sharee.bike-App/TINK/TINK/ViewModel/RootMasterDetail/MasterPageViewModel.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using TINK.Services;
using TINK.Services.CopriApi.ServerUris;
using TINK.View;
using TINK.View.Account;
using TINK.View.Contact;
using TINK.View.FindBike;
using TINK.View.Info;
using TINK.View.Login;
using TINK.View.Map;
using TINK.View.MyBikes;
using TINK.View.Settings;
using TINK.View.Themes;
using Xamarin.Forms;

namespace TINK.ViewModel
{
    /// <summary>
    /// View model managing master detail menu.
    /// </summary>
    class MasterPageViewModel : INotifyPropertyChanged
    {
        /// <summary>
        /// Dictionary to manage collection of menu items.
        /// </summary>
        private Dictionary<Type, int> m_oEntryDictionary;

        /// <summary> Updates menu entries depending on state. </summary>
        private void UpdateMenuEntries()
        {
            var l_oSelectedMenuItem = SelectedMenuItem ?? new MainPageMenuItem(0, typeof(MapPage));

            for (int l_iIndex = MenuItems.Count - 1;  l_iIndex >= 0; l_iIndex--)
            {
                MenuItems.Clear();
                m_oEntryDictionary.Clear();
            }

            CheckAddItem(typeof(MapPage));

            if (App.ModelRoot.ActiveUser.IsLoggedIn)
            {
                CheckAddItem(typeof(MyBikesPage));
                CheckAddItem(typeof(FindBikePage));
                CheckAddItem(typeof(AccountPage));
            }
            else
            {
                CheckAddItem(typeof(LoginPage));
            }

            if (App.ModelRoot.Uris.ActiveUri.Host.GetIsCopri()
                || App.ModelRoot.ActiveUser.IsLoggedIn)
            {
                CheckAddItem(typeof(SettingsPage));
            }

            CheckAddItem(typeof(FeesAndBikesPage)); // Fees and bikes

            CheckAddItem(typeof(ContactPage)); // Feedback and contact

            CheckAddItem(typeof(TabbedPageInfo)); // About sharee.bike
        }

        /// <summary>Adds a menu item to master detail menu.</summary>
        /// <param name="p_oType">Type decribing entry to be added.</param>
        private void CheckAddItem(Type p_oType)
        {
            if (m_oEntryDictionary.ContainsKey(p_oType))
            {
                // Nothing to do because has already been added.
                return;
            }

            m_oEntryDictionary.Add(
                p_oType, 
                m_oEntryDictionary.Count);

            MenuItems.Add(
                new MainPageMenuItem(m_oEntryDictionary[p_oType], 
                p_oType));
        }

        /// <summary> Removes a page from menu.</summary>
        /// <param name="p_oType"></param>
        private void RemoveItem(Type p_oType)
        {
            if (!m_oEntryDictionary.ContainsKey(p_oType))
            {
                // Nothing to do because item was never added/ already removed.
                return;
            }

            MenuItems.Remove(MenuItems[m_oEntryDictionary[p_oType]]);
            m_oEntryDictionary.Remove(p_oType);
        }

        public MasterPageViewModel()
        {
            MenuItems = new ObservableCollection<MainPageMenuItem>();
            m_oEntryDictionary = new Dictionary<Type, int>();

            App.ModelRoot.ActiveUser.StateChanged += (sender, eventargs) => OnUpdateRequired();

            // Update flyout view model whenever theme is switched.
            App.ModelRoot.Themes.PropertyChanged += (sender, eventargs) =>
            {
                if (!(sender is ServicesContainerMutable<object> themes))
                    return;

                MasterDetailMenuTitlte = GetMasterDetailMenuTitle(themes.Active);

                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(MasterDetailMenuTitlte)));
            };

            MasterDetailMenuTitlte = GetMasterDetailMenuTitle(App.ModelRoot.Themes.Active);

            UpdateMenuEntries();
        }

        /// <summary>
        /// Gets the flyout title from theme name
        /// </summary>
        /// <param name="theme">Name of theme.</param>
        /// <returns>Flyout title.</returns>
        private string GetMasterDetailMenuTitle(object theme)
        {
            if (!(theme is ITheme active))
                return "sharee.bike";

            return $"sharee.bike{(!string.IsNullOrEmpty(active.OperatorInfo) ? ($"\r\n{active.OperatorInfo}") : string.Empty)}";
        }

        private string masterDetailMenuTitlte;

        /// <summary>
        /// Holds the title of the fylout page.
        /// </summary>
        public string MasterDetailMenuTitlte
        {
            get
            {
                return masterDetailMenuTitlte;
            }
            set
            {
                if (masterDetailMenuTitlte == value)
                    return;

                masterDetailMenuTitlte = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(MasterDetailMenuTitlte)));
            }
        }

        /// <summary>
        /// Provides collection of menu items for master page.
        /// </summary>
        public ObservableCollection<MainPageMenuItem> MenuItems
        {
            get; private set;
        }

        /// <summary>
        /// View service used to manage menu state.
        /// </summary>
        public ShowPageDelegate ShowPageViewService { get; set; }

        /// <summary>
        /// Gets or sets the selected item.
        /// </summary>
        public MainPageMenuItem SelectedMenuItem
        {
            get;
            set;
        }

        /// <summary>
        /// Command object which is invoked from view when an item is selected.
        /// </summary>
        public Command MenuItemSelected
        {
            get
            {
                return new Command(OnUpdateRequired);
            }

        }

        /// <summary> Manges updates required due to selection of a menu or login events.</summary>
        public void OnUpdateRequired()
        {
            if (ShowPageViewService == null)
                return;

            UpdateMenuEntries();

            if (SelectedMenuItem == null)
            {
                // Nothing to do if no menu entry is selected.
                return;
            }

            ShowPageViewService(SelectedMenuItem.TargetType);
        }

        #region INotifyPropertyChanged Implementation
        public event PropertyChangedEventHandler PropertyChanged;
        void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            if (PropertyChanged == null)
                return;

            PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion
    }
}