Add intersect util method for StringSet

pkg/common/stringset/stringset.go

@@ -93,3 +93,60 @@ func (s *stringSet) ToSlice() []string {
 	}
 	return keys
 }
+
+// Intersect returns the intersection between two StringSet
+func (s *stringSet) Intersect(other *stringSet) (intersection *stringSet) {
+	var ret *stringSet
+	var wg sync.WaitGroup
+
+	var slen, otherlen int
+
+	createIntersect := func(smallerlen int, smaller, greater *stringSet) (ret *stringSet) {
+		ret = &stringSet{
+			m: make(map[string]bool, smallerlen),
+		}
+		// Copy smaller set in ret
+		smaller.Lock()
+		for str := range smaller.m {
+			ret.m[str] = true
+		}
+		smaller.Unlock()
+
+		greater.Lock()
+		defer greater.Unlock()
+		for element := range ret.m {
+			// If element in smaller exists also in greater moves along
+			if _, exists := greater.m[element]; exists {
+				continue
+			}
+			// otherwise deletes it also from ret
+			ret.Lock()
+			delete(ret.m, element)
+			ret.Unlock()
+		}
+		return ret
+	}
+
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		s.Lock()
+		slen = len(s.m)
+		s.Unlock()
+	}()
+	go func() {
+		defer wg.Done()
+		other.Lock()
+		otherlen = len(other.m)
+		other.Unlock()
+	}()
+	wg.Wait()
+	switch {
+	case slen >= otherlen:
+		ret = createIntersect(otherlen, other, s)
+
+	case slen < otherlen:
+		ret = createIntersect(slen, s, other)
+	}
+	return ret
+}

pkg/common/stringset/stringset_test.go

@@ -15,6 +15,7 @@
 package stringset
 
 import (
+	"sort"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -97,3 +98,56 @@ func TestStringSet_ToSlice(t *testing.T) {
 		assert.True(t, testSet.Contains(item))
 	}
 }
+
+var flagtests = []struct {
+	name      string
+	testdata1 []string
+	testdata2 []string
+	out       []string
+}{
+	{"both sets void", []string{}, []string{}, []string{}},
+	{"first set void", []string{}, []string{"testitem1", "testitem2"}, []string{}},
+	{"second set void", []string{"testitem2", "testitem1"}, []string{}, []string{}},
+	{"intersect all first set", []string{"testitem1"}, []string{"testitem1", "testitem2"}, []string{"testitem1"}},
+	{"intersect all second set", []string{"testitem1", "testitem2"}, []string{"testitem1"}, []string{"testitem1"}},
+	{"interscet subset of first set", []string{"testitem1", "testitem2", "testitem3"}, []string{"testitem1", "testitem2"}, []string{"testitem1", "testitem2"}},
+	{"interscet subset of second set", []string{"testitem1", "testitem2"}, []string{"testitem1", "testitem2", "testitem3"}, []string{"testitem1", "testitem2"}},
+}
+
+func TestStringSet_Intersect(t *testing.T) {
+
+	for _, tt := range flagtests {
+		t.Run(tt.name, func(t *testing.T) {
+
+			// Creates first testSet
+			testSet1 := &stringSet{
+				m: make(map[string]bool),
+			}
+
+			// Add testItems to testSet1
+			for _, item := range tt.testdata1 {
+				testSet1.m[item] = true
+			}
+
+			// Creates second testSet
+			testSet2 := &stringSet{
+				m: make(map[string]bool),
+			}
+
+			// Add testItems to testSet2
+			for _, item := range tt.testdata2 {
+				testSet2.m[item] = true
+			}
+			s := testSet1.Intersect(testSet2)
+			slice := s.ToSlice()
+			sort.Strings(slice)
+			sort.Strings(tt.out)
+
+			for i := range slice {
+				if slice[i] != tt.out[i] {
+					t.Errorf("got %q, want %q", slice[i], tt.out[i])
+				}
+			}
+		})
+	}
+}