1 files changed, 58 insertions, 2 deletions
diff --git a/internal/store/compat.go b/internal/store/compat.go
index c0ef6dd7..0db2f5f2 100644
--- a/internal/store/compat.go
+++ b/internal/store/compat.go
@@ -1,6 +1,8 @@
 package store
 
 import (
+	"errors"
+	"maps"
 	"strconv"
 
 	"hakurei.app/container/check"
@@ -10,7 +12,7 @@ import (
 
 /* this provides an implementation of Store on top of the improved state tracking to ease in the changes */
 
-type Store interface {
+type Compat interface {
 	// Do calls f exactly once and ensures store exclusivity until f returns.
 	// Returns whether f is called and any errors during the locking process.
 	// Cursor provided to f becomes invalid as soon as f returns.
@@ -58,7 +60,7 @@ func (s storeAdapter) List() ([]int, error) {
 }
 
 // NewMulti returns an instance of the multi-file store.
-func NewMulti(msg message.Msg, prefix *check.Absolute) Store {
+func NewMulti(msg message.Msg, prefix *check.Absolute) Compat {
 	return storeAdapter{msg, newStore(prefix.Append("state"))}
 }
 
@@ -128,3 +130,57 @@ func (h *storeHandle) Len() (int, error) {
 	}
 	return n, err
 }
+
+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 Compat) (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
+}