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.

2 files changed, 278 insertions, 0 deletions

diff --git a/plumbing/revlist/revlist.go b/plumbing/revlist/revlist.go
new file mode 100644
index 0000000..106e78b
--- /dev/null
+++ b/plumbing/revlist/revlist.go
@@ -0,0 +1,128 @@
+// Package revlist implements functions to walk the objects referenced by a
+// commit history. Roughly equivalent to git-rev-list command.
+package revlist
+
+import (
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+// Objects applies a complementary set. It gets all the hashes from all
+// the reachable objects from the given commits. Ignore param are object hashes
+// that we want to ignore on the result. It is a list because is
+// easier to interact with other porcelain elements, but internally it is
+// converted to a map. All that objects must be accessible from the object
+// storer.
+func Objects(
+	s storer.EncodedObjectStorer,
+	commits []*object.Commit,
+	ignore []plumbing.Hash) ([]plumbing.Hash, error) {
+
+	seen := hashListToSet(ignore)
+	result := make(map[plumbing.Hash]bool)
+	for _, c := range commits {
+		err := reachableObjects(s, c, seen, func(h plumbing.Hash) error {
+			if !seen[h] {
+				result[h] = true
+				seen[h] = true
+			}
+
+			return nil
+		})
+
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return hashSetToList(result), nil
+}
+
+// reachableObjects returns, using the callback function, all the reachable
+// objects from the specified commit. To avoid to iterate over seen commits,
+// if a commit hash is into the 'seen' set, we will not iterate all his trees
+// and blobs objects.
+func reachableObjects(
+	s storer.EncodedObjectStorer,
+	commit *object.Commit,
+	seen map[plumbing.Hash]bool,
+	cb func(h plumbing.Hash) error) error {
+
+	return iterateCommits(commit, func(commit *object.Commit) error {
+		if seen[commit.Hash] {
+			return nil
+		}
+
+		if err := cb(commit.Hash); err != nil {
+			return err
+		}
+
+		return iterateCommitTrees(s, commit, func(h plumbing.Hash) error {
+			return cb(h)
+		})
+	})
+}
+
+// iterateCommits iterate all reachable commits from the given one
+func iterateCommits(commit *object.Commit, cb func(c *object.Commit) error) error {
+	if err := cb(commit); err != nil {
+		return err
+	}
+
+	return object.WalkCommitHistory(commit, func(c *object.Commit) error {
+		return cb(c)
+	})
+}
+
+// iterateCommitTrees iterate all reachable trees from the given commit
+func iterateCommitTrees(
+	s storer.EncodedObjectStorer,
+	commit *object.Commit,
+	cb func(h plumbing.Hash) error) error {
+
+	tree, err := commit.Tree()
+	if err != nil {
+		return err
+	}
+	if err := cb(tree.Hash); err != nil {
+		return err
+	}
+
+	treeWalker := object.NewTreeWalker(tree, true)
+
+	for {
+		_, e, err := treeWalker.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		if err := cb(e.Hash); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func hashSetToList(hashes map[plumbing.Hash]bool) []plumbing.Hash {
+	var result []plumbing.Hash
+	for key := range hashes {
+		result = append(result, key)
+	}
+
+	return result
+}
+
+func hashListToSet(hashes []plumbing.Hash) map[plumbing.Hash]bool {
+	result := make(map[plumbing.Hash]bool)
+	for _, h := range hashes {
+		result[h] = true
+	}
+
+	return result
+}
diff --git a/plumbing/revlist/revlist_test.go b/plumbing/revlist/revlist_test.go
new file mode 100644
index 0000000..60ae660
--- /dev/null
+++ b/plumbing/revlist/revlist_test.go
@@ -0,0 +1,150 @@
+package revlist
+
+import (
+	"testing"
+
+	"gopkg.in/src-d/go-git.v4/fixtures"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+	"gopkg.in/src-d/go-git.v4/storage/filesystem"
+
+	. "gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type RevListSuite struct {
+	fixtures.Suite
+	Storer storer.EncodedObjectStorer
+}
+
+var _ = Suite(&RevListSuite{})
+
+const (
+	initialCommit = "b029517f6300c2da0f4b651b8642506cd6aaf45d"
+	secondCommit  = "b8e471f58bcbca63b07bda20e428190409c2db47"
