move plumbing from top level package to plumbing (#183)

* plumbing: rename Object -> EncodedObject.

* plumbing/storer: rename ObjectStorer -> EncodedObjectStorer.

* move difftree to plumbing/difftree.

* move diff -> utils/diff

* make Object/Tag/Blob/Tree/Commit/File depend on storer.

* Object and its implementations now depend only on
  storer.EncodedObjectStorer, not git.Repository.
* Tests are decoupled accordingly.

* move Object/Commit/File/Tag/Tree to plumbing/object.

* move Object/Commit/File/Tag/Tree to plumbing/object.
* move checkClose to utils/ioutil.

* move RevListObjects to plumbing/revlist.Objects.

* move DiffTree to plumbing/difftree package.

* rename files with plural nouns to singular

* plumbing/object: add GetBlob/GetCommit/GetTag/GetTree.

1 files changed, 65 insertions, 0 deletions

diff --git a/plumbing/difftree/internal/merkletrie/node.go b/plumbing/difftree/internal/merkletrie/node.go
new file mode 100644
index 0000000..99be5b8
--- /dev/null
+++ b/plumbing/difftree/internal/merkletrie/node.go
@@ -0,0 +1,65 @@
+package merkletrie
+
+import (
+	"sort"
+	"strings"
+)
+
+// A node is a Noder implementation for testing purposes:  It is easier
+// to create test trees using nodes than using real git tree objects.
+type node struct {
+	hash     []byte
+	key      string
+	children []*node
+}
+
+// newNode returns a new Node with the given hash, key and children
+// (children can be specified in any order).
+func newNode(hash []byte, key string, children []*node) *node {
+	sort.Sort(reverseAlphabeticallyByKey(children))
+
+	return &node{
+		hash:     hash,
+		key:      key,
+		children: children,
+	}
+}
+
+// Hash returns the hash of the node.
+func (n *node) Hash() []byte {
+	return n.hash
+}
+
+// Key returns the key of the node.
+func (n *node) Key() string {
+	return n.key
+}
+
+// NumChildren returns the number of children.
+func (n *node) NumChildren() int {
+	return len(n.children)
+}
+
+// Children returns the node's children in reverse key alphabetical
+// order.
+func (n *node) Children() []Noder {
+	ret := make([]Noder, n.NumChildren())
+	for i := range n.children {
+		ret[i] = n.children[i]
+	}
+	return ret
+}
+
+type reverseAlphabeticallyByKey []*node
+
+func (a reverseAlphabeticallyByKey) Len() int {
+	return len(a)
+}
+
+func (a reverseAlphabeticallyByKey) Swap(i, j int) {
+	a[i], a[j] = a[j], a[i]
+}
+
+func (a reverseAlphabeticallyByKey) Less(i, j int) bool {
+	return strings.Compare(a[i].key, a[j].key) > 0
+}