Add initial project structure with core functionality for book and stationery uploads

- Created main application entry point in `main.go`.
- Added configuration management in `config/config.go` and tests in `config/config_test.go`.
- Implemented handlers for book and stationery uploads in `handlers/book.go` and `handlers/stationery.go`, including validation logic.
- Established database connection and services in `services/database.go` and `services/book_service.go`.
- Defined models for books and stationery in `models/book.go` and `models/stationery.go`.
- Set up Firebase integration for image uploads in `services/firebase.go`.
- Created migration scripts for database schema in `migrations/001_create_tables.sql` and subsequent updates.
- Added CORS and error handling middleware.
- Included comprehensive tests for handlers, services, and utilities.
- Documented API endpoints and usage in `README.md` and migration instructions in `migrations/README.md`.
- Introduced `.gitignore` to exclude unnecessary files and directories.
- Added Go module support with `go.mod` and `go.sum` files.
- Implemented utility functions for slug generation and validation in `utils/slug.go` and `utils/validation.go`.

services/book_service.go

@@ -0,0 +1,151 @@
+package services
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
+	"jd-book-uploader/models"
+	"jd-book-uploader/utils"
+)
+
+// CreateBook creates a new book record in the database
+func CreateBook(ctx context.Context, req *models.BookCreateRequest) (*models.Book, error) {
+	if DB == nil {
+		return nil, fmt.Errorf("database connection not initialized")
+	}
+
+	// Generate UUID for book_code
+	bookCode := uuid.New().String()
+
+	// Generate slug from book name
+	slug := utils.GenerateSlug(req.BookName)
+
+	// Set default discount if not provided
+	discount := req.Discount
+	if discount < 0 {
+		discount = 0
+	}
+
+	now := time.Now()
+
+	// Insert book into database
+	query := `
+		INSERT INTO books (
+			book_code, book_name, cost, price, discount, quantity,
+			publisher_author, category, description, image_url, slug,
+			created_at, updated_at
+		) VALUES (
+			$1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13
+		) RETURNING 
+			book_code, book_name, cost, price, discount, quantity,
+			publisher_author, category, description, image_url, slug,
+			created_at, updated_at
+	`
+
+	var book models.Book
+	err := DB.QueryRow(ctx, query,
+		bookCode,
+		req.BookName,
+		req.Cost,
+		req.Price,
+		discount,
+		req.Quantity,
+		req.PublisherAuthor,
+		req.Category,
+		req.Description,
+		req.ImageURL,
+		slug,
+		now,
+		now,
+	).Scan(
+		&book.BookCode,
+		&book.BookName,
+		&book.Cost,
+		&book.Price,
+		&book.Discount,
+		&book.Quantity,
+		&book.PublisherAuthor,
+		&book.Category,
+		&book.Description,
+		&book.ImageURL,
+		&book.Slug,
+		&book.CreatedAt,
+		&book.UpdatedAt,
+	)
+
+	if err != nil {
+		// Check for duplicate key error
+		var pgErr *pgconn.PgError
+		if errors.As(err, &pgErr) {
+			if pgErr.Code == "23505" { // unique_violation
+				return nil, fmt.Errorf("book with this code already exists")
+			}
+		}
+		return nil, fmt.Errorf("failed to create book: %w", err)
+	}
+
+	return &book, nil
+}
+
+// GetBookByCode retrieves a book by its code
+func GetBookByCode(ctx context.Context, bookCode string) (*models.Book, error) {
+	if DB == nil {
+		return nil, fmt.Errorf("database connection not initialized")
+	}
+
+	query := `
+		SELECT 
+			book_code, book_name, cost, price, discount, quantity,
+			publisher_author, category, description, image_url, slug,
+			created_at, updated_at
+		FROM books
+		WHERE book_code = $1
+	`
+
+	var book models.Book
+	err := DB.QueryRow(ctx, query, bookCode).Scan(
+		&book.BookCode,
+		&book.BookName,
+		&book.Cost,
+		&book.Price,
+		&book.Discount,
+		&book.Quantity,
+		&book.PublisherAuthor,
+		&book.Category,
+		&book.Description,
+		&book.ImageURL,
+		&book.Slug,
+		&book.CreatedAt,
+		&book.UpdatedAt,
+	)
+
+	if err != nil {
+		if err == pgx.ErrNoRows {
+			return nil, fmt.Errorf("book not found")
+		}
+		return nil, fmt.Errorf("failed to get book: %w", err)
+	}
+
+	return &book, nil
+}
+
+// BookSlugExists checks if a slug already exists in the books table
+func BookSlugExists(ctx context.Context, slug string) (bool, error) {
+	if DB == nil {
+		return false, fmt.Errorf("database connection not initialized")
+	}
+
+	query := `SELECT EXISTS(SELECT 1 FROM books WHERE slug = $1)`
+	var exists bool
+	err := DB.QueryRow(ctx, query, slug).Scan(&exists)
+	if err != nil {
+		return false, fmt.Errorf("failed to check slug existence: %w", err)
+	}
+
+	return exists, nil
+}