1 files changed, 64 insertions, 0 deletions
diff --git a/internal/store/join.go b/internal/store/join.go
new file mode 100644
index 00000000..0bb69df7
--- /dev/null
+++ b/internal/store/join.go
@@ -0,0 +1,64 @@
+package store
+
+import (
+	"errors"
+	"maps"
+
+	"hakurei.app/hst"
+)
+
+var (
+	ErrDuplicate = errors.New("store contains duplicates")
+)
+
+/*
+Joiner is the interface that wraps the Join method.
+
+The Join function uses Joiner if available.
+*/
+type Joiner interface {
+	Join() (map[hst.ID]*hst.State, error)
+}
+
+// Join returns joined state entries of all active identities.
+func Join(s Store) (map[hst.ID]*hst.State, error) {
+	if j, ok := s.(Joiner); ok {
+		return j.Join()
+	}
+
+	var (
+		aids    []int
+		entries = make(map[hst.ID]*hst.State)
+
+		el      int
+		res     map[hst.ID]*hst.State
+		loadErr error
+	)
+
+	if ln, err := s.List(); err != nil {
+		return nil, err
+	} else {
+		aids = ln
+	}
+
+	for _, aid := range aids {
+		if _, err := s.Do(aid, func(c Cursor) {
+			res, loadErr = c.Load()
+		}); err != nil {
+			return nil, err
+		}
+
+		if loadErr != nil {
+			return nil, loadErr
+		}
+
+		// save expected length
+		el = len(entries) + len(res)
+		maps.Copy(entries, res)
+		if len(entries) != el {
+			return nil, ErrDuplicate
+		}
+	}
+
+	return entries, nil
+}