refactor: remove go-appdir dependency

internal/locations/provider.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2021 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 locations
+
+import (
+	"os"
+	"path/filepath"
+)
+
+// Provider provides standard locations.
+type Provider interface {
+	UserConfig() string
+	UserCache() string
+}
+
+// DefaultProvider is a locations provider using the system-default storage locations.
+type DefaultProvider struct {
+	config, cache string
+}
+
+func NewDefaultProvider(name string) (*DefaultProvider, error) {
+	config, err := os.UserConfigDir()
+	if err != nil {
+		return nil, err
+	}
+
+	cache, err := os.UserCacheDir()
+	if err != nil {
+		return nil, err
+	}
+
+	return &DefaultProvider{
+		config: filepath.Join(config, name),
+		cache:  filepath.Join(cache, name),
+	}, nil
+}
+
+func (p *DefaultProvider) UserConfig() string {
+	return p.config
+}
+
+func (p *DefaultProvider) UserCache() string {
+	return p.cache
+}