using System;
using System.ComponentModel;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Data;
using System.Windows.Interactivity;
using Chernobyl.Timing;
using Chernobyl.Utility;

namespace Chernobyl.App.Core
{
    /// <summary>
    /// A <see cref="Behavior{T}"/> that periodically triggers an update to the target or source
    /// of a binding. This is useful if you want a displayed property value or the property itself to
    /// be periodically refreshed/updated but the associated object or view doesn't trigger the
    /// updated as often as you would like (i.e. <see cref="INotifyPropertyChanged.PropertyChanged"/> event for example).
    /// </summary>
    /// <example><![CDATA[
    ///     <!-- The following is an example of this behavior being used in code. The content property
    ///     is bound to a property whose value should be updated on screen every .2 seconds. -->
    ///     <Label Content="{Binding CurrentTimeInSeconds}">
    ///         <i:Interaction.Behaviors>
    ///             <local:BindingUpdater Interval = "0:00:00.2" Property="{x:Static ContentControl.ContentProperty}" Mode="UpdateTarget" />
    ///         </i:Interaction.Behaviors>
    ///     </Label>
    /// ]]></example>
    public class BindingUpdater : Behavior<DependencyObject>
    {
        // This code is a modified version of the code found here: https://stackoverflow.com/a/44253691.

        /// <summary>
        /// The time between updates of the binding. This property is one second by default.
        /// </summary>
        public TimeSpan Interval { get; set; } = TimeSpan.FromSeconds(1);

        /// <summary>
        /// The property that is bound to.
        /// </summary>
        public DependencyProperty Property { get; set; }

        /// <summary>
        /// Determines whether the property should be updated with the value on screen or the value
        /// on screen should be updated with the property.
        /// </summary>
        public BindingUpdateMode Mode { get; set; } = BindingUpdateMode.UpdateTarget;

        /// <inheritdoc />
        protected override void OnAttached()
        {
            Property.ThrowIfNull(nameof(Property));

            //Save a reference to the callback of the timer so this object will keep the timer alive but not vice versa.
            _timerCallback = s =>
            {
                try
                {
                    switch (Mode)
                    {
                        case BindingUpdateMode.UpdateTarget:
                            Dispatcher.Invoke(() => BindingOperations.GetBindingExpression(AssociatedObject, Property)?.UpdateTarget());
                            break;
                        case BindingUpdateMode.UpdateSource:
                            Dispatcher.Invoke(() => BindingOperations.GetBindingExpression(AssociatedObject, Property)?.UpdateSource());
                            break;
                    }
                }
                catch (TaskCanceledException) { }//This exception will be thrown when application is shutting down.
            };
            _timer = new WeakTimer(_timerCallback, null, Interval, Interval);

            base.OnAttached();
        }

        /// <inheritdoc />
        protected override void OnDetaching()
        {
            _timer.Dispose();
            _timerCallback = null;
            base.OnDetaching();
        }

        // Determines when the target/source of the property should be updated.
        WeakTimer _timer;

        // The method invoked to perform the update.
        TimerCallback _timerCallback;
    }

    /// <summary>
    /// Determines the direction of the data transfer.
    /// </summary>
    public enum BindingUpdateMode
    {
        /// <summary>
        /// Forces a data transfer from the binding source property to the binding target property.
        /// </summary>
        UpdateTarget,

        /// <summary>
        /// Forces a data transfer from the binding target property to the binding source property.
        /// </summary>
        UpdateSource
    }
}