using System.Globalization;

using Avalonia;
using Avalonia.Automation;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Layout;
using Avalonia.Media;

// Avalonia's Button, not Android.Widget's. .NET for Android puts Android.Widget in this project's
// implicit usings, so the bare name is ambiguous — the same collision the namespace itself causes
// for Android.App. See the note at the top of MainActivity.
using Application = Avalonia.Application;
using Button = Avalonia.Controls.Button;

namespace DodoSSH.Client.Android.Views;

/// <summary>
/// One destination in the bottom bar.
/// </summary>
/// <remarks>
/// <para>
/// Written in C# rather than as a XAML control because it is a button with an icon, a label and a rule about
/// the indicator, and a templated control for that would be more machinery than the thing it draws.
/// </para>
/// <para>
/// ◆ <b>The indicator is a pill behind the icon, where it was a bar along the top edge.</b> The bar was put at
/// the top because the bottom of the screen is under the system's gesture bar, and an indicator drawn there is
/// one nobody sees; the pill answers the same worry from the other side, by sitting in the middle of the
/// control rather than at either edge. It is the shape Android's own navigation bar has drawn since Material 3
/// and the one the 2026-10-04 redesign asks for. The rule the bar existed to keep is kept: the current entry is
/// still told apart three ways — the filled pill, the accent colour and the heavier label — because colour
/// alone at this size is the one signal a user with a colour deficiency would be left with.
/// </para>
/// <para>
/// ◆ <b>An icon from the embedded Material font rather than a Unicode glyph.</b> The glyphs (▤ ⌗ ⚙) came from
/// whichever symbol font the phone had, at whatever weight it drew them, and ⚙ meant both this tab and the
/// Preferences row under it (audit M7). The icon font is the one the desktop's rail uses.
/// </para>
/// <para>
/// <b>A count, when there is one.</b> Connections carries the number of open sessions in a green badge, which
/// was otherwise only said by the strip of shells above the bar. Zero draws nothing: a "0" is a number about
/// nothing, and the badge being absent already says it.
/// </para>
/// <para>
/// <b>It has a name.</b> Its content is a panel, and Avalonia's automation peer reported that panel's type name
/// to TalkBack — "Avalonia.Controls.Panel", three times across the bar (audit H4). The label is the name.
/// </para>
/// <para>
/// Every colour here is resolved from <c>Theme/Palette.axaml</c> rather than written out. A nav bar that
/// named its own blues is exactly how the fourth place a colour appears ends up one shade off — which is the
/// argument the desktop head's <c>Ellipse.dot</c> style makes for being a style rather than a converter.
/// </para>
/// </remarks>
internal sealed class NavButton : Button
{
    public static readonly StyledProperty<string> LabelProperty =
        AvaloniaProperty.Register<NavButton, string>(nameof(Label), string.Empty);

    /// <summary>The icon drawn above the label: one codepoint of the embedded Material Icons font.</summary>
    public static readonly StyledProperty<string> GlyphProperty =
        AvaloniaProperty.Register<NavButton, string>(nameof(Glyph), string.Empty);

    public static readonly StyledProperty<bool> IsCurrentProperty =
        AvaloniaProperty.Register<NavButton, bool>(nameof(IsCurrent));

    /// <summary>A count drawn over the icon, or zero for none.</summary>
    public static readonly StyledProperty<int> CountProperty =
        AvaloniaProperty.Register<NavButton, int>(nameof(Count));

    private readonly Border pill;
    private readonly TextBlock glyph;
    private readonly TextBlock text;
    private readonly Border badge;
    private readonly TextBlock badgeText;

    // Resolved from the palette once the control is in the tree; see Repaint.
    private IBrush? currentBrush;
    private IBrush? currentIconBrush;
    private IBrush? idleBrush;
    private IBrush? pillBrush;

    public NavButton()
    {
        Background = Brushes.Transparent;
        BorderThickness = new Thickness(0);
        CornerRadius = new CornerRadius(0);
        Padding = new Thickness(0);
        HorizontalAlignment = HorizontalAlignment.Stretch;
        VerticalAlignment = VerticalAlignment.Stretch;
        HorizontalContentAlignment = HorizontalAlignment.Stretch;
        VerticalContentAlignment = VerticalAlignment.Stretch;

        glyph = new TextBlock
        {
            FontSize = 21,
            HorizontalAlignment = HorizontalAlignment.Center,
            VerticalAlignment = VerticalAlignment.Center,
        };
        AutomationProperties.SetAccessibilityView(glyph, AccessibilityView.Raw);

        (badge, badgeText) = MakeBadge();

        pill = new Border
        {
            Width = 64,
            Height = 32,
            CornerRadius = new CornerRadius(16),
            HorizontalAlignment = HorizontalAlignment.Center,
            Background = Brushes.Transparent,
            Child = glyph,
        };

        text = new TextBlock
        {
            FontSize = 12,
            FontWeight = FontWeight.Medium,
            HorizontalAlignment = HorizontalAlignment.Center,
        };

        Content = new StackPanel
        {
            Spacing = 4,
            HorizontalAlignment = HorizontalAlignment.Center,
            VerticalAlignment = VerticalAlignment.Center,
            Children = { new Panel { Children = { pill, badge } }, text },
        };
    }

    /// <summary>The count's badge, over the pill's top-right corner.</summary>
    /// <remarks>
    /// Over the corner rather than beside the label, so it reads as belonging to the icon and costs the
    /// label no width.
    /// </remarks>
    private static (Border Badge, TextBlock Text) MakeBadge()
    {
        var count = new TextBlock
        {
            FontSize = 10.5,
            FontWeight = FontWeight.Bold,
            HorizontalAlignment = HorizontalAlignment.Center,
            VerticalAlignment = VerticalAlignment.Center,
        };

        var holder = new Border
        {
            MinWidth = 18,
            Height = 18,
            CornerRadius = new CornerRadius(9),
            Padding = new Thickness(5, 0),
            HorizontalAlignment = HorizontalAlignment.Right,
            VerticalAlignment = VerticalAlignment.Top,
            Margin = new Thickness(0, -4, 8, 0),
            IsVisible = false,
            Child = count,
        };

        return (holder, count);
    }

    public string Label
    {
        get => GetValue(LabelProperty);
        set => SetValue(LabelProperty, value);
    }

    /// <inheritdoc cref="GlyphProperty" />
    public string Glyph
    {
        get => GetValue(GlyphProperty);
        set => SetValue(GlyphProperty, value);
    }

    /// <summary>Whether this is the destination currently showing.</summary>
    public bool IsCurrent
    {
        get => GetValue(IsCurrentProperty);
        set => SetValue(IsCurrentProperty, value);
    }

    /// <inheritdoc cref="CountProperty" />
    public int Count
    {
        get => GetValue(CountProperty);
        set => SetValue(CountProperty, value);
    }

    /// <inheritdoc />
    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
    {
        base.OnPropertyChanged(change);

        if (change.Property == LabelProperty)
        {
            text.Text = Label;
            AutomationProperties.SetName(this, Label);
        }
        else if (change.Property == GlyphProperty)
        {
            glyph.Text = Glyph;
        }
        else if (change.Property == IsCurrentProperty)
        {
            Repaint();
        }
        else if (change.Property == CountProperty)
        {
            badge.IsVisible = Count > 0;
            badgeText.Text = Count.ToString(CultureInfo.InvariantCulture);
        }
    }

    /// <inheritdoc />
    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
    {
        base.OnApplyTemplate(e);

        // Resolved here rather than in the constructor: application resources are not reachable while the
        // control is still being constructed, and a hard-coded stack would drift from Palette.axaml.
        if (Application.Current?.FindResource("IconFont") is FontFamily icons)
        {
            glyph.FontFamily = icons;
        }

        currentBrush = Application.Current?.FindResource("Text") as IBrush;
        currentIconBrush = Application.Current?.FindResource("AccentText") as IBrush;
        idleBrush = Application.Current?.FindResource("TextFaint") as IBrush;
        pillBrush = Application.Current?.FindResource("AccentSoft") as IBrush;
        badge.Background = Application.Current?.FindResource("Live") as IBrush;
        badgeText.Foreground = Application.Current?.FindResource("Canvas") as IBrush;

        // IsCurrent is normally bound and so has usually already been set by the time the template applies,
        // which is why this runs again here rather than only on the property change.
        Repaint();
    }

    private void Repaint()
    {
        // The pill, the colour and the weight together. See the remark on the type.
        var paint = IsCurrent ? currentBrush : idleBrush;
        var iconPaint = IsCurrent ? currentIconBrush : idleBrush;

        if (paint is not null)
        {
            text.Foreground = paint;
        }

        if (iconPaint is not null)
        {
            glyph.Foreground = iconPaint;
        }

        text.FontWeight = IsCurrent ? FontWeight.Bold : FontWeight.Medium;
        pill.Background = IsCurrent && pillBrush is not null ? pillBrush : Brushes.Transparent;
    }
}