namespace AcDream.UI.Abstractions;

/// <summary>
/// Owns the set of live <see cref="IPanel"/>s and drives per-frame draw
/// dispatch. The backend (Hexa.NET.ImGui in D.2a, custom in D.2b) implements
/// this; <c>GameWindow</c> creates one at startup and registers panels.
///
/// <para>
/// <b>Does not</b> call <c>ImGui.NewFrame</c> / <c>ImGui.Render</c> — those
/// belong to the caller so GL-state ownership is unambiguous. Caller pattern:
/// </para>
///
/// <code>
/// // per frame, render thread
/// inputBridge.BeginFrame(size, dt);
/// ImGui.NewFrame();
/// panelHost.RenderAll(ctx);
/// ImGui.Render();
/// ImGuiImplOpenGL3.RenderDrawData(ImGui.GetDrawData());
/// </code>
/// </summary>
public interface IPanelHost
{
    /// <summary>Register a panel for per-frame rendering. Idempotent by <see cref="IPanel.Id"/>.</summary>
    void Register(IPanel panel);

    /// <summary>Remove the panel with the matching id. No-op if not present.</summary>
    void Unregister(string panelId);

    /// <summary>
    /// Iterate every visible panel and call <see cref="IPanel.Render"/>. Call
    /// order within a frame is the registration order; panels with
    /// <see cref="IPanel.IsVisible"/> set to <c>false</c> are skipped entirely.
    /// </summary>
    void RenderAll(PanelContext ctx);
}