/* ElementPickerViewModel.cs
 * part of zaaReloaded2
 * 
 * Copyright 2015-2017 Daniel Kraus
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Bovender.Mvvm;
using Bovender.Mvvm.Messaging;
using Bovender.Mvvm.ViewModels;
using System.Collections.ObjectModel;
using zaaReloaded2.Controller.Elements;

namespace zaaReloaded2.ViewModels
{
    /// <summary>
    /// View model that presents a list of zaaReloaded2.Contorller.Elements.ElementBase
    /// classes to choose from. Depending on which constructor is used, this view model
    /// presents either a list of ControlElementBase-derived classes, a list of
    /// FormatElementBase-derived classes, or both.
    /// </summary>
    class ElementPickerViewModel : ViewModelBase
    {
        #region Properties

        /// <summary>
        /// A two-dimensional tree 
        /// </summary>
        public IList<CategoryViewModel> Categories { get; private set; }

        /// <summary>
        /// Gets the currently selected element, or null if no element is selected.
        /// </summary>
        /// <remarks>
        /// TODO: Raise PropertyChanged event.
        /// </remarks>
        public ElementViewModel Selected { get; private set; }

        #endregion

        #region Commands

        public DelegatingCommand ChooseElementCommand
        {
            get
            {
                if (_chooseElementCommand == null)
                {
                    _chooseElementCommand = new DelegatingCommand(
                        param => DoChooseElement(),
                        param => CanChooseElement());
                }
                return _chooseElementCommand;
            }
        }

        #endregion

        #region Messages

        /// <summary>
        /// A message that is sent out when an element has been chosen;
        /// the message content is the element's view model with the element
        /// wrapped inside.
        /// </summary>
        public Message<ViewModelMessageContent> ElementChosenMessage
        {
            get
            {
                if (_elementChosenMessage == null)
                {
                    _elementChosenMessage = new Message<ViewModelMessageContent>();
                }
                return _elementChosenMessage;
            }
        }

        #endregion

        #region Constructors

        public ElementPickerViewModel(bool allowControlElements)
        {
            Categories = new List<CategoryViewModel>();
            if (allowControlElements)
            {
                AddCategory(
                    new CategoryViewModel(
                        Properties.Settings.Default.ControlElementLabel,
                        new Collection<ViewModelBase>()
                        {
                            CreateControlElementViewModel(new SelectFirstDay()),
                            CreateControlElementViewModel(new SelectLastDay()),
                            CreateControlElementViewModel(new SelectEachDay()),
                            CreateControlElementViewModel(new TwoColumns()),
                            CreateControlElementViewModel(new NextColumn()),
                        }
                    )
                );
            }
            CreateFormatElementViewModels();
        }

        /// <summary>
        /// Creates a new element picker for control elements only;
        /// the selected ControlElementVieModel will copy the Elements
        /// property from a source view model.
        /// </summary>
        /// <param name="copyFromViewModel">ControlElementViewModel
        /// whose Elements property to copy.</param>
        public ElementPickerViewModel(ControlElementViewModel copyFromViewModel)
        {
            Categories = new List<CategoryViewModel>();
            AddCategory(
                new CategoryViewModel(
                    Properties.Settings.Default.ControlElementLabel,
                    new Collection<ViewModelBase>()
                        {
                            CreateControlElementViewModel(new SelectFirstDay(), copyFromViewModel),
                            CreateControlElementViewModel(new SelectLastDay(), copyFromViewModel),
                            CreateControlElementViewModel(new SelectEachDay(), copyFromViewModel),
                            CreateControlElementViewModel(new TwoColumns()),
                            CreateControlElementViewModel(new NextColumn()),
                        }
                )
            );
        }

        #endregion

        #region Private methods

        void CreateFormatElementViewModels()
        {
            AddCategory(
                new CategoryViewModel(
                    Properties.Settings.Default.FormatElementLabel,
                    new Collection<ViewModelBase>()
                        {
                            CreateFormatElementViewModel(new Items()),
                            CreateFormatElementViewModel(new CustomText()),
                        }
                )
            );
        }

        void AddCategory(CategoryViewModel category)
        {
            category.PropertyChanged += ElementViewModel_PropertyChanged;
            Categories.Add(category);
        }

        /// <summary>
        /// Creates a new ControlElementViewModel that wraps a ControlElementBase
        /// object. The display string of the ControlElementViewModel is taken
        /// from the canonical Label of the control element.
        /// </summary>
        ViewModelBase CreateControlElementViewModel(ControlElementBase element)
        {
            ControlElementViewModel vm = new ControlElementViewModel(element);
            vm.DisplayString = element.Label;
            vm.PropertyChanged += ElementViewModel_PropertyChanged;
            return vm;
        }

        ViewModelBase CreateControlElementViewModel(
            ControlElementBase element, ControlElementViewModel copyFromViewModel)
        {
            ControlElementViewModel vm = new ControlElementViewModel(element, copyFromViewModel);
            vm.DisplayString = element.Label;
            vm.PropertyChanged += ElementViewModel_PropertyChanged;
            return vm;
        }

        /// <summary>
        /// Creates a new FormatElementViewModel that wraps a FormatElementBase
        /// object and has a custom display string. The custom display string
        /// is necessary because format elements do not have a canonical label.
        /// </summary>
        ViewModelBase CreateFormatElementViewModel(FormatElementBase element)
        {
            FormatElementViewModel vm = new FormatElementViewModel(element);
            vm.PropertyChanged += ElementViewModel_PropertyChanged;
            return vm;
        }

        void ElementViewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            // Casting sender as ElementViewModel may result in Null, but this
            // is a desired effect because category headings may be selected
            // in a view, but are not valid ElementViewModels that we could
            // 'choose'. In addition, when an element is selected, another one
            // is deselected, and the event triggers twice, once for the selected
            // element and once for the deselected one.
            ElementViewModel elementVM = sender as ElementViewModel;
            if (elementVM != null && elementVM.IsSelected && e.PropertyName == "IsSelected")
            {
                Selected = elementVM;
            }
        }

        void DoChooseElement()
        {
            if (CanChooseElement())
            {
                ElementChosenMessage.Send(new ViewModelMessageContent(Selected));
                DoCloseView();
            }
        }

        bool CanChooseElement()
        {
            return Selected != null && Selected.IsSelected == true;
        }

        #endregion

        #region Implementation ov ViewModelBase

        public override object RevealModelObject()
        {
            throw new NotImplementedException();
        }

        #endregion

        #region Fields

        DelegatingCommand _chooseElementCommand;
        Message<ViewModelMessageContent> _elementChosenMessage;

        #endregion
    }
}