1 files changed, 71 insertions, 0 deletions
diff --git a/plumbing/format/commitgraph/memory.go b/plumbing/format/commitgraph/memory.go
new file mode 100644
index 0000000..316bc6d
--- /dev/null
+++ b/plumbing/format/commitgraph/memory.go
@@ -0,0 +1,71 @@
+package commitgraph
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+type MemoryIndex struct {
+	commitData []*Node
+	indexMap   map[plumbing.Hash]int
+}
+
+// NewMemoryIndex creates in-memory commit graph representation
+func NewMemoryIndex() *MemoryIndex {
+	return &MemoryIndex{
+		indexMap: make(map[plumbing.Hash]int),
+	}
+}
+
+// GetIndexByHash gets the index in the commit graph from commit hash, if available
+func (mi *MemoryIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
+	i, ok := mi.indexMap[h]
+	if ok {
+		return i, nil
+	}
+
+	return 0, plumbing.ErrObjectNotFound
+}
+
+// GetNodeByIndex gets the commit node from the commit graph using index
+// obtained from child node, if available
+func (mi *MemoryIndex) GetNodeByIndex(i int) (*Node, error) {
+	if int(i) >= len(mi.commitData) {
+		return nil, plumbing.ErrObjectNotFound
+	}
+
+	node := mi.commitData[i]
+
+	// Map parent hashes to parent indexes
+	if node.ParentIndexes == nil {
+		parentIndexes := make([]int, len(node.ParentHashes))
+		for i, parentHash := range node.ParentHashes {
+			var err error
+			if parentIndexes[i], err = mi.GetIndexByHash(parentHash); err != nil {
+				return nil, err
+			}
+		}
+		node.ParentIndexes = parentIndexes
+	}
+
+	return node, nil
+}
+
+// Hashes returns all the hashes that are available in the index
+func (mi *MemoryIndex) Hashes() []plumbing.Hash {
+	hashes := make([]plumbing.Hash, 0, len(mi.indexMap))
+	for k := range mi.indexMap {
+		hashes = append(hashes, k)
+	}
+	return hashes
+}
+
+// Add adds new node to the memory index
+func (mi *MemoryIndex) Add(hash plumbing.Hash, node *Node) error {
+	// The parent indexes are calculated lazily in GetNodeByIndex
+	// which allows adding nodes out of order as long as all parents
+	// are eventually resolved
+	node.ParentIndexes = nil
+	mi.indexMap[hash] = len(mi.commitData)
+	mi.commitData = append(mi.commitData, node)
+	return nil
+}