feat(ui): Allow configuring default dark-mode value (#1015)

* fix: theme flickering

* chore(ui): added dark mode tests

* feat(ui): Expose new ui.dark-mode parameter to set default theme

* refactor(ui): Rename theme variable to themeFromCookie for clarity

---------

Co-authored-by: TwiN <twin@linux.com>
Co-authored-by: TwiN <chris@twin.sh>

README.md

@@ -242,6 +242,7 @@ If you want to test it locally, see [Docker](#docker).
 | `ui.buttons[].name`          | Text to display on the button.                                                                                                       | Required `""`              |
 | `ui.buttons[].link`          | Link to open when the button is clicked.                                                                                             | Required `""`              |
 | `ui.custom-css`              | Custom CSS                                                                                                                           | `""`                       |
+| `ui.dark-mode`               | Whether to enable dark mode by default. Note that this is superseded by the user's operating system theme preferences.               | `true`                     |
 | `maintenance`                | [Maintenance configuration](#maintenance).                                                                                           | `{}`                       |
 
 If you want more verbose logging, you may set the `GATUS_LOG_LEVEL` environment variable to `DEBUG`.

api/spa.go

@@ -10,8 +10,19 @@ import (
 	"github.com/gofiber/fiber/v2"
 )
 
-func SinglePageApplication(ui *ui.Config) fiber.Handler {
+func SinglePageApplication(uiConfig *ui.Config) fiber.Handler {
 	return func(c *fiber.Ctx) error {
+		vd := ui.ViewData{UI: uiConfig}
+		{
+			themeFromCookie := string(c.Request().Header.Cookie("theme"))
+			if len(themeFromCookie) > 0 {
+				if themeFromCookie == "dark" {
+					vd.Theme = "dark"
+				}
+			} else if uiConfig.IsDarkMode() { // Since there's no theme cookie, we'll rely on ui.DarkMode
+				vd.Theme = "dark"
+			}
+		}
 		t, err := template.ParseFS(static.FileSystem, static.IndexPath)
 		if err != nil {
 			// This should never happen, because ui.ValidateAndSetDefaults validates that the template works.
@@ -19,7 +30,7 @@ func SinglePageApplication(ui *ui.Config) fiber.Handler {
 			return c.Status(500).SendString("Failed to parse template. This should never happen, because the template is validated on start.")
 		}
 		c.Set("Content-Type", "text/html")
-		err = t.Execute(c, ui)
+		err = t.Execute(c, vd)
 		if err != nil {
 			// This should never happen, because ui.ValidateAndSetDefaults validates that the template works.
 			logr.Errorf("[api.SinglePageApplication] Failed to execute template. This should never happen, because the template is validated on start. Error: %s", err.Error())

api/spa_test.go

@@ -41,27 +41,48 @@ func TestSinglePageApplication(t *testing.T) {
 	type Scenario struct {
 		Name              string
 		Path              string
-		ExpectedCode int
 		Gzip              bool
+		CookieDarkMode    bool
+		UIDarkMode        bool
+		ExpectedCode      int
+		ExpectedDarkTheme bool
 	}
 	scenarios := []Scenario{
 		{
 			Name:              "frontend-home",
 			Path:              "/",
+			CookieDarkMode:    true,
+			UIDarkMode:        false,
+			ExpectedDarkTheme: true,
 			ExpectedCode:      200,
 		},
 		{
-			Name:         "frontend-endpoint",
+			Name:              "frontend-endpoint-light",
 			Path:              "/endpoints/core_frontend",
+			CookieDarkMode:    false,
+			UIDarkMode:        false,
+			ExpectedDarkTheme: false,
+			ExpectedCode:      200,
+		},
+		{
+			Name:              "frontend-endpoint-dark",
+			Path:              "/endpoints/core_frontend",
+			CookieDarkMode:    false,
+			UIDarkMode:        true,
+			ExpectedDarkTheme: true,
 			ExpectedCode:      200,
 		},
 	}
 	for _, scenario := range scenarios {
 		t.Run(scenario.Name, func(t *testing.T) {
+			cfg.UI.DarkMode = &scenario.UIDarkMode
 			request := httptest.NewRequest("GET", scenario.Path, http.NoBody)
 			if scenario.Gzip {
 				request.Header.Set("Accept-Encoding", "gzip")
 			}
+			if scenario.CookieDarkMode {
+				request.Header.Set("Cookie", "theme=dark")
+			}
 			response, err := router.Test(request)
 			if err != nil {
 				return
@@ -71,9 +92,16 @@ func TestSinglePageApplication(t *testing.T) {
 				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, response.StatusCode)
 			}
 			body, _ := io.ReadAll(response.Body)
-			if !strings.Contains(string(body), cfg.UI.Title) {
+			strBody := string(body)
+			if !strings.Contains(strBody, cfg.UI.Title) {
 				t.Errorf("%s %s should have contained the title", request.Method, request.URL)
 			}
+			if scenario.ExpectedDarkTheme && !strings.Contains(strBody, "class=\"dark\"") {
+				t.Errorf("%s %s should have responded with dark mode headers", request.Method, request.URL)
+			}
+			if !scenario.ExpectedDarkTheme && strings.Contains(strBody, "class=\"dark\"") {
+				t.Errorf("%s %s should not have responded with dark mode headers", request.Method, request.URL)
+			}
 		})
 	}
 }

config/ui/ui.go

@@ -18,6 +18,8 @@ const (
 )
 
 var (
+	defaultDarkMode = true
+
 	ErrButtonValidationFailed = errors.New("invalid button configuration: missing required name or link")
 )
 
@@ -30,6 +32,14 @@ type Config struct {
 	Link        string   `yaml:"link,omitempty"`        // Link to open when clicking on the logo
 	Buttons     []Button `yaml:"buttons,omitempty"`     // Buttons to display below the header
 	CustomCSS   string   `yaml:"custom-css,omitempty"`  // Custom CSS to include in the page
+	DarkMode    *bool    `yaml:"dark-mode,omitempty"`   // DarkMode is a flag to enable dark mode by default
+}
+
+func (cfg *Config) IsDarkMode() bool {
+	if cfg.DarkMode != nil {
+		return *cfg.DarkMode
+	}
+	return defaultDarkMode
 }
 
 // Button is the configuration for a button on the UI
@@ -55,6 +65,7 @@ func GetDefaultConfig() *Config {
 		Logo:        defaultLogo,
 		Link:        defaultLink,
 		CustomCSS:   defaultCustomCSS,
+		DarkMode:    &defaultDarkMode,
 	}
 }
 
@@ -78,6 +89,9 @@ func (cfg *Config) ValidateAndSetDefaults() error {
 	if len(cfg.CustomCSS) == 0 {
 		cfg.CustomCSS = defaultCustomCSS
 	}
+	if cfg.DarkMode == nil {
+		cfg.DarkMode = &defaultDarkMode
+	}
 	for _, btn := range cfg.Buttons {
 		if err := btn.Validate(); err != nil {
 			return err
@@ -89,5 +103,10 @@ func (cfg *Config) ValidateAndSetDefaults() error {
 		return err
 	}
 	var buffer bytes.Buffer
-	return t.Execute(&buffer, cfg)
+	return t.Execute(&buffer, ViewData{UI: cfg, Theme: "dark"})
+}
+
+type ViewData struct {
+	UI    *Config
+	Theme string
 }

web/app/public/index.html

@@ -1,11 +1,11 @@
 <!DOCTYPE html>
-<html lang="en">
+<html lang="en" class="{{ .Theme }}">
   <head>
     <meta charset="utf-8" />
     <script type="text/javascript">
-      window.config = {logo: "{{ .Logo }}", header: "{{ .Header }}", link: "{{ .Link }}", buttons: []};{{- range .Buttons}}window.config.buttons.push({name:"{{ .Name }}",link:"{{ .Link }}"});{{end}}
+      window.config = {logo: "{{ .UI.Logo }}", header: "{{ .UI.Header }}", link: "{{ .UI.Link }}", buttons: []};{{- range .UI.Buttons}}window.config.buttons.push({name:"{{ .Name }}",link:"{{ .Link }}"});{{end}}
     </script>
-    <title>{{ .Title }}</title>
+    <title>{{ .UI.Title }}</title>
     <meta http-equiv="X-UA-Compatible" content="IE=edge" />
     <meta name="viewport" content="width=device-width,initial-scale=1.0" />
     <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
@@ -14,10 +14,10 @@
     <link rel="manifest" href="/manifest.json" crossorigin="use-credentials" />
     <link rel="shortcut icon" href="/favicon.ico" />
     <link rel="stylesheet" href="/css/custom.css" />
-    <meta name="description" content="{{ .Description }}" />
+    <meta name="description" content="{{ .UI.Description }}" />
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
-    <meta name="apple-mobile-web-app-title" content="{{ .Title }}" />
+    <meta name="apple-mobile-web-app-title" content="{{ .UI.Title }}" />
-    <meta name="application-name" content="{{ .Title }}" />
+    <meta name="application-name" content="{{ .UI.Title }}" />
     <meta name="theme-color" content="#f7f9fb" />
   </head>
   <body class="dark:bg-gray-900">

web/app/src/App.vue

@@ -78,13 +78,13 @@ export default {
   },
   computed: {
     logo() {
-      return window.config && window.config.logo && window.config.logo !== '{{ .Logo }}' ? window.config.logo : "";
+      return window.config && window.config.logo && window.config.logo !== '{{ .UI.Logo }}' ? window.config.logo : "";
     },
     header() {
-      return window.config && window.config.header && window.config.header !== '{{ .Header }}' ? window.config.header : "Health Status";
+      return window.config && window.config.header && window.config.header !== '{{ .UI.Header }}' ? window.config.header : "Health Status";
     },
     link() {
-      return window.config && window.config.link && window.config.link !== '{{ .Link }}' ? window.config.link : null;
+      return window.config && window.config.link && window.config.link !== '{{ .UI.Link }}' ? window.config.link : null;
     },
     buttons() {
       return window.config && window.config.buttons ? window.config.buttons : [];

web/app/src/components/Settings.vue

@@ -23,6 +23,11 @@
 import { MoonIcon, SunIcon } from '@heroicons/vue/20/solid'
 import { ArrowPathIcon } from '@heroicons/vue/24/solid'
 
+function wantsDarkMode() {
+  const themeFromCookie = document.cookie.match(/theme=(dark|light);?/)?.[1];
+  return themeFromCookie === 'dark' || !themeFromCookie && (window.matchMedia('(prefers-color-scheme: dark)').matches || document.documentElement.classList.contains("dark"));
+}
+
 export default {
   name: 'Settings',
   components: {
@@ -48,15 +53,15 @@ export default {
       this.setRefreshInterval(this.$refs.refreshInterval.value);
     },
     toggleDarkMode() {
-      if (localStorage.theme === 'dark') {
+      if (wantsDarkMode()) {
-        localStorage.theme = 'light';
+        document.cookie = `theme=light; path=/; max-age=31536000; samesite=strict`;
       } else {
-        localStorage.theme = 'dark';
+        document.cookie = `theme=dark; path=/; max-age=31536000; samesite=strict`;
       }
       this.applyTheme();
     },
     applyTheme() {
-      if (localStorage.theme === 'dark' || (!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
+      if (wantsDarkMode()) {
         this.darkMode = true;
         document.documentElement.classList.add('dark');
       } else {
@@ -70,7 +75,6 @@ export default {
       this.refreshInterval = 300;
     }
     this.setRefreshInterval(this.refreshInterval);
-    // dark mode
     this.applyTheme();
   },
   unmounted() {
@@ -80,7 +84,7 @@ export default {
     return {
       refreshInterval: localStorage.getItem('gatus:refresh-interval') < 10 ? 300 : parseInt(localStorage.getItem('gatus:refresh-interval')),
       refreshIntervalHandler: 0,
-      darkMode: true
+      darkMode: wantsDarkMode()
     }
   },
 }

web/static/index.html

@@ -1 +1 @@
-<!doctype html><html lang="en"><head><meta charset="utf-8"/><script>window.config = {logo: "{{ .Logo }}", header: "{{ .Header }}", link: "{{ .Link }}", buttons: []};{{- range .Buttons}}window.config.buttons.push({name:"{{ .Name }}",link:"{{ .Link }}"});{{end}}</script><title>{{ .Title }}</title><meta http-equiv="X-UA-Compatible" content="IE=edge"/><meta name="viewport" content="width=device-width,initial-scale=1"/><link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png"/><link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png"/><link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png"/><link rel="manifest" href="/manifest.json" crossorigin="use-credentials"/><link rel="shortcut icon" href="/favicon.ico"/><link rel="stylesheet" href="/css/custom.css"/><meta name="description" content="{{ .Description }}"/><meta name="apple-mobile-web-app-status-bar-style" content="black-translucent"/><meta name="apple-mobile-web-app-title" content="{{ .Title }}"/><meta name="application-name" content="{{ .Title }}"/><meta name="theme-color" content="#f7f9fb"/><script defer="defer" src="/js/chunk-vendors.js"></script><script defer="defer" src="/js/app.js"></script><link href="/css/app.css" rel="stylesheet"></head><body class="dark:bg-gray-900"><noscript><strong>Enable JavaScript to view this page.</strong></noscript><div id="app"></div></body></html>
+<!doctype html><html lang="en" class="{{ .Theme }}"><head><meta charset="utf-8"/><script>window.config = {logo: "{{ .UI.Logo }}", header: "{{ .UI.Header }}", link: "{{ .UI.Link }}", buttons: []};{{- range .UI.Buttons}}window.config.buttons.push({name:"{{ .Name }}",link:"{{ .Link }}"});{{end}}</script><title>{{ .UI.Title }}</title><meta http-equiv="X-UA-Compatible" content="IE=edge"/><meta name="viewport" content="width=device-width,initial-scale=1"/><link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png"/><link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png"/><link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png"/><link rel="manifest" href="/manifest.json" crossorigin="use-credentials"/><link rel="shortcut icon" href="/favicon.ico"/><link rel="stylesheet" href="/css/custom.css"/><meta name="description" content="{{ .UI.Description }}"/><meta name="apple-mobile-web-app-status-bar-style" content="black-translucent"/><meta name="apple-mobile-web-app-title" content="{{ .UI.Title }}"/><meta name="application-name" content="{{ .UI.Title }}"/><meta name="theme-color" content="#f7f9fb"/><script defer="defer" src="/js/chunk-vendors.js"></script><script defer="defer" src="/js/app.js"></script><link href="/css/app.css" rel="stylesheet"></head><body class="dark:bg-gray-900"><noscript><strong>Enable JavaScript to view this page.</strong></noscript><div id="app"></div></body></html>