feat: add user service layer with business logic

- Create services/user_service.go with user creation and verification
- Add input validation for username, email, and password
- Implement duplicate user checking and password hashing
- Add comprehensive error handling and logging

services/user_service.go

@@ -0,0 +1,73 @@
+package services
+
+import (
+	"errors"
+	"log"
+	"strings"
+
+	"github.com/rideaware/rideaware-api/models"
+	"gorm.io/gorm"
+)
+
+type UserService struct {
+	db *gorm.DB
+}
+
+func NewUserService(db *gorm.DB) *UserService {
+	return &UserService{db: db}
+}
+
+func (s *UserService) CreateUser(username, email, password string) (*models.User, error) {
+	if username == "" || email == "" || password == "" {
+		return nil, errors.New("username, email, and password are required")
+	}
+
+	if len(username) < 3 || len(password) < 8 {
+		return nil, errors.New("username must be at least 3 characters and password must be at least 8 characters")
+	}
+
+	// Basic email validation
+	if !strings.Contains(email, "@") {
+		return nil, errors.New("invalid email format")
+	}
+
+	// Check if user exists (by username or email)
+	var existingUser models.User
+	if err := s.db.Where("username = ? OR email = ?", username, email).First(&existingUser).Error; err == nil {
+		return nil, errors.New("user with this username or email already exists")
+	}
+
+	// Create new user
+	user := models.User{
+		Username: username,
+		Email:    email,
+	}
+	if err := user.SetPassword(password); err != nil {
+		log.Printf("Error hashing password: %v", err)
+		return nil, errors.New("could not create user")
+	}
+
+	if err := s.db.Create(&user).Error; err != nil {
+		log.Printf("Error creating user: %v", err)
+		return nil, errors.New("could not create user")
+	}
+
+	return &user, nil
+}
+
+func (s *UserService) VerifyUser(username, password string) (*models.User, error) {
+	var user models.User
+	// Allow login with either username or email
+	if err := s.db.Where("username = ? OR email = ?", username, username).First(&user).Error; err != nil {
+		log.Printf("User not found: %s", username)
+		return nil, errors.New("invalid username or password")
+	}
+
+	if !user.CheckPassword(password) {
+		log.Printf("Invalid password for user: %s", username)
+		return nil, errors.New("invalid username or password")
+	}
+
+	log.Printf("User verified: %s", username)
+	return &user, nil
+}