using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DataPro.Core.ServiceManager
{
    /// <summary>
    /// Service manager allows a component to publish an implementation of a singleton interface (service) that
    /// other components can retrieve reference to without knowing who published it
    /// </summary>
    public static class ServiceManager
    {
        /// <summary>
        /// Stores all published interfaces
        /// </summary>
        private static readonly Dictionary<Type, object> Services = new Dictionary<Type, object>();

        /// <summary>
        /// Publishes a service
        /// </summary>
        /// <typeparam name="T">interface type of service</typeparam>
        /// <param name="item">implementation of service</param>
        public static void Publish<T>(T item) where T : class
        {
            if (Services.ContainsKey(typeof(T)))
            {
                throw new ArgumentException(string.Format("{0}: has already been published", typeof(T).Name));
            }

            Services.Add(typeof(T), item);
            SendServicePublishedEvent(typeof(T), true);
        }


        /// <summary>
        /// Publishes a list of services
        /// </summary>
        /// <param name="item">class that will implement all the listed interfaces</param>
        /// <param name="interfaceList">list of interfaces</param>
        /// <param name="skipPublishedInterfaces">true to avoid errors on already published interfaces</param>
        public static void Publish(object item, IEnumerable<Type> interfaceList, bool skipPublishedInterfaces)
        {
            foreach (var t in interfaceList)
            {
                if (Exists(t))
                {
                    if (!skipPublishedInterfaces)
                    {
                        // service already published and caller indicated we should error out
                        throw new ArgumentException(string.Format("{0}: has already been published", t.Name));
                    }
                }
                else
                {
                    // service doesn't exist so publish it
                    Services.Add(t, item);
                    SendServicePublishedEvent(t, true);
                }
            }
        }

        /// <summary>
        /// Returns true if specifed interface has been published, false if not
        /// </summary>
        /// <typeparam name="T">type of interface to check</typeparam>
        /// <returns>true if interface has been published; false if not published</returns>
        public static bool Exists<T>() where T : class
        {
            return Services.ContainsKey(typeof(T));
        }

        /// <summary>
        /// Returns true if specifed interface has been published, false if not
        /// </summary>
        /// <param name="t">type of interface to check</param>
        /// <returns>true if interface has been published; false if not published</returns>
        public static bool Exists(Type t)
        {
            return Services.ContainsKey(t);
        }

        /// <summary>
        /// Returns published service
        /// </summary>
        /// <typeparam name="T">interface type of service</typeparam>
        /// <returns>published service or exception if not currently published</returns>
        public static T Get<T>() where T : class
        {
            if (!Services.ContainsKey(typeof(T)))
            {
                throw new ArgumentException(string.Format("{0}: has not been published", typeof(T).Name));
            }

            return Services[typeof(T)] as T;
        }

        /// <summary>
        /// Clears specified service
        /// </summary>
        /// <typeparam name="T">interface type of service to clear</typeparam>
        public static void Clear<T>() where T : class
        {
            if (Services.ContainsKey(typeof(T)))
            {
                SendServicePublishedEvent(typeof(T), false);
                Services.Remove(typeof(T));
            }
        }

        /// <summary>
        /// Clears list of published interfaces
        /// </summary>
        /// <param name="interfaceList">list of interfaces to unpublish</param>
        public static void Clear(IEnumerable<Type> interfaceList)
        {
            foreach (var t in interfaceList)
            {
                if (!Services.ContainsKey(t)) continue;

                SendServicePublishedEvent(t, false);
                Services.Remove(t);
            }
        }


        /// <summary>
        /// Sends a IServicePublishedEvent through the Event Manger to let subscribers know when
        /// a service is published or unpublished
        /// </summary>
        /// <param name="type">type of interface</param>
        /// <param name="published">true if being published, false if being unpublished</param>
        private static void SendServicePublishedEvent(Type type, bool published)
        {
            EventManager.EventManager.Publish<IServicePublishedEvent>(new ServicePublishedEvent
            {
                IsPublished = published,
                ServiceType = type
            });
        }
    }
}