// -----------------------------------------------------------------------
// <copyright file="SelectingItemsControl.cs" company="Steven Kirk">
// Copyright 2014 MIT Licence. See licence.md for more information.
// </copyright>
// -----------------------------------------------------------------------

namespace Perspex.Controls.Primitives
{
    using System;
    using System.Collections;
    using System.Collections.Specialized;
    using System.Linq;
    using Perspex.Controls.Generators;
    using Perspex.Input;
    using Perspex.Interactivity;
    using Perspex.Styling;
    using Perspex.VisualTree;

    /// <summary>
    /// An <see cref="ItemsControl"/> that maintains a selection.
    /// </summary>
    /// <remarks>
    /// TODO: Support multiple selection.
    /// </remarks>
    public abstract class SelectingItemsControl : ItemsControl
    {
        /// <summary>
        /// Defines the <see cref="SelectedIndex"/> property.
        /// </summary>
        public static readonly PerspexProperty<int> SelectedIndexProperty =
            PerspexProperty.Register<SelectingItemsControl, int>(
                nameof(SelectedIndex),
                defaultValue: -1,
                validate: ValidateSelectedIndex);

        /// <summary>
        /// Defines the <see cref="SelectedItem"/> property.
        /// </summary>
        public static readonly PerspexProperty<object> SelectedItemProperty =
            PerspexProperty.Register<SelectingItemsControl, object>(
                nameof(SelectedItem),
                validate: ValidateSelectedItem);

        /// <summary>
        /// Event that should be raised by items that implement <see cref="ISelectable"/> to
        /// notify the parent <see cref="SelectingItemsControl"/> that their selection state
        /// has changed.
        /// </summary>
        public static readonly RoutedEvent<RoutedEventArgs> IsSelectedChangedEvent =
            RoutedEvent.Register<SelectingItemsControl, RoutedEventArgs>("IsSelectedChanged", RoutingStrategies.Bubble);

        /// <summary>
        /// Initializes static members of the <see cref="SelectingItemsControl"/> class.
        /// </summary>
        static SelectingItemsControl()
        {
            IsSelectedChangedEvent.AddClassHandler<SelectingItemsControl>(x => x.ContainerSelectionChanged);
            SelectedIndexProperty.Changed.AddClassHandler<SelectingItemsControl>(x => x.SelectedIndexChanged);
            SelectedItemProperty.Changed.AddClassHandler<SelectingItemsControl>(x => x.SelectedItemChanged);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="SelectingItemsControl"/> class.
        /// </summary>
        public SelectingItemsControl()
        {
            this.ItemContainerGenerator.ContainersInitialized.Subscribe(this.ContainersInitialized);
        }

        /// <summary>
        /// Gets or sets the index of the selected item.
        /// </summary>
        public int SelectedIndex
        {
            get { return this.GetValue(SelectedIndexProperty); }
            set { this.SetValue(SelectedIndexProperty, value); }
        }

        /// <summary>
        /// Gets or sets the selected item.
        /// </summary>
        public object SelectedItem
        {
            get { return this.GetValue(SelectedItemProperty); }
            set { this.SetValue(SelectedItemProperty, value); }
        }

        /// <inheritdoc/>
        protected override void ItemsChanged(IEnumerable oldValue, IEnumerable newValue)
        {
            base.ItemsChanged(oldValue, newValue);
            this.SelectedIndex = IndexOf(newValue, this.SelectedItem);
        }

        /// <inheritdoc/>
        protected override void ItemsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            base.ItemsCollectionChanged(sender, e);

            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Remove:
                case NotifyCollectionChangedAction.Replace:
                    var selectedIndex = this.SelectedIndex;

                    if (selectedIndex >= e.OldStartingIndex &&
                        selectedIndex < e.OldStartingIndex + e.OldItems.Count)
                    {
                        this.SelectedIndex = -1;
                    }

                    break;

                case NotifyCollectionChangedAction.Reset:
                    this.SelectedIndex = IndexOf(e.NewItems, this.SelectedItem);
                    break;
            }
        }

        /// <inheritdoc/>
        protected override void OnGotFocus(GotFocusEventArgs e)
        {
            base.OnGotFocus(e);
            this.TrySetSelectionFromContainerEvent(e.Source);
        }

        /// <summary>
        /// Gets the index of an item in a collection.
        /// </summary>
        /// <param name="items">The collection.</param>
        /// <param name="item">The item.</param>
        /// <returns>The index of the item or -1 if the item was not found.</returns>
        private static int IndexOf(IEnumerable items, object item)
        {
            if (items != null && item != null)
            {
                var list = items as IList;

                if (list != null)
                {
                    return list.IndexOf(item);
                }
                else
                {
                    int index = 0;

                    foreach (var i in items)
                    {
                        if (object.Equals(i, item))
                        {
                            return index;
                        }

