Split code into modules

This is a massive commit that restructures the code into modules:

db/
    All functions related to modifying the Database

types/
    All type definitions and methods that can be exclusivly used on
    these types without dependencies

policy/
    All Policy related code, now without dependencies on the Database.

policy/matcher/
    Dedicated code to match machines in a list of FilterRules

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/db/users.go

@@ -0,0 +1,194 @@
+package db
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/juanfont/headscale/hscontrol/types"
+	"github.com/juanfont/headscale/hscontrol/util"
+	"github.com/rs/zerolog/log"
+	"gorm.io/gorm"
+	"tailscale.com/tailcfg"
+)
+
+var (
+	ErrUserExists        = errors.New("user already exists")
+	ErrUserNotFound      = errors.New("user not found")
+	ErrUserStillHasNodes = errors.New("user not empty: node(s) found")
+)
+
+// CreateUser creates a new User. Returns error if could not be created
+// or another user already exists.
+func (hsdb *HSDatabase) CreateUser(name string) (*types.User, error) {
+	err := util.CheckForFQDNRules(name)
+	if err != nil {
+		return nil, err
+	}
+	user := types.User{}
+	if err := hsdb.db.Where("name = ?", name).First(&user).Error; err == nil {
+		return nil, ErrUserExists
+	}
+	user.Name = name
+	if err := hsdb.db.Create(&user).Error; err != nil {
+		log.Error().
+			Str("func", "CreateUser").
+			Err(err).
+			Msg("Could not create row")
+
+		return nil, err
+	}
+
+	return &user, nil
+}
+
+// DestroyUser destroys a User. Returns error if the User does
+// not exist or if there are machines associated with it.
+func (hsdb *HSDatabase) DestroyUser(name string) error {
+	user, err := hsdb.GetUser(name)
+	if err != nil {
+		return ErrUserNotFound
+	}
+
+	machines, err := hsdb.ListMachinesByUser(name)
+	if err != nil {
+		return err
+	}
+	if len(machines) > 0 {
+		return ErrUserStillHasNodes
+	}
+
+	keys, err := hsdb.ListPreAuthKeys(name)
+	if err != nil {
+		return err
+	}
+	for _, key := range keys {
+		err = hsdb.DestroyPreAuthKey(key)
+		if err != nil {
+			return err
+		}
+	}
+
+	if result := hsdb.db.Unscoped().Delete(&user); result.Error != nil {
+		return result.Error
+	}
+
+	return nil
+}
+
+// RenameUser renames a User. Returns error if the User does
+// not exist or if another User exists with the new name.
+func (hsdb *HSDatabase) RenameUser(oldName, newName string) error {
+	var err error
+	oldUser, err := hsdb.GetUser(oldName)
+	if err != nil {
+		return err
+	}
+	err = util.CheckForFQDNRules(newName)
+	if err != nil {
+		return err
+	}
+	_, err = hsdb.GetUser(newName)
+	if err == nil {
+		return ErrUserExists
+	}
+	if !errors.Is(err, ErrUserNotFound) {
+		return err
+	}
+
+	oldUser.Name = newName
+
+	if result := hsdb.db.Save(&oldUser); result.Error != nil {
+		return result.Error
+	}
+
+	return nil
+}
+
+// GetUser fetches a user by name.
+func (hsdb *HSDatabase) GetUser(name string) (*types.User, error) {
+	user := types.User{}
+	if result := hsdb.db.First(&user, "name = ?", name); errors.Is(
+		result.Error,
+		gorm.ErrRecordNotFound,
+	) {
+		return nil, ErrUserNotFound
+	}
+
+	return &user, nil
+}
+
+// ListUsers gets all the existing users.
+func (hsdb *HSDatabase) ListUsers() ([]types.User, error) {
+	users := []types.User{}
+	if err := hsdb.db.Find(&users).Error; err != nil {
+		return nil, err
+	}
+
+	return users, nil
+}
+
+// ListMachinesByUser gets all the nodes in a given user.
+func (hsdb *HSDatabase) ListMachinesByUser(name string) (types.Machines, error) {
+	err := util.CheckForFQDNRules(name)
+	if err != nil {
+		return nil, err
+	}
+	user, err := hsdb.GetUser(name)
+	if err != nil {
+		return nil, err
+	}
+
+	machines := types.Machines{}
+	if err := hsdb.db.Preload("AuthKey").Preload("AuthKey.User").Preload("User").Where(&types.Machine{UserID: user.ID}).Find(&machines).Error; err != nil {
+		return nil, err
+	}
+
+	return machines, nil
+}
+
+// SetMachineUser assigns a Machine to a user.
+func (hsdb *HSDatabase) SetMachineUser(machine *types.Machine, username string) error {
+	err := util.CheckForFQDNRules(username)
+	if err != nil {
+		return err
+	}
+	user, err := hsdb.GetUser(username)
+	if err != nil {
+		return err
+	}
+	machine.User = *user
+	if result := hsdb.db.Save(&machine); result.Error != nil {
+		return result.Error
+	}
+
+	return nil
+}
+
+func (hsdb *HSDatabase) GetMapResponseUserProfiles(
+	machine types.Machine,
+	peers types.Machines,
+) []tailcfg.UserProfile {
+	userMap := make(map[string]types.User)
+	userMap[machine.User.Name] = machine.User
+	for _, peer := range peers {
+		userMap[peer.User.Name] = peer.User // not worth checking if already is there
+	}
+
+	profiles := []tailcfg.UserProfile{}
+	for _, user := range userMap {
+		displayName := user.Name
+
+		if hsdb.baseDomain != "" {
+			displayName = fmt.Sprintf("%s@%s", user.Name, hsdb.baseDomain)
+		}
+
+		profiles = append(profiles,
+			tailcfg.UserProfile{
+				ID:          tailcfg.UserID(user.ID),
+				LoginName:   user.Name,
+				DisplayName: displayName,
+			})
+	}
+
+	return profiles
+}