namespace SharedDATA.Api
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Reflection;
    using System.Threading;
    using System.Threading.Tasks;
    using Microsoft.EntityFrameworkCore;
    using Microsoft.EntityFrameworkCore.Metadata;
    using Microsoft.EntityFrameworkCore.Query;
    using Microsoft.EntityFrameworkCore.ChangeTracking;
    using SharedDATA.Context;

    /// <summary>
    /// Represents a default generic repository implements the <see cref="IRepository{TEntity}"/> interface.
    /// </summary>
    /// <typeparam name="TEntity">The type of the entity.</typeparam>
    public class Repository<TEntity> : IRepository<TEntity> where TEntity : class
    {
        protected readonly DbContext _dbContext;
        protected readonly DbSet<TEntity> _dbSet;

        /// <summary>
        /// Initializes a new instance of the <see cref="Repository{TEntity}"/> class.
        /// </summary>
        /// <param name="dbContext">The database context.</param>
        public Repository(DbContext dbContext)
        {
            _dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
            _dbSet = _dbContext.Set<TEntity>();
        }

        /// <summary>
        /// Changes the table name. This require the tables in the same database.
        /// </summary>
        /// <param name="table"></param>
        /// <remarks>
        /// This only been used for supporting multiple tables in the same model. This require the tables in the same database.
        /// </remarks>
        public virtual void ChangeTable(string table)
        {
            if (_dbContext.Model.FindEntityType(typeof(TEntity)) is IConventionEntityType relational)
            {
                relational.SetTableName(table);
            }
        }

        /// <summary>
        /// Gets all entities. This method is not recommended
        /// </summary>
        /// <returns>The <see cref="IQueryable{TEntity}"/>.</returns>
        public IQueryable<TEntity> GetAll()
        {
            return _dbSet;
        }

        /// <summary>
        /// Gets all entities. This method is not recommended
        /// </summary>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="disableTracking"><c>true</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>Ex: This method defaults to a read-only, no-tracking query.</remarks>
        public IQueryable<TEntity> GetAll(
            Expression<Func<TEntity, bool>> predicate = null,
            Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
            Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null, bool disableTracking = true, bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query);
            }
            else
            {
                return query;
            }
        }
        /// <summary>
        /// Gets the <see cref="IPagedList{TEntity}"/> based on a predicate, orderby delegate and page information. This method default no-tracking query.
        /// </summary>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="pageIndex">The index of page.</param>
        /// <param name="pageSize">The size of the page.</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual IPagedList<TEntity> GetPagedList(Expression<Func<TEntity, bool>> predicate = null,
                                                Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                int pageIndex = 0,
                                                int pageSize = 20,
                                                bool disableTracking = true,
                                                bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).ToPagedList(pageIndex, pageSize);
            }
            else
            {
                return query.ToPagedList(pageIndex, pageSize);
            }
        }

        /// <summary>
        /// Gets the <see cref="IPagedList{TEntity}"/> based on a predicate, orderby delegate and page information. This method default no-tracking query.
        /// </summary>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="pageIndex">The index of page.</param>
        /// <param name="pageSize">The size of the page.</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="cancellationToken">
        ///     A <see cref="CancellationToken" /> to observe while waiting for the task to complete.
        /// </param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual Task<IPagedList<TEntity>> GetPagedListAsync(Expression<Func<TEntity, bool>> predicate = null,
                                                           Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                           Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                           int pageIndex = 0,
                                                           int pageSize = 20,
                                                           bool disableTracking = true,
                                                           CancellationToken cancellationToken = default(CancellationToken),
                                                           bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).ToPagedListAsync(pageIndex, pageSize, 0, cancellationToken);
            }
            else
            {
                return query.ToPagedListAsync(pageIndex, pageSize, 0, cancellationToken);
            }
        }

