using System;
using System.Data.Entity;
using EnVisage.Models;
using NLog;

namespace EnVisage.Code.BLL
{
    public class ManagerBase<TDALClass, TModel>: IDisposable where TDALClass : class, new() where TModel : IBaseModel<TDALClass>, new()
    {
        private readonly EnVisageEntities _dbContext;
        private readonly bool _isContexLocal;
        protected readonly Logger Logger = LogManager.GetCurrentClassLogger();

        protected EnVisageEntities DbContext => _dbContext;

	    public virtual DbSet<TDALClass> DataTable
        {
            get { throw new NotImplementedException(); }
        }
        protected bool IsContextLocal => _isContexLocal;

	    public ManagerBase(EnVisageEntities dbContext)
        {
            if (dbContext == null)
            {
                _dbContext = new EnVisageEntities();
                _isContexLocal = true;
            }
            else
            {
                _dbContext = dbContext;
            }
        }
        
        public void Dispose()
        {
            if (_isContexLocal)
                _dbContext.Dispose();
        }

        #region Public Methods
        
        /// <summary>
        /// Loads a TDALClass from the database.
        /// </summary>
        /// <param name="value">Unique identifier of the TDALClass.</param>
        /// <param name="isReadOnly">Indicates that object will not be saved later in the code. Use <b>false</b> if you need to save an updated object.</param>
        /// <returns>A <see cref="TDALClass"/> object retrieved from database.</returns>
        public virtual TDALClass Load(Guid? value, bool isReadOnly = true)
        {
            if (value == null || value == Guid.Empty)
                return new TDALClass();

            return isReadOnly
                       ? RetrieveReadOnlyById(value.Value)
                       : DataTable.Find(value);
        }
        /// <summary>
        /// Retrieves a readonly DAL object from database.
        /// </summary>
        /// <returns>An instance of <see cref="TDALClass"/> class.</returns>
        protected virtual TDALClass RetrieveReadOnlyById(Guid key)
        {
            throw new NotImplementedException();
        }

	    /// <summary>
	    /// Saves an instance of the <see cref="TDALClass"/> into the database.
	    /// </summary>
	    /// <param name="model">A model object with data from the form.</param>
	    public virtual TDALClass Save(TModel model)
		{
            if (model == null)
                throw new ArgumentNullException(nameof(model));

            #region Save data
            TDALClass dbObj = null;
	        bool newDbObject = false;
			if (model.Id != Guid.Empty)
                dbObj = DataTable.Find(model.Id);
            if (dbObj == null)
            {
	            newDbObject = true;
				dbObj = InitInstance();
            }
            model.CopyTo(dbObj);
            if (model.Id == Guid.Empty || newDbObject)
            {
                DataTable.Add(dbObj);
            }
            else
                _dbContext.Entry(dbObj).State = EntityState.Modified;

			#endregion

			if (_isContexLocal)
                _dbContext.SaveChanges();
            return dbObj;
        }
        /// <summary>
        /// Creates an instance of the  <see cref="TDALClass"/> class and initializes it.
        /// </summary>
        /// <returns>An instance of the <see cref="TDALClass"/> class.</returns>
        protected virtual TDALClass InitInstance()
        {
            return new TDALClass();
        }
        #endregion
    }
}