using System;
using System.Collections.Generic;

namespace AcDream.App.UI;

/// <summary>
/// A container of item cells (port of retail UIElement_ItemList, class 0x10000031).
/// Behavioral LEAF: it creates/owns its UiItemSlot children procedurally, so the
/// LayoutImporter must NOT build dat children. The toolbar uses single-cell
/// instances (one slot); the inventory phase will grow this to an N-cell grid.
/// </summary>
public sealed class UiItemList : UiElement
{
    private readonly List<UiItemSlot> _cells = new();

    public UiItemList(Func<uint, (uint tex, int w, int h)>? spriteResolve = null)
    {
        SpriteResolve = spriteResolve;
        // Single-cell default: every toolbar slot always shows one cell (empty or filled).
        AddItem(new UiItemSlot { SpriteResolve = spriteResolve });
    }

    public override bool ConsumesDatChildren => true;

    public Func<uint, (uint tex, int w, int h)>? SpriteResolve { get; set; }

    /// <summary>Convenience for single-cell slots (the toolbar): the first cell.
    /// Valid only while the list has at least one cell; after <see cref="Flush"/>
    /// (the inventory-phase rebuild path) the list is empty until <see cref="AddItem"/>
    /// runs, so use <see cref="GetItem"/> there instead.</summary>
    /// <exception cref="InvalidOperationException">the list has no cells (e.g. after Flush).</exception>
    public UiItemSlot Cell => _cells.Count > 0
        ? _cells[0]
        : throw new InvalidOperationException("UiItemList has no cells; call AddItem first or use GetItem(index).");

    public int GetNumUIItems() => _cells.Count;

    public UiItemSlot? GetItem(int index)
        => index >= 0 && index < _cells.Count ? _cells[index] : null;

    public void AddItem(UiItemSlot cell)
    {
        cell.SpriteResolve ??= SpriteResolve;
        cell.Left = 0; cell.Top = 0; cell.Width = Width; cell.Height = Height;
        _cells.Add(cell);
        AddChild(cell);
    }

    public void Flush()
    {
        foreach (var c in _cells) RemoveChild(c);
        _cells.Clear();
    }

    protected override void OnDraw(UiRenderContext ctx)
    {
        // The factory sets THIS list's Width/Height AFTER construction, so the cell
        // (added in the ctor) starts 0x0. For the single-cell toolbar slot, keep the
        // cell sized to the list each frame; the cell paints itself in the children
        // pass that follows. (N-cell grid layout is the inventory phase.)
        if (_cells.Count > 0)
        {
            var cell = _cells[0];
            cell.Left = 0; cell.Top = 0; cell.Width = Width; cell.Height = Height;
        }
    }
}