using System;
using System.Collections.Generic;
using Robust.Shared.GameObjects.Components.Transform;
using Robust.Shared.Interfaces.GameObjects;
using Robust.Shared.Interfaces.Map;
using Robust.Shared.Interfaces.Timing;
using Robust.Shared.IoC;
using Robust.Shared.Map;
using Robust.Shared.Maths;
using Robust.Shared.Network.Messages;
using Robust.Shared.Prototypes;
using Robust.Shared.Timing;
using Robust.Shared.Utility;

namespace Robust.Shared.GameObjects
{
    /// <inheritdoc />
    public abstract class EntityManager : IEntityManager
    {
        #region Dependencies

        [Dependency]
#pragma warning disable 649
        private readonly IEntityNetworkManager EntityNetworkManager;

        [Dependency]
        private readonly IPrototypeManager PrototypeManager;

        [Dependency]
        protected readonly IEntitySystemManager EntitySystemManager;

        [Dependency]
        private readonly IComponentFactory ComponentFactory;

        [Dependency]
        private readonly IComponentManager _componentManager;

        [Dependency]
        private readonly IGameTiming _gameTiming;

        [Dependency] private readonly IMapManager _mapManager;
#pragma warning restore 649

        #endregion Dependencies

        /// <inheritdoc />
        public GameTick CurrentTick => _gameTiming.CurTick;

        /// <inheritdoc />
        public IComponentManager ComponentManager => _componentManager;

        /// <inheritdoc />
        public IEntityNetworkManager EntityNetManager => EntityNetworkManager;

        /// <summary>
        ///     All entities currently stored in the manager.
        /// </summary>
        protected readonly Dictionary<EntityUid, IEntity> Entities = new Dictionary<EntityUid, IEntity>();

        /// <summary>
        /// List of all entities, used for iteration.
        /// </summary>
        protected readonly List<Entity> _allEntities = new List<Entity>();

        protected readonly Queue<IncomingEntityMessage> NetworkMessageBuffer = new Queue<IncomingEntityMessage>();

        protected int NextUid = (int)EntityUid.FirstUid;

        private readonly IEntityEventBus _eventBus = new EntityEventBus();

        /// <inheritdoc />
        public IEventBus EventBus => _eventBus;

        public bool Started { get; protected set; }

        public virtual void Initialize()
        {
            EntityNetworkManager.SetupNetworking();
            _componentManager.ComponentRemoved += (sender, args) => _eventBus.UnsubscribeEvents(args.Component);
        }

        public virtual void Startup()
        {
        }

        public virtual void Shutdown()
        {
            FlushEntities();
            EntitySystemManager.Shutdown();
            Started = false;
            _componentManager.Clear();
        }

        public virtual void Update(float frameTime)
        {
            ProcessMessageBuffer();
            EntitySystemManager.Update(frameTime);
            _eventBus.ProcessEventQueue();
            CullDeletedEntities();
        }

        public virtual void FrameUpdate(float frameTime)
        {
            EntitySystemManager.FrameUpdate(frameTime);
        }

        #region Entity Management

        public abstract IEntity CreateEntityUninitialized(string prototypeName, GridCoordinates coordinates);

        public abstract IEntity CreateEntityUninitialized(string prototypeName, MapCoordinates coordinates);

        public abstract IEntity SpawnEntity(string protoName, GridCoordinates coordinates);
        public abstract IEntity SpawnEntityNoMapInit(string protoName, GridCoordinates coordinates);

        public abstract IEntity SpawnEntityAt(string entityType, GridCoordinates coordinates);

        public IEntity SpawnEntityAt(string entityType, MapCoordinates coordinates)
        {
            var grid = _mapManager.FindGridAt(coordinates);
            var gridCoords = new GridCoordinates(grid.WorldToLocal(coordinates.Position), grid);

            return SpawnEntityAt(entityType, gridCoords);
        }

        /// <summary>
        /// Returns an entity by id
        /// </summary>
        /// <param name="uid"></param>
        /// <returns>Entity or null if entity id doesn't exist</returns>
        public IEntity GetEntity(EntityUid uid)
        {
            return Entities[uid];
        }