        /// <summary>
        /// Gets the <see cref="IPagedList{TResult}"/> based on a predicate, orderby delegate and page information. This method default no-tracking query.
        /// </summary>
        /// <param name="selector">The selector for projection.</param>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="pageIndex">The index of page.</param>
        /// <param name="pageSize">The size of the page.</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TResult}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual IPagedList<TResult> GetPagedList<TResult>(Expression<Func<TEntity, TResult>> selector,
                                                         Expression<Func<TEntity, bool>> predicate = null,
                                                         Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                         Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                         int pageIndex = 0,
                                                         int pageSize = 20,
                                                         bool disableTracking = true,
                                                         bool ignoreQueryFilters = false)
            where TResult : class
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).Select(selector).ToPagedList(pageIndex, pageSize);
            }
            else
            {
                return query.Select(selector).ToPagedList(pageIndex, pageSize);
            }
        }

        /// <summary>
        /// Gets the <see cref="IPagedList{TEntity}"/> based on a predicate, orderby delegate and page information. This method default no-tracking query.
        /// </summary>
        /// <param name="selector">The selector for projection.</param>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="pageIndex">The index of page.</param>
        /// <param name="pageSize">The size of the page.</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="cancellationToken">
        ///     A <see cref="CancellationToken" /> to observe while waiting for the task to complete.
        /// </param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual Task<IPagedList<TResult>> GetPagedListAsync<TResult>(Expression<Func<TEntity, TResult>> selector,
                                                                    Expression<Func<TEntity, bool>> predicate = null,
                                                                    Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                                    Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                                    int pageIndex = 0,
                                                                    int pageSize = 20,
                                                                    bool disableTracking = true,
                                                                    CancellationToken cancellationToken = default(CancellationToken),
                                                                    bool ignoreQueryFilters = false)
            where TResult : class
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).Select(selector).ToPagedListAsync(pageIndex, pageSize, 0, cancellationToken);
            }
            else
            {
                return query.Select(selector).ToPagedListAsync(pageIndex, pageSize, 0, cancellationToken);
            }
        }

        /// <summary>
        /// Gets the first or default entity based on a predicate, orderby delegate and include delegate. This method default no-tracking query.
        /// </summary>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual TEntity GetFirstOrDefault(Expression<Func<TEntity, bool>> predicate = null,
                                         Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                         Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                         bool disableTracking = true,
                                         bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).FirstOrDefault();
            }
            else
            {
                return query.FirstOrDefault();
            }
        }


        /// <inheritdoc />
        public virtual async Task<TEntity> GetFirstOrDefaultAsync(Expression<Func<TEntity, bool>> predicate = null,
            Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
            Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
            bool disableTracking = true,
            bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return await orderBy(query).FirstOrDefaultAsync();
            }
            else
            {
                return await query.FirstOrDefaultAsync();
            }
        }

        /// <summary>
        /// Gets the first or default entity based on a predicate, orderby delegate and include delegate. This method default no-tracking query.
        /// </summary>
        /// <param name="selector">The selector for projection.</param>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="disableTracking"><c>True</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>This method default no-tracking query.</remarks>
        public virtual TResult GetFirstOrDefault<TResult>(Expression<Func<TEntity, TResult>> selector,
                                                  Expression<Func<TEntity, bool>> predicate = null,
                                                  Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                  Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                  bool disableTracking = true,
                                                  bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return orderBy(query).Select(selector).FirstOrDefault();
            }
            else
            {
                return query.Select(selector).FirstOrDefault();
            }
        }

        /// <inheritdoc />
        public virtual async Task<TResult> GetFirstOrDefaultAsync<TResult>(Expression<Func<TEntity, TResult>> selector,
                                                  Expression<Func<TEntity, bool>> predicate = null,
                                                  Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
                                                  Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
                                                  bool disableTracking = true, bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return await orderBy(query).Select(selector).FirstOrDefaultAsync();
            }
            else
            {
                return await query.Select(selector).FirstOrDefaultAsync();
            }
        }

        /// <summary>
        /// Uses raw SQL queries to fetch the specified <typeparamref name="TEntity" /> data.
        /// </summary>
        /// <param name="sql">The raw SQL.</param>
        /// <param name="parameters">The parameters.</param>
        /// <returns>An <see cref="IQueryable{TEntity}" /> that contains elements that satisfy the condition specified by raw SQL.</returns>
        public virtual IQueryable<TEntity> FromSql(string sql, params object[] parameters) => _dbSet.FromSqlRaw(sql, parameters);

