using System;
using System.Collections.Generic;

namespace Mono.Event
{
    public class EventManager
    {
        private static EventManager instance;

        public static EventManager Instance
        {
            get
            {
                if (instance == null)
                {
                    instance = new EventManager();
                }

                return instance;
            }
        }

        private readonly Dictionary<int, List<EventHandler<GameEventArgs>>> m_EventPool;
        private EventHandler<GameEventArgs> m_DefaultHandler;
        private Queue<EventInfo> m_EventInfos;
        private Queue<EventHandler<GameEventArgs>> _cache;

        public EventManager()
        {
            m_EventInfos = new Queue<EventInfo>();
            _cache = new Queue<EventHandler<GameEventArgs>>();
            m_EventPool = new Dictionary<int, List<EventHandler<GameEventArgs>>>();
        }

        public int EventHandlerCount
        {
            get { return m_EventPool.Count; }
        }

        public int EventCount
        {
            get { return m_EventPool.Count; }
        }

        public int Count(int id)
        {
            if (!m_EventPool.TryGetValue(id, out var list))
            {
                return 0;
            }

            return list.Count;
        }

        public bool Check(int id, EventHandler<GameEventArgs> handler)
        {
            if (handler == null)
            {
                throw new Exception("Event handler is invalid.");
            }

            if (!m_EventPool.TryGetValue(id, out var list) || list.Count == 0)
            {
                return false;
            }

            return list.Contains(handler);
        }

        public void Subscribe(int id, EventHandler<GameEventArgs> handler)
        {
            if (handler == null)
            {
                throw new Exception("Event handler is invalid.");
            }

            if (!m_EventPool.TryGetValue(id, out var list))
            {
                m_EventPool[id] = list = new List<EventHandler<GameEventArgs>>();
            }

            list.Add(handler);
        }

        public void Unsubscribe(int id, EventHandler<GameEventArgs> handler)
        {
            if (handler == null)
            {
                throw new Exception("Event handler is invalid.");
            }

            if (!m_EventPool.TryGetValue(id, out var list))
            {
                throw new Exception($"Event '{id}' not exists specified handler.");
            }

            if (list.Count == 0)
            {
                throw new Exception($"Event '{id}' not exists specified handler.");
            }

            var indexOf = list.IndexOf(handler);
            if (indexOf == -1)
            {
                throw new Exception($"Event '{id}' not exists specified handler.");
            }

            list.RemoveAt(indexOf);
            if (list.Count == 0)
            {
                m_EventPool.Remove(id);
            }
        }

        public void SetDefaultHandler(EventHandler<GameEventArgs> handler)
        {
            m_DefaultHandler = handler;
        }

        struct EventInfo
        {
            public object sender { get; }
            public GameEventArgs args { get; }

            public EventInfo(object sender, GameEventArgs args)
            {
                this.sender = sender;
                this.args = args;
            }
        }

        public void Fire(object sender, GameEventArgs e)
        {
            if (e == null)
            {
                throw new Exception("Event is invalid.");
            }

            m_EventInfos.Enqueue(new EventInfo(sender, e));
        }

        public void FireNow(object sender, GameEventArgs e)
        {
            if (e == null)
            {
                throw new Exception("Event is invalid.");
            }

            HandleEvent(sender, e);
        }

        public void Update()
        {
            while (m_EventInfos.Count > 0)
            {
                var eventInfo = m_EventInfos.Dequeue();
                HandleEvent(eventInfo.sender, eventInfo.args);
            }
        }

        private void HandleEvent(object sender, GameEventArgs e)
        {
            if (!m_EventPool.TryGetValue(e.Id, out var list) || list.Count == 0)
            {
                if (m_DefaultHandler != null)
                {
                    m_DefaultHandler(sender, e);
                    return;
                }
                else
                    throw new ArgumentException(string.Format("Event '{0}' not allow no handler.", e.Id));
            }

            foreach (var eventHandler in list)
            {
                _cache.Enqueue(eventHandler);
            }

            while (_cache.Count > 0)
            {
                var eventHandler = _cache.Dequeue();
                eventHandler.Invoke(sender, e);
            }
        }
    }
}