add: book categories and filter

Backend/Features/Books/BookController.cs

@@ -16,9 +16,9 @@ namespace Backend.Features.Books
 
         [HttpGet]
         [Authorize]
-        public async Task<ActionResult<IEnumerable<BookDto>>> GetBooks()
+        public async Task<ActionResult<IEnumerable<BookDto>>> GetBooks([FromQuery] int? categoryId = null)
         {
-            var books = await _bookService.GetAllBooksAsync();
+            var books = await _bookService.GetAllBooksAsync(categoryId);
             return Ok(books);
         }
 

Backend/Features/Books/BookService.cs

@@ -5,7 +5,7 @@ namespace Backend.Features.Books
 {
     public interface IBookService
     {
-        Task<IEnumerable<BookDto>> GetAllBooksAsync();
+        Task<IEnumerable<BookDto>> GetAllBooksAsync(int? categoryId = null);
         Task<BookDto?> GetBookByIdAsync(int id);
         Task<BookDto> CreateBookAsync(BookCreateRequest request);
         Task<BookDto?> UpdateBookAsync(int id, BookUpdateRequest request);
@@ -21,17 +21,26 @@ namespace Backend.Features.Books
             _context = context;
         }
 
-        public async Task<IEnumerable<BookDto>> GetAllBooksAsync()
+        public async Task<IEnumerable<BookDto>> GetAllBooksAsync(int? categoryId = null)
         {
-            return await _context.Books
-                .Where(b => b.IsActive)
-                .Select(b => MapToDto(b))
-                .ToListAsync();
+            var query = _context.Books
+                .Include(b => b.Categories)
+                .Where(b => b.IsActive);
+
+            if (categoryId.HasValue)
+            {
+                query = query.Where(b => b.Categories.Any(c => c.Id == categoryId.Value));
+            }
+
+            var books = await query.ToListAsync();
+            return books.Select(b => MapToDto(b));
         }
 
         public async Task<BookDto?> GetBookByIdAsync(int id)
         {
-            var book = await _context.Books.FindAsync(id);
+            var book = await _context.Books
+                .Include(b => b.Categories)
+                .FirstOrDefaultAsync(b => b.Id == id);
             if (book == null || !book.IsActive) return null;
             return MapToDto(book);
         }
@@ -56,6 +65,16 @@ namespace Backend.Features.Books
                 CreatedAt = DateTime.UtcNow
             };
 
+            // Attach selected categories
+            if (request.CategoryIds != null && request.CategoryIds.Any())
+            {
+                var categories = await _context.Categories
+                    .Where(c => request.CategoryIds.Contains(c.Id))
+                    .ToListAsync();
+                foreach (var cat in categories)
+                    book.Categories.Add(cat);
+            }
+
             _context.Books.Add(book);
             await _context.SaveChangesAsync();
 
@@ -64,7 +83,9 @@ namespace Backend.Features.Books
 
         public async Task<BookDto?> UpdateBookAsync(int id, BookUpdateRequest request)
         {
-            var book = await _context.Books.FindAsync(id);
+            var book = await _context.Books
+                .Include(b => b.Categories)
+                .FirstOrDefaultAsync(b => b.Id == id);
             if (book == null || !book.IsActive) return null;
 
             book.Title = request.Title;
@@ -81,6 +102,17 @@ namespace Backend.Features.Books
             
             book.UpdatedAt = DateTime.UtcNow;
 
