feat(auth): Implement database-backed user authentication and

persistence

This commit introduces a major architectural change by replacing the
previous hardcoded user and data system with a robust, database-driven
approach. It lays the foundation for persistent data storage for all
application models.

Key Changes:

- **Database Integration:** - Added `GORM` and `SQLite` for the database
layer. - The database is now initialized and migrated on application
startup. - Configuration is managed through environment variables
(`DATABASE`, `USERS_FILE`).

- **User Authentication & Management:** - The login endpoint
(`/api/token`) now authenticates users against the database. - JWT
claims are now populated with real user data (`id`, `username`,
`is_superuser`). - Implemented a system to seed the database with
initial users from a `users.json` file.

- **New User API Endpoints:** - `GET /api/users`: Retrieves a list of
all users (superuser access required). - `GET /api/users/user`: Fetches
the data for the currently authenticated user based on their JWT.

- **Data Model Overhaul:** - Refactored all data models (`User`,
`Category`, `Operation`, `Subcategory`) to include GORM tags,
relationships, and a `BaseModel` with auto-generated UUIDs for primary
keys. - Separated user-related structs into `User` (database model),
`AuthRequest` (login payload), and `UserResponse` (safe API response).

- **Middleware & Routing:** - Improved JWT error handling for clearer
client-side messages. - Added a new middleware to allow passing the JWT
in the request body for more flexible client integration.

backend/database/db.go

@@ -0,0 +1,46 @@
+package database
+
+import (
+	"backend/model"
+	"os"
+
+	"github.com/glebarez/sqlite"
+	"github.com/gofiber/fiber/v2/log"
+	"gorm.io/gorm"
+)
+
+var Db *gorm.DB
+
+func Init() error {
+	if os.Getenv("DATABASE") == "" {
+		log.Fatal("Error no DATABASE path or url")
+	}
+	var err error
+	Db, err = gorm.Open(sqlite.Open(os.Getenv("DATABASE")), &gorm.Config{})
+	if err != nil {
+		log.Error("Failed to connect database")
+		return err
+	}
+	return nil
+}
+
+func Migrate() {
+	Db.AutoMigrate(
+		&model.User{},
+		&model.Category{},
+		&model.Subcategory{},
+		&model.Operation{},
+	)
+}
+
+func InitDatabase() {
+	Init()
+	Migrate()
+
+	if os.Getenv("USERS_FILE") != "" {
+		allusers := GetUsersFromFile(os.Getenv("USERS_FILE"))
+		for i := range allusers {
+			CreateUser(&allusers[i])
+		}
+	}
+}

backend/database/users.go

@@ -0,0 +1,85 @@
+package database
+
+import (
+	"backend/model"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"gorm.io/gorm"
+)
+
+func CreateUser(user *model.User) error {
+	e := Db.Where(model.User{
+		Username: user.Username,
+	}).FirstOrCreate(&user).Error
+	if e != nil {
+		return e
+	}
+	return nil
+}
+
+func GetUserById(id string) (*model.User, error) {
+	var user model.User
+	e := Db.First(&user, "id = ?", id).Error
+	if e != nil {
+		if errors.Is(e, gorm.ErrRecordNotFound) {
+			return nil, fmt.Errorf("user not found")
+		}
+		return nil, e
+	}
+	return &user, nil
+}
+
+func GetUserByUsername(username string) (*model.User, error) {
+	var user model.User
+	e := Db.First(&user, "username = ?", username).Error
+	if e != nil {
+		if errors.Is(e, gorm.ErrRecordNotFound) {
+			return nil, fmt.Errorf("user not found")
+		}
+		return nil, e
+	}
+	return &user, nil
+}
+
+func DeleteUser(id string) error {
+	var user model.User
+	e := Db.First(&user, "id = ?", id).Error
+	if e != nil {
+		if errors.Is(e, gorm.ErrRecordNotFound) {
+			return fmt.Errorf("user not found")
+		}
+		return e
+	}
+	e = Db.Unscoped().Delete(&user).Error
+	if e != nil {
+		if errors.Is(e, gorm.ErrRecordNotFound) {
+			return fmt.Errorf("user not found")
+		}
+		return e
+	}
+	return nil
+}
+
+func GetUsersFromFile(filename string) []model.User {
+	data, e := os.ReadFile(filename)
+	if e != nil {
+		panic(e)
+	}
+	decoder := json.NewDecoder(strings.NewReader(string(data)))
+	var res []model.User
+	decoder.Decode(&res)
+	return res
+}
+
+func GetAllUsers() ([]model.User, error) {
+	var users []model.User
+	e := Db.Find(&users).Error
+	if e != nil {
+		return nil, e
+	}
+	return users, nil
+}