Refactor: support multiple users under the same account (#170)

* feature: add User entity to Account

* test: new file store creation test

* test: add FileStore persist-restore tests

* test: add GetOrCreateAccountByUser Accountmanager test

* refactor: rename account manager users file

* refactor: use userId instead of accountId when handling Management HTTP API

* fix: new account creation for every request

* fix: golint

* chore: add account creator to Account Entity to identify who created the account.

* chore: use xid ID generator for account IDs

* fix: test failures

* test: check that CreatedBy is stored when account is stored

* chore: add account copy method

* test: remove test for non existent GetOrCreateAccount func

* chore: add accounts conversion function

* fix: golint

* refactor: simplify admin user creation

* refactor: move migration script to a separate package

management/server/user.go

@@ -0,0 +1,71 @@
+package server
+
+import (
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+const (
+	UserRoleAdmin UserRole = "admin"
+	UserRoleUser  UserRole = "user"
+)
+
+// UserRole is the role of the User
+type UserRole string
+
+// User represents a user of the system
+type User struct {
+	Id   string
+	Role UserRole
+}
+
+func (u *User) Copy() *User {
+	return &User{
+		Id:   u.Id,
+		Role: u.Role,
+	}
+}
+
+// NewUser creates a new user
+func NewUser(id string, role UserRole) *User {
+	return &User{
+		Id:   id,
+		Role: role,
+	}
+}
+
+// NewAdminUser creates a new user with role UserRoleAdmin
+func NewAdminUser(id string) *User {
+	return NewUser(id, UserRoleAdmin)
+}
+
+// GetOrCreateAccountByUser returns an existing account for a given user id or creates a new one if doesn't exist
+func (am *AccountManager) GetOrCreateAccountByUser(userId string) (*Account, error) {
+	am.mux.Lock()
+	defer am.mux.Unlock()
+
+	account, err := am.Store.GetUserAccount(userId)
+	if err != nil {
+		if s, ok := status.FromError(err); ok && s.Code() == codes.NotFound {
+			account, _ = newAccount(userId)
+			account.Users[userId] = NewAdminUser(userId)
+			err = am.Store.SaveAccount(account)
+			if err != nil {
+				return nil, status.Errorf(codes.Internal, "failed creating account")
+			}
+		} else {
+			// other error
+			return nil, err
+		}
+	}
+
+	return account, nil
+}
+
+// GetAccountByUser returns an existing account for a given user id, NotFound if account couldn't be found
+func (am *AccountManager) GetAccountByUser(userId string) (*Account, error) {
+	am.mux.Lock()
+	defer am.mux.Unlock()
+
+	return am.Store.GetUserAccount(userId)
+}