1 files changed, 83 insertions, 0 deletions
diff --git a/reachability/walk_expand_objects.go b/reachability/walk_expand_objects.go
new file mode 100644
index 00000000..97cab79c
--- /dev/null
+++ b/reachability/walk_expand_objects.go
@@ -0,0 +1,83 @@
+package reachability
+
+import (
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/object"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+func (walk *Walk) expandObjects(item walkItem) ([]walkItem, error) {
+	ty, err := walk.readHeaderType(item.id)
+	if err != nil {
+		return nil, err
+	}
+
+	if item.want != objecttype.TypeInvalid && ty != item.want {
+		return nil, &ErrObjectType{OID: item.id, Got: ty, Want: item.want}
+	}
+
+	switch ty {
+	case objecttype.TypeBlob:
+		return nil, nil
+	case objecttype.TypeCommit:
+		content, err := walk.readBytesContent(item.id)
+		if err != nil {
+			return nil, err
+		}
+
+		commit, err := object.ParseCommit(content, item.id.Algorithm())
+		if err != nil {
+			return nil, err
+		}
+
+		next := make([]walkItem, 0, len(commit.Parents)+1)
+
+		next = append(next, walkItem{id: commit.Tree, want: objecttype.TypeTree})
+		for _, parent := range commit.Parents {
+			next = append(next, walkItem{id: parent, want: objecttype.TypeCommit})
+		}
+
+		return next, nil
+	case objecttype.TypeTree:
+		content, err := walk.readBytesContent(item.id)
+		if err != nil {
+			return nil, err
+		}
+
+		tree, err := object.ParseTree(content, item.id.Algorithm())
+		if err != nil {
+			return nil, err
+		}
+
+		next := make([]walkItem, 0, len(tree.Entries))
+		for _, entry := range tree.Entries {
+			switch entry.Mode {
+			case object.FileModeGitlink:
+				continue
+			case object.FileModeDir:
+				next = append(next, walkItem{id: entry.ID, want: objecttype.TypeTree})
+			case object.FileModeRegular, object.FileModeExecutable, object.FileModeSymlink:
+				next = append(next, walkItem{id: entry.ID, want: objecttype.TypeBlob})
+			}
+		}
+
+		return next, nil
+	case objecttype.TypeTag:
+		content, err := walk.readBytesContent(item.id)
+		if err != nil {
+			return nil, err
+		}
+
+		tag, err := object.ParseTag(content, item.id.Algorithm())
+		if err != nil {
+			return nil, err
+		}
+
+		return []walkItem{{id: tag.Target, want: tag.TargetType}}, nil
+	case objecttype.TypeInvalid, objecttype.TypeFuture, objecttype.TypeOfsDelta, objecttype.TypeRefDelta:
+		return nil, &ErrObjectType{OID: item.id, Got: ty, Want: item.want}
+	}
+
+	return nil, fmt.Errorf("reachability: unreachable object type %d", ty)
+}