using System;
using System.Collections.Generic;
using System.Reflection;
using System.Linq;
using Encompass.Exceptions;
using Encompass.Engines;

namespace Encompass
{
    public class WorldBuilder
    {
        private readonly List<Engine> engines = new List<Engine>();
        private readonly DirectedGraph<Engine> engineGraph = new DirectedGraph<Engine>();

        private readonly ComponentManager componentManager;
        private readonly EntityManager entityManager;
        private readonly MessageManager messageManager;
        private readonly DrawLayerManager drawLayerManager;
        private readonly RenderManager renderManager;

        private readonly Dictionary<Type, HashSet<Engine>> typeToReaders = new Dictionary<Type, HashSet<Engine>>();

        private readonly HashSet<Engine> senders = new HashSet<Engine>();

        private readonly HashSet<Type> registeredComponentTypes = new HashSet<Type>();

        public WorldBuilder()
        {
            var entitiesWithAddedComponents = new HashSet<Guid>();
            var entitiesWithRemovedComponents = new HashSet<Guid>();
            drawLayerManager = new DrawLayerManager();
            componentManager = new ComponentManager(drawLayerManager, entitiesWithAddedComponents, entitiesWithRemovedComponents);
            entityManager = new EntityManager(componentManager, entitiesWithAddedComponents, entitiesWithRemovedComponents);
            messageManager = new MessageManager();
            renderManager = new RenderManager(entityManager, componentManager, drawLayerManager);
        }

        public Entity CreateEntity()
        {
            return entityManager.CreateEntity();
        }

        public void EmitMessage<TMessage>(TMessage message) where TMessage : struct, IMessage
        {
            messageManager.AddMessage(message);
        }

        public Guid AddComponent<TComponent>(Entity entity, TComponent component) where TComponent : struct, IComponent
        {
            return componentManager.AddComponent(entity.ID, component);
        }

        public Guid AddDrawComponent<TComponent>(Entity entity, TComponent component, int layer = 0) where TComponent : struct, IComponent
        {
            return componentManager.AddDrawComponent(entity.ID, component, layer);
        }

        public void DeactivateComponent(Guid componentID)
        {
            componentManager.MarkForDeactivation(componentID);
        }

        internal void RegisterComponent(Type componentType)
        {
            registeredComponentTypes.Add(componentType);
            AddEngine((Engine)Activator.CreateInstance(typeof(ComponentMessageEmitter<>).MakeGenericType(componentType)));
        }

        public Engine AddEngine<TEngine>(TEngine engine) where TEngine : Engine
        {
            engine.AssignEntityManager(entityManager);
            engine.AssignComponentManager(componentManager);
            engine.AssignMessageManager(messageManager);

            engines.Add(engine);
            engineGraph.AddVertex(engine);

            foreach (var activateType in engine.activateTypes)
            {
                engine.sendTypes.Add(activateType);
            }

            var messageReadTypes = engine.readTypes;
            var messageSendTypes = engine.sendTypes;

            foreach (var messageType in messageReadTypes.Intersect(messageSendTypes))
            {
                // ComponentMessages can safely self-cycle
                // this does introduce a gotcha though: if you AddComponent and then HasComponent or GetComponent you will receive a false negative
                // there is no point to doing this but it is a gotcha i suppose
                if (!(messageType.IsGenericType && messageType.GetGenericTypeDefinition() == typeof(ComponentMessage<>)))
                {
                    throw new EngineMessageSelfCycleException("Engine {0} both reads and writes Message {1}", engine.GetType().Name, messageType.Name);
                }
            }

            if (messageSendTypes.Any())
            {
                senders.Add(engine);
            }

            foreach (var readType in engine.readTypes)
            {
                if (readType.IsGenericType && readType.GetGenericTypeDefinition() == typeof(ComponentMessage<>))
                {
                    var componentType = readType.GetGenericArguments().Single();
                    if (!registeredComponentTypes.Contains(componentType))
                    {
                        RegisterComponent(componentType);
                    }
                }

