1 files changed, 130 insertions, 0 deletions
diff --git a/plumbing/object/commitnode_graph.go b/plumbing/object/commitnode_graph.go
new file mode 100644
index 0000000..ac790ab
--- /dev/null
+++ b/plumbing/object/commitnode_graph.go
@@ -0,0 +1,130 @@
+package object
+
+import (
+	"fmt"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/commitgraph"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+// graphCommitNode is a reduced representation of Commit as presented in the commit
+// graph file (commitgraph.Node). It is merely useful as an optimization for walking
+// the commit graphs.
+//
+// graphCommitNode implements the CommitNode interface.
+type graphCommitNode struct {
+	// Hash for the Commit object
+	hash plumbing.Hash
+	// Index of the node in the commit graph file
+	index int
+
+	commitData *commitgraph.CommitData
+	gci        *graphCommitNodeIndex
+}
+
+// graphCommitNodeIndex is an index that can load CommitNode objects from both the commit
+// graph files and the object store.
+//
+// graphCommitNodeIndex implements the CommitNodeIndex interface
+type graphCommitNodeIndex struct {
+	commitGraph commitgraph.Index
+	s           storer.EncodedObjectStorer
+}
+
+// NewGraphCommitNodeIndex returns CommitNodeIndex implementation that uses commit-graph
+// files as backing storage and falls back to object storage when necessary
+func NewGraphCommitNodeIndex(commitGraph commitgraph.Index, s storer.EncodedObjectStorer) CommitNodeIndex {
+	return &graphCommitNodeIndex{commitGraph, s}
+}
+
+func (gci *graphCommitNodeIndex) Get(hash plumbing.Hash) (CommitNode, error) {
+	// Check the commit graph first
+	parentIndex, err := gci.commitGraph.GetIndexByHash(hash)
+	if err == nil {
+		parent, err := gci.commitGraph.GetCommitDataByIndex(parentIndex)
+		if err != nil {
+			return nil, err
+		}
+
+		return &graphCommitNode{
+			hash:       hash,
+			index:      parentIndex,
+			commitData: parent,
+			gci:        gci,
+		}, nil
+	}
+
+	// Fallback to loading full commit object
+	commit, err := GetCommit(gci.s, hash)
+	if err != nil {
+		return nil, err
+	}
+
+	return &objectCommitNode{
+		nodeIndex: gci,
+		commit:    commit,
+	}, nil
+}
+
+func (c *graphCommitNode) ID() plumbing.Hash {
+	return c.hash
+}
+
+func (c *graphCommitNode) Tree() (*Tree, error) {
+	return GetTree(c.gci.s, c.commitData.TreeHash)
+}
+
+func (c *graphCommitNode) CommitTime() time.Time {
+	return c.commitData.When
+}
+
+func (c *graphCommitNode) NumParents() int {
+	return len(c.commitData.ParentIndexes)
+}
+
+func (c *graphCommitNode) ParentNodes() CommitNodeIter {
+	return newParentgraphCommitNodeIter(c)
+}
+
+func (c *graphCommitNode) ParentNode(i int) (CommitNode, error) {
+	if i < 0 || i >= len(c.commitData.ParentIndexes) {
+		return nil, ErrParentNotFound
+	}
+
+	parent, err := c.gci.commitGraph.GetCommitDataByIndex(c.commitData.ParentIndexes[i])
+	if err != nil {
+		return nil, err
+	}
+
+	return &graphCommitNode{
+		hash:       c.commitData.ParentHashes[i],
+		index:      c.commitData.ParentIndexes[i],
+		commitData: parent,
+		gci:        c.gci,
+	}, nil
+}
+
+func (c *graphCommitNode) ParentHashes() []plumbing.Hash {
+	return c.commitData.ParentHashes
+}
+
+func (c *graphCommitNode) Generation() uint64 {
+	// If the commit-graph file was generated with older Git version that
+	// set the generation to zero for every commit the generation assumption
+	// is still valid. It is just less useful.
+	return uint64(c.commitData.Generation)
+}
+
+func (c *graphCommitNode) Commit() (*Commit, error) {
+	return GetCommit(c.gci.s, c.hash)
+}
+
+func (c *graphCommitNode) String() string {
+	return fmt.Sprintf(
+		"%s %s\nDate:   %s",
+		plumbing.CommitObject, c.ID(),
+		c.CommitTime().Format(DateFormat),
+	)
+}