[feature] User-selectable preset CSS themes for accounts (#2777)

* [feature] User-selectable preset themes

* docs, more theme stuff

* lint, tests

* fix css name

* correct some little issues

* add another theme

* fix poll background

* okay last theme i swear

* make retrieval of apimodel themes more conventional

* preallocate stylesheet slices

internal/processing/account/themes_test.go

@@ -0,0 +1,52 @@
+// 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 account_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/processing/account"
+)
+
+type ThemesTestSuite struct {
+	AccountStandardTestSuite
+}
+
+func (suite *ThemesTestSuite) TestPopulateThemes() {
+	config.SetWebAssetBaseDir("../../../web/assets")
+
+	themes := account.PopulateThemes()
+	if themes == nil {
+		suite.FailNow("themes was nil")
+	}
+
+	suite.NotEmpty(themes.SortedByTitle)
+	theme := themes.ByFileName["blurple-light.css"]
+	if theme == nil {
+		suite.FailNow("theme was nil")
+	}
+	suite.Equal("Blurple (light)", theme.Title)
+	suite.Equal("Official light blurple theme", theme.Description)
+	suite.Equal("blurple-light.css", theme.FileName)
+}
+
+func TestThemesTestSuite(t *testing.T) {
+	suite.Run(t, new(ThemesTestSuite))
+}