+
+	someCommit            = "918c48b83bd081e863dbe1b80f8998f058cd8294"
+	someCommitBranch      = "e8d3ffab552895c19b9fcf7aa264d277cde33881"
+	someCommitOtherBranch = "6ecf0ef2c2dffb796033e5a02219af86ec6584e5"
+)
+
+// Created using: git log --graph --oneline --all
+//
+// Basic fixture repository commits tree:
+//
+// * 6ecf0ef vendor stuff
+// | * e8d3ffa some code in a branch
+// |/
+// * 918c48b some code
+// * af2d6a6 some json
+// *   1669dce Merge branch 'master'
+// |\
+// | *   a5b8b09 Merge pull request #1
+// | |\
+// | | * b8e471f Creating changelog
+// | |/
+// * | 35e8510 binary file
+// |/
+// * b029517 Initial commit
+
+func (s *RevListSuite) SetUpTest(c *C) {
+	s.Suite.SetUpSuite(c)
+	sto, err := filesystem.NewStorage(fixtures.Basic().One().DotGit())
+	c.Assert(err, IsNil)
+	s.Storer = sto
+}
+
+func (s *RevListSuite) commit(c *C, h plumbing.Hash) *object.Commit {
+	commit, err := object.GetCommit(s.Storer, h)
+	c.Assert(err, IsNil)
+	return commit
+}
+
+// ---
+// | |\
+// | | * b8e471f Creating changelog
+// | |/
+// * | 35e8510 binary file
+// |/
+// * b029517 Initial commit
+func (s *RevListSuite) TestRevListObjects(c *C) {
+	revList := map[string]bool{
+		"b8e471f58bcbca63b07bda20e428190409c2db47": true, // second commit
+		"c2d30fa8ef288618f65f6eed6e168e0d514886f4": true, // init tree
+		"d3ff53e0564a9f87d8e84b6e28e5060e517008aa": true, // CHANGELOG
+	}
+
+	initCommit := s.commit(c, plumbing.NewHash(initialCommit))
+	secondCommit := s.commit(c, plumbing.NewHash(secondCommit))
+
+	localHist, err := Objects(s.Storer, []*object.Commit{initCommit}, nil)
+	c.Assert(err, IsNil)
+
+	remoteHist, err := Objects(s.Storer, []*object.Commit{secondCommit}, localHist)
+	c.Assert(err, IsNil)
+
+	for _, h := range remoteHist {
+		c.Assert(revList[h.String()], Equals, true)
+	}
+	c.Assert(len(remoteHist), Equals, len(revList))
+}
+
+func (s *RevListSuite) TestRevListObjectsReverse(c *C) {
+	initCommit := s.commit(c, plumbing.NewHash(initialCommit))
+	secondCommit := s.commit(c, plumbing.NewHash(secondCommit))
+
+	localHist, err := Objects(s.Storer, []*object.Commit{secondCommit}, nil)
+	c.Assert(err, IsNil)
+
+	remoteHist, err := Objects(s.Storer, []*object.Commit{initCommit}, localHist)
+	c.Assert(err, IsNil)
+
+	c.Assert(len(remoteHist), Equals, 0)
+}
+
+func (s *RevListSuite) TestRevListObjectsSameCommit(c *C) {
+	commit := s.commit(c, plumbing.NewHash(secondCommit))
+
+	localHist, err := Objects(s.Storer, []*object.Commit{commit}, nil)
+	c.Assert(err, IsNil)
+
+	remoteHist, err := Objects(s.Storer, []*object.Commit{commit}, localHist)
+	c.Assert(err, IsNil)
+
+	c.Assert(len(remoteHist), Equals, 0)
+}
+
+// * 6ecf0ef vendor stuff
+// | * e8d3ffa some code in a branch
+// |/
+// * 918c48b some code
+// -----
+func (s *RevListSuite) TestRevListObjectsNewBranch(c *C) {
+	someCommit := s.commit(c, plumbing.NewHash(someCommit))
+	someCommitBranch := s.commit(c, plumbing.NewHash(someCommitBranch))
+	someCommitOtherBranch := s.commit(c, plumbing.NewHash(someCommitOtherBranch))
+
+	localHist, err := Objects(s.Storer, []*object.Commit{someCommit}, nil)
+	c.Assert(err, IsNil)
+
+	remoteHist, err := Objects(
+		s.Storer, []*object.Commit{someCommitBranch, someCommitOtherBranch}, localHist)
+	c.Assert(err, IsNil)
+
+	revList := map[string]bool{
+		"a8d315b2b1c615d43042c3a62402b8a54288cf5c": true, // init tree
+		"cf4aa3b38974fb7d81f367c0830f7d78d65ab86b": true, // vendor folder
+		"9dea2395f5403188298c1dabe8bdafe562c491e3": true, // foo.go
+		"e8d3ffab552895c19b9fcf7aa264d277cde33881": true, // branch commit
+		"dbd3641b371024f44d0e469a9c8f5457b0660de1": true, // init tree
+		"7e59600739c96546163833214c36459e324bad0a": true, // README
+		"6ecf0ef2c2dffb796033e5a02219af86ec6584e5": true, // otherBranch commit
+	}
+
+	for _, h := range remoteHist {
+		c.Assert(revList[h.String()], Equals, true)
+	}
+	c.Assert(len(remoteHist), Equals, len(revList))
+}