/** 小程序/访客：无需登录浏览图书 */
    @GetMapping("/browse")
    public ApiResponse<PageResult<Book>> browse(
            @RequestParam(required = false) String keyword,
            @RequestParam(required = false) String category,
            @RequestParam(defaultValue = "1") int page,
            @RequestParam(defaultValue = "10") int size) {
        return ApiResponse.ok(bookService.list(keyword, category, page, size));
    }

    /** 小程序/访客：无需登录查看图书详情 */
    @GetMapping("/{id}")
    public ApiResponse<Book> detail(@PathVariable Long id) {
        return ApiResponse.ok(bookService.getById(id));
    }

    @GetMapping("/categories/browse")
    public ApiResponse<List<String>> browseCategories() {
        return ApiResponse.ok(bookService.categories());
    }

    @GetMapping
    @RequireRole({UserRole.ADMIN, UserRole.USER})
    public ApiResponse<PageResult<Book>> list(
            @RequestParam(required = false) String keyword,
            @RequestParam(required = false) String category,
            @RequestParam(defaultValue = "1") int page,
            @RequestParam(defaultValue = "10") int size) {
        return ApiResponse.ok(bookService.list(keyword, category, page, size));
    }

    @GetMapping("/categories")
    @RequireRole({UserRole.ADMIN, UserRole.USER})
    public ApiResponse<List<String>> categories() {
        return ApiResponse.ok(bookService.categories());
    }

    @DeleteMapping("/batch")
    @RequireRole(UserRole.ADMIN)
    public ApiResponse<Void> batchDelete(@RequestBody List<Long> ids) {
        bookService.batchDelete(ids);
        return ApiResponse.ok("删除成功", null);
    }

    @PostMapping
    @RequireRole(UserRole.ADMIN)
    public ApiResponse<Book> create(@Valid @RequestBody BookDTO dto) {
        return ApiResponse.ok("添加成功", bookService.create(dto));
    }

    @PutMapping("/{id}")
    @RequireRole(UserRole.ADMIN)
    public ApiResponse<Book> update(@PathVariable Long id, @Valid @RequestBody BookDTO dto) {
        return ApiResponse.ok("更新成功", bookService.update(id, dto));
    }

    @DeleteMapping("/{id}")
    @RequireRole(UserRole.ADMIN)
    public ApiResponse<Void> delete(@PathVariable Long id) {
        bookService.delete(id);
        return ApiResponse.ok("删除成功", null);
    }

@Service
@RequiredArgsConstructor
public class BookService extends ServiceImpl<BookMapper, Book> {

    private final BorrowRecordMapper borrowRecordMapper;

    public PageResult<Book> list(String keyword, String category, int page, int size) {
        Page<Book> result = lambdaQuery()
                .and(StringUtils.hasText(keyword), w -> w
                        .like(Book::getTitle, keyword)
                        .or().like(Book::getAuthor, keyword)
                        .or().like(Book::getIsbn, keyword))
                .eq(StringUtils.hasText(category), Book::getCategory, category)
                .orderByDesc(Book::getId)
                .page(new Page<>(page, size));
        return PageResult.of(result);
    }

    public Book getById(Long id) {
        Book book = super.getById(id);
        if (book == null) {
            throw new RuntimeException("图书不存在，ID: " + id);
        }
        return book;
    }

    @Transactional
    public Book create(BookDTO dto) {
        if (lambdaQuery().eq(Book::getIsbn, dto.getIsbn()).exists()) {
            throw new RuntimeException("ISBN已存在: " + dto.getIsbn());
        }
        Book book = new Book();
        BeanUtils.copyProperties(dto, book);
        book.setAvailable_stock(dto.getTotal_stock());
        save(book);
        return book;
    }

    @Transactional
    public Book update(Long id, BookDTO dto) {
        Book book = getById(id);
        if (lambdaQuery().eq(Book::getIsbn, dto.getIsbn()).ne(Book::getId, id).exists()) {
            throw new RuntimeException("ISBN已被其他图书使用: " + dto.getIsbn());
        }
        int borrowed = book.getTotal_stock() - book.getAvailable_stock();
        if (dto.getTotal_stock() < borrowed) {
            throw new RuntimeException("总库存不能小于已借出数量(" + borrowed + ")");
        }
        BeanUtils.copyProperties(dto, book, "id", "available_stock", "created_at", "updated_at");
        book.setAvailable_stock(dto.getTotal_stock() - borrowed);
        updateById(book);
        return book;
    }

    @Transactional
    public void delete(Long id) {
        getById(id);
        boolean borrowing = borrowRecordMapper.exists(
                Wrappers.<BorrowRecord>lambdaQuery()
                        .eq(BorrowRecord::getBook_id, id)
                        .eq(BorrowRecord::getStatus, "BORROWED"));
        if (borrowing) {
            throw new RuntimeException("该图书存在未归还的借阅记录，无法删除");
        }
        removeById(id);
    }

    @Transactional
    public void batchDelete(List<Long> ids) {
        for (Long id : ids) {
            delete(id);
        }
    }

    public List<String> categories() {
        return lambdaQuery()
                .select(Book::getCategory)
                .isNotNull(Book::getCategory)
                .ne(Book::getCategory, "")
                .list()
                .stream()
                .map(Book::getCategory)
                .distinct()
                .sorted()
                .toList();
    }
}