using System;
using System.Collections.Generic;

using UnityEngine;

using Framework.Services;
using Framework.Support;

namespace Framework.Selection {

  /// <summary>Tracks the objects selected by the player</summary>
  /// <remarks>
  ///   <para>
  ///     Many genres have a need to store selections. A strategy game may have a set of
  ///     currently selected units to which commands are issued, while an action adventure
  ///     might mark an object as highlighted so the "use" button can perform an action on it,
  ///     without caring if the object was selected by touch, gaze or mouse hover.
  ///   </para>
  ///   <para>
  ///     The selection tracker is added to an actor and tracks which objects are currently
  ///     selected by it. The component is added to an individual actor so it can be looked
  ///     up by other components executing actions on behalf of that actor.
  ///   </para>
  ///   <para>
  ///     Highlighted objects are stored separately from selected objects in the expectation
  ///     that these are the only two channels of selections a typical game needs. Future
  ///     implementations may offer named sets to which items can be added or removed while
  ///     keeping the <see cref="SelectedObjects" /> and <see cref="HighlightedObjects" />
  ///     properties around for easy access.
  ///   </para>
  /// </remarks>
  public class SelectionTracker : ScriptComponent {

    /// <summary>Triggered when the CanSelect property changes its value</summary>
    public Action CanSelectChanged;
    /// <summary>Triggered when the CanHighlight property changes its value</summary>
    public Action CanHighlightChanged;

    /// <summary>Whether the actor is currently allowed to select objects</summary>
    public bool CanSelect = true;

    /// <summary>Whether the actor is currently allowed to highlight objects</summary>
    public bool CanHighlight = true;

#if false
    /// <summary>Whether the actor is currently allowed to select objects</summary>
    public bool CanSelect {
      get { return this.canSelect; }
      set {
        if (value != this.canSelect) {
          this.canSelect = value;
          OnCanSelectChanged();
        }
      }
    }

    /// <summary>Whether the actor is currently allowed to highlight objects</summary>
    public bool CanHighlight {
      get { return this.canHighlight; }
      set {
        if (value != this.canHighlight) {
          this.canHighlight = value;
          OnCanHighlightChanged();
        }
      }
    }
#endif

    /// <summary>Objects that are currently selected</summary>
    public ICollection<Selectable> SelectedObjects {
      get {
        if(this.selectedObjects == null) {
          this.selectedObjects = new ObservableCollection<Selectable>();
        }

        return this.selectedObjects;
      }
    }

    /// <summary>Objects that are currently highlighted</summary>
    public ICollection<Selectable> HighlightedObjects {
      get {
        if(this.highlightedObjects == null) {
          this.highlightedObjects = new ObservableCollection<Selectable>();
        }

        return this.highlightedObjects;
      }
    }

    /// <summary>Fires the <see cref="CanSelectChanged" /> event</summary>
    protected virtual void OnCanSelectChanged() {
      if (CanSelectChanged != null) {
        CanSelectChanged();
      }
    }

    /// <summary>Fires the <see cref="CanHighlightChanged" /> event</summary>
    protected virtual void OnCanHighlightChanged() {
      if (CanHighlightChanged != null) {
        CanHighlightChanged();
      }
    }

    /// <summary>Stores the currently selected objects</summary>
    private ObservableCollection<Selectable> selectedObjects;
    /// <summary>Stores the currently highlighted objects</summary>
    private ObservableCollection<Selectable> highlightedObjects;

#if false
    /// <summary>Whether the actor is currently allowed to select objects</summary>
    private bool canSelect = true;
    /// <summary>Whether the actor is currently allowed to highlight objects</summary>
    private bool canHighlight = true;
#endif

  }

} // namespace Framework.Selection