+            // Sync categories: replace existing with new selection
+            book.Categories.Clear();
+            if (request.CategoryIds != null && request.CategoryIds.Any())
+            {
+                var categories = await _context.Categories
+                    .Where(c => request.CategoryIds.Contains(c.Id))
+                    .ToListAsync();
+                foreach (var cat in categories)
+                    book.Categories.Add(cat);
+            }
+
             await _context.SaveChangesAsync();
             return MapToDto(book);
         }
@@ -111,7 +143,8 @@ namespace Backend.Features.Books
                 TotalCopies = book.TotalCopies,
                 AvailableCopies = book.AvailableCopies,
                 CreatedAt = book.CreatedAt,
-                UpdatedAt = book.UpdatedAt
+                UpdatedAt = book.UpdatedAt,
+                Categories = book.Categories.Select(c => new BookCategoryDto { Id = c.Id, Name = c.Name }).ToList()
             };
         }
     }
@@ -129,6 +162,13 @@ namespace Backend.Features.Books
         public int AvailableCopies { get; set; }
         public DateTime CreatedAt { get; set; }
         public DateTime? UpdatedAt { get; set; }
+        public List<BookCategoryDto> Categories { get; set; } = new();
+    }
+
+    public class BookCategoryDto
+    {
+        public int Id { get; set; }
+        public string Name { get; set; } = string.Empty;
     }
 
     public class BookCreateRequest
@@ -138,6 +178,7 @@ namespace Backend.Features.Books
         public string Author { get; set; } = string.Empty;
         public string? Description { get; set; }
         public int TotalCopies { get; set; }
+        public List<int>? CategoryIds { get; set; }
     }
 
     public class BookUpdateRequest
@@ -146,5 +187,6 @@ namespace Backend.Features.Books
         public string Author { get; set; } = string.Empty;
         public string? Description { get; set; }
         public int TotalCopies { get; set; }
+        public List<int>? CategoryIds { get; set; }
     }
 }

Backend/Features/Categories/CategoryController.cs

@@ -22,6 +22,13 @@ namespace Backend.Features.Categories
             return Ok(categories);
         }
 
+        [HttpGet("with-books")]
+        public async Task<ActionResult<IEnumerable<CategoryDto>>> GetCategoriesWithBooks()
+        {
+            var categories = await _categoryService.GetCategoriesWithBooksAsync();
+            return Ok(categories);
+        }
+
         [HttpPost]
         //[Authorize(Roles = "Librarian")]
         public async Task<ActionResult<CategoryDto>> CreateCategory([FromBody] CategoryCreateRequest request)

Backend/Features/Categories/CategoryService.cs

@@ -6,6 +6,7 @@ namespace Backend.Features.Categories
     public interface ICategoryService
     {
         Task<IEnumerable<CategoryDto>> GetAllCategoriesAsync();
+        Task<IEnumerable<CategoryDto>> GetCategoriesWithBooksAsync();
         Task<CategoryDto> CreateCategoryAsync(CategoryCreateRequest request);
         Task<bool> DeleteCategoryAsync(int id);
     }
@@ -26,6 +27,15 @@ namespace Backend.Features.Categories
                 .ToListAsync();
         }
 
+        public async Task<IEnumerable<CategoryDto>> GetCategoriesWithBooksAsync()
+        {
+            // Only return categories that have at least one active book in BookCategories
+            return await _context.Categories
+                .Where(c => c.Books.Any(b => b.IsActive))
+                .Select(c => new CategoryDto { Id = c.Id, Name = c.Name })
+                .ToListAsync();
+        }
+
         public async Task<CategoryDto> CreateCategoryAsync(CategoryCreateRequest request)
         {
             if (await _context.Categories.AnyAsync(c => c.Name == request.Name))

Frontend/Controllers/BooksController.cs

@@ -13,10 +13,10 @@ namespace Frontend.Controllers
             _apiClient = apiClient;
         }
 
-        public async Task<IActionResult> Index(int page = 1)
+        public async Task<IActionResult> Index(int page = 1, int? categoryId = null)
         {
             const int pageSize = 8;
-            var allBooks = await _apiClient.GetBooksAsync() ?? Enumerable.Empty<BookDto>();
+            var allBooks = await _apiClient.GetBooksAsync(categoryId) ?? Enumerable.Empty<BookDto>();
             var totalCount = allBooks.Count();
             var totalPages = (int)Math.Ceiling(totalCount / (double)pageSize);
             page = Math.Max(1, Math.Min(page, Math.Max(1, totalPages)));
@@ -30,6 +30,9 @@ namespace Frontend.Controllers
                 PageSize = pageSize
             };
 
+            ViewBag.Categories = await _apiClient.GetCategoriesWithBooksAsync();
+            ViewBag.SelectedCategoryId = categoryId;
+
             return View(pagedResult);
         }
 
@@ -80,7 +83,8 @@ namespace Frontend.Controllers
                 Title = book.Title, 
                 Author = book.Author, 
                 Description = book.Description,
-                TotalCopies = book.TotalCopies
+                TotalCopies = book.TotalCopies,
+                CategoryIds = book.Categories.Select(c => c.Id).ToList()
             });
         }
 

Frontend/Models/Dtos/LibraryDtos.cs

@@ -41,6 +41,13 @@ namespace Frontend.Models.Dtos
         public int AvailableCopies { get; set; }
         public DateTime CreatedAt { get; set; }
         public DateTime? UpdatedAt { get; set; }
+        public List<BookCategoryDto> Categories { get; set; } = new();
+    }
+
+    public class BookCategoryDto
+    {
+        public int Id { get; set; }
+        public string Name { get; set; } = string.Empty;
     }
 
     public class BookCreateRequest
@@ -50,6 +57,7 @@ namespace Frontend.Models.Dtos
         public string Author { get; set; } = string.Empty;
         public string? Description { get; set; }
         public int TotalCopies { get; set; }
+        public List<int>? CategoryIds { get; set; }
     }
 
     public class BookUpdateRequest
@@ -58,6 +66,7 @@ namespace Frontend.Models.Dtos
         public string Author { get; set; } = string.Empty;
         public string? Description { get; set; }
         public int TotalCopies { get; set; }
+        public List<int>? CategoryIds { get; set; }
     }
 
     // Borrowing DTOs

Frontend/Services/LibraryApiClient.cs

@@ -54,9 +54,10 @@ namespace Frontend.Services
         #endregion
 
         #region Books
-        public async Task<IEnumerable<BookDto>> GetBooksAsync()
+        public async Task<IEnumerable<BookDto>> GetBooksAsync(int? categoryId = null)
         {
-            return await _httpClient.GetFromJsonAsync<IEnumerable<BookDto>>("api/books") ?? Enumerable.Empty<BookDto>();
+            var url = categoryId.HasValue ? $"api/books?categoryId={categoryId}" : "api/books";
+            return await _httpClient.GetFromJsonAsync<IEnumerable<BookDto>>(url) ?? Enumerable.Empty<BookDto>();
         }
 
         public async Task<BookDto?> GetBookAsync(int id)
@@ -113,6 +114,11 @@ namespace Frontend.Services
             return await _httpClient.GetFromJsonAsync<IEnumerable<CategoryDto>>("api/categories") ?? Enumerable.Empty<CategoryDto>();
         }
 
+        public async Task<IEnumerable<CategoryDto>> GetCategoriesWithBooksAsync()
+        {
+            return await _httpClient.GetFromJsonAsync<IEnumerable<CategoryDto>>("api/categories/with-books") ?? Enumerable.Empty<CategoryDto>();
+        }
+
         public async Task<CategoryDto?> CreateCategoryAsync(CategoryCreateRequest request)
         {
             var response = await _httpClient.PostAsJsonAsync("api/categories", request);

