From 37c800a2ca7c90dbc9447a20dd31abb81af1dfc5 Mon Sep 17 00:00:00 2001
From: Georges Gomes <georges.gomes@gmail.com>
Date: Fri, 25 Mar 2022 17:06:15 +0100
Subject: [PATCH] Re-enable update of tags

---
 src/client/app/composables/head.ts | 81 ++++++++++++++++++++++++++++++
 src/client/app/index.ts            |  6 +++
 2 files changed, 87 insertions(+)
 create mode 100644 src/client/app/composables/head.ts

diff --git a/src/client/app/composables/head.ts b/src/client/app/composables/head.ts
new file mode 100644
index 00000000..878d9da7
--- /dev/null
+++ b/src/client/app/composables/head.ts
@@ -0,0 +1,81 @@
+import { watchEffect, Ref } from 'vue'
+import { HeadConfig, processHead, SiteData } from '../../shared'
+import { Route } from '../router'
+
+export function useUpdateHead(route: Route, siteDataByRouteRef: Ref<SiteData>) {
+  let managedHeadTags: HTMLElement[] = []
+  let isFirstUpdate = true
+
+  const updateHeadTags = (newTags: HeadConfig[]) => {
+    if (import.meta.env.PROD && isFirstUpdate) {
+      // in production, the initial meta tags are already pre-rendered so we
+      // skip the first update.
+      isFirstUpdate = false
+      return
+    }
+
+    const newEls: HTMLElement[] = []
+    const commonLength = Math.min(managedHeadTags.length, newTags.length)
+    for (let i = 0; i < commonLength; i++) {
+      let el = managedHeadTags[i]
+      const [tag, attrs, innerHTML = ''] = newTags[i]
+      if (el.tagName.toLocaleLowerCase() === tag) {
+        for (const key in attrs) {
+          if (el.getAttribute(key) !== attrs[key]) {
+            el.setAttribute(key, attrs[key])
+          }
+        }
+        for (let i = 0; i < el.attributes.length; i++) {
+          const name = el.attributes[i].name
+          if (!(name in attrs)) {
+            el.removeAttribute(name)
+          }
+        }
+        if (el.innerHTML !== innerHTML) {
+          el.innerHTML = innerHTML
+        }
+      } else {
+        document.head.removeChild(el)
+        el = createHeadElement(newTags[i])
+        document.head.append(el)
+      }
+      newEls.push(el)
+    }
+
+    managedHeadTags
+      .slice(commonLength)
+      .forEach((el) => document.head.removeChild(el))
+    newTags.slice(commonLength).forEach((headConfig) => {
+      const el = createHeadElement(headConfig)
+      document.head.appendChild(el)
+      newEls.push(el)
+    })
+    managedHeadTags = newEls
+  }
+
+  watchEffect(() => {
+    const pageData = route.data
+    const siteData = siteDataByRouteRef.value
+    const pageTitle = pageData && pageData.title
+    const pageDescription = pageData && pageData.description
+
+    // update title and description
+    document.title = (pageTitle ? pageTitle + ` | ` : ``) + siteData.title
+    document
+      .querySelector(`meta[name=description]`)!
+      .setAttribute('content', pageDescription || siteData.description)
+
+    updateHeadTags(processHead(siteData.head, pageData));
+  })
+}
+
+function createHