Improve delta reutilization

- Remove wrong 'if' on delta selector that causes poor delta reutilizations
- packfile.Encoder now can write deltas and objects in a non specific order
- ObjectToPack now saves the Offset on the packfile to be able to obtain base
offset in a recursive manner and write them before the delta itself
- Added encoder test to check cyclic delta chains
- Check the output packfile hash in all encoder tests

Signed-off-by: Antonio Jesus Navarro Perez <antnavper@gmail.com>

1 files changed, 31 insertions, 1 deletions

diff --git a/plumbing/format/packfile/object_pack.go b/plumbing/format/packfile/object_pack.go
index e22e783..1563517 100644
--- a/plumbing/format/packfile/object_pack.go
+++ b/plumbing/format/packfile/object_pack.go
@@ -13,12 +13,16 @@ type ObjectToPack struct {
 	// If the main object is not a delta, Base will be null
 	Base *ObjectToPack
 	// Original is the object that we can generate applying the delta to
-	// Base, or the same object as EncodedObject in the case of a non-delta
+	// Base, or the same object as Object in the case of a non-delta
 	// object.
 	Original plumbing.EncodedObject
 	// Depth is the amount of deltas needed to resolve to obtain Original
 	// (delta based on delta based on ...)
 	Depth int
+
+	// offset in pack when object has been already written, or 0 if it
+	// has not been written yet
+	Offset int64
 }
 
 // newObjectToPack creates a correct ObjectToPack based on a non-delta object
@@ -41,6 +45,32 @@ func newDeltaObjectToPack(base *ObjectToPack, original, delta plumbing.EncodedOb
 	}
 }
 
+// BackToOriginal converts that ObjectToPack to a non-deltified object if it was one
+func (o *ObjectToPack) BackToOriginal() {
+	if o.IsDelta() {
+		o.Object = o.Original
+		o.Base = nil
+		o.Depth = 0
+	}
+}
+
+// IsWritten returns if that ObjectToPack was
+// already written into the packfile or not
+func (o *ObjectToPack) IsWritten() bool {
+	return o.Offset > 1
+}
+
+// MarkWantWrite marks this ObjectToPack as WantWrite
+// to avoid delta chain loops
+func (o *ObjectToPack) MarkWantWrite() {
+	o.Offset = 1
+}
+
+// WantWrite checks if this ObjectToPack was marked as WantWrite before
+func (o *ObjectToPack) WantWrite() bool {
+	return o.Offset == 1
+}
+
 func (o *ObjectToPack) Type() plumbing.ObjectType {
 	if o.Original != nil {
 		return o.Original.Type()