1 files changed, 43 insertions, 0 deletions
diff --git a/commitquery/generation.go b/commitquery/generation.go
new file mode 100644
index 00000000..05228b29
--- /dev/null
+++ b/commitquery/generation.go
@@ -0,0 +1,43 @@
+package commitquery
+
+import (
+	"math"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// EffectiveGeneration returns one node's generation value.
+func (query *Query) effectiveGeneration(idx nodeIndex) uint64 {
+	if !query.nodes[idx].hasGeneration {
+		return generationInfinity
+	}
+
+	return query.nodes[idx].generation
+}
+
+const (
+	generationInfinity = uint64(math.MaxUint64)
+)
+
+func compareByGeneration(query *Query) func(nodeIndex, nodeIndex) int {
+	return func(left, right nodeIndex) int {
+		leftGeneration := query.effectiveGeneration(left)
+		rightGeneration := query.effectiveGeneration(right)
+
+		switch {
+		case leftGeneration < rightGeneration:
+			return -1
+		case leftGeneration > rightGeneration:
+			return 1
+		}
+
+		switch {
+		case query.nodes[left].commitTime < query.nodes[right].commitTime:
+			return -1
+		case query.nodes[left].commitTime > query.nodes[right].commitTime:
+			return 1
+		}
+
+		return objectid.Compare(query.nodes[left].id, query.nodes[right].id)
+	}
+}