                if (!typeToReaders.ContainsKey(readType))
                {
                    typeToReaders.Add(readType, new HashSet<Engine>());
                }

                typeToReaders[readType].Add(engine);
            }

            return engine;
        }

        public TRenderer AddEntityRenderer<TRenderer>(TRenderer renderer) where TRenderer : Renderer
        {
            renderer.AssignEntityManager(entityManager);
            renderer.AssignComponentManager(componentManager);

            if (renderer is EntityRenderer)
            {
                entityManager.RegisterEntityTracker(renderer as IEntityTracker);
                renderManager.RegisterEntityRenderer(renderer as EntityRenderer);
            }

            return renderer;
        }

        public TRenderer AddGeneralRenderer<TRenderer>(TRenderer renderer, int layer) where TRenderer : GeneralRenderer
        {
            renderer.AssignEntityManager(entityManager);
            renderer.AssignComponentManager(componentManager);

            renderManager.RegisterGeneralRendererWithLayer(renderer, layer);

            return renderer;
        }

        private void BuildEngineGraph()
        {
            foreach (var senderEngine in senders)
            {
                foreach (var messageType in senderEngine.sendTypes.Where((type) => type.GetInterfaces().Contains(typeof(IMessage))))
                {
                    if (typeToReaders.ContainsKey(messageType))
                    {
                        foreach (var readerEngine in typeToReaders[messageType])
                        {
                            engineGraph.AddEdge(senderEngine, readerEngine);
                        }
                    }
                }
            }
        }

        public World Build()
        {
            BuildEngineGraph();

            if (engineGraph.Cyclic())
            {
                var cycles = engineGraph.SimpleCycles();
                var errorString = "Cycle(s) found in Engines: ";
                foreach (var cycle in cycles.Reverse())
                {
                    errorString += "\n" +
                    string.Join(" -> ", cycle.Select((engine) => engine.GetType().Name)) +
                    " -> " +
                    cycle.First().GetType().Name;
                }
                throw new EngineCycleException(errorString);
            }

            var mutatedComponentTypes = new HashSet<Type>();
            var duplicateMutations = new List<Type>();
            var componentToEngines = new Dictionary<Type, List<Engine>>();

            foreach (var engine in engines)
            {
                foreach (var updateType in engine.updateTypes)
                {
                    if (updateType.GetInterfaces().Contains(typeof(IComponent))) // if our write type is a component
                    {
                        if (mutatedComponentTypes.Contains(updateType))
                        {
                            duplicateMutations.Add(updateType);
                        }
                        else
                        {
                            mutatedComponentTypes.Add(updateType);
                        }

                        if (!componentToEngines.ContainsKey(updateType))
                        {
                            componentToEngines[updateType] = new List<Engine>();
                        }

                        componentToEngines[updateType].Add(engine);
                    }
                }
            }

            if (duplicateMutations.Count > 0)
            {
                var errorString = "Multiple Engines write the same Component: ";
                foreach (var componentType in duplicateMutations)
                {
                    errorString += "\n" +
                    componentType.Name + " written by: " +
                    string.Join(", ", componentToEngines[componentType].Select((engine) => engine.GetType().Name));
                }

                throw new EngineWriteConflictException(errorString);
            }

            var engineOrder = new List<Engine>();
            foreach (var engine in engineGraph.TopologicalSort())
            {
                engineOrder.Add(engine);
            }

            var world = new World(
                engineOrder,
                entityManager,
                componentManager,
                messageManager,
                renderManager
            );

            componentManager.PerformComponentUpdates();
            componentManager.DeactivateMarkedComponents();
            componentManager.RemoveMarkedComponents();

            entityManager.CheckEntitiesWithAddedComponents();
            entityManager.CheckEntitiesWithRemovedComponents();

            return world;
        }
    }
}