#nullable enable

using System;
using ShrinkEventBus;
using Unity.Collections;

namespace ShrinkEventBus.Entities
{
    /// <summary>Burst-safe producer queue; playback enters the regular Bus instance.</summary>
    public sealed class ShrinkEcsEventQueue<TEvent> : IDisposable where TEvent : unmanaged, IShrinkEvent
    {
        private NativeQueue<TEvent> _queue;

        public ShrinkEcsEventQueue(Allocator allocator = Allocator.Persistent)
        {
            _queue = new NativeQueue<TEvent>(allocator);
            Writer = new ShrinkEcsEventWriter<TEvent>(_queue.AsParallelWriter());
        }

        public ShrinkEcsEventWriter<TEvent> Writer { get; }

        public int Playback(IShrinkEventBus bus)
        {
            if (bus == null)
                throw new ArgumentNullException(nameof(bus));
            var count = 0;
            while (_queue.TryDequeue(out var eventData))
            {
                bus.Post(in eventData);
                count++;
            }
            return count;
        }

        public void Dispose()
        {
            if (_queue.IsCreated)
                _queue.Dispose();
        }
    }

    public readonly struct ShrinkEcsEventWriter<TEvent> where TEvent : unmanaged, IShrinkEvent
    {
        private readonly NativeQueue<TEvent>.ParallelWriter _writer;

        internal ShrinkEcsEventWriter(NativeQueue<TEvent>.ParallelWriter writer)
        {
            _writer = writer;
        }

        public void Post(in TEvent eventData) => _writer.Enqueue(eventData);
    }
}