        /// <summary>
        /// Finds an entity with the given primary key values. If found, is attached to the context and returned. If no entity is found, then null is returned.
        /// </summary>
        /// <param name="keyValues">The values of the primary key for the entity to be found.</param>
        /// <returns>The found entity or null.</returns>
        public virtual TEntity Find(params object[] keyValues) => _dbSet.Find(keyValues);

        /// <summary>
        /// Finds an entity with the given primary key values. If found, is attached to the context and returned. If no entity is found, then null is returned.
        /// </summary>
        /// <param name="keyValues">The values of the primary key for the entity to be found.</param>
        /// <returns>A <see cref="Task{TEntity}" /> that represents the asynchronous insert operation.</returns>
        public virtual ValueTask<TEntity> FindAsync(params object[] keyValues) => _dbSet.FindAsync(keyValues);

        /// <summary>
        /// Finds an entity with the given primary key values. If found, is attached to the context and returned. If no entity is found, then null is returned.
        /// </summary>
        /// <param name="keyValues">The values of the primary key for the entity to be found.</param>
        /// <param name="cancellationToken">A <see cref="CancellationToken"/> to observe while waiting for the task to complete.</param>
        /// <returns>A <see cref="Task{TEntity}"/> that represents the asynchronous find operation. The task result contains the found entity or null.</returns>
        public virtual ValueTask<TEntity> FindAsync(object[] keyValues, CancellationToken cancellationToken) => _dbSet.FindAsync(keyValues, cancellationToken);

        /// <summary>
        /// Gets the count based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public virtual int Count(Expression<Func<TEntity, bool>> predicate = null)
        {
            if (predicate == null)
            {
                return _dbSet.Count();
            }
            else
            {
                return _dbSet.Count(predicate);
            }
        }

        /// <summary>
        /// Gets async the count based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public virtual async Task<int> CountAsync(Expression<Func<TEntity, bool>> predicate = null)
        {
            if (predicate == null)
            {
                return await _dbSet.CountAsync();
            }
            else
            {
                return await _dbSet.CountAsync(predicate);
            }
        }

        /// <summary>
        /// Gets the long count based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public virtual long LongCount(Expression<Func<TEntity, bool>> predicate = null)
        {
            if (predicate == null)
            {
                return _dbSet.LongCount();
            }
            else
            {
                return _dbSet.LongCount(predicate);
            }
        }

        /// <summary>
        /// Gets async the long count based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public virtual async Task<long> LongCountAsync(Expression<Func<TEntity, bool>> predicate = null)
        {
            if (predicate == null)
            {
                return await _dbSet.LongCountAsync();
            }
            else
            {
                return await _dbSet.LongCountAsync(predicate);
            }
        }

        /// <summary>
        /// Gets the max based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual T Max<T>(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, T>> selector = null)
        {
            if (predicate == null)
                return _dbSet.Max(selector);
            else
                return _dbSet.Where(predicate).Max(selector);
        }

        /// <summary>
        /// Gets the async max based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual async Task<T> MaxAsync<T>(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, T>> selector = null)
        {
            if (predicate == null)
                return await _dbSet.MaxAsync(selector);
            else
                return await _dbSet.Where(predicate).MaxAsync(selector);
        }

        /// <summary>
        /// Gets the min based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual T Min<T>(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, T>> selector = null)
        {
            if (predicate == null)
                return _dbSet.Min(selector);
            else
                return _dbSet.Where(predicate).Min(selector);
        }

        /// <summary>
        /// Gets the async min based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual async Task<T> MinAsync<T>(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, T>> selector = null)
        {
            if (predicate == null)
                return await _dbSet.MinAsync(selector);
            else
                return await _dbSet.Where(predicate).MinAsync(selector);
        }

        /// <summary>
        /// Gets the average based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual decimal Average(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, decimal>> selector = null)
        {
            if (predicate == null)
                return _dbSet.Average(selector);
            else
                return _dbSet.Where(predicate).Average(selector);
        }

        /// <summary>
        /// Gets the async average based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual async Task<decimal> AverageAsync(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, decimal>> selector = null)
        {
            if (predicate == null)
                return await _dbSet.AverageAsync(selector);
            else
                return await _dbSet.Where(predicate).AverageAsync(selector);
        }

