Add SQLite persistence, import-snapshot tool, and karma functionality

server/internal/database/database.go

@@ -0,0 +1,42 @@
+package database
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	_ "modernc.org/sqlite"
+)
+
+func Open(path string) (*sql.DB, error) {
+	if dir := filepath.Dir(path); dir != "." && dir != "" {
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			return nil, fmt.Errorf("create db directory %q: %w", dir, err)
+		}
+	}
+
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, fmt.Errorf("open sqlite %q: %w", path, err)
+	}
+
+	pragmas := []string{
+		"PRAGMA journal_mode=WAL",
+		"PRAGMA foreign_keys=ON",
+		"PRAGMA busy_timeout=5000",
+	}
+	for _, p := range pragmas {
+		if _, err := db.Exec(p); err != nil {
+			db.Close()
+			return nil, fmt.Errorf("exec %q: %w", p, err)
+		}
+	}
+
+	if err := db.Ping(); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("ping sqlite %q: %w", path, err)
+	}
+
+	return db, nil
+}