        /// <summary>
        /// Attempt to get an entity, returning whether or not an entity was gotten.
        /// </summary>
        /// <param name="uid"></param>
        /// <param name="entity">The requested entity or null if the entity couldn't be found.</param>
        /// <returns>True if a value was returned, false otherwise.</returns>
        public bool TryGetEntity(EntityUid uid, out IEntity entity)
        {
            if (Entities.TryGetValue(uid, out entity) && !entity.Deleted)
            {
                return true;
            }

            // entity might get assigned if it's deleted but still found,
            // prevent somebody from being "smart".
            entity = null;
            return false;
        }

        public IEnumerable<IEntity> GetEntities(IEntityQuery query)
        {
            return query.Match(this);
        }

        public IEnumerable<IEntity> GetEntitiesAt(Vector2 position)
        {
            foreach (var entity in GetEntities())
            {
                var transform = entity.Transform;
                if (FloatMath.CloseTo(transform.GridPosition.X, position.X) && FloatMath.CloseTo(transform.GridPosition.Y, position.Y))
                {
                    yield return entity;
                }
            }
        }

        public IEnumerable<IEntity> GetEntities()
        {
            // Manual index loop to allow adding to the list while iterating.
            // ReSharper disable once ForCanBeConvertedToForeach
            // ReSharper disable once LoopCanBeConvertedToQuery
            for (var i = 0; i < _allEntities.Count; i++)
            {
                var entity = _allEntities[i];
                if (entity.Deleted)
                {
                    continue;
                }

                yield return entity;
            }
        }

        /// <summary>
        /// Shuts-down and removes given Entity. This is also broadcast to all clients.
        /// </summary>
        /// <param name="e">Entity to remove</param>
        public virtual void DeleteEntity(IEntity e)
        {
            e.Shutdown();
        }

        public void DeleteEntity(EntityUid uid)
        {
            if (TryGetEntity(uid, out var entity))
            {
                DeleteEntity(entity);
            }
        }

        public bool EntityExists(EntityUid uid)
        {
            return TryGetEntity(uid, out var _);
        }

        /// <summary>
        /// Disposes all entities and clears all lists.
        /// </summary>
        public void FlushEntities()
        {
            foreach (IEntity e in GetEntities())
            {
                e.Shutdown();
            }

            CullDeletedEntities();
        }

        /// <summary>
        ///     Allocates an entity and stores it but does not load components or do initialization.
        /// </summary>
        private protected Entity AllocEntity(string prototypeName, EntityUid? uid = null)
        {
            var entity = AllocEntity(uid);

            if (String.IsNullOrWhiteSpace(prototypeName))
                return entity;

            var prototype = PrototypeManager.Index<EntityPrototype>(prototypeName);
            entity.Prototype = prototype;

            return entity;
        }

        /// <summary>
        ///     Allocates an entity and stores it but does not load components or do initialization.
        /// </summary>
        private protected Entity AllocEntity(EntityUid? uid = null)
        {
            if (uid == null)
            {
                uid = new EntityUid(NextUid++);
            }

            if (EntityExists(uid.Value))
            {
                throw new InvalidOperationException($"UID already taken: {uid}");
            }

            var entity = new Entity();

            entity.SetManagers(this);
            entity.SetUid(uid.Value);

            // allocate the required MetaDataComponent
            _componentManager.AddComponent<MetaDataComponent>(entity);

            // allocate the required TransformComponent
            _componentManager.AddComponent<TransformComponent>(entity);