                        ++index;
                    }
                }
            }

            return -1;
        }

        /// <summary>
        /// Sets a container's 'selected' class or <see cref="ISelectable.IsSelected"/>.
        /// </summary>
        /// <param name="container">The container.</param>
        /// <param name="selected">Whether the control is selected</param>
        private static void MarkContainerSelected(IControl container, bool selected)
        {
            var selectable = container as ISelectable;
            var styleable = container as IStyleable;

            if (selectable != null)
            {
                selectable.IsSelected = selected;
            }
            else if (styleable != null)
            {
                if (selected)
                {
                    styleable.Classes.Add("selected");
                }
                else
                {
                    styleable.Classes.Remove("selected");
                }
            }
        }

        /// <summary>
        /// Coerces the <see cref="SelectedIndex"/> property.
        /// </summary>
        /// <param name="sender">The object with the property.</param>
        /// <param name="index">The proposed value of the property.</param>
        /// <returns>The final value of the property.</returns>
        private static int ValidateSelectedIndex(SelectingItemsControl sender, int index)
        {
            var items = sender.Items;
            return (index >= 0 && index < items?.Cast<object>().Count()) ? index : -1;
        }

        /// <summary>
        /// Coerces the <see cref="SelectedItem"/> property.
        /// </summary>
        /// <param name="sender">The object with the property.</param>
        /// <param name="item">The proposed value of the property.</param>
        /// <returns>The final value of the property.</returns>
        private static object ValidateSelectedItem(SelectingItemsControl sender, object item)
        {
            var items = sender.Items;
            return items?.Cast<object>().Contains(item) == true ? item : null;
        }

        /// <summary>
        /// Called when new containers are initialized by the <see cref="ItemContainerGenerator"/>.
        /// </summary>
        /// <param name="containers">The containers.</param>
        private void ContainersInitialized(ItemContainers containers)
        {
            var selectedIndex = this.SelectedIndex;
            var selectedContainer = containers.Items.OfType<ISelectable>().FirstOrDefault(x => x.IsSelected);

            if (selectedContainer != null)
            {
                this.SelectedIndex = containers.Items.IndexOf((IControl)selectedContainer) + containers.StartingIndex;
            }
            else if (selectedIndex >= containers.StartingIndex &&
                     selectedIndex < containers.StartingIndex + containers.Items.Count)
            {
                var container = containers.Items[selectedIndex - containers.StartingIndex];
                MarkContainerSelected(container, true);
            }
        }

        /// <summary>
        /// Called when a container raises the <see cref="IsSelectedChangedEvent"/>.
        /// </summary>
        /// <param name="e">The event.</param>
        private void ContainerSelectionChanged(RoutedEventArgs e)
        {
            this.TrySetSelectionFromContainerEvent(e.Source);
        }

        /// <summary>
        /// Called when the <see cref="SelectedIndex"/> property changes.
        /// </summary>
        /// <param name="e">The event args.</param>
        private void SelectedIndexChanged(PerspexPropertyChangedEventArgs e)
        {
            var index = (int)e.OldValue;

            if (index != -1)
            {
                var container = this.ItemContainerGenerator.ContainerFromIndex(index);
                MarkContainerSelected(container, false);
            }

            index = (int)e.NewValue;

            if (index == -1)
            {
                this.SelectedItem = null;
            }
            else
            {
                this.SelectedItem = this.Items.Cast<object>().ElementAt((int)e.NewValue);
                var container = this.ItemContainerGenerator.ContainerFromIndex(index);
                MarkContainerSelected(container, true);
            }
        }

        /// <summary>
        /// Called when the <see cref="SelectedItem"/> property changes.
        /// </summary>
        /// <param name="e">The event args.</param>
        private void SelectedItemChanged(PerspexPropertyChangedEventArgs e)
        {
            this.SelectedIndex = IndexOf(this.Items, e.NewValue);
        }

        /// <summary>
        /// Tries to set the selection to a container that raised an event.
        /// </summary>
        /// <param name="eventSource">The control that raised the event.</param>
        private void TrySetSelectionFromContainerEvent(IInteractive eventSource)
        {
            var item = ((IVisual)eventSource).GetSelfAndVisualAncestors()
                .OfType<ILogical>()
                .FirstOrDefault(x => x.LogicalParent == this);

            if (item != null)
            {
                var index = this.ItemContainerGenerator.IndexFromContainer((IControl)item);

                if (index != -1)
                {
                    this.SelectedIndex = index;
                }
            }
        }
    }
}