added user independent sections and started db migration work

pkg/db/migration.go

@@ -0,0 +1,72 @@
+package db
+
+import (
+	"git.giftfish.de/ston1th/gowiki/pkg/core"
+	"git.giftfish.de/ston1th/gowiki/pkg/log"
+)
+
+const (
+	versionKey     = "version/version"
+	currentVersion = 2
+)
+
+type migrator func(*DB) (int, error)
+
+var migrators = []migrator{
+	func(db *DB) (int, error) {
+		return 0, nil
+	},
+	func(db *DB) (version int, err error) {
+		version = 1
+		return
+	},
+	func(db *DB) (version int, err error) {
+		version = 2
+		// recreate all pages with new format
+		var pages []string
+		db.store.ForEach(func(k string, _ []byte) error {
+			if trim, ok := hasTrimPrefix(k, pagePrefix); ok {
+				pages = append(pages, trim)
+			}
+			return nil
+		})
+		var p core.Page
+		for _, v := range pages {
+			k := pagePrefix + v
+			err := db.store.Get(k, &p)
+			if err != nil {
+				log.Printf("db: migrator[%d]: pageGet %s: %s", version, k, err)
+				continue
+			}
+			err = db.store.Set(k, &p)
+			if err != nil {
+				log.Printf("db: migrator[%d]: pageSet %s: %s", version, k, err)
+				continue
+			}
+		}
+		return
+	},
+}
+
+func (db *DB) RunMigrations() (err error) {
+	var version int
+	err = db.store.Get(versionKey, &version)
+	if err == ErrKeyNotFound {
+		err = db.store.Set(versionKey, 0)
+		if err != nil {
+			return
+		}
+	}
+	log.Printf("db: detected database version %d", version)
+	for version < currentVersion {
+		log.Printf("db: running migration %d", version)
+		version, err = migrators[version](db)
+		if err != nil {
+			return
+		}
+		err = db.store.Set(versionKey, version)
+		if err != nil {
+			return
+		}
+	}
+}