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// SqlGdbc (SQL Go database connection) is a wrapper for SQL database handler ( can be *sql.DB or *sql.Tx)
// It should be able to work with all SQL data that follows SQL standard.
type SqlGdbc interface {
	Exec(query string, args ...interface{}) (sql.Result, error)
	Prepare(query string) (*sql.Stmt, error)
	Query(query string, args ...interface{}) (*sql.Rows, error)
	QueryRow(query string, args ...interface{}) *sql.Row
	// If need transaction support, add this interface
	Transactioner
}

// SqlDBTx is the concrete implementation of sqlGdbc by using *sql.DB
type SqlDBTx struct {
	DB *sql.DB
}

// SqlConnTx is the concrete implementation of sqlGdbc by using *sql.Tx
type SqlConnTx struct {
	DB *sql.Tx
}

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// Transactioner is the transaction interface for database handler
// It should only be applicable to SQL database
type Transactioner interface {
	// Rollback a transaction
	Rollback() error
	// Commit a transaction
	Commit() error
	// TxEnd commits a transaction if no errors, otherwise rollback
	// txFunc is the operations wrapped in a transaction
	TxEnd(txFunc func() error) error
	// TxBegin gets *sql.DB from receiver and return a SqlGdbc, which has a *sql.Tx
	TxBegin() (SqlGdbc, error)
}

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// TransactionBegin starts a transaction
func (sdt *SqlDBTx) TxBegin() (gdbc.SqlGdbc, error) {
	tx, err := sdt.DB.Begin()
	sct := SqlConnTx{tx}
	return &sct, err
}

func (sct *SqlConnTx) TxEnd(txFunc func() error) error {
	var err error
	tx := sct.DB

	defer func() {
		if p := recover(); p != nil {
			tx.Rollback()
			panic(p) // re-throw panic after Rollback
		} else if err != nil {
			tx.Rollback() // err is non-nil; don't change it
		} else {
			err = tx.Commit() // if Commit returns error update err with commit err
		}
	}()
	err = txFunc()
	return err
}

func (sct *SqlConnTx) Rollback() error {
	return sct.DB.Rollback()
}

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type RegistrationUseCaseInterface interface {
...
	// ModifyAndUnregister change user information and then unregister the user based on the User.Id passed in.
	// It is created to illustrate transaction, no real use.
	ModifyAndUnregister(user *model.User) error
	// ModifyAndUnregisterWithTx change user information and then unregister the user based on the User.Id passed in.
	// It supports transaction
	// It is created to illustrate transaction, no real use.
	ModifyAndUnregisterWithTx(user *model.User) error
	// EnableTx enable transaction support on use case. Need to be included for each use case needs transaction
	// It replaces the underline database handler to sql.Tx for each data service that used by this use case
	EnableTxer
}
// EnableTxer is the transaction interface for use case layer
type EnableTxer interface {
	EnableTx()
}

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// The use case of ModifyAndUnregister without transaction
func (ruc *RegistrationUseCase) ModifyAndUnregister(user *model.User) error {
	return modifyAndUnregister(ruc, user)
}

// The use case of ModifyAndUnregister with transaction
func (ruc *RegistrationUseCase) ModifyAndUnregisterWithTx(user *model.User) error {
	tdi, err := ruc.TxDataInterface.TxBegin()
	if err != nil {
		return errors.Wrap(err, "")
	}
	ruc.EnableTx()
	return tdi.TxEnd(func() error {
		// wrap the business function inside the TxEnd function
		return modifyAndUnregister(ruc, user)
	})
}

// The business function will be wrapped inside a transaction and inside a non-transaction function
// It needs to be written in a way that every error will be returned so it can be catched by TxEnd() function,
// which will handle commit and rollback
func modifyAndUnregister(ruc *RegistrationUseCase, user *model.User) error {
	udi := ruc.UserDataInterface
	err := modifyUser(udi, user)
	if err != nil {
		return errors.Wrap(err, "")
	}
	err = unregisterUser(udi, user.Name)
	if err != nil {
		return errors.Wrap(err, "")
	}
	return nil
}

func (ruc *RegistrationUseCase) EnableTx() {
	// Only UserDataInterface need transaction support here. If there are other data services need it,
	// then they also need to enable transaction here
	ruc.UserDataInterface.EnableTx(ruc.TxDataInterface)
}

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// TxDataInterface represents operations needed for transaction support.
// It only needs to be implemented once for each database
// For sqlGdbc, it is implemented for SqlDBTx in transaction.go
type TxDataInterface interface {
	// TxBegin starts a transaction. It gets a DB handler from the receiver and return a TxDataInterface, which has a
	// *sql.Tx inside. Any data access wrapped inside a transaction will go through the *sql.Tx
	TxBegin() (TxDataInterface, error)
	// TxEnd is called at the end of a transaction and based on whether there is an error, it commits or rollback the
	// transaction.
	// txFunc is the business function wrapped in a transaction
	TxEnd(txFunc func() error) error
	// Return the underline transaction handler, sql.Tx
	GetTx() gdbc.SqlGdbc
}

// This interface needs to be included in every data service interface that needs transaction support
type EnableTxer interface {
	// EnableTx enables transaction, basically it replaces the underling database handle sql.DB with sql.Tx
	EnableTx(dataInterface TxDataInterface)
}

// UserDataInterface represents interface for user data access through database
type UserDataInterface interface {
...
	Update(user *model.User) (rowsAffected int64, err error)
	// Insert adds a user to a database. The returned resultUser has a Id, which is auto generated by database
	Insert(user *model.User) (resultUser *model.User, err error)
	// Need to add this for transaction support
	EnableTxer
}

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// TxDataSql is the generic implementation for transaction for SQL database
// You only need to do it once for each SQL database
type TxDataSql struct {
	DB gdbc.SqlGdbc
}

func (tds *TxDataSql) TxEnd(txFunc func() error) error {
	return tds.DB.TxEnd(txFunc)
}

func (tds *TxDataSql) TxBegin() (dataservice.TxDataInterface, error) {

	sqlTx, error := tds.DB.TxBegin()
	tdi := TxDataSql{sqlTx}
	tds.DB = tdi.DB
	return &tdi, error
}
func (tds *TxDataSql) GetTx() gdbc.SqlGdbc {
	return tds.DB
}

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// UserDataSql is the SQL implementation of UserDataInterface
type UserDataSql struct {
	DB gdbc.SqlGdbc
}

func (uds *UserDataSql) EnableTx(tx dataservice.TxDataInterface) {
	uds.DB = tx.GetTx()
}

func (uds *UserDataSql) FindByName(name string) (*model.User, error) {
	//logger.Log.Debug("call FindByName() and name is:", name)
	rows, err := uds.DB.Query(QUERY_USER_BY_NAME, name)
	if err != nil {
		return nil, errors.Wrap(err, "")
	}
	defer rows.Close()
	return retrieveUser(rows)
}

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func (uds *UserDataSql) Find(id int) (*model.User, error) {
	rows, err := uds.DB.Query(QUERY_USER_BY_ID, id)
	if err != nil {
		return nil, errors.Wrap(err, "")
	}
	defer rows.Close()
	return retrieveUser(rows)
}