using System;
using System.Collections.Generic;
using System.Reflection;
using System.Linq;
using Encompass.Exceptions;
using Encompass.Engines;
using MoonTools.Core.Graph;
using MoonTools.Core.Graph.Extensions;

namespace Encompass
{
    /// <summary>
    /// WorldBuilder is used to construct a World from Engines, Renderers, and an initial state of Entities, Components, and Messages.
    /// </summary>
    /// <remarks>
    /// WorldBuilder enforces certain rules about Engine structure. It is forbidden to have messages create cycles between Engines,
    /// and no Component may be written by more than one Engine.
    /// The WorldBuilder uses Engines and their Message read/emit information to determine a valid ordering of the Engines, which is given to the World.
    /// </remarks>
    public class WorldBuilder
    {
        private readonly List<Engine> engines = new List<Engine>();
        private readonly DirectedGraph<Engine, Unit> engineGraph = GraphBuilder.DirectedGraph<Engine>();

        private readonly ComponentManager componentManager;
        private readonly EntityManager entityManager;
        private readonly MessageManager messageManager;
        private readonly ComponentMessageManager componentMessageManager;
        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()
        {
            drawLayerManager = new DrawLayerManager();
            componentManager = new ComponentManager(drawLayerManager);
            messageManager = new MessageManager();
            componentMessageManager = new ComponentMessageManager();
            entityManager = new EntityManager(componentManager, componentMessageManager);
            renderManager = new RenderManager(componentManager, drawLayerManager);
        }

        /// <summary>
        /// Creates and returns a new empty Entity.
        /// </summary>
        public Entity CreateEntity()
        {
            return entityManager.CreateEntity();
        }

        /// <summary>
        /// Specifies that the given Message should be sent immediately on the first World Update.
        /// </summary>
        public void SendMessage<TMessage>(TMessage message) where TMessage : struct, IMessage
        {
            messageManager.AddMessage(message);
        }

        /// <summary>
        /// Specifies that the given Message should be sent after the specified number of seconds after the first World Update.
        /// </summary>
        public void SendMessageDelayed<TMessage>(TMessage message, double time) where TMessage : struct, IMessage
        {
            messageManager.AddMessageDelayed(message, time);
        }

        /// <summary>
        /// Sets Component data for the specified Component Type on the specified Entity.
        /// </summary>
        public Guid SetComponent<TComponent>(Entity entity, TComponent component, int priority = 0) where TComponent : struct, IComponent
        {
            return componentManager.MarkComponentForWrite(entity, component, priority);
        }

        /// <summary>
        /// Sets Draw Component data for the specified Component Type on the specified Entity. 
        /// This method must be used for the Draw Component to be readable by an OrderedRenderer.
        /// </summary>
        public Guid SetDrawComponent<TComponent>(Entity entity, TComponent component, int priority = 0, int layer = 0) where TComponent : struct, IComponent, IDrawComponent
        {
            return componentManager.MarkDrawComponentForWrite(entity, component, priority, layer);
        }

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

        /// <summary>
        /// Adds the specified Engine to the World.
        /// </summary>
        /// <param name="engine">An instance of an Engine.</param>
        public Engine AddEngine<TEngine>(TEngine engine) where TEngine : Engine
        {
            engine.AssignEntityManager(entityManager);
            engine.AssignComponentManager(componentManager);
            engine.AssignMessageManager(messageManager);
            engine.AssignComponentMessageManager(componentMessageManager);

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

            var messageReceiveTypes = engine.receiveTypes;
            var messageSendTypes = engine.sendTypes;

            foreach (var messageType in messageReceiveTypes.Union(messageSendTypes))
            {
                messageManager.RegisterMessageType(messageType);
            }

            foreach (var messageType in messageReceiveTypes.Intersect(messageSendTypes))
            {
                if ((messageType.IsGenericType && messageType.GetGenericTypeDefinition() == typeof(PendingComponentMessage<>)))
                {
                    var componentType = messageType.GetGenericArguments().Single();
                    throw new EngineSelfCycleException("Engine {0} both activates and reads pending Component {1}", engine.GetType().Name, componentType.Name);
                }

                throw new EngineSelfCycleException("Engine {0} both receives and sends Message {1}", engine.GetType().Name, messageType.Name);
            }

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

            foreach (var receiveType in engine.receiveTypes)
            {
                if (receiveType.IsGenericType)
                {
                    var genericTypeDefinition = receiveType.GetGenericTypeDefinition();
                    if (genericTypeDefinition == typeof(ComponentMessage<>) || genericTypeDefinition == typeof(PendingComponentMessage<>))
                    {
                        var componentType = receiveType.GetGenericArguments().Single();
                        if (!registeredComponentTypes.Contains(componentType))
                        {
                            RegisterComponent(componentType);
                        }
                    }
                }