Frontend/Views/Books/Create.cshtml

@@ -67,6 +67,31 @@
                             <span asp-validation-for="Description" class="mt-1 text-xs text-rose-500"></span>
                         </div>
                     </div>
+
+                    <!-- Categories -->
+                    <div class="sm:col-span-2">
+                        <label class="block text-sm font-medium text-slate-700 mb-2">Categories</label>
+                        @{
+                            var allCategories = ViewBag.Categories as IEnumerable<Frontend.Models.Dtos.CategoryDto>;
+                        }
+                        @if (allCategories != null && allCategories.Any())
+                        {
+                            <div class="grid grid-cols-2 sm:grid-cols-3 gap-2">
+                                @foreach (var cat in allCategories)
+                                {
+                                    <label class="flex items-center gap-2 px-3 py-2 rounded-md border border-slate-200 bg-slate-50 hover:bg-slate-100 cursor-pointer text-sm text-slate-700 transition-colors">
+                                        <input type="checkbox" name="CategoryIds" value="@cat.Id"
+                                               class="h-4 w-4 rounded border-slate-300 text-slate-900 focus:ring-slate-900" />
+                                        @cat.Name
+                                    </label>
+                                }
+                            </div>
+                        }
+                        else
+                        {
+                            <p class="text-sm text-slate-400 italic">No categories available. Add some first.</p>
+                        }
+                    </div>
                 </div>
 
                 <div class="pt-5 border-t border-slate-100 flex justify-end gap-3">

Frontend/Views/Books/Edit.cshtml

@@ -58,6 +58,33 @@
                             <span asp-validation-for="Description" class="mt-1 text-xs text-rose-500"></span>
                         </div>
                     </div>
+
+                    <!-- Categories -->
+                    <div class="sm:col-span-2">
+                        <label class="block text-sm font-medium text-slate-700 mb-2">Categories</label>
+                        @{
+                            var allCategories = ViewBag.Categories as IEnumerable<Frontend.Models.Dtos.CategoryDto>;
+                            var selectedIds = Model.CategoryIds ?? new List<int>();
+                        }
+                        @if (allCategories != null && allCategories.Any())
+                        {
+                            <div class="grid grid-cols-2 sm:grid-cols-3 gap-2">
+                                @foreach (var cat in allCategories)
+                                {
+                                    <label class="flex items-center gap-2 px-3 py-2 rounded-md border border-slate-200 bg-slate-50 hover:bg-slate-100 cursor-pointer text-sm text-slate-700 transition-colors">
+                                        <input type="checkbox" name="CategoryIds" value="@cat.Id"
+                                               class="h-4 w-4 rounded border-slate-300 text-slate-900 focus:ring-slate-900"
+                                               @(selectedIds.Contains(cat.Id) ? "checked" : "") />
+                                        @cat.Name
+                                    </label>
+                                }
+                            </div>
+                        }
+                        else
+                        {
+                            <p class="text-sm text-slate-400 italic">No categories available. Add some first.</p>
+                        }
+                    </div>
                 </div>
 
                 <div class="pt-5 border-t border-slate-100 flex justify-end gap-3">

Frontend/Views/Books/Index.cshtml

@@ -22,7 +22,7 @@
     }
 </div>
 
-<div class="grid grid-cols-1 md:grid-cols-4 gap-4 mb-10">
+<div class="grid grid-cols-1 md:grid-cols-4 gap-4 mb-6">
     <div class="md:col-span-3">
         <div class="relative">
             <div class="absolute inset-y-0 left-0 pl-3 flex items-center pointer-events-none">
@@ -35,6 +35,30 @@
     </div>
 </div>
 
