[chore] much improved paging package (#2182)

internal/paging/util.go

@@ -0,0 +1,49 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package paging
+
+// Reverse will reverse the given input slice.
+func Reverse(in []string) []string {
+	var (
+		// Start at front.
+		i = 0
+
+		// Start at back.
+		j = len(in) - 1
+	)
+
+	for i < j {
+		// Swap i,j index values in slice.
+		in[i], in[j] = in[j], in[i]
+
+		// incr + decr,
+		// looping until
+		// they meet in
+		// the middle.
+		i++
+		j--
+	}
+
+	return in
+}
+
+// zero is a shorthand to check a generic value is its zero value.
+func zero[T comparable](t T) bool {
+	var z T
+	return t == z
+}