feat(useIsDarkTheme): add useIsDarkTheme composable

Signed-off-by: Grigorii K. Shartsev <[email protected]>

docs/composables/useIsDarkTheme.md

@@ -0,0 +1,72 @@
+<!--
+  - SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+  - SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+
+```ts static
+import {
+    useIsDarkTheme,
+    useIsDarkThemeElement,
+} from '@nextcloud/vue/dist/Composables/useIsDarkTheme.js'
+```
+
+Same as `isDarkTheme` functions, but with reactivity.
+
+## Definition
+
+```ts static
+/**
+ * Check whether the dark theme is enabled on a specific element.
+ * If you need to check an entire page, use `useIsDarkTheme` instead for better performance.
+ * Reacts on element attributes change and system theme change.
+ * @param el - The element to check for the dark theme enabled on
+ * @return - computed boolean whether the dark theme is enabled
+ */
+declare function useIsDarkThemeElement(el: MaybeRef<HTMLElement> = document.body): DeepReadonly<Ref<boolean>>
+
+/**
+ * Shared composable to check whether the dark theme is enabled on the page.
+ * Reacts on body data-theme-* attributes change and system theme change.
+ * @return - computed boolean whether the dark theme is enabled
+ */
+declare function useIsDarkTheme(): DeepReadonly<Ref<boolean>>
+```
+
+## Example
+
+```vue
+<template>
+    <div>
+        <div :style="{ backgroundColor: isDarkTheme ? 'black' : 'white' }">
+            Is dark theme enabled? {{ isDarkTheme }}
+        </div>
+        <NcButton @click="switchTheme">Switch theme</NcButton>
+    </div>
+</template>
+
+<script>
+export default {
+    setup() {
+        const isDarkTheme = useIsDarkTheme()
+
+        // For documentation only. Do not use in production.
+        function switchTheme() {
+            if (isDarkTheme.value) {
+                document.body.setAttribute('data-theme-light', '')
+                document.body.removeAttribute('data-theme-dark')
+                document.body.setAttribute('data-themes', 'light')
+            } else {
+                document.body.setAttribute('data-theme-dark', '')
+                document.body.removeAttribute('data-theme-light')
+                document.body.setAttribute('data-themes', 'dark')
+            }
+        }
+
+        return {
+            isDarkTheme,
+            switchTheme,
+        }
+    },
+}
+</script>
+```

src/composables/index.js

@@ -7,3 +7,4 @@ export * from './useIsFullscreen/index.js'
 export * from './useIsMobile/index.js'
 export * from './useFormatDateTime.ts'
 export * from './useHotKey/index.js'
+export * from './useIsDarkTheme/index.ts'

src/composables/useIsDarkTheme/index.ts

@@ -0,0 +1,40 @@
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import type { DeepReadonly, Ref } from 'vue'
+import { ref, readonly, watch } from 'vue'
+import { createSharedComposable, usePreferredDark, useMutationObserver } from '@vueuse/core'
+import { checkIfDarkTheme } from '../../functions/isDarkTheme/index.ts'
+
+/**
+ * Check whether the dark theme is enabled on a specific element.
+ * If you need to check an entire page, use `useIsDarkTheme` instead for better performance.
+ * Reacts on element attributes change and system theme change.
+ * @param el - The element to check for the dark theme enabled on
+ * @return {DeepReadonly<Ref<boolean>>} - computed boolean whether the dark theme is enabled
+ */
+export function useIsDarkThemeElement(el: HTMLElement = document.body): DeepReadonly<Ref<boolean>> {
+	const isDarkTheme = ref(checkIfDarkTheme(el))
+	const isDarkSystemTheme = usePreferredDark()
+
+	/** Update the isDarkTheme */
+	function updateIsDarkTheme() {
+		isDarkTheme.value = checkIfDarkTheme(el)
+	}
+
+	// Watch for element change to handle data-theme* attributes change
+	useMutationObserver(el, updateIsDarkTheme, { attributes: true })
+	// Watch for system theme change for the default theme
+	watch(isDarkSystemTheme, updateIsDarkTheme, { immediate: true })
+
+	return readonly(isDarkTheme)
+}
+
+/**
+ * Shared composable to check whether the dark theme is enabled on the page.
+ * Reacts on body data-theme-* attributes change and system theme change.
+ * @return {DeepReadonly<Ref<boolean>>} - computed boolean whether the dark theme is enabled
+ */
+export const useIsDarkTheme = createSharedComposable(() => useIsDarkThemeElement())

styleguide.config.js

@@ -155,6 +155,11 @@ module.exports = async () => {
 					{
 						name: 'useHotKey',
 						content: 'docs/composables/useHotKey.md',
+
+					},
+					{
+						name: 'useIsDarkTheme',
+						content: 'docs/composables/useIsDarkTheme.md',
 					},
 				],
 			},

styleguide/global.requires.js

@@ -11,6 +11,7 @@ import usernameToColor from '../src/functions/usernameToColor/index.js'
 import Tooltip from './../src/directives/Tooltip/index.js'
 import Focus from './../src/directives/Focus/index.js'
 import Linkify from './../src/directives/Linkify/index.js'
+import { useIsDarkTheme } from '../src/composables/index.js'
 
 import axios from '@nextcloud/axios'
 
@@ -166,6 +167,8 @@ window.emojiAddRecent = emojiAddRecent
 window.getCurrentSkinTone = getCurrentSkinTone
 window.setCurrentSkinTone = setCurrentSkinTone
 window.usernameToColor = usernameToColor
+// Exported composables
+window.useIsDarkTheme = useIsDarkTheme
 
 // Directives
 Vue.directive('Tooltip', Tooltip)