.go

const (
	stmtCreateUser = iota
	stmtGetUser
	stmtUpdateUser
)

var stmtPairs = []struct {
	id   int
	stmt string
}{
	{stmtGetUser, `SELECT u.email, u.data
		FROM user u
			WHERE u.id=$1
		FOR UPDATE`},

	{stmtUpdateUser, `UPDATE user SET data=$1
		WHERE id=$2`},
}

func (d *DB) prepareStmts() error {
	for _, stmtPair := range stmtPairs {
		st, err := d.DB.Prepare(stmtPair.stmt)
		if err != nil {
			return fmt.Errorf("Failed to prepare statement %s: %s", stmtPair.stmt, err.Error())
		}
		d.stmts[stmtPair.id] = st
	}

	return nil
}

// NewDB creates new Postgres connection
func NewDB(dataSource string) (*DB, error) {
	db, err := sql.Open("postgres", dataSource)
	if err != nil {
		return nil, err
	}

	res := &DB{DB: db, stmts: map[int]*sql.Stmt{}}
	if err := res.prepareStmts(); err != nil {
		return nil, err
	}

	return res, nil
}