Split id.go into several files

backend/ids.go

@@ -0,0 +1,50 @@
+package backend
+
+// IDs is an ordered list of IDs that implements sort.Interface.
+type IDs []ID
+
+func (ids IDs) Len() int {
+	return len(ids)
+}
+
+func (ids IDs) Less(i, j int) bool {
+	if len(ids[i]) < len(ids[j]) {
+		return true
+	}
+
+	for k, b := range ids[i] {
+		if b == ids[j][k] {
+			continue
+		}
+
+		if b < ids[j][k] {
+			return true
+		}
+
+		return false
+	}
+
+	return false
+}
+
+func (ids IDs) Swap(i, j int) {
+	ids[i], ids[j] = ids[j], ids[i]
+}
+
+// Uniq returns list without duplicate IDs. The returned list retains the order
+// of the original list so that the order of the first occurrence of each ID
+// stays the same.
+func (ids IDs) Uniq() (list IDs) {
+	seen := NewIDSet()
+
+	for _, id := range ids {
+		if seen.Has(id) {
+			continue
+		}
+
+		list = append(list, id)
+		seen.Insert(id)
+	}
+
+	return list
+}