1 files changed, 109 insertions, 0 deletions
diff --git a/plumbing/storer/reference.go b/plumbing/storer/reference.go
new file mode 100644
index 0000000..5e818c6
--- /dev/null
+++ b/plumbing/storer/reference.go
@@ -0,0 +1,109 @@
+package storer
+
+import (
+	"errors"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+const MaxResolveRecursion = 1024
+
+// ErrMaxResolveRecursion is returned by ResolveReference is MaxResolveRecursion
+// is exceeded
+var ErrMaxResolveRecursion = errors.New("max. recursion level reached")
+
+// ReferenceStorer generic storage of references
+type ReferenceStorer interface {
+	SetReference(*plumbing.Reference) error
+	Reference(plumbing.ReferenceName) (*plumbing.Reference, error)
+	IterReferences() (ReferenceIter, error)
+}
+
+// ReferenceIter is a generic closable interface for iterating over references
+type ReferenceIter interface {
+	Next() (*plumbing.Reference, error)
+	ForEach(func(*plumbing.Reference) error) error
+	Close()
+}
+
+// ReferenceSliceIter implements ReferenceIter. It iterates over a series of
+// references stored in a slice and yields each one in turn when Next() is
+// called.
+//
+// The ReferenceSliceIter must be closed with a call to Close() when it is no
+// longer needed.
+type ReferenceSliceIter struct {
+	series []*plumbing.Reference
+	pos    int
+}
+
+// NewReferenceSliceIter returns a reference iterator for the given slice of
+// objects.
+func NewReferenceSliceIter(series []*plumbing.Reference) *ReferenceSliceIter {
+	return &ReferenceSliceIter{
+		series: series,
+	}
+}
+
+// Next returns the next reference from the iterator. If the iterator has
+// reached the end it will return io.EOF as an error.
+func (iter *ReferenceSliceIter) Next() (*plumbing.Reference, error) {
+	if iter.pos >= len(iter.series) {
+		return nil, io.EOF
+	}
+
+	obj := iter.series[iter.pos]
+	iter.pos++
+	return obj, nil
+}
+
+// ForEach call the cb function for each reference contained on this iter until
+// an error happends or the end of the iter is reached. If ErrStop is sent
+// the iteration is stop but no error is returned. The iterator is closed.
+func (iter *ReferenceSliceIter) ForEach(cb func(*plumbing.Reference) error) error {
+	defer iter.Close()
+	for _, r := range iter.series {
+		if err := cb(r); err != nil {
+			if err == ErrStop {
+				return nil
+			}
+
+			return nil
+		}
+	}
+
+	return nil
+}
+
+// Close releases any resources used by the iterator.
+func (iter *ReferenceSliceIter) Close() {
+	iter.pos = len(iter.series)
+}
+
+// ResolveReference resolve a SymbolicReference to a HashReference
+func ResolveReference(s ReferenceStorer, n plumbing.ReferenceName) (*plumbing.Reference, error) {
+	r, err := s.Reference(n)
+	if err != nil || r == nil {
+		return r, err
+	}
+	return resolveReference(s, r, 0)
+}
+
+func resolveReference(s ReferenceStorer, r *plumbing.Reference, recursion int) (*plumbing.Reference, error) {
+	if r.Type() != plumbing.SymbolicReference {
+		return r, nil
+	}
+
+	if recursion > MaxResolveRecursion {
+		return nil, ErrMaxResolveRecursion
+	}
+
+	t, err := s.Reference(r.Target())
+	if err != nil {
+		return nil, err
+	}
+
+	recursion++
+	return resolveReference(s, t, recursion)
+}