using EFCache;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Data.Entity;
using System.Data.Entity.Core.Objects;
using System.Data.Entity.Infrastructure;
using System.Data.SqlClient;
using System.Data.SQLite;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Tango.BL.Entities;
using Tango.Core;
using Tango.Settings;

namespace Tango.BL
{
    //[DbConfigurationType(typeof(ObservablesContextConfiguration))]
    public partial class ObservablesContext
    {
        private List<ObservableModifiedEventArgs> _pending_notifications = new List<ObservableModifiedEventArgs>();
        private ObservablesContextAdapter _adapter;
        private static DataSource _override_datasource;
        private DataSource _dataSource;
        private static ConcurrentList<ObservablesContext> _open_contexts;

        /// <summary>
        /// Gets a value indicating whether this instance is disposed.
        /// </summary>
        public bool IsDisposed { get; private set; }

        /// <summary>
        /// Initializes the <see cref="ObservablesContext"/> class.
        /// </summary>
        static ObservablesContext()
        {
            _open_contexts = new ConcurrentList<ObservablesContext>();
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ObservablesContext"/> class.
        /// </summary>
        public ObservablesContext()
        {
            _open_contexts.Add(this);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ObservablesContext" /> class.
        /// </summary>
        /// <param name="path">The server file path.</param>
        /// <param name="isFile">if set to <c>true</c> will try to connect to an .mdf file.</param>
        public ObservablesContext(DataSource dataSource) : base(dataSource.ToConnection(), true)
        {
            _open_contexts.Add(this);
            _dataSource = dataSource;
            Database.SetInitializer<ObservablesContext>(null);
            Configuration.LazyLoadingEnabled = false;
            _adapter = new ObservablesContextAdapter(this);
        }

        /// <summary>
        /// Creates a default remote database context by the address specified in <see cref="SettingsManager.Default.DataBase.SQLServerAddress" />.
        /// </summary>
        /// <returns></returns>
        public static ObservablesContext CreateDefault()
        {
            return new ObservablesContext(_override_datasource != null ? _override_datasource : SettingsManager.Default.GetOrCreate<CoreSettings>().DataSource);
        }

        /// <summary>
        /// Creates a default remote database context.
        /// </summary>
        /// <returns></returns>
        public static ObservablesContext CreateDefault(DataSource dataSource)
        {
            return new ObservablesContext(dataSource);
        }

        /// <summary>
        /// Creates a default remote database context.
        /// </summary>
        /// <returns></returns>
        public static ObservablesContext CreateDefault(String address, String catalog, DataSourceType type)
        {
            return new ObservablesContext(new DataSource()
            {
                Address = address,
                Catalog = catalog,
                IntegratedSecurity = true,
                Type = type
            });
        }

        /// <summary>
        /// Creates a default remote database context.
        /// </summary>
        /// <returns></returns>
        public static ObservablesContext CreateDefault(String address, DataSourceType type)
        {
            return CreateDefault(address, "Tango", type);
        }

        /// <summary>
        /// Creates a default remote database context.
        /// </summary>
        /// <returns></returns>
        public static ObservablesContext CreateDefault(String address)
        {
            return CreateDefault(address, "Tango", DataSourceType.SQLServer);
        }

        /// <summary>
        /// Gets the inner object context.
        /// </summary>
        /// <returns></returns>
        private ObjectContext GetObjectContext()
        {
            return ((IObjectContextAdapter)this).ObjectContext;
        }

        /// <summary>
        /// Saves all changes made in this context to the underlying database.
        /// </summary>
        /// <returns>
        /// The number of objects written to the underlying database.
        /// </returns>
        public override int SaveChanges()
        {
            foreach (var entity in ChangeTracker.Entries().Where(x => x.State == EntityState.Added || x.State == EntityState.Modified).ToList())
            {
                if (entity is IObservableEntity en)
                {
                    en?.OnBeforeSave();
                }
                else if (entity.Entity is IObservableEntity en2)
                {
                    en2?.OnBeforeSave();
                }
            }

            var result = base.SaveChanges();
            RaisePendingNotifications();
            return result;
        }

        /// <summary>
        /// Asynchronously saves all changes made in this context to the underlying database.
        /// </summary>
        /// <param name="cancellationToken">A <see cref="T:System.Threading.CancellationToken" /> to observe while waiting for the task to complete.</param>
        /// <returns>
        /// A task that represents the asynchronous save operation.
        /// The task result contains the number of objects written to the underlying database.
        /// </returns>
        /// <remarks>
        /// Multiple active operations on the same context instance are not supported.  Use 'await' to ensure
        /// that any asynchronous operations have completed before calling another method on this context.
        /// </remarks>
        public override Task<int> SaveChangesAsync(CancellationToken cancellationToken)
        {
            foreach (var entity in ChangeTracker.Entries().Where(x => x.State == EntityState.Added || x.State == EntityState.Modified).ToList().Select(x => x.Entity).ToList())
            {
                if (entity is IObservableEntity && entity != null)
                {
                    (entity as IObservableEntity).OnBeforeSave();
                }
            }

            var result = base.SaveChangesAsync(cancellationToken);
            RaisePendingNotifications();
            return result;
        }

        /// <summary>
        /// Raises the pending notifications.
        /// </summary>
        private void RaisePendingNotifications()
        {
            Task.Factory.StartNew(() =>
            {
                foreach (var e in _pending_notifications.DistinctBy(x => x.NotifiedEntity))
                {
                    try
                    {
                        e.NotifiedEntity.RaiseModified(e.Context, e.ModifiedEntity, e.NotifiedEntity);
                    }
                    catch { }
                }

                _pending_notifications.Clear();
            });
        }

        /// <summary>
        /// Extension point allowing the user to override the default behavior of validating only
        /// added and modified entities.
        /// </summary>
        /// <param name="entityEntry">DbEntityEntry instance that is supposed to be validated.</param>
        /// <returns>
        /// true to proceed with validation; false otherwise.
        /// </returns>
        protected override bool ShouldValidateEntity(DbEntityEntry entityEntry)
        {
            if (entityEntry.State == EntityState.Modified && entityEntry.Entity is IObservableEntity)
            {
                IObservableEntity modified = entityEntry.Entity as IObservableEntity;

                foreach (var toNotify in ObservableEntitiesContainer.RegisteredEntities.ToList().Where(x => x.Guid == modified.Guid).ToList())
                {
                    _pending_notifications.Add(new ObservableModifiedEventArgs(this, modified, toNotify));
                }
            }

            return base.ShouldValidateEntity(entityEntry);
        }

        /// <summary>
        /// Gets an instance of <see cref="ObservablesContextAdapter"/> which wraps this instance.
        /// </summary>
        public ObservablesContextAdapter Adapter
        {
            get { return _adapter; }
        }

        /// <summary>
        /// Overrides the default data source that is read from the core settings.
        /// </summary>
        /// <param name="dataSource">The data source.</param>
        public static void OverrideSettingsDataSource(DataSource dataSource)
        {
            _override_datasource = dataSource;
        }

        /// <summary>
        /// Gets the current data source.
        /// </summary>
        /// <returns></returns>
        public DataSource GetDataSource()
        {
            return _dataSource;
        }

        /// <summary>
        /// Gets the actual data source (settings or overridden).
        /// </summary>
        /// <returns></returns>
        public static DataSource GetActualDataSource()
        {
            return _override_datasource != null ? _override_datasource : SettingsManager.Default.GetOrCreate<CoreSettings>().DataSource;
        }

        /// <summary>
        /// Returns a <see cref="System.String" /> that represents this instance.
        /// </summary>
        /// <returns>
        /// A <see cref="System.String" /> that represents this instance.
        /// </returns>
        /// <inheritdoc />
        public override string ToString()
        {
            return GetDataSource().ToString();
        }

        /// <summary>
        /// Clears the model store on the file system.
        /// </summary>
        public static void ClearModelStore()
        {
            //ObservablesContextConfiguration.ClearModelStore();
        }

        /// <summary>
        /// Enables the in memory cache.
        /// </summary>
        /// <param name="cacheTime">Maximum cache time to preserve a single entity cache.</param>
        public static void EnableInMemoryCache(TimeSpan cacheTime, ObservablesContextInMemoryCachingMode mode)
        {
            if (mode != ObservablesContextInMemoryCachingMode.None)
            {
                var cache = new ObservablesContextInMemoryCache() { Expiration = cacheTime };

                if (mode == ObservablesContextInMemoryCachingMode.Relative)
                {
                    cache.ResetAccessTimeOnAccess = true;
                }

                EntityFrameworkCache.Initialize(cache);
            }
        }

        /// <summary>
        /// Disposes the context. The underlying <see cref="T:System.Data.Entity.Core.Objects.ObjectContext" /> is also disposed if it was created
        /// is by this context or ownership was passed to this context when this context was created.
        /// The connection to the database (<see cref="T:System.Data.Common.DbConnection" /> object) is also disposed if it was created
        /// is by this context or ownership was passed to this context when this context was created.
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
        protected override void Dispose(bool disposing)
        {
            _open_contexts.Remove(this);
            base.Dispose(disposing);
            IsDisposed = true;
        }

        public static void UpdateAccessToken(String accessToken, DateTime expiration)
        {
            if (_override_datasource != null)
            {
                _override_datasource.AccessToken = accessToken;
                _override_datasource.AccessTokenExpiration = expiration;

                foreach (var context in _open_contexts.Where(x => x._dataSource.Type == DataSourceType.AccessToken))
                {
                    context._dataSource = _override_datasource;
                    var connection = context.Database.Connection as SqlConnection;
                    if (connection != null)
                    {
                        connection.AccessToken = context._dataSource.AccessToken;
                    }
                }
            }
        }
    }
}