink.OnEnterRegion, the cheap
    ///                         per-player movement signal PLAN.md §5.6 recommends over Movement.
    ///
    ///     The snapshot is derived each sweep from the online PlayerMobiles (NetState != null), the
    ///     same population the vitals sweep already walks; counting them by map and region is a handful
    ///     of field reads. region.enter is filtered to players.
    /// </summary>
    public static class BridgePresence
    {
        private static Timer _timer;

        // Signature of the last-emitted snapshot, so an unchanged population emits nothing.
        private static string _lastSig;

        private static long _sweeps, _emitted, _regionEnters;

        public static void Initialize()
        {
            if (!BridgeConfig.Enabled)
                return;

            EventSink.OnEnterRegion += OnEnterRegion;
            EventSink.ServerStarted += OnServerStarted;
        }

        private static void OnServerStarted()
        {
            // Force the next sweep to emit after a (re)connect, so a sidecar that restarted gets the
            // current population within one sweep.
            BridgeLink.Connected_Core += OnConnected;
            Rearm();
        }

        private static void OnConnected()
        {
            _lastSig = null;
        }

        /// <summary>Stops and recreates the timer from current config. Called by `[bridge reload`.</summary>
        public static void Rearm()
        {
            Stop();

            _timer = Timer.DelayCall(
                TimeSpan.FromSeconds(BridgeConfig.PresenceSweepSeconds),
                TimeSpan.FromSeconds(BridgeConfig.PresenceSweepSeconds),
                PresenceSweep);
        }

        public static void Stop()
        {
            if (_timer != null) { _timer.Stop(); _timer = null; }
        }

        public static string Status()
        {
            return String.Format("presence(sweeps={0} emitted={1} regionEnters={2})",
                _sweeps, _emitted, _regionEnters);
        }

        /// <summary>Runs one sweep now. Wired into `[bridge sweepnow`.</summary>
        public static void SweepOnce()
        {
            PresenceSweep();
        }

        private static void PresenceSweep()
        {
            try
            {
                _sweeps++;

                if (!BridgeLink.Connected)
                    return; // nothing is listening; do not fill the queue with perishable snapshots

                int total = 0;
                var byFacet = new SortedDictionary<string, int>(StringComparer.Ordinal);
                var byRegion = new SortedDictionary<string, int>(StringComparer.Ordinal);

                foreach (var m in World.Mobiles.Values)
                {
                    var pm = m as PlayerMobile;

                    if (pm == null || pm.NetState == null || pm.Deleted)
                        continue;

                    total++;

                    var facet = pm.Map == null ? "Internal" : pm.Map.Name;
                    Bump(byFacet, facet);

                    var region = pm.Region;
                    var regionName = (region == null || String.IsNullOrEmpty(region.Name)) ? "Wilderness" : region.Name;
                    Bump(byRegion, regionName);
                }

                var sig = Signature(total, byFacet, byRegion);
                if (sig == _lastSig)
                    return; // population unchanged since last emit

                _lastSig = sig;
                BridgeLink.Emit(WriteOnline(total, byFacet, byRegion));
                _emitted++;
            }
            catch (Exception ex)
            {
                Console.WriteLine("[Bridge] presence sweep threw: {0}", ex.Message);
            }
        }

        private static void Bump(IDictionary<string, int> map, string key)
        {
            int n;
            map[key] = map.TryGetValue(key, out n) ? n + 1 : 1;
        }

        private static string Signature(int total, SortedDictionary<string, int> byFacet, SortedDictionary<string, int> byRegion)
        {
            var sb = new System.Text.StringBuilder();
            sb.Append(total);
            foreach (var kv in byFacet) sb.Append('|').Append(kv.Key).Append(':').Append(kv.Value);
            sb.Append('#');
            foreach (var kv in byRegion) sb.Append('|').Append(kv.Key).Append(':').Append(kv.Value);
            return sb.ToString();
        }

        private static string WriteOnline(int total, SortedDictionary<string, int> byFacet, SortedDictionary<string, int> byRegion)
        {
            var sb = BridgeJson.Begin("presence.online").Num("count", total);

            WriteCounts(sb, "byFacet", byFacet);
            WriteCounts(sb, "byRegion", byRegion);

            return sb.End();
        }

        /// <summary>Writes a nested object of {name: count} pairs.</summary>
        private static void WriteCounts(System.Text.StringBuilder sb, string field, SortedDictionary<string, int> counts)
        {
            sb.Append(",\"").Append(field).Append("\":{");

            bool first = true;
            foreach (var kv in counts)
            {
                if (!first)
                    sb.Append(',');
                first = false;

                BridgeJson.Escape(sb, kv.Key);
                sb.Append(':').Append(kv.Value);
            }

            sb.Append('}');
        }

        // ---- real-time region transitions ----

        private static void OnEnterRegion(OnEnterRegionEventArgs e)
        {
            try
            {
                if (e == null || e.From == null || !e.From.Player)
                    return;

                var from = e.OldRegion;
                var to = e.NewRegion;

                // Only meaningful when the named region actually changed.
                var fromName = from == null ? null : from.Name;
                var toName = to == null ? null : to.Name;
                if (String.Equals(fromName, toName, StringComparison.Ordinal))
                    return;

                var sb = BridgeJson.Begin("region.enter")
                    .Str("from", fromName)
                    .Str("to", toName)
                    .Str("map", e.From.Map == null ? null : e.From.Map.Name);

                sb.Actor("who", e.From);

                BridgeLink.Emit(sb.End());
                _regionEnters++;
            }
            catch (Exception ex)
            {
                Console.WriteLine("[Bridge] region enter handler threw: {0}", ex.Message);
            }
        }
    }
}