Refactor db code

The versioning now happens using the user_version pragma, provided by
sqlite. From the docs:

> The user-version is an integer that is available to applications to use
> however they want. SQLite makes no use of the user-version itself.

Also the migrations happen in their own loop. Each migratin should
get tested(?)

db/db.go

@@ -1,3 +1,5 @@
+/// This package is in charge of connecting to the DB and migrations
+
 package db
 
 import (
@@ -10,61 +12,95 @@ import (
 
 var __version = 1
 
-type LogCtx struct {
+type DbCtx struct {
 	db      *sql.DB
 	version int
 }
 
-func Init(db_location string) (*LogCtx, error) {
-	db, err := sql.Open("sqlite3", db_location)
-	if err != nil {
-		return nil, fmt.Errorf("Could not connect to DB. %w", err)
-	}
-	if err := db.Ping(); err != nil {
-		return nil, fmt.Errorf("Could not ping DB. %w", err)
+func initVersion(tx *sql.Tx) (int, error) {
+	var version int
+	// Check the version
+	if err := tx.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
+		tx.Rollback()
+		return 0, fmt.Errorf("Could not select user_version. %w", err)
 	}
 
-	ctx := context.Background()
-	tx, err := db.BeginTx(ctx, nil)
+	if version == 0 {
+		_, err := tx.Exec(fmt.Sprintf("PRAGMA user_version=%d", __version))
 		if err != nil {
-		return nil, err
+			tx.Rollback()
+			return 0, fmt.Errorf("Could not update pragma version. %w", err)
+		}
+		version = __version
+	} else if version != __version {
+		tx.Rollback()
+		return 0, errors.New(fmt.Sprintf("Wrong version. Expected %d got %d", __version, version))
+	}
+	return version, nil
 }
 
+func migration0(tx *sql.Tx) error {
 	// Optionally add the version table
 	if _, err := tx.Exec(`
 		create table if not exists eng_log_version (id integer not null);
 	`); err != nil {
 		tx.Rollback()
-		return nil, fmt.Errorf("Could not create eng_log_version. %w", err)
+		return fmt.Errorf("Could not create eng_log_version. %w", err)
 	}
 	// Optionally add the log table
 	if _, err := tx.Exec(`
 		create table if not exists log (id integer not null primary key, title string)
 	`); err != nil {
 		tx.Rollback()
-		return nil, fmt.Errorf("Could not create log. %w", err)
+		return fmt.Errorf("Could not create log. %w", err)
+	}
+	return nil
 }
 
-	var version int
-	// Check the version
-	if err := tx.QueryRow("SELECT IFNULL((SELECT id FROM eng_log_version LIMIT 1), 0)").Scan(&version); err != nil {
+func initMigrations(tx *sql.Tx, start_from_versiono int) error {
+	var migrations = []func(*sql.Tx) error{migration0}
+	for migration_idx, migration := range migrations {
+		// Version is 1 indexed, while the migration_idx is 0 indexed
+		var migration_num = migration_idx + 1
+		if migration_num < start_from_versiono {
+			continue
+		}
+		err := migration(tx)
+		if err != nil {
 			tx.Rollback()
-		return nil, fmt.Errorf("Could not query for eng_log_version id. %w", err)
+			return fmt.Errorf("Failed migration %d. %w", migration_num, err)
+		}
+	}
+	return nil
 }
 
-	if version == 0 {
-		_, err := tx.Exec("INSERT INTO eng_log_version (id) VALUES (?)", __version)
+func Init(db_location string) (*DbCtx, error) {
+	db, err := sql.Open("sqlite3", db_location)
 	if err != nil {
-			tx.Rollback()
-			return nil, fmt.Errorf("Could not insert log-version. %w", err)
+		return nil, fmt.Errorf("Could not connect to DB. %w", err)
 	}
-		version = __version
-	} else if version != __version {
-		tx.Rollback()
-		return nil, errors.New(fmt.Sprintf("Wrong version. Expected %d got %d", __version, version))
+	if err := db.Ping(); err != nil {
+		return nil, fmt.Errorf("Could not ping DB. %w", err)
+	}
+
+	ctx := context.Background()
+	tx, err := db.BeginTx(ctx, nil)
+
+	if err != nil {
+		return nil, err
+	}
+
+	version, err := initVersion(tx)
+	if err != nil {
+		return nil, err
+	}
+
+	err = initMigrations(tx, version)
+	if err != nil {
+		return nil, err
 	}
 
 	tx.Commit()
 
-	return &LogCtx{db, version}, nil
+	return &DbCtx{db, version}, nil
 }

db/db_test.go

@@ -29,11 +29,6 @@ func TestInitBasic(t *testing.T) {
 	// check that the tables exist
 	var table_name string
 
-	ctx.db.QueryRow(
-		"SELECT name FROM sqlite_master WHERE type='table' AND name='eng_log_version';",
-	).Scan(&table_name)
-	assert_string(t, "eng_log_version", table_name)
-
 	ctx.db.QueryRow(
 		"SELECT name FROM sqlite_master WHERE type='table' AND name='log';",
 	).Scan(&table_name)
@@ -41,26 +36,12 @@ func TestInitBasic(t *testing.T) {
 
 	// Check that the version stored is correct
 	var version int
-	ctx.db.QueryRow("SELECT id FROM eng_log_version").Scan(&version)
+	ctx.db.QueryRow("PRAGMA user_version").Scan(&version)
 	assert_int(t, __version, ctx.version)
 	assert_int(t, __version, version)
 }
 
-func TestInitLogVersionTableExists(t *testing.T) {
-	var db_location = ":memory:"
-	db, err := sql.Open("sqlite3", db_location)
-
-	db.Exec(`
-		CREATE TABLE eng_log_version (id INTEGER NOT NULL);
-		INSERT INTO eng_log_version (id) VALUES (1);
-	`)
-	_, err = Init(db_location)
-	if err != nil {
-		t.Fatalf(err.Error())
-	}
-}
-
-func TestInitWrongLogVersionExists(t *testing.T) {
+func TestInitWrongVersion(t *testing.T) {
 	file, err := ioutil.TempFile("", "log_test_init_wrong.*.db")
 	defer os.Remove(file.Name()) // clean up
 
@@ -69,15 +50,10 @@ func TestInitWrongLogVersionExists(t *testing.T) {
 		log.Fatal(err.Error())
 	}
 
-	db.Exec(`
-		CREATE TABLE eng_log_version (id INTEGER NOT NULL);
-	`)
-	db.Exec(`
-		INSERT INTO eng_log_version (id) VALUES (?);
-	`, __version+1)
+	db.Exec(fmt.Sprintf(`PRAGMA user_version=%d`, __version+1))
 
 	var version int
-	db.QueryRow("SELECT id FROM eng_log_version LIMIT 1").Scan(&version)
+	db.QueryRow("PRAGMA user_version").Scan(&version)
 
 	_, err = Init(file.Name())
 	if err == nil {