Add preferences for analytics

.gitignore

@@ -25,6 +25,9 @@ node_modules/
 npm-debug.log*
 .pnpm-debug.log
 
+# Nuxt
+.nuxt
+
 # Local certificates
 *.pem
 *.crt

documentation/reference/frontend/feature_flags.md

@@ -0,0 +1,119 @@
+# Feature flags
+
+Feature flags control how the app works in different environments and for
+different users.
+
+## Concepts
+
+### Status
+
+The status of a feature can be one of three values:
+
+- `enabled`
+- `disabled`
+- `switchable`
+
+This is configurable and must be set in the feature flags configuration file,
+`~/feat/feature-flags.json`.
+
+A `switchable` flag in a public environment like 'staging' or 'production'
+effectively becomes a user-level preferences toggle.
+
+### State
+
+The state of a feature can be one of two values:
+
+- `on`
+- `off`
+
+This is determined by the [feature status](#status) and user-preferences.
+
+- An `enabled` feature is always `on`.
+- A `disabled` feature is always `off`.
+- A switchable feature can be `on` or `off` based on the user's preference. This
+  `preferredState` is recorded in a cookie. If no preference has been set, the
+  [`defaultState`](#defaultstate) will be used.
+
+### Cascade
+
+The current environment can be 'local', 'development', 'staging' or 'production'
+based on the `DEPLOYMENT_ENV` environment variable (assumed 'local' by default).
+
+If a feature status is set for an environment, it is assumed to be same value
+for all environments before it and `disabled` for all environments after it
+(unless specified otherwise). For example, consider the following configuration:
+
+```json
+{
+  "local": "enabled",
+  "staging": "switchable"
+}
+```
+
+Here the feature will be
+
+- `enabled` for 'local' environment (configured)
+- `switchable` for 'development' environment (cascaded from staging)
+- `switchable` for 'staging' environment (configured)
+- `disabled` for 'production' environment (default)
+
+## File structure
+
+The feature flags configuration file, `~/feat/feature-flags.json` contains two
+top-level keys, `features` and `groups`.
+
+### `features`
+
+This is a mapping of feature names to feature configurations.
+
+#### Key: title
+
+This is an identifier for the feature. This identifier is looked up in the i18n
+strings to generate a human-readable purpose (`pref-page.features.${title}`) for
+the feature.
+
+Conventionally, `_` is used as the separator for the name so that the name is a
+valid JS identifier.
+
+#### Value: configuration
+
+This controls the behavior of the feature flag. It is an object containing three
+fields, `status`, `description` and `defaultState`.
+
+##### `status`
+
+It is a mapping of different environments with the status of the flag in that
+environment. For example, a feature that's in development may be 'switchable' in
+'staging' but 'disabled' in 'production'.
+
+##### `defaultState`
+
+This is the state of a switchable feature when the user has not switched it. For
+example, a feature that's in development may start as 'opt-in', being 'off' by
+default and may gradually change to opt-out, becoming 'on' by default.
+
+##### `description`
+
+This is a description of the feature that appears in the internal `/preferences`
+page.
+
+⚠️ This field is not internationalised because it's for internal use only. You
+should [populate `en.json5`](#key-title) if the feature is switchable and
+visible to the user.
+
+### `groups`
+
+This setting pertains to how feature flags can serve as user-level preferences.
+It is an array of objects, each containing two fields, `title` and `features`.
+
+#### `title`
+
+This is an identifier for the group. This identifier is looked up in the i18n
+strings to generate a human-readable name (`pref-page.groups.${title}.title`)
+and description (`pref-page.groups.${title}.desc`) for the group.
+
+#### `features`
+
+This is a list of strings where each string must be a
+[key from the upper `features` section](#key-title). Each switchable feature
+from this list will show up in the preferences modal.

documentation/reference/frontend/index.md

@@ -0,0 +1,7 @@
+# Frontend
+
+```{toctree}
+:maxdepth: 1
+
+feature_flags
+```

documentation/reference/index.md

@@ -6,5 +6,6 @@
 github_contribution_practices
 dev_flow
 api/index
+frontend/index
 search_algorithm
 ```

frontend/feat/feature-flags.json

@@ -15,18 +15,18 @@
       },
       "description": "Toggle the new header, including recent searches."
     },
-    "feat_disabled": {
-      "status": "disabled",
-      "description": "Will always be disabled"
-    },
-    "feat_enabled": {
-      "status": "enabled",
-      "description": "Will always be enabled"
-    },
-    "feat_switchable": {
-      "status": "switchable",
-      "description": "Can be switched between on and off",
-      "defaultState": "on"
+    "analytics": {
+      "status": {
+        "staging": "switchable",
+        "production": "disabled"
+      },
+      "description": "Record custom events and page views."
+    }
+  },
+  "groups": [
+    {
+      "title": "analytics",
+      "features": ["analytics"]
     }
-  }
+  ]
 }

frontend/src/components/VCheckbox/VCheckbox.vue

@@ -4,24 +4,55 @@
     class="relative flex text-sm leading-5"
     :class="labelClasses"
   >
-    <!--
-    The checkbox focus style is a slight variation on the `focus-slim-tx` style.
-    Because it becomes filled when checked, it also needs the
-    `checked:focus-visible:border-white` class.
-    -->
-    <input
-      :id="id"
-      type="checkbox"
-      class="checkbox h-5 w-5 flex-shrink-0 appearance-none rounded-sm border border-dark-charcoal bg-white me-3 focus-slim-tx checked:bg-dark-charcoal checked:focus-visible:border-white disabled:border-dark-charcoal-40 disabled:bg-dark-charcoal-10 checked:disabled:border-dark-charcoal-40 checked:disabled:bg-dark-charcoal-40"
-      v-bind="inputAttrs"
-      @change="onChange"
-    />
-    <VIcon
-      v-show="localCheckedState"
-      class="absolute transform text-white"
-      :icon-path="checkIcon"
-      :size="5"
-    />
+    <div class="relative">
+      <!--
+      The checkbox focus style is a slight variation on the `focus-slim-tx` style.
+      Because it becomes filled when checked, it also needs the
+      `checked:focus-visible:border-white` class.
+      -->
+      <input
+        :id="id"
+        type="checkbox"
+        class="block appearance-none border border-dark-charcoal bg-white transition-colors duration-100 me-3 checked:bg-dark-charcoal disabled:border-dark-charcoal-40 disabled:bg-dark-charcoal-10 checked:disabled:border-dark-charcoal-40 checked:disabled:bg-dark-charcoal-40"
+        :class="
+          isSwitch
+            ? ['h-4.5', 'w-9', 'rounded-full', 'focus-slim-offset']
+            : [
+                'h-5',
+                'w-5',
+                'rounded-sm',
+                'focus-slim-tx',
+                'checked:focus-visible:border-white',
+              ]
+        "
+        v-bind="inputAttrs"
+        @click="onChange"
+      />
+
+      <!-- Knob, for when `ifSwitch` is `true` -->
+      <div
+        v-if="isSwitch"
+        class="absolute top-0.75 left-0.75 h-3 w-3 rounded-full transition-transform duration-100"
+        :class="
+          localCheckedState
+            ? ['bg-white', 'translate-x-[1.125rem]']
+            : disabled
+            ? ['bg-dark-charcoal-40']
+            : ['bg-dark-charcoal']
+        "
+        aria-hidden="true"
+      />
+
+      <!-- Checkmark, for when `ifSwitch` is `false` -->
+      <VIcon
+        v-else
+        v-show="localCheckedState"
+        class="absolute inset-0 transform text-white"
+        :icon-path="checkIcon"
+        :size="5"
+      />
+    </div>
+
     <!--  @slot The checkbox label  --><slot />
   </label>
 </template>
@@ -103,6 +134,13 @@ export default defineComponent({
       type: Boolean,
       default: false,
     },
+    /**
+     * whether to make the checkbox appear like a switch
+     */
+    isSwitch: {
+      type: Boolean,
+      default: false,
+    },
   },
   emits: {
     change: defineEvent<[Omit<CheckboxAttrs, "disabled">]>(),

frontend/src/components/VCheckbox/meta/VCheckbox.stories.mdx

@@ -42,6 +42,8 @@ export const Template = (args) => ({
 
 <Description of={VCheckbox} />
 
+<ArgsTable of={VCheckbox} />
+
 ## Default checkbox
 
 <Canvas>
@@ -58,7 +60,25 @@ export const Template = (args) => ({
   </Story>
 </Canvas>
 
-<ArgsTable of={VCheckbox} />
+## Switch
+
+The checkbox can alternatively be rendered as a switch, when the choice is
+between an on/off decision.
+
+<Canvas>
+  <Story
+    name="Switch"
+    args={{
+      id: "default",
+      name: "storybook",
+      value: "codeIsPoetry",
+      isSwitch: true,
+    }}
+    argTypes={checkboxArgTypes}
+  >
+    {Template.bind({})}
+  </Story>
+</Canvas>
 
 export const LicenseCheckboxTemplate = (args) => ({
   template: `<fieldset>

frontend/src/locales/scripts/en.json5

@@ -680,6 +680,15 @@
   "skip-to-content": "Skip to content",
   "pref-page": {
     title: "Preferences",
+    groups: {
+      analytics: {
+        title: "Analytics",
+        desc: "Participate in anonymous analytics to improve user experience.",
+      },
+    },
+    features: {
+      analytics: "Record custom events and page views.",
+    },
     "non-switchable": {
       title: "Non-switchable features",
       desc: "You cannot modify the status of these features.",