using AcDream.UI.Abstractions;

namespace AcDream.UI.ImGui;

/// <summary>
/// <see cref="IPanelHost"/> implementation for the ImGui backend. Owns the
/// registered panel set; iterates + draws every frame when the caller is
/// inside an ImGui frame (between <c>ImGui.NewFrame</c> and
/// <c>ImGui.Render</c>).
///
/// <para>
/// <b>This class does not call <c>ImGui.NewFrame</c> / <c>ImGui.Render</c>
/// itself.</b> Those belong to the caller (GameWindow) so GL-state
/// ownership is explicit and the render-loop integration point is obvious.
/// </para>
/// </summary>
public sealed class ImGuiPanelHost : IPanelHost
{
    private readonly Dictionary<string, IPanel> _panels = new();
    private readonly ImGuiPanelRenderer _renderer = new();

    /// <inheritdoc />
    public void Register(IPanel panel)
    {
        ArgumentNullException.ThrowIfNull(panel);
        _panels[panel.Id] = panel;   // idempotent by Id
    }

    /// <inheritdoc />
    public void Unregister(string panelId) => _panels.Remove(panelId);

    /// <inheritdoc />
    public void RenderAll(PanelContext ctx)
    {
        // Order-independent — ImGui windows stack in the order they're drawn
        // for focus purposes but we have <=1 panel in D.2a.
        foreach (var panel in _panels.Values)
        {
            if (!panel.IsVisible) continue;
            panel.Render(ctx, _renderer);
        }
    }

    /// <summary>Current registered count (for diagnostics).</summary>
    public int Count => _panels.Count;
}