We build too many walls and not enough bridges

pkg/algo/algo.go

@@ -0,0 +1,19 @@
+// 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 provides some algorithm utils.
+package algo

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
+}

pkg/algo/sets_test.go

@@ -0,0 +1,71 @@
+// 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 (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type T struct {
+	k, v int
+}
+
+func TestSetIntersection(t *testing.T) {
+	keysAreEqual := func(a, b interface{}) bool {
+		return a.(T).k == b.(T).k
+	}
+
+	type args struct {
+		a  interface{}
+		b  interface{}
+		eq func(a, b interface{}) bool
+	}
+
+	tests := []struct {
+		name string
+		args args
+		want interface{}
+	}{
+		{
+			name: "integer sets",
+			args: args{a: []int{1, 2, 3}, b: []int{3, 4, 5}, eq: func(a, b interface{}) bool { return a == b }},
+			want: []int{3},
+		},
+		{
+			name: "string sets",
+			args: args{a: []string{"1", "2", "3"}, b: []string{"3", "4", "5"}, eq: func(a, b interface{}) bool { return a == b }},
+			want: []string{"3"},
+		},
+		{
+			name: "custom comp, only compare on keys, prefer first set if keys are the same",
+			args: args{a: []T{{k: 1, v: 1}, {k: 2, v: 2}}, b: []T{{k: 2, v: 1234}, {k: 3, v: 3}}, eq: keysAreEqual},
+			want: []T{{k: 2, v: 2}},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// using cmp.Equal because it handles the interfaces correctly; testify/assert doesn't
+			// treat these as equal because their types are different ([]interface vs []int)
+			if got := SetIntersection(tt.args.a, tt.args.b, tt.args.eq); cmp.Equal(got, tt.want) {
+				t.Errorf("SetIntersection() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}