1 files changed, 122 insertions, 0 deletions
diff --git a/gerrit/series.go b/gerrit/series.go
new file mode 100644
index 000000000000..06d49805d35d
--- /dev/null
+++ b/gerrit/series.go
@@ -0,0 +1,122 @@
+package gerrit
+
+import (
+	"sort"
+
+	"github.com/apex/log"
+)
+
+// AssembleSeries consumes a list of `Changeset`, and groups them together to series
+//
+// We initially put every Changeset in its own Serie
+//
+// As we have no control over the order of the passed changesets,
+// we maintain a lookup table, mapLeafToSerie,
+// which allows to lookup a serie by its leaf commit id
+// We concat series in a fixpoint approach
+// because both appending and prepending is much more complex.
+// Concatenation moves changesets of the later changeset in the previous one
+// in a cleanup phase, we remove orphaned series (those without any changesets inside)
+// afterwards, we do an integrity check, just to be on the safe side.
+func AssembleSeries(changesets []*Changeset, log *log.Logger) ([]*Serie, error) {
+	series := make([]*Serie, 0)
+	mapLeafToSerie := make(map[string]*Serie, 0)
+
+	for _, changeset := range changesets {
+		logger := log.WithField("changeset", changeset.String())
+
+		logger.Debug("creating initial serie")
+		serie := &Serie{
+			ChangeSets: []*Changeset{changeset},
+		}
+		series = append(series, serie)
+		mapLeafToSerie[changeset.CommitID] = serie
+	}
+
+	// Combine series using a fixpoint approach, with a max iteration count.
+	log.Debug("glueing together phase")
+	for i := 1; i < 100; i++ {
+		didUpdate := false
+		log.Debugf("at iteration %d", i)
+		for _, serie := range series {
+			logger := log.WithField("serie", serie.String())
+			parentCommitIDs, err := serie.GetParentCommitIDs()
+			if err != nil {
+				return series, err
+			}
+			if len(parentCommitIDs) != 1 {
+				// We can't append merge commits to other series
+				logger.Infof("No single parent, skipping.")
+				continue
+			}
+			parentCommitID := parentCommitIDs[0]
+			logger.Debug("Looking for a predecessor.")
+			// if there's another serie that has this parent as a leaf, glue together
+			if otherSerie, ok := mapLeafToSerie[parentCommitID]; ok {
+				if otherSerie == serie {
+					continue
+				}
+				logger := logger.WithField("otherSerie", otherSerie)
+
+				myLeafCommitID, err := serie.GetLeafCommitID()
+				if err != nil {
+					return series, err
+				}
+
+				// append our changesets to the other serie
+				logger.Debug("Splicing together.")
+				otherSerie.ChangeSets = append(otherSerie.ChangeSets, serie.ChangeSets...)
+
+				delete(mapLeafToSerie, parentCommitID)
+				mapLeafToSerie[myLeafCommitID] = otherSerie
+
+				// orphan our serie
+				serie.ChangeSets = []*Changeset{}
+				// remove the orphaned serie from the lookup table
+				delete(mapLeafToSerie, myLeafCommitID)
+
+				didUpdate = true
+			} else {
+				logger.Debug("Not found.")
+			}
+		}
+		series = removeOrphanedSeries(series)
+		if !didUpdate {
+			log.Infof("converged after %d iterations", i)
+			break
+		}
+	}
+
+	// Check integrity, just to be on the safe side.
+	for _, serie := range series {
+		logger := log.WithField("serie", serie.String())
+		logger.Debugf("checking integrity")
+		err := serie.CheckIntegrity()
+		if err != nil {
+			logger.Errorf("checking integrity failed: %s", err)
+		}
+	}
+	return series, nil
+}
+
+// removeOrphanedSeries removes all empty series (that contain zero changesets)
+func removeOrphanedSeries(series []*Serie) []*Serie {
+	newSeries := []*Serie{}
+	for _, serie := range series {
+		if len(serie.ChangeSets) != 0 {
+			newSeries = append(newSeries, serie)
+		}
+	}
+	return newSeries
+}
+
+// SortSeries sorts a list of series by the number of changesets in each serie, descending
+func SortSeries(series []*Serie) []*Serie {
+	newSeries := make([]*Serie, len(series))
+	copy(newSeries, series)
+	sort.Slice(newSeries, func(i, j int) bool {
+		// the weight depends on the amount of changesets series changeset size
+		return len(series[i].ChangeSets) > len(series[j].ChangeSets)
+	})
+	return newSeries
+}