2 files changed, 194 insertions, 0 deletions
diff --git a/utils/merkletrie/index/node.go b/utils/merkletrie/index/node.go
new file mode 100644
index 0000000..2c72f6d
--- /dev/null
+++ b/utils/merkletrie/index/node.go
@@ -0,0 +1,86 @@
+package index
+
+import (
+	"path/filepath"
+	"strings"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/format/index"
+	"gopkg.in/src-d/go-git.v4/utils/merkletrie/noder"
+)
+
+// The node represents a index.Entry or a directory inferred from the path
+// of all entries. It implements the interface noder.Noder of merkletrie
+// package.
+//
+// This implementation implements a "standard" hash method being able to be
+// compared with any other noder.Noder implementation inside of go-git
+type node struct {
+	path     string
+	entry    index.Entry
+	children []noder.Noder
+	isDir    bool
+}
+
+// NewRootNode returns the root node of a computed tree from a index.Index,
+func NewRootNode(idx *index.Index) noder.Noder {
+	const rootNode = ""
+
+	m := map[string]*node{rootNode: {isDir: true}}
+
+	for _, e := range idx.Entries {
+		parts := strings.Split(e.Name, string(filepath.Separator))
+
+		var path string
+		for _, part := range parts {
+			parent := path
+			path = filepath.Join(path, part)
+
+			if _, ok := m[path]; ok {
+				continue
+			}
+
+			n := &node{path: path}
+			if path == e.Name {
+				n.entry = e
+			} else {
+				n.isDir = true
+			}
+
+			m[n.path] = n
+			m[parent].children = append(m[parent].children, n)
+		}
+	}
+
+	return m[rootNode]
+}
+
+func (n *node) String() string {
+	return n.path
+}
+
+// Hash the hash of a filesystem is a 24-byte slice, is the result of
+// concatenating the computed plumbing.Hash of the file as a Blob and its
+// plumbing.FileMode; that way the difftree algorithm will detect changes in the
+// contents of files and also in their mode.
+//
+// If the node is computed and not based on a index.Entry the hash is equals
+// to a 24-bytes slices of zero values.
+func (n *node) Hash() []byte {
+	return append(n.entry.Hash[:], n.entry.Mode.Bytes()...)
+}
+
+func (n *node) Name() string {
+	return filepath.Base(n.path)
+}
+
+func (n *node) IsDir() bool {
+	return n.isDir
+}
+
+func (n *node) Children() ([]noder.Noder, error) {
+	return n.children, nil
+}
+
+func (n *node) NumChildren() (int, error) {
+	return len(n.children), nil
+}
diff --git a/utils/merkletrie/index/node_test.go b/utils/merkletrie/index/node_test.go
new file mode 100644
index 0000000..48aa35f
--- /dev/null
+++ b/utils/merkletrie/index/node_test.go
@@ -0,0 +1,108 @@
+package index
+
+import (
+	"bytes"
+	"testing"
+
+	. "gopkg.in/check.v1"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/index"
+	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
+	"gopkg.in/src-d/go-git.v4/utils/merkletrie/noder"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type NoderSuite struct{}
+
+var _ = Suite(&NoderSuite{})
+
+func (s *NoderSuite) TestDiff(c *C) {
+	indexA := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/qux", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/baz/foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	indexB := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/qux", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "bar/baz/foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	ch, err := merkletrie.DiffTree(NewRootNode(indexA), NewRootNode(indexB), isEquals)
+	c.Assert(err, IsNil)
+	c.Assert(ch, HasLen, 0)
+}
+
+func (s *NoderSuite) TestDiffChange(c *C) {
+	indexA := &index.Index{
+		Entries: []index.Entry{
+			{Name: "bar/baz/bar", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	indexB := &index.Index{
+		Entries: []index.Entry{
+			{Name: "bar/baz/foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	ch, err := merkletrie.DiffTree(NewRootNode(indexA), NewRootNode(indexB), isEquals)
+	c.Assert(err, IsNil)
+	c.Assert(ch, HasLen, 2)
+}
+
+func (s *NoderSuite) TestDiffDir(c *C) {
+	indexA := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	indexB := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo/bar", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	ch, err := merkletrie.DiffTree(NewRootNode(indexA), NewRootNode(indexB), isEquals)
+	c.Assert(err, IsNil)
+	c.Assert(ch, HasLen, 2)
+}
+
+func (s *NoderSuite) TestDiffSameRoot(c *C) {
+	indexA := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo.go", Hash: plumbing.NewHash("aab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "foo/bar", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	indexB := &index.Index{
+		Entries: []index.Entry{
+			{Name: "foo/bar", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+			{Name: "foo.go", Hash: plumbing.NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")},
+		},
+	}
+
+	ch, err := merkletrie.DiffTree(NewRootNode(indexA), NewRootNode(indexB), isEquals)
+	c.Assert(err, IsNil)
+	c.Assert(ch, HasLen, 1)
+}
+
+var empty = make([]byte, 24)
+
+func isEquals(a, b noder.Hasher) bool {
+	if bytes.Equal(a.Hash(), empty) || bytes.Equal(b.Hash(), empty) {
+		return false
+	}
+
+	return bytes.Equal(a.Hash(), b.Hash())
+}