Move queries into DataLayer

Source/DataLayer/QueryObjects/BookQueries.cs

@@ -35,5 +35,15 @@ namespace DataLayer
                 .Include(b => b.SeriesLink).ThenInclude(sb => sb.Series)
                 .Include(b => b.ContributorsLink).ThenInclude(c => c.Contributor)
                 .Include(b => b.Category).ThenInclude(c => c.ParentCategory);
+
+        public static bool IsProduct(this Book book)
+            => book.ContentType is not ContentType.Episode and not ContentType.Parent;
+
+        public static bool IsEpisodeChild(this Book book)
+            => book.ContentType is ContentType.Episode;
+
+        public static bool IsEpisodeParent(this Book book)
+            => book.ContentType is ContentType.Parent;
+
     }
 }

Source/DataLayer/QueryObjects/LibraryBookQueries.cs

@@ -41,5 +41,23 @@ namespace DataLayer
                 .Include(le => le.Book).ThenInclude(b => b.SeriesLink).ThenInclude(sb => sb.Series)
                 .Include(le => le.Book).ThenInclude(b => b.ContributorsLink).ThenInclude(c => c.Contributor)
                 .Include(le => le.Book).ThenInclude(b => b.Category).ThenInclude(c => c.ParentCategory);
+
+#nullable enable
+        public static LibraryBook? FindSeriesParent(this IEnumerable<LibraryBook> libraryBooks, LibraryBook seriesEpisode)
+        {
+            if (seriesEpisode.Book.SeriesLink is null) return null;
+
+            //Parent books will always have exactly 1 SeriesBook due to how
+            //they are imported in ApiExtended.getChildEpisodesAsync()
+            return libraryBooks.FirstOrDefault(
+                lb =>
+                lb.Book.IsEpisodeParent() &&
+                seriesEpisode.Book.SeriesLink.Any(
+                    s => s.Series.AudibleSeriesId == lb.Book.SeriesLink.Single().Series.AudibleSeriesId));
+        }
+#nullable disable
+
+        public static IEnumerable<LibraryBook> FindChildren(this IEnumerable<LibraryBook> bookList, LibraryBook parent)
+            => bookList.Where(lb => lb.Book.SeriesLink?.Any(s => s.Series.AudibleSeriesId == parent.Book.AudibleProductId) == true).ToList();
     }
 }