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

                typeToReaders[receiveType].Add(engine);
            }

            return engine;
        }

        /// <summary>
        /// Adds the specified OrderedRenderer to the World.
        /// </summary>
        public OrderedRenderer<TComponent> AddOrderedRenderer<TComponent>(OrderedRenderer<TComponent> renderer) where TComponent : struct, IComponent, IDrawComponent
        {
            renderer.AssignEntityManager(entityManager);
            renderer.AssignComponentManager(componentManager);
            renderManager.RegisterOrderedRenderer<TComponent>(renderer.InternalRender);
            return renderer;
        }

        /// <summary>
        /// Adds the specified GeneralRenderer to the World at the specified layer.
        /// Higher layer numbers draw on top of lower layer numbers.
        /// </summary>
        /// <param name="renderer">An instance of a GeneralRenderer.</param>
        /// <param name="layer">The layer at which the GeneralRenderer should render. Higher numbers draw over lower numbers.</param>
        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)
                {
                    if (typeToReaders.ContainsKey(messageType))
                    {
                        foreach (var readerEngine in typeToReaders[messageType])
                        {
                            if (senderEngine != readerEngine)
                            {
                                if (!engineGraph.Exists(senderEngine, readerEngine))
                                {
                                    engineGraph.AddEdge(senderEngine, readerEngine);
                                }
                            }
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Builds the World out of the state specified on the WorldBuilder.
        /// Validates and constructs an ordering of the given Engines.
        /// </summary>
        /// <returns>An instance of World.</returns>
        public World Build()
        {
            BuildEngineGraph();

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

            var writtenComponentTypesWithoutPriority = new HashSet<Type>();
            var writtenComponentTypesWithPriority = new HashSet<Type>();
            var duplicateWritesWithoutPriority = new List<Type>();
            var duplicateWritesWithSamePriority = new List<Type>();
            var writePriorities = new Dictionary<Type, HashSet<int>>();
            var writeMessageToEngines = new Dictionary<Type, List<Engine>>();

            foreach (var engine in engines)
            {
                var defaultWritePriorityAttribute = engine.GetType().GetCustomAttribute<DefaultWritePriority>(false);

                var writeTypes = engine.sendTypes.Where((type) => type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ComponentWriteMessage<>));

                foreach (var writeType in writeTypes)
                {
                    var componentType = writeType.GetGenericArguments()[0];

                    int? priority = null;
                    if (engine.writePriorities.ContainsKey(componentType))
                    {
                        priority = engine.writePriorities[componentType];
                    }
                    else if (defaultWritePriorityAttribute != null)
                    {
                        priority = defaultWritePriorityAttribute.writePriority;
                    }

                    if (priority.HasValue)
                    {
                        writtenComponentTypesWithPriority.Add(componentType);

                        if (!writePriorities.ContainsKey(componentType))
                        {
                            writePriorities[componentType] = new HashSet<int>();
                        }

                        if (writePriorities[componentType].Contains(priority.Value))
                        {
                            duplicateWritesWithSamePriority.Add(componentType);
                        }
                        else if (writtenComponentTypesWithoutPriority.Contains(componentType))
                        {
                            duplicateWritesWithoutPriority.Add(componentType);
                        }
                        else
                        {
                            writePriorities[componentType].Add(priority.Value);
                        }
                    }
                    else
                    {
                        if (writtenComponentTypesWithoutPriority.Contains(componentType) || writtenComponentTypesWithPriority.Contains(componentType))
                        {
                            duplicateWritesWithoutPriority.Add(componentType);
                        }
                        else
                        {
                            writtenComponentTypesWithoutPriority.Add(componentType);
                        }
                    }

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

                    writeMessageToEngines[componentType].Add(engine);
                }
            }

            if (duplicateWritesWithoutPriority.Count > 0)
            {
                var errorString = "Multiple Engines write the same Component without declaring priority: ";
                foreach (var componentType in duplicateWritesWithoutPriority)
                {
                    errorString += "\n" +
                    componentType.Name + " written by: " +
                    string.Join(", ", writeMessageToEngines[componentType].Select((engine) => engine.GetType().Name));
                }
                errorString += "\nTo resolve the conflict, add priority arguments to the Writes declarations or use a DefaultWritePriority attribute.";

                throw new EngineWriteConflictException(errorString);
            }

            if (duplicateWritesWithSamePriority.Count > 0)
            {
                var errorString = "Multiple Engines write the same Component with the same priority: ";
                foreach (var componentType in duplicateWritesWithSamePriority)
                {
                    errorString += "\n" +
                    componentType.Name + " written by: " +
                    string.Join(", ", writeMessageToEngines[componentType].Select(engine => engine.GetType().Name));
                }
                errorString += "\nTo resolve the conflict, add priority arguments to the Writes declarations or use a DefaultWritePriority attribute.";

                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,
                componentMessageManager,
                renderManager
            );

            componentManager.RemoveMarkedComponents();
            componentManager.WriteComponents();

            return world;
        }
    }
}