using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Media;
using System.Windows.Threading;

namespace Main.Test;

public partial class StyledDataGrid
{
    private DispatcherTimer? imageResumeTimer;
    private bool draggingScrollThumb;

    private void InitializeImageLoadingPause()
    {
        imageResumeTimer = new DispatcherTimer(DispatcherPriority.Background, Dispatcher)
        {
            Interval = TimeSpan.FromMilliseconds(500)
        };
        imageResumeTimer.Tick += (_, _) =>
        {
            imageResumeTimer.Stop();
            if (!draggingScrollThumb && IsLoaded) SetImageLoadingSuspended(false);
        };
        AddHandler(Thumb.DragStartedEvent, new DragStartedEventHandler(ScrollThumbDragStarted), true);
        AddHandler(Thumb.DragCompletedEvent, new DragCompletedEventHandler(ScrollThumbDragCompleted), true);
        AddHandler(ScrollViewer.ScrollChangedEvent, new ScrollChangedEventHandler(ImageScrollChanged), true);
        Unloaded += (_, _) =>
        {
            imageResumeTimer.Stop(); draggingScrollThumb = false;
            SetImageLoadingSuspended(true);
        };
        Loaded += (_, _) => { ApplyImageLoadingOptions(); SetImageLoadingSuspended(false); };
        ApplyImageLoadingOptions();
    }

    private void SetImageLoadingSuspended(bool suspended)
    {
        SetValue(IsImageLoadingSuspendedPropertyKey, suspended);
        NetworkThumbnail.SetIsLoadingSuspended(this, suspended);
    }

    private void ApplyImageLoadingOptions()
    {
        NetworkThumbnail.SetCacheEnabled(this, EnableImageCache);
        if (imageResumeTimer == null) return;
        if (!PauseImageLoadingWhileDragging)
        {
            imageResumeTimer.Stop(); draggingScrollThumb = false; SetImageLoadingSuspended(false);
        }
    }

    private bool IsOwnScrollBar(DependencyObject? source)
    {
        var foundScrollBar = false;
        for (var parent = source; parent != null; parent = VisualTreeHelper.GetParent(parent))
        {
            if (parent is ScrollBar) foundScrollBar = true;
            if (parent is DataGrid) return ReferenceEquals(parent, this) && foundScrollBar;
        }
        return false;
    }

    private void ScrollThumbDragStarted(object sender, DragStartedEventArgs e)
    {
        if (!PauseImageLoadingWhileDragging || !IsOwnScrollBar(e.OriginalSource as DependencyObject)) return;
        draggingScrollThumb = true;
        imageResumeTimer!.Stop();
        // 继承到可见图片及随后回收生成的新行，立即取消请求并清空图片。
        SetImageLoadingSuspended(true);
    }

    private void ScrollThumbDragCompleted(object sender, DragCompletedEventArgs e)
    {
        if (!PauseImageLoadingWhileDragging || !IsOwnScrollBar(e.OriginalSource as DependencyObject)) return;
        draggingScrollThumb = false;
        RestartImageResumeTimer();
    }

    private void ImageScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        if (!NetworkThumbnail.GetIsLoadingSuspended(this) || draggingScrollThumb ||
            (e.VerticalChange == 0 && e.HorizontalChange == 0) ||
            !IsOwnScrollViewer(e.OriginalSource as DependencyObject)) return;
        RestartImageResumeTimer();
    }

    private bool IsOwnScrollViewer(DependencyObject? source)
    {
        for (var parent = source; parent != null; parent = VisualTreeHelper.GetParent(parent))
            if (parent is DataGrid) return ReferenceEquals(parent, this);
        return false;
    }

    private void RestartImageResumeTimer()
    {
        imageResumeTimer!.Stop();
        imageResumeTimer.Start();
    }
}