sqldb: extract migration into method

Based on: https://github.com/lightninglabs/taproot-assets/pull/707

sqldb/migrations.go

@@ -8,16 +8,71 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/btcsuite/btclog"
 	"github.com/golang-migrate/migrate/v4"
 	"github.com/golang-migrate/migrate/v4/database"
 	"github.com/golang-migrate/migrate/v4/source/httpfs"
 )
 
+// MigrationTarget is a functional option that can be passed to applyMigrations
+// to specify a target version to migrate to.
+type MigrationTarget func(mig *migrate.Migrate) error
+
+var (
+	// TargetLatest is a MigrationTarget that migrates to the latest
+	// version available.
+	TargetLatest = func(mig *migrate.Migrate) error {
+		return mig.Up()
+	}
+
+	// TargetVersion is a MigrationTarget that migrates to the given
+	// version.
+	TargetVersion = func(version uint) MigrationTarget {
+		return func(mig *migrate.Migrate) error {
+			return mig.Migrate(version)
+		}
+	}
+)
+
+// migrationLogger is a logger that wraps the passed btclog.Logger so it can be
+// used to log migrations.
+type migrationLogger struct {
+	log btclog.Logger
+}
+
+// Printf is like fmt.Printf. We map this to the target logger based on the
+// current log level.
+func (m *migrationLogger) Printf(format string, v ...interface{}) {
+	// Trim trailing newlines from the format.
+	format = strings.TrimRight(format, "\n")
+
+	switch m.log.Level() {
+	case btclog.LevelTrace:
+		m.log.Tracef(format, v...)
+	case btclog.LevelDebug:
+		m.log.Debugf(format, v...)
+	case btclog.LevelInfo:
+		m.log.Infof(format, v...)
+	case btclog.LevelWarn:
+		m.log.Warnf(format, v...)
+	case btclog.LevelError:
+		m.log.Errorf(format, v...)
+	case btclog.LevelCritical:
+		m.log.Criticalf(format, v...)
+	case btclog.LevelOff:
+	}
+}
+
+// Verbose should return true when verbose logging output is wanted
+func (m *migrationLogger) Verbose() bool {
+	return m.log.Level() <= btclog.LevelDebug
+}
+
 // applyMigrations executes all database migration files found in the given file
 // system under the given path, using the passed database driver and database
 // name.
 func applyMigrations(fs fs.FS, driver database.Driver, path,
-	dbName string) error {
+	dbName string, targetVersion MigrationTarget) error {
 
 	// With the migrate instance open, we'll create a new migration source
 	// using the embedded file system stored in sqlSchemas. The library
@@ -37,7 +92,22 @@ func applyMigrations(fs fs.FS, driver database.Driver, path,
 	if err != nil {
 		return err
 	}
-	err = sqlMigrate.Up()
+
+	migrationVersion, _, err := sqlMigrate.Version()
+	if err != nil && !errors.Is(err, migrate.ErrNilVersion) {
+		log.Errorf("Unable to determine current migration version: %v",
+			err)
+
+		return err
+	}
+
+	log.Infof("Applying migrations from version=%v", migrationVersion)
+
+	// Apply our local logger to the migration instance.
+	sqlMigrate.Log = &migrationLogger{log}
+
+	// Execute the migration based on the target given.
+	err = targetVersion(sqlMigrate)
 	if err != nil && !errors.Is(err, migrate.ErrNoChange) {
 		return err
 	}