Layers Pattern in Practice

using System;
using System.Collections.Generic;
using System.Linq;
using BillsEntityLib;
using System.Collections.ObjectModel;
using BillsBusinessLogicLib;


namespace BillPayManager
{
    public class RecentBillsDataGridProxy : IDataGridProxy
    {
        private ObservableCollection<Bill> _collection;
        private Microsoft.Windows.Controls.DataGrid _datagrid;
        private readonly List<string> _updateList = new List<string>();
        private readonly List<string> _insertList = new List<string>();
        private readonly List<string> _deleteList = new List<string>();
        private readonly BillsBusinessLogicLib.IBillsManager _billsManager = BillsBusinessLogicLib.BillsManager.GetInstance();
        #region Constructors

        #endregion

        #region IDataGridProxy Members
        /// <summary>
        /// Initialize DataGrid control
        /// </summary>
        /// <param name="dataGrid">DataGrid to populate</param>
        /// <param name="bills">Bills which will populate datagrid</param>
        public void Initialize(Microsoft.Windows.Controls.DataGrid dataGrid, BillsEntityLib.Bills bills)
        {
            if (bills == null)
                return;
            this._datagrid = dataGrid;
            foreach (Bill bill in bills.Items)
            {
                bill.PropertyChanged += new System.ComponentModel.PropertyChangedEventHandler(bill_PropertyChanged);
            }

            _collection = new ObservableCollection<Bill>(bills.Items);   //define the ObservableCollection<T> class
            this._datagrid.ItemsSource = _collection;                      //bind the data to the datasource
            //Collection Changed Event Handler
            _collection.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(CollectionCollectionChanged);

            //dataGrid.Cells

        }

        /// <summary>
        /// Updates Datagrid control
        /// </summary>
        /// <param name="bills"></param>
        public void UpdateDataGrid(BillsEntityLib.Bills bills)
        {
            if (this._datagrid == null) return;
            _collection = new ObservableCollection<Bill>(bills.Items);   //define the ObservableCollection<T> class
            this._datagrid.ItemsSource = _collection;                      //bind the data to the datasource
            //Collection Changed Event Handler
            _collection.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(CollectionCollectionChanged);
        }
        
        /// <summary>
        /// Commit changes in the bill collection to the datasource
        /// </summary>
        /// <exception cref="BillManagerException">BillManager Exception</exception>
        public void CommitChangesToDataSource()
        {
            if (_collection == null)
                return;
            List<Bill> listOfBills = _collection.ToList<Bill>();
            try
            {
                if (_insertList.Count != 0) //if there have been inserted bills
                {
                    //select bills which were inserted
                    var queryInsert = from totalBill in listOfBills
                                      join insertBill in _insertList on totalBill.ID equals insertBill
                                      select
                                          new Bill(totalBill.Name, totalBill.DueDate, totalBill.Amount,
                                                   totalBill.AddedOn,
                                                   totalBill.Status, totalBill.ID);
                    Bills bills = new Bills(queryInsert);
                    _billsManager.Insert(bills); //insert the bills into the datasource
                    _insertList.Clear();
                }
                if (_deleteList.Count != 0) //delete the bills from the datasource
                {
                    foreach (string id in _deleteList)
                        _billsManager.Delete(new Guid(id));
                    _deleteList.Clear();
                }
                if (_updateList.Count == 0) return;
                var queryUpdate = from totalBill in listOfBills
                                  join updateBill in _updateList on totalBill.ID equals updateBill
                                  select
                                      new Bill(totalBill.Name, totalBill.DueDate, totalBill.Amount, totalBill.AddedOn,
                                               totalBill.Status, totalBill.ID);
                foreach (Bill newBill in queryUpdate)
                    _billsManager.Update(new Guid(newBill.ID), newBill);
                _updateList.Clear();
            }
            catch
            {
                _insertList.Clear();
                _updateList.Clear();
                _deleteList.Clear();
                throw;
            }
        }

        public Microsoft.Windows.Controls.DataGrid DataGrid
        {
            get { return this._datagrid; }
        }

        public ObservableCollection<Bill> Collection
        {
            get { return this._collection; }
        }

        public void InsertBillToDataGrid(Bill bill)
        {
            bill.PropertyChanged += bill_PropertyChanged;
            this._collection.Add(bill);
        }

        public event System.Collections.Specialized.NotifyCollectionChangedEventHandler CollectionChanged;

        public event System.ComponentModel.PropertyChangedEventHandler BillPropertyChanged;


        protected virtual void OnCollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            System.Collections.Specialized.NotifyCollectionChangedEventHandler temp = CollectionChanged;
            if (temp != null)
            {
                temp.Invoke(sender, e);
            }
        }

        protected virtual void OnPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            System.ComponentModel.PropertyChangedEventHandler temp = BillPropertyChanged;
            if (temp != null)
            {
                temp.Invoke(sender, e);
            }
        }

        #endregion

        //Observable collection changed
        private void CollectionCollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            ///Add new Bill in the DataGrid
            if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
            {
                foreach (Bill bill in e.NewItems)
                {
                    if (!_insertList.Contains(bill.ID))
                        _insertList.Add(bill.ID);
                }
                this.OnCollectionChanged(sender, e);
            }
            else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
            {
                //Delete new Bill from DataGrid
                foreach (Bill bill in e.OldItems)
                {
                    if (!_deleteList.Contains(bill.ID))
                        _deleteList.Add(bill.ID);
                }
                this.OnCollectionChanged(sender, e);
            }
        }
        //Bill property changed
        private void bill_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            BillPropertyChangeEventArgs args = (BillPropertyChangeEventArgs)e;
            if (!_updateList.Contains(args.ChangedId))
                _updateList.Add(args.ChangedId);
            this.OnPropertyChanged(sender, e);
        }
        
    }
}