            Entities[entity.Uid] = entity;
            _allEntities.Add(entity);

            return entity;
        }

        /// <summary>
        ///     Allocates an entity and loads components but does not do initialization.
        /// </summary>
        private protected Entity CreateEntity(string prototypeName, EntityUid? uid = null)
        {
            if (prototypeName == null)
                return AllocEntity(uid);

            var entity = AllocEntity(prototypeName, uid);
            EntityPrototype.LoadEntity(entity.Prototype, entity, ComponentFactory, null);
            return entity;
        }

        private protected void LoadEntity(Entity entity, IEntityLoadContext context)
        {
            EntityPrototype.LoadEntity(entity.Prototype, entity, ComponentFactory, context);
        }

        private protected static void InitializeAndStartEntity(Entity entity)
        {
            InitializeEntity(entity);
            StartEntity(entity);
        }

        private protected static void InitializeEntity(Entity entity)
        {
            entity.InitializeComponents();
        }

        private protected static void StartEntity(Entity entity)
        {
            entity.StartAllComponents();
        }

        private void CullDeletedEntities()
        {
            // Culling happens in updates.
            // It doesn't matter because to-be culled entities can't be accessed.
            // This should prevent most cases of "somebody is iterating while we're removing things"
            for (var i = 0; i < _allEntities.Count; i++)
            {
                var entity = _allEntities[i];
                if (!entity.Deleted)
                {
                    continue;
                }

                _allEntities.RemoveSwap(i);
                Entities.Remove(entity.Uid);

                // Process the one we just swapped next.
                i--;
            }
        }

        #endregion Entity Management

        #region message processing

        /// <inheritdoc />
        public void HandleEntityNetworkMessage(MsgEntity msg)
        {
            var incomingEntity = new IncomingEntityMessage(msg);

            if (!Started)
            {
                if (incomingEntity.Message.Type != EntityMessageType.Error) NetworkMessageBuffer.Enqueue(incomingEntity);
                return;
            }

            if (!Entities.TryGetValue(incomingEntity.Message.EntityUid, out var entity))
                NetworkMessageBuffer.Enqueue(incomingEntity);
            else
                ProcessEntityMessage(incomingEntity.Message);
        }

        private void ProcessMessageBuffer()
        {
            if (!Started) return;

            if (NetworkMessageBuffer.Count == 0) return;

            var misses = new List<IncomingEntityMessage>();

            while (NetworkMessageBuffer.Count != 0)
            {
                var incomingEntity = NetworkMessageBuffer.Dequeue();
                if (!Entities.TryGetValue(incomingEntity.Message.EntityUid, out var entity))
                {
                    incomingEntity.LastProcessingAttempt = DateTime.Now;
                    if ((incomingEntity.LastProcessingAttempt - incomingEntity.ReceivedTime).TotalSeconds > incomingEntity.Expires)
                        misses.Add(incomingEntity);
                }
                else
                {
                    ProcessEntityMessage(incomingEntity.Message);
                }
            }

            foreach (var miss in misses)
            {
                NetworkMessageBuffer.Enqueue(miss);
            }
        }

        private void ProcessEntityMessage(MsgEntity msgEntity)
        {
            switch (msgEntity.Type)
            {
                case EntityMessageType.ComponentMessage:
                    DispatchComponentMessage(msgEntity);
                    break;
            }
        }

        private void DispatchComponentMessage(MsgEntity msgEntity)
        {
            var compMsg = msgEntity.ComponentMessage;
            var compChannel = msgEntity.MsgChannel;
            compMsg.Remote = true;

            var uid = msgEntity.EntityUid;
            if (compMsg.Directed)
            {
                if (_componentManager.TryGetComponent(uid, msgEntity.NetId, out var component))
                    component.HandleMessage(compMsg, compChannel);
            }
            else
            {
                foreach (var component in _componentManager.GetComponents(uid))
                {
                    component.HandleMessage(compMsg, compChannel);
                }
            }
        }

        #endregion message processing
    }

    public enum EntityMessageType
    {
        Error = 0,
        ComponentMessage,
        EntityMessage,
        SystemMessage
    }
}