logger: implement logger option

Add a Logger interface, along with a LoggerFunc and a new WithLogger option.

This would enable:

- Customizing migrator output
- Integrating a 3rd party logging tool

By default, migrator will work as before, just outputting to stdout.

Closes #6

README.md

@@ -77,7 +77,23 @@ func main() {
 ```
 
 Notes on examples above:
-- Migrator creates/manages a table named `migrations` to keep track of the applied versions. However, if want to customize the table name `migrator.TableName("my_migrations")` can be passed to `migrator.New` function as an additional option. 
+
+- Migrator creates/manages a table named `migrations` to keep track of the applied versions. However, if you want to customize the table name `migrator.TableName("my_migrations")` can be passed to `migrator.New` function as an additional option. 
+
+### Logging
+
+By default, migrator prints applying/applied migration info to stdout. 
+If that's enough for you, you can skip this section.
+
+If you need some special formatting or want to use a 3rd party logging library, this could be done by using `WithLogger` option as follows:
+
+```go
+logger := migrator.WithLogger(migrator.LoggerFunc(func(msg string, args ...interface{}) {
+	// Your code here 
+})))
+```
+
+Then you will only need to pass the logger as an option to `migrator.New`. 
 
 ### Looking for more examples?
 

migrator.go

@@ -4,13 +4,16 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"log"
+	"os"
 )
 
 const defaultTableName = "migrations"
 
 // Migrator is the migrator implementation
 type Migrator struct {
 	tableName  string
+	logger     Logger
 	migrations []interface{}
 }
 
@@ -24,6 +27,26 @@ func TableName(tableName string) Option {
 	}
 }
 
+// Logger interface
+type Logger interface {
+	Printf(string, ...interface{})
+}
+
+// LoggerFunc is a bridge between Logger and any third party logger
+type LoggerFunc func(string, ...interface{})
+
+// Printf implements Logger interface
+func (f LoggerFunc) Printf(msg string, args ...interface{}) {
+	f(msg, args...)
+}
+
+// WithLogger creates an option to allow overriding the stdout logging
+func WithLogger(logger Logger) Option {
+	return func(m *Migrator) {
+		m.logger = logger
+	}
+}
+
 // Migrations creates an option with provided migrations
 func Migrations(migrations ...interface{}) Option {
 	return func(m *Migrator) {
@@ -34,6 +57,7 @@ func Migrations(migrations ...interface{}) Option {
 // New creates a new migrator instance
 func New(opts ...Option) (*Migrator, error) {
 	m := &Migrator{
+		logger:    log.New(os.Stdout, "migrator: ", 0),
 		tableName: defaultTableName,
 	}
 	for _, opt := range opts {
@@ -83,13 +107,13 @@ func (m *Migrator) Migrate(db *sql.DB) error {
 	// plan migrations
 	for idx, migration := range m.migrations[count:len(m.migrations)] {
 		insertVersion := fmt.Sprintf("INSERT INTO %s (id, version) VALUES (%d, '%s')", m.tableName, idx+count, migration.(fmt.Stringer).String())
-		switch m := migration.(type) {
+		switch mig := migration.(type) {
 		case *Migration:
-			if err := migrate(db, insertVersion, m); err != nil {
+			if err := migrate(db, m.logger, insertVersion, mig); err != nil {
 				return fmt.Errorf("migrator: error while running migrations: %v", err)
 			}
 		case *MigrationNoTx:
-			if err := migrateNoTx(db, insertVersion, m); err != nil {
+			if err := migrateNoTx(db, m.logger, insertVersion, mig); err != nil {
 				return fmt.Errorf("migrator: error while running migrations: %v", err)
 			}
 		}
@@ -149,7 +173,7 @@ func (m *MigrationNoTx) String() string {
 	return m.Name
 }
 
-func migrate(db *sql.DB, insertVersion string, migration *Migration) error {
+func migrate(db *sql.DB, logger Logger, insertVersion string, migration *Migration) error {
 	tx, err := db.Begin()
 	if err != nil {
 		return err
@@ -163,27 +187,27 @@ func migrate(db *sql.DB, insertVersion string, migration *Migration) error {
 		}
 		err = tx.Commit()
 	}()
-	fmt.Println(fmt.Sprintf("migrator: applying migration named '%s'...", migration.Name))
+	logger.Printf("applying migration named '%s'...", migration.Name)
 	if err = migration.Func(tx); err != nil {
 		return fmt.Errorf("error executing golang migration: %s", err)
 	}
 	if _, err = tx.Exec(insertVersion); err != nil {
 		return fmt.Errorf("error updating migration versions: %s", err)
 	}
-	fmt.Println(fmt.Sprintf("migrator: applied migration named '%s'", migration.Name))
+	logger.Printf("applied migration named '%s'", migration.Name)
 
 	return err
 }
 
-func migrateNoTx(db *sql.DB, insertVersion string, migration *MigrationNoTx) error {
-	fmt.Println(fmt.Sprintf("migrator: applying no tx migration named '%s'...", migration.Name))
+func migrateNoTx(db *sql.DB, logger Logger, insertVersion string, migration *MigrationNoTx) error {
+	logger.Printf("applying no tx migration named '%s'...", migration.Name)
 	if err := migration.Func(db); err != nil {
 		return fmt.Errorf("error executing golang migration: %s", err)
 	}
 	if _, err := db.Exec(insertVersion); err != nil {
 		return fmt.Errorf("error updating migration versions: %s", err)
 	}
-	fmt.Println(fmt.Sprintf("migrator: applied no tx migration named '%s'...", migration.Name))
+	logger.Printf("applied no tx migration named '%s'", migration.Name)
 
 	return nil
 }

migrator_test.go

@@ -5,6 +5,7 @@ package migrator
 import (
 	"database/sql"
 	"fmt"
+	"log"
 	"os"
 	"strings"
 	"testing"
@@ -167,7 +168,7 @@ func TestBadMigrate(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := migrate(db, "BAD INSERT VERSION", &Migration{Name: "bad insert version", Func: func(tx *sql.Tx) error {
+	if err := migrate(db, log.New(os.Stdout, "migrator: ", 0), "BAD INSERT VERSION", &Migration{Name: "bad insert version", Func: func(tx *sql.Tx) error {
 		return nil
 	}}); err == nil {
 		t.Fatal("BAD INSERT VERSION should fail!")
@@ -179,7 +180,7 @@ func TestBadMigrateNoTx(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := migrateNoTx(db, "BAD INSERT VERSION", &MigrationNoTx{Name: "bad migrate no tx", Func: func(db *sql.DB) error {
+	if err := migrateNoTx(db, log.New(os.Stdout, "migrator: ", 0), "BAD INSERT VERSION", &MigrationNoTx{Name: "bad migrate no tx", Func: func(db *sql.DB) error {
 		return nil
 	}}); err == nil {
 		t.Fatal("BAD INSERT VERSION should fail!")