Added code for backend glue

backend/internal/db/db.go

@@ -0,0 +1,47 @@
+package db
+
+import (
+	"database/sql"
+	"embed"
+	"fmt"
+	"strings"
+
+	_ "github.com/go-sql-driver/mysql"
+	_ "modernc.org/sqlite"
+
+	"mind/internal/config"
+)
+
+//go:embed migrations/*.sql
+var migrationFS embed.FS
+
+func OpenAndMigrate(cfg config.Config) (*sql.DB, error) {
+	dsn := cfg.DSN
+	drv := strings.ToLower(cfg.Driver)
+	if drv != "mysql" && drv != "sqlite" {
+		drv = "sqlite"
+	}
+	db, err := sql.Open(drv, dsn)
+	if err != nil { return nil, err }
+	if err := db.Ping(); err != nil { return nil, err }
+	if err := runMigrations(db, drv); err != nil { return nil, err }
+	return db, nil
+}
+
+func runMigrations(db *sql.DB, driver string) error {
+	files, err := migrationFS.ReadDir("migrations")
+	if err != nil { return err }
+	for _, f := range files {
+		b, err := migrationFS.ReadFile("migrations/"+f.Name())
+		if err != nil { return err }
+		sqlText := string(b)
+		if driver == "sqlite" {
+			// very minor compatibility tweak: drop ENUM
+			sqlText = strings.ReplaceAll(sqlText, "ENUM('user','assistant')", "TEXT")
+		}
+		if _, err := db.Exec(sqlText); err != nil {
+			return fmt.Errorf("migration %s: %w", f.Name(), err)
+		}
+	}
+	return nil
+}