MenuViewComponentBase{T}.cs

/*==============================================================================================================================
| Author        Ignia, LLC
| Client        Ignia, LLC
| Project       Topics Library
\=============================================================================================================================*/
using OnTopic.AspNetCore.Mvc.Controllers;
using OnTopic.AspNetCore.Mvc.Models;
using OnTopic.Mapping.Hierarchical;
using OnTopic.Models;

namespace OnTopic.AspNetCore.Mvc.Components {

  /*============================================================================================================================
  | CLASS: MENU VIEW COMPONENT
  \---------------------------------------------------------------------------------------------------------------------------*/
  /// <summary>
  ///   Defines a <see cref="ViewComponent"/> which provides access to a menu of <typeparamref name="T"/> instances.
  /// </summary>
  /// <remarks>
  ///   <para>
  ///     As a best practice, global data required by the layout view are requested independent of the current page. This allows
  ///     each layout element to be provided with its own layout data, in the form of a <see cref="NavigationViewModel{T}"/>s,
  ///     instead of needing to add this data to every view model returned by e.g. a <see cref="TopicController"/>.
  ///   </para>
  ///   <para>
  ///     In order to remain view model agnostic, the <see cref="NavigationViewModel{T}"/> does not assume that a particular
  ///     view model will be used, and instead accepts a generic argument for any view model that implements the interface <see
  ///     cref="IHierarchicalTopicViewModel{T}"/>. Since generic view components cannot be effectively routed to, however, that
  ///     means implementors must, at minimum, provide a local instance of <see cref="NavigationViewModel{T}"/>, which sets the
  ///     generic value to the desired view model. To help enforce this, while avoiding ambiguity, this class is marked as
  ///     <c>abstract</c> and suffixed with <c>Base</c>.
  ///   </para>
  ///   <para>
  ///     While the <see cref="MenuViewComponentBase{T}"/> only requires that the <typeparamref name="T"/> implement <see cref="
  ///     IHierarchicalTopicViewModel{T}"/>, views will require additional properties. These can be determined on a per-case
  ///     basis, as required by the implementation. Implementaters, however, should consider implementing the <see cref="
  ///     INavigationTopicViewModel{T}"/> interface, which provides the standard properties that most views will likely need, as
  ///     well as a <see cref="INavigationTopicViewModel{T}.IsSelected(String)"/> method for determining if the navigation item
  ///     is currently selected.
  ///   </para>
  /// </remarks>
  public abstract class MenuViewComponentBase<T> :
    NavigationTopicViewComponentBase<T> where T : class, IHierarchicalTopicViewModel<T>, new()
  {

    /*==========================================================================================================================
    | CONSTRUCTOR
    \-------------------------------------------------------------------------------------------------------------------------*/
    /// <summary>
    ///   Initializes a new instance of a <see cref="MenuViewComponentBase{T}"/> with necessary dependencies.
    /// </summary>
    protected MenuViewComponentBase(
      ITopicRepository topicRepository,
      IHierarchicalTopicMappingService<T> hierarchicalTopicMappingService
    ) : base(
      topicRepository,
      hierarchicalTopicMappingService
    ) {
    }

    /*==========================================================================================================================
    | METHOD: GET NAVIGATION ROOT
    \-------------------------------------------------------------------------------------------------------------------------*/
    /// <inheritdoc />
    /// <summary>
    ///   Retrieves the root <see cref="Topic"/> from which to map the <typeparamref name="T"/> objects.
    /// </summary>
    /// <remarks>
    ///   The navigation root in the case of the main menu is the namespace; i.e., the first topic underneath the root.
    /// </remarks>
    protected Topic? GetNavigationRoot() {

      /*------------------------------------------------------------------------------------------------------------------------
      | Validate dependencies
      \-----------------------------------------------------------------------------------------------------------------------*/
      Contract.Assume(CurrentTopic, nameof(CurrentTopic));

      /*------------------------------------------------------------------------------------------------------------------------
      | Identify navigation root
      \-----------------------------------------------------------------------------------------------------------------------*/
      var                       navigationRootTopic             = (Topic?)null;
      var                       configuredRoot                  = CurrentTopic.Attributes.GetValue("NavigationRoot", true);

      if (!String.IsNullOrEmpty(configuredRoot)) {
        navigationRootTopic = TopicRepository.Load("Root:" + configuredRoot, CurrentTopic);
      }
      if (navigationRootTopic is null) {
        navigationRootTopic = HierarchicalTopicMappingService.GetHierarchicalRoot(CurrentTopic, 2, "Web");
      }

      /*------------------------------------------------------------------------------------------------------------------------
      | Return root
      \-----------------------------------------------------------------------------------------------------------------------*/
      return navigationRootTopic;

    }

    /*==========================================================================================================================
    | METHOD: MAP NAVIGATION TOPIC VIEW MODELS
    \-------------------------------------------------------------------------------------------------------------------------*/
    /// <summary>
    ///   Maps a list of <typeparamref name="T"/> instances based on the <paramref name="navigationRootTopic"/>.
    /// </summary>
    protected async Task<T?> MapNavigationTopicViewModels(Topic? navigationRootTopic) =>
      await HierarchicalTopicMappingService.GetRootViewModelAsync(
        navigationRootTopic!,
        3,
        t => t is not { ContentType: "List" } and not { Parent: { ContentType: "PageGroup" } }
      ).ConfigureAwait(false);

    /*==========================================================================================================================
    | METHOD: INVOKE (ASYNC)
    \-------------------------------------------------------------------------------------------------------------------------*/
    /// <summary>
    ///   Provides the global menu for the site layout, which exposes the top two tiers of navigation.
    /// </summary>
    public async Task<IViewComponentResult> InvokeAsync() {

      /*------------------------------------------------------------------------------------------------------------------------
      | Retrieve root topic
      \-----------------------------------------------------------------------------------------------------------------------*/
      var navigationRootTopic = GetNavigationRoot();

      /*------------------------------------------------------------------------------------------------------------------------
      | Construct view model
      \-----------------------------------------------------------------------------------------------------------------------*/
      var navigationViewModel = new NavigationViewModel<T>() {
        NavigationRoot = await MapNavigationTopicViewModels(navigationRootTopic).ConfigureAwait(true),
        CurrentWebPath = CurrentTopic?.GetWebPath()?? HttpContext.Request.Path
      };

      /*------------------------------------------------------------------------------------------------------------------------
      | Return the corresponding view
      \-----------------------------------------------------------------------------------------------------------------------*/
      return View(navigationViewModel);

    }

  } //Class
} //Namespace