Move wisski instance code to separate package

internal/component/meta/meta.go

@@ -0,0 +1,44 @@
+package meta
+
+import (
+	"sync"
+
+	"github.com/FAU-CDI/wisski-distillery/internal/component"
+	"github.com/FAU-CDI/wisski-distillery/internal/component/sql"
+)
+
+// Component meta is responsible for managing metadata per WissKI Instance
+type Meta struct {
+	component.ComponentBase
+
+	SQL *sql.SQL
+
+	sl sync.Mutex
+	sc map[string]*Storage
+}
+
+func (*Meta) Name() string { return "metadata" }
+
+// Storage returns a Storage for the instance with the given slug.
+// When slug is nil, returns a global storage.
+func (meta *Meta) Storage(slug string) *Storage {
+	meta.sl.Lock()
+	defer meta.sl.Unlock()
+
+	// create the cache (unless it already exists)
+	if meta.sc == nil {
+		meta.sc = make(map[string]*Storage)
+	}
+
+	// cache hit
+	if storage, ok := meta.sc[slug]; ok {
+		return storage
+	}
+
+	// create a new storage
+	meta.sc[slug] = &Storage{
+		Slug: slug,
+		sql:  meta.SQL,
+	}
+	return meta.sc[slug]
+}