Describe method initial implementation

Signed-off-by: Eduardo Lezcano <eduardo.lezcano@be.atlascopco.com>

Author: Eduardo Lezcano

repository.go

@@ -1223,3 +1223,102 @@ func (r *Repository) createNewObjectPack(cfg *RepackConfig) (h plumbing.Hash, er
 
 	return h, err
 }
+
+type DescribeOptions struct {
+	// Contains find the tag that comes after the commit
+	//Contains bool
+	// Debug search strategy on stderr
+	//Debug bool
+	// All Use any reference
+	//All bool
+	// Tags use any tag, even unannotated
+	//Tags bool
+	// FirstParent only follow first parent
+	//FirstParent bool
+	// Use <Abbrev> digits to display SHA-1s
+	// By default is 8
+	//Abbrev int
+	// Only output exact matches
+	//ExactMatch bool
+	// Consider <Candidates> most recent tags
+	// By default is 10
+	//Candidates int
+	// Only consider tags matching <Match> pattern
+	//Match string
+	// Show abbreviated commit object as fallback
+	//Always bool
+	// Append <mark> on dirty working tree (default: "-dirty")
+	Dirty string
+}
+
+type Describe struct {
+	// Reference being described
+	Hash *plumbing.Hash
+	// Tag of the describe object
+	Tag *plumbing.Reference
+	// Distance to the tag object in commits
+	Distance int
+	// Dirty string to append
+	Dirty string
+}
+
+func (d *Describe) String() string {
+	return fmt.Sprintf("%v-%v-%v-%v",
+		d.Tag.Name().Short(),
+		d.Distance,
+		d.Hash.String()[0:8],
+		d.Dirty)
+}
+
+func (r *Repository) Describe(options *DescribeOptions, hashes ...*plumbing.Hash) ([]Describe, error) {
+
+	var describes []Describe
+
+	for _, hash := range hashes {
+
+		// Fetch the reference log
+		commitIterator, err := r.Log(&LogOptions{
+			From:  *hash,
+			Order: LogOrderCommitterTime,
+		})
+		if err != nil {
+			return nil, err
+		}
+
+		// Tag map for rapid (?) query
+		tagIterator, err := r.Tags()
+		if err != nil {
+			return nil, err
+		}
+		tags := make(map[plumbing.Hash]*plumbing.Reference)
+		tagIterator.ForEach(func(t *plumbing.Reference) error {
+			tags[t.Hash()] = t
+			return nil
+		})
+
+
+		// Search the tag
+		var tag *plumbing.Reference
+		var count int
+		err = commitIterator.ForEach(func(c *object.Commit) error {
+			if t, ok := tags[c.Hash]; ok {
+				tag = t
+			}
+			if tag != nil {
+				return storer.ErrStop
+			}
+			count++
+			return nil
+		})
+
+		describes = append(describes, Describe{
+			hash,
+			tag,
+			count,
+			options.Dirty,
+		})
+
+	}
+
+	return describes, nil
+}