#nullable enable

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Threading;
using Cysharp.Threading.Tasks;

namespace ShrinkEventBus
{
    internal readonly struct ShrinkEventTrace
    {
        public ShrinkEventTrace(DateTime timestampUtc, Type eventType, ShrinkBusKey busKey,
            ShrinkBusOptions options, int threadId, long elapsedTimestampTicks,
            ShrinkPostResult result, bool isAsync)
        {
            TimestampUtc = timestampUtc;
            EventType = eventType;
            BusKey = busKey;
            Scheduler = options.Scheduler;
            DispatchMode = options.DispatchMode;
            ThreadId = threadId;
            ElapsedTimestampTicks = elapsedTimestampTicks;
            Result = result;
            IsAsync = isAsync;
        }

        public DateTime TimestampUtc { get; }
        public Type EventType { get; }
        public ShrinkBusKey BusKey { get; }
        public ShrinkBusSchedulerKind Scheduler { get; }
        public ShrinkDispatchMode DispatchMode { get; }
        public int ThreadId { get; }
        public long ElapsedTimestampTicks { get; }
        public ShrinkPostResult Result { get; }
        public bool IsAsync { get; }
    }

    public static class EventBus
    {
        private sealed class GlobalBusResolver : IShrinkBusResolver
        {
            public IShrinkEventBus GetBus(ShrinkBusKey key)
            {
                if (TryGetBus(key, out var bus))
                    return bus;
                throw new KeyNotFoundException($"Bus '{key}' is not registered.");
            }

            public bool TryGetBus(ShrinkBusKey key, out IShrinkEventBus bus) =>
                EventBus.TryGetBus(key, out bus);
        }

        private static readonly ConcurrentDictionary<ShrinkBusKey, IShrinkEventBus> Buses = new();
        internal static readonly IShrinkBusResolver Resolver = new GlobalBusResolver();
        private static readonly IShrinkEventBus DefaultBus = CreateDefaultBus();
        private static Action<IShrinkEvent, Type, ShrinkBusKey>? _posted;
        private static Action<ShrinkEventTrace>? _detailedPosted;

        internal static event Action<IShrinkEvent, Type, ShrinkBusKey> Posted
        {
            add
            {
                _posted += value;
            }
            remove
            {
                _posted -= value;
            }
        }

        internal static bool HasPostedObservers
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => Volatile.Read(ref _posted) != null;
        }

        internal static event Action<ShrinkEventTrace> DetailedPosted
        {
            add => _detailedPosted += value;
            remove => _detailedPosted -= value;
        }

        internal static bool HasDetailedPostedObservers
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => Volatile.Read(ref _detailedPosted) != null;
        }

        public static IShrinkEventBus Default => DefaultBus;

        public static IShrinkEventBus CreateBus(ShrinkBusKey key, ShrinkBusOptions options)
        {
            if (options == null)
                throw new ArgumentNullException(nameof(options));

            var bus = BuildBus(key, options);
            if (!Buses.TryAdd(key, bus))
            {
                bus.Dispose();
                throw new InvalidOperationException($"Bus '{key}' is already registered.");
            }
            ShrinkStaticBindingRegistry.AttachForBus(key, Resolver);
            return bus;
        }

        public static IShrinkEventBus GetOrCreateBus(ShrinkBusKey key, ShrinkBusOptions options)
        {
            if (options == null)
                throw new ArgumentNullException(nameof(options));
            var bus = Buses.GetOrAdd(key, busKey => BuildBus(busKey, options));
            ShrinkStaticBindingRegistry.AttachForBus(key, Resolver);
            return bus;
        }

        public static bool TryGetBus(ShrinkBusKey key, out IShrinkEventBus bus) =>
            Buses.TryGetValue(key, out bus!);

        public static bool RemoveBus(ShrinkBusKey key)
        {
            if (key == ShrinkBusKey.Game || !Buses.TryRemove(key, out var bus))
                return false;
            ShrinkStaticBindingRegistry.DetachBus(key);
            bus.Dispose();
            return true;
        }

        public static ShrinkPostResult Post<TEvent>(in TEvent eventData)
            where TEvent : IShrinkEvent => DefaultBus.Post(in eventData);

        public static UniTask<ShrinkPostResult> PostAsync<TEvent>(TEvent eventData,
            CancellationToken cancellationToken = default)
            where TEvent : IShrinkEvent => DefaultBus.PostAsync(eventData, cancellationToken);

        public static IDisposable Attach(object target, ShrinkBusKey? defaultBus = null)
        {
            if (target == null)
                throw new ArgumentNullException(nameof(target));
            if (target is not IShrinkGeneratedSubscriber generated)
                throw new InvalidOperationException(
                    $"Type {target.GetType().FullName} has no generated [ShrinkSubscribe] binding.");
            return generated.AttachGenerated(Resolver, defaultBus ?? ShrinkBusKey.Game);
        }

        internal static IReadOnlyList<(ShrinkBusKey Key, ShrinkBusOptions Options, int Subscribers)> Snapshot()
        {
            var snapshot = new List<(ShrinkBusKey, ShrinkBusOptions, int)>(Buses.Count);
            foreach (var pair in Buses)
            {
                var subscribers = pair.Value is ShrinkEventBusInstance instance
                    ? instance.SubscriberCount
                    : 0;
                snapshot.Add((pair.Key, pair.Value.Options, subscribers));
            }
            return snapshot;
        }

        private static IShrinkEventBus CreateDefaultBus()
        {
            var bus = BuildBus(ShrinkBusKey.Game, ShrinkBusOptions.MainThread());
            Buses[ShrinkBusKey.Game] = bus;
            ShrinkStaticBindingRegistry.AttachForBus(ShrinkBusKey.Game, Resolver);
            return bus;
        }

        private static IShrinkEventBus BuildBus(ShrinkBusKey key, ShrinkBusOptions options) =>
            new ShrinkEventBusBuilder()
                .WithKey(key)
                .WithOptions(options)
                .WithPostObserver(NotifyPostedObject)
                .Build();

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void NotifyPostedObject(IShrinkEvent eventData, Type eventType, ShrinkBusKey key)
        {
            _posted?.Invoke(eventData, eventType, key);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static void NotifyDetailedPosted(ShrinkEventTrace trace)
        {
            var observers = Volatile.Read(ref _detailedPosted);
            if (observers == null)
                return;
            try
            {
                observers(trace);
            }
            catch (Exception exception)
            {
#if UNITY_5_3_OR_NEWER
                UnityEngine.Debug.LogException(exception);
#else
                System.Diagnostics.Trace.TraceError(exception.ToString());
#endif
            }
        }
    }
}