We build too many walls and not enough bridges

pkg/algo/sets.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2020 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// ProtonMail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package algo
+
+import "reflect"
+
+// SetIntersection complexity: O(n^2), could be better but this is simple enough
+func SetIntersection(a, b interface{}, eq func(a, b interface{}) bool) []interface{} {
+	set := make([]interface{}, 0)
+	av := reflect.ValueOf(a)
+
+	for i := 0; i < av.Len(); i++ {
+		el := av.Index(i).Interface()
+		if contains(b, el, eq) {
+			set = append(set, el)
+		}
+	}
+
+	return set
+}
+
+func contains(a, e interface{}, eq func(a, b interface{}) bool) bool {
+	v := reflect.ValueOf(a)
+
+	for i := 0; i < v.Len(); i++ {
+		if eq(v.Index(i).Interface(), e) {
+			return true
+		}
+	}
+
+	return false
+}