using Annulus;
using Azimuth;

namespace Glass.Testbed
{
    /// <summary>
    /// A ScrollingPanel: children laid out in a content region taller than the panel, with the panel showing a
    /// scrolled-and-clipped window onto it.  The buttons drive it through ScrollBy, and the mouse wheel through its
    /// StepAmount.
    /// </summary>
    public class ScrollingPanelTestCase : TestCase
    {
        private static readonly Material[] RowPalette =
        {
            UiPacksheetMaterials.RedFlatPanel,
            UiPacksheetMaterials.YellowFlatPanel,
            UiPacksheetMaterials.BlueFlatPanel,
        };

        public ScrollingPanelTestCase(string name) : base(name) { }

        /// <summary>
        /// The height that fits a row label inside every palette material, so the rows stay uniform whichever
        /// material each one wears.
        /// </summary>
        private static Scalar RowHeightFor(Scalar width)
        {
            TextMaterial label = Widgets.ButtonLabel("Row 0");
            Constraints offer = Constraints.TightWidth(width, Scalar.PositiveInfinity);

            Vector returnMe = Vector.Zero;

            foreach (Material rowMaterial in RowPalette)
            {
                returnMe = Vector.Max(returnMe, Material.SolveBoundsFor(rowMaterial, label, offer));
            }

            return returnMe.Y;
        }

        private static Button BuildScrollButton(
            StringView caption, Vector labelSize, ScrollingPanel scroller, Scalar deltaY)
        {
            Button button = Widgets.ButtonLabel(caption)
                .BuildControl(Constraints.Tight(labelSize))
                .WrapIn(UiPacksheetMaterials.YellowButton);

            button.OnClick += delegate (in MouseState _, MouseButtonFlags __)
            {
                scroller.ScrollBy(new Vector(0, deltaY));
            };

            return button;
        }

        // The row is consumed a column at a time, so it has to be the caller's rect rather than a copy of it.
        private void AddToRow(ref Rect row, Button button)
        {
            Rect slot = row.NewCol(button.Bounds.Width, margin: Margin);
            button.Bounds = button.Bounds.WithPosition(slot.TopLeft);
            Add(button);
        }

        protected override void Populate()
        {
            var viewportSize = new Vector(240, 190);
            const int rowCount = 16;

            AddCaption("A list too tall for its panel — the panel clips and scrolls a window onto it");
            AddCaption("Scroll up / down shift the content; rows past the edge are clipped, not laid out short");
            AddCaption("The mouse wheel scrolls the panel too, a quarter of its height per notch");

            Rect stage = ContentAggregator.NewRow(viewportSize.Y);

            var scroller = NewChild<ScrollingPanel>("scroller");
            scroller.Material = UiPacksheetMaterials.GreenFlatPanel;
            scroller.Bounds = stage.NewCol(viewportSize.X);

            Scalar rowHeight = RowHeightFor(scroller.ViewportRect.Width);

            var content = new RectAggregator(
                Rect.FromPositionAndSize(Vector.Zero, new Vector(scroller.ViewportRect.Width, 0)),
                new Vector(0, Margin));

            for (int index = 0; index < rowCount; ++index)
            {
                Rect rowSlot = content.NewRow(rowHeight);

                var row = scroller.CanvasChildren.NewChild<Panel>($"row {index}");
                row.Material = RowPalette[index % RowPalette.Length];
                row.Bounds = rowSlot;

                Panel label = Widgets.ButtonLabel($"Row {index}").BuildControl(Constraints.Unbounded);
                label.Bounds = Rect.FromPositionAndSize(
                    Control.CenteredIn(row.CanvasRect.Size, label.Bounds.Size), label.Bounds.Size);
                row.CanvasChildren.Add(label);
            }

            scroller.ContentSize = content.Rect.Size;

            // Both buttons share the wider label's size, so the pair reads as a set.
            Vector labelSize = Vector.Max(
                Widgets.ButtonLabel("Scroll up").PreferredSize(Constraints.Unbounded),
                Widgets.ButtonLabel("Scroll down").PreferredSize(Constraints.Unbounded));

            Scalar step = (rowHeight + Margin) * 3;

            Button scrollUp = BuildScrollButton("Scroll up", labelSize, scroller, -step);
            Button scrollDown = BuildScrollButton("Scroll down", labelSize, scroller, step);

            Rect buttonRow = ContentAggregator.NewRow(scrollUp.Bounds.Height);
            AddToRow(ref buttonRow, scrollUp);
            AddToRow(ref buttonRow, scrollDown);
        }
    }
}