+@* Category Filter Pills *@
+@{
+    var categories = ViewBag.Categories as IEnumerable<Frontend.Models.Dtos.CategoryDto> ?? Enumerable.Empty<Frontend.Models.Dtos.CategoryDto>();
+    int? selectedCategoryId = ViewBag.SelectedCategoryId;
+}
+@if (categories.Any())
+{
+    <div class="flex flex-wrap items-center gap-2 mb-8">
+        <span class="text-xs font-semibold text-slate-400 uppercase tracking-wider mr-1">Filter:</span>
+        <a asp-action="Index" asp-route-page="1"
+           class="inline-flex items-center px-3 py-1 rounded-full text-xs font-semibold border transition-colors @(selectedCategoryId == null ? "bg-slate-900 text-white border-slate-900" : "bg-white text-slate-600 border-slate-200 hover:border-slate-400 hover:text-slate-900")">
+            All
+        </a>
+        @foreach (var cat in categories)
+        {
+            <a asp-action="Index" asp-route-page="1" asp-route-categoryId="@cat.Id"
+               class="inline-flex items-center px-3 py-1 rounded-full text-xs font-semibold border transition-colors @(selectedCategoryId == cat.Id ? "bg-slate-900 text-white border-slate-900" : "bg-white text-slate-600 border-slate-200 hover:border-slate-400 hover:text-slate-900")">
+                @cat.Name
+            </a>
+        }
+    </div>
+}
+
+
 <!-- Book Grid -->
 <div class="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 xl:grid-cols-4 gap-8">
     @foreach (var book in Model.Items)
@@ -62,7 +86,19 @@
                         <p class="text-xs text-slate-500 mt-0.5 truncate">@book.Author</p>
                     </div>
                 </div>
-                <div class="mt-4 flex items-center justify-between">
+                @if (book.Categories.Any())
+                {
+                    <div class="mt-2 flex flex-wrap gap-1">
+                        @foreach (var cat in book.Categories)
+                        {
+                            <a asp-action="Index" asp-route-page="1" asp-route-categoryId="@cat.Id"
+                               class="inline-flex items-center rounded-full bg-amber-50 border border-amber-200 px-2 py-0.5 text-[9px] font-semibold text-amber-700 hover:bg-amber-100 transition-colors">
+                                @cat.Name
+                            </a>
+                        }
+                    </div>
+                }
+                <div class="mt-3 flex items-center justify-between">
                     <span class="inline-flex items-center rounded-full bg-slate-100 px-2 py-0.5 text-[10px] font-medium text-slate-600">@book.Status</span>
                     <span class="text-[10px] font-medium @(book.AvailableCopies > 0 ? "text-emerald-600" : "text-rose-600")">
                         @book.AvailableCopies / @book.TotalCopies
@@ -96,7 +132,7 @@
             @* Previous *@
             @if (Model.HasPreviousPage)
             {
-                <a asp-action="Index" asp-route-page="@(Model.CurrentPage - 1)"
+                <a asp-action="Index" asp-route-page="@(Model.CurrentPage - 1)" asp-route-categoryId="@selectedCategoryId"
                    class="inline-flex items-center px-3 py-1.5 rounded-md border border-slate-200 text-sm font-medium text-slate-600 hover:bg-slate-50 hover:text-slate-900 transition-colors">
                     <svg class="w-4 h-4 mr-1" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                         <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7" />
@@ -123,7 +159,7 @@
                 }
                 else if (p == 1 || p == Model.TotalPages || (p >= Model.CurrentPage - 2 && p <= Model.CurrentPage + 2))
                 {
-                    <a asp-action="Index" asp-route-page="@p"
+                    <a asp-action="Index" asp-route-page="@p" asp-route-categoryId="@selectedCategoryId"
                        class="inline-flex items-center justify-center w-8 h-8 rounded-md border border-slate-200 text-sm font-medium text-slate-600 hover:bg-slate-50 hover:text-slate-900 transition-colors">@p</a>
                 }
                 else if (p == Model.CurrentPage - 3 || p == Model.CurrentPage + 3)
@@ -135,7 +171,7 @@
             @* Next *@
             @if (Model.HasNextPage)
             {
-                <a asp-action="Index" asp-route-page="@(Model.CurrentPage + 1)"
+                <a asp-action="Index" asp-route-page="@(Model.CurrentPage + 1)" asp-route-categoryId="@selectedCategoryId"
                    class="inline-flex items-center px-3 py-1.5 rounded-md border border-slate-200 text-sm font-medium text-slate-600 hover:bg-slate-50 hover:text-slate-900 transition-colors">
                     Next
                     <svg class="w-4 h-4 ml-1" fill="none" stroke="currentColor" viewBox="0 0 24 24">