using System.Numerics;

namespace AcDream.App.UI;

/// <summary>
/// Lightweight, data-bound string list for plugin markup. It owns only row
/// selection and scroll position; the plugin binding remains the sole owner of
/// rows and selected index. This deliberately avoids exposing App widget types
/// through the BCL plugin contract.
/// </summary>
public sealed class UiMarkupList : UiElement
{
    public Func<IReadOnlyList<string>> ItemsSource { get; set; } =
        static () => Array.Empty<string>();
    public Func<IReadOnlyList<uint>> ItemColorsSource { get; set; } =
        static () => Array.Empty<uint>();
    public Func<int> SelectedIndexSource { get; set; } = static () => -1;
    public Action<int>? SelectionChanged { get; set; }
    public UiDatFont? DatFont { get; set; }
    public float RowHeight { get; set; } = 18f;
    public float Padding { get; set; } = 3f;
    public Vector4 BackgroundColor { get; set; } = new(0f, 0f, 0f, 0.92f);
    public Vector4 BorderColor { get; set; } = new(0.46f, 0.37f, 0.16f, 1f);
    public Vector4 TextColor { get; set; } = new(0.91f, 0.87f, 0.76f, 1f);
    public Vector4 SelectedColor { get; set; } = new(0.28f, 0.23f, 0.08f, 0.95f);

    private int _topRow;

    public override bool HandlesClick => true;

    protected override void OnDraw(UiRenderContext context)
    {
        IReadOnlyList<string> items = ItemsSource();
        IReadOnlyList<uint> itemColors = ItemColorsSource();
        int visibleRows = VisibleRows;
        int selected = SelectedIndexSource();
        if (selected >= 0 && selected < items.Count)
        {
            if (selected < _topRow)
                _topRow = selected;
            else if (selected >= _topRow + visibleRows)
                _topRow = selected - visibleRows + 1;
        }
        ClampTop(items.Count, visibleRows);

        context.DrawFill(0f, 0f, Width, Height, BackgroundColor);
        context.DrawRectOutline(0f, 0f, Width, Height, BorderColor, 1f);
        int end = Math.Min(items.Count, _topRow + visibleRows);
        for (int index = _topRow; index < end; index++)
        {
            float y = (index - _topRow) * RowHeight;
            if (index == selected)
                context.DrawFill(1f, y + 1f, Width - 2f, RowHeight - 1f, SelectedColor);
            string text = items[index];
            Vector4 textColor = index < itemColors.Count
                ? Rgb(itemColors[index])
                : TextColor;
            float textY = y + MathF.Max(0f,
                (RowHeight - (DatFont?.LineHeight ?? 14f)) * 0.5f);
            if (DatFont is { } font)
                context.DrawStringDat(font, text, Padding, textY, textColor, true);
            else
                context.DrawString(text, Padding, textY, textColor);
        }
    }

    public override bool OnEvent(in UiEvent e)
    {
        IReadOnlyList<string> items = ItemsSource();
        if (e.Type == UiEventType.Scroll)
        {
            _topRow -= Math.Sign(e.Data0);
            ClampTop(items.Count, VisibleRows);
            return true;
        }
        if (e.Type != UiEventType.MouseDown || !Enabled)
            return false;
        int row = (int)MathF.Floor(e.Data2 / MathF.Max(1f, RowHeight));
        int index = _topRow + row;
        if (row >= 0 && row < VisibleRows && index >= 0 && index < items.Count)
            SelectionChanged?.Invoke(index);
        return true;
    }

    private int VisibleRows => Math.Max(1, (int)MathF.Floor(
        Height / MathF.Max(1f, RowHeight)));

    private void ClampTop(int count, int visibleRows) =>
        _topRow = Math.Clamp(_topRow, 0, Math.Max(0, count - visibleRows));

    private static Vector4 Rgb(uint value) => new(
        ((value >> 16) & 0xFFu) / 255f,
        ((value >> 8) & 0xFFu) / 255f,
        (value & 0xFFu) / 255f,
        1f);
}