using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;

namespace Encompass
{
    internal abstract class TypedComponentStore
    {
        public abstract int Count { get; }
        public abstract bool Has(int entity);
        public abstract bool Remove(int entity, int priority);
        public abstract void ForceRemove(int entity);
        public abstract void Clear();
        public abstract void ClearPriorities();
    }

    internal class TypedComponentStore<TComponent> : TypedComponentStore where TComponent : unmanaged
    {
        private readonly Dictionary<int, int> _indices = new Dictionary<int, int>(512);
        private readonly Dictionary<int, int> _priorities = new Dictionary<int, int>(512);
        private readonly TComponent[] _components = new TComponent[512];
        private readonly IDManager _idManager = new IDManager();

        public override int Count { get => _indices.Count; }

        public unsafe ref readonly TComponent Get(int entityID)
        {
            if (!_indices.ContainsKey(entityID)) { throw new Exceptions.NoComponentOfTypeOnEntityException("No component of type {0} exists on Entity with ID {1}", typeof(TComponent), entityID); }
            ref var refVal = ref _components[_indices[entityID]];
            return ref Unsafe.AsRef<TComponent>(Unsafe.AsPointer(ref refVal));
        }

        public unsafe void Set(int entityID, TComponent component)
        {
            InternalSet(entityID, component);
        }

        public unsafe bool Set(int entityID, TComponent component, int priority)
        {
            if (!_priorities.ContainsKey(entityID) || priority < _priorities[entityID])
            {
                InternalSet(entityID, component);
                _priorities[entityID] = priority;
                return true;
            }

            return false;
        }

        private unsafe void InternalSet(int entityID, TComponent component)
        {
            if (!_indices.ContainsKey(entityID))
            {
                _indices[entityID] = _idManager.NextID();
            }

            _components[_indices[entityID]] = Unsafe.AsRef<TComponent>(Unsafe.AsPointer(ref component));
        }

        public override bool Remove(int entityID, int priority)
        {
            if (!_priorities.ContainsKey(entityID) || priority < _priorities[entityID])
            {
                _priorities[entityID] = priority;
                ForceRemove(entityID);
                return true;
            }

            return false;
        }

        public override void ForceRemove(int entityID)
        {
            _indices.Remove(entityID);
            _priorities.Remove(entityID);
            _idManager.Free(entityID);
        }

        public override bool Has(int entityID)
        {
            return _indices.ContainsKey(entityID);
        }

        public override void Clear()
        {
            foreach (var entityID in _indices.Keys)
            {
                _idManager.Free(entityID);
            }
            _indices.Clear();
            _priorities.Clear();
        }

        public override void ClearPriorities()
        {
            _priorities.Clear();
        }

        public IEnumerable<(TComponent, int)> All()
        {
            foreach (var kvp in _indices)
            {
                yield return (_components[kvp.Value], kvp.Key);
            }
        }
    }
}