        /// <summary>
        /// Gets the sum based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual decimal Sum(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, decimal>> selector = null)
        {
            if (predicate == null)
                return _dbSet.Sum(selector);
            else
                return _dbSet.Where(predicate).Sum(selector);
        }

        /// <summary>
        /// Gets the async sum based on a predicate.
        /// </summary>
        /// <param name="predicate"></param>
        ///  /// <param name="selector"></param>
        /// <returns>decimal</returns>
        public virtual async Task<decimal> SumAsync(Expression<Func<TEntity, bool>> predicate = null, Expression<Func<TEntity, decimal>> selector = null)
        {
            if (predicate == null)
                return await _dbSet.SumAsync(selector);
            else
                return await _dbSet.Where(predicate).SumAsync(selector);
        }

        /// <summary>
        /// Gets the exists based on a predicate.
        /// </summary>
        /// <param name="selector"></param>
        /// <returns></returns>
        public bool Exists(Expression<Func<TEntity, bool>> selector = null)
        {
            if (selector == null)
            {
                return _dbSet.Any();
            }
            else
            {
                return _dbSet.Any(selector);
            }
        }
        /// <summary>
        /// Gets the async exists based on a predicate.
        /// </summary>
        /// <param name="selector"></param>
        /// <returns></returns>
        public async Task<bool> ExistsAsync(Expression<Func<TEntity, bool>> selector = null)
        {
            if (selector == null)
            {
                return await _dbSet.AnyAsync();
            }
            else
            {
                return await _dbSet.AnyAsync(selector);
            }
        }
        /// <summary>
        /// Inserts a new entity synchronously.
        /// </summary>
        /// <param name="entity">The entity to insert.</param>
        public virtual TEntity Insert(TEntity entity)
        {
            return _dbSet.Add(entity).Entity;
        }

        /// <summary>
        /// Inserts a range of entities synchronously.
        /// </summary>
        /// <param name="entities">The entities to insert.</param>
        public virtual void Insert(params TEntity[] entities) => _dbSet.AddRange(entities);

        /// <summary>
        /// Inserts a range of entities synchronously.
        /// </summary>
        /// <param name="entities">The entities to insert.</param>
        public virtual void Insert(IEnumerable<TEntity> entities) => _dbSet.AddRange(entities);

        /// <summary>
        /// Inserts a new entity asynchronously.
        /// </summary>
        /// <param name="entity">The entity to insert.</param>
        /// <param name="cancellationToken">A <see cref="CancellationToken"/> to observe while waiting for the task to complete.</param>
        /// <returns>A <see cref="Task"/> that represents the asynchronous insert operation.</returns>
        public virtual ValueTask<EntityEntry<TEntity>> InsertAsync(TEntity entity, CancellationToken cancellationToken = default(CancellationToken))
        {
            return _dbSet.AddAsync(entity, cancellationToken);

            // Shadow properties?
            //var property = _dbContext.Entry(entity).Property("Created");
            //if (property != null) {
            //property.CurrentValue = DateTime.Now;
            //}
        }

        /// <summary>
        /// Inserts a range of entities asynchronously.
        /// </summary>
        /// <param name="entities">The entities to insert.</param>
        /// <returns>A <see cref="Task" /> that represents the asynchronous insert operation.</returns>
        public virtual Task InsertAsync(params TEntity[] entities) => _dbSet.AddRangeAsync(entities);

        /// <summary>
        /// Inserts a range of entities asynchronously.
        /// </summary>
        /// <param name="entities">The entities to insert.</param>
        /// <param name="cancellationToken">A <see cref="CancellationToken"/> to observe while waiting for the task to complete.</param>
        /// <returns>A <see cref="Task"/> that represents the asynchronous insert operation.</returns>
        public virtual Task InsertAsync(IEnumerable<TEntity> entities, CancellationToken cancellationToken = default(CancellationToken)) => _dbSet.AddRangeAsync(entities, cancellationToken);

        /// <summary>
        /// Updates the specified entity.
        /// </summary>
        /// <param name="entity">The entity.</param>
        public virtual void Update(TEntity entity)
        {
            _dbSet.Update(entity);
        }

        /// <summary>
        /// Updates the specified entity.
        /// </summary>
        /// <param name="entity">The entity.</param>
        public virtual void UpdateAsync(TEntity entity)
        {
            _dbSet.Update(entity);

        }

        /// <summary>
        /// Updates the specified entities.
        /// </summary>
        /// <param name="entities">The entities.</param>
        public virtual void Update(params TEntity[] entities) => _dbSet.UpdateRange(entities);

        /// <summary>
        /// Updates the specified entities.
        /// </summary>
        /// <param name="entities">The entities.</param>
        public virtual void Update(IEnumerable<TEntity> entities) => _dbSet.UpdateRange(entities);

        /// <summary>
        /// Deletes the specified entity.
        /// </summary>
        /// <param name="entity">The entity to delete.</param>
        public virtual void Delete(TEntity entity) => _dbSet.Remove(entity);

        /// <summary>
        /// Deletes the entity by the specified primary key.
        /// </summary>
        /// <param name="id">The primary key value.</param>
        public virtual void Delete(object id)
        {
            // using a stub entity to mark for deletion
            var typeInfo = typeof(TEntity).GetTypeInfo();
            var key = _dbContext.Model.FindEntityType(typeInfo).FindPrimaryKey().Properties.FirstOrDefault();
            var property = typeInfo.GetProperty(key?.Name);
            if (property != null)
            {
                var entity = Activator.CreateInstance<TEntity>();
                property.SetValue(entity, id);
                _dbContext.Entry(entity).State = EntityState.Deleted;
            }
            else
            {
                var entity = _dbSet.Find(id);
                if (entity != null)
                {
                    Delete(entity);
                }
            }
        }

        /// <summary>
        /// Deletes the specified entities.
        /// </summary>
        /// <param name="entities">The entities.</param>
        public virtual void Delete(params TEntity[] entities) => _dbSet.RemoveRange(entities);

        /// <summary>
        /// Deletes the specified entities.
        /// </summary>
        /// <param name="entities">The entities.</param>
        public virtual void Delete(IEnumerable<TEntity> entities) => _dbSet.RemoveRange(entities);

        /// <summary>
        /// Gets all entities. This method is not recommended
        /// </summary>
        /// <returns>The <see cref="IQueryable{TEntity}"/>.</returns>
        public async Task<IList<TEntity>> GetAllAsync()
        {
            return await _dbSet.ToListAsync();
        }

        /// <summary>
        /// Gets all entities. This method is not recommended
        /// </summary>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="orderBy">A function to order elements.</param>
        /// <param name="include">A function to include navigation properties</param>
        /// <param name="disableTracking"><c>true</c> to disable changing tracking; otherwise, <c>false</c>. Default to <c>true</c>.</param>
        /// <param name="ignoreQueryFilters">Ignore query filters</param>
        /// <returns>An <see cref="IPagedList{TEntity}"/> that contains elements that satisfy the condition specified by <paramref name="predicate"/>.</returns>
        /// <remarks>Ex: This method defaults to a read-only, no-tracking query.</remarks>
        public async Task<IList<TEntity>> GetAllAsync(Expression<Func<TEntity, bool>> predicate = null,
            Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
            Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>> include = null,
            bool disableTracking = true, bool ignoreQueryFilters = false)
        {
            IQueryable<TEntity> query = _dbSet;

            if (disableTracking)
            {
                query = query.AsNoTracking();
            }

            if (include != null)
            {
                query = include(query);
            }

            if (predicate != null)
            {
                query = query.Where(predicate);
            }

            if (ignoreQueryFilters)
            {
                query = query.IgnoreQueryFilters();
            }

            if (orderBy != null)
            {
                return await orderBy(query).ToListAsync();
            }
            else
            {
                return await query.ToListAsync();
            }
        }

        /// <summary>
        /// Change entity state for patch method on web api.
        /// </summary>
        /// <param name="entity">The entity.</param>
        /// /// <param name="state">The entity state.</param>
        public void ChangeEntityState(TEntity entity, EntityState state)
        {
            _dbContext.Entry(entity).State = state;
        }
    }
}