// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence. // See the LICENCE file in the repository root for full licence text. #nullable disable using System; using System.Collections.Generic; using System.Linq; namespace osu.Game.Screens.Select.Carousel { /// <summary> /// A group which ensures at least one child is selected (if the group itself is selected). /// </summary> public class CarouselGroupEagerSelect : CarouselGroup { public CarouselGroupEagerSelect() { State.ValueChanged += state => { if (state.NewValue == CarouselItemState.Selected) attemptSelection(); }; } /// <summary> /// The last selected item. /// </summary> protected CarouselItem LastSelected { get; private set; } /// <summary> /// We need to keep track of the index for cases where the selection is removed but we want to select a new item based on its old location. /// </summary> private int lastSelectedIndex; /// <summary> /// To avoid overhead during filter operations, we don't attempt any selections until after all /// children have been filtered. This bool will be true during the base <see cref="Filter(FilterCriteria)"/> /// operation. /// </summary> private bool filteringChildren; public override void Filter(FilterCriteria criteria) { filteringChildren = true; base.Filter(criteria); filteringChildren = false; attemptSelection(); } public override void RemoveChild(CarouselItem i) { base.RemoveChild(i); if (i != LastSelected) updateSelectedIndex(); } private bool addingChildren; public void AddChildren(IEnumerable<CarouselItem> items) { addingChildren = true; foreach (var i in items) AddChild(i); addingChildren = false; attemptSelection(); } public override void AddChild(CarouselItem i) { base.AddChild(i); if (!addingChildren) attemptSelection(); } protected override void ChildItemStateChanged(CarouselItem item, CarouselItemState value) { base.ChildItemStateChanged(item, value); switch (value) { case CarouselItemState.Selected: updateSelected(item); break; case CarouselItemState.NotSelected: case CarouselItemState.Collapsed: attemptSelection(); break; } } private void attemptSelection() { if (filteringChildren) return; // we only perform eager selection if we are a currently selected group. if (State.Value != CarouselItemState.Selected) return; // we only perform eager selection if none of our children are in a selected state already. if (Children.Any(i => i.State.Value == CarouselItemState.Selected)) return; PerformSelection(); } protected virtual CarouselItem GetNextToSelect() { return Children.Skip(lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value) ?? Children.Reverse().Skip(InternalChildren.Count - lastSelectedIndex).FirstOrDefault(i => !i.Filtered.Value); } protected virtual void PerformSelection() { CarouselItem nextToSelect = GetNextToSelect(); if (nextToSelect != null) nextToSelect.State.Value = CarouselItemState.Selected; else updateSelected(null); } private void updateSelected(CarouselItem newSelection) { if (newSelection != null) LastSelected = newSelection; updateSelectedIndex(); } private void updateSelectedIndex() => lastSelectedIndex = LastSelected == null ? 0 : Math.Max(0, InternalChildren.IndexOf(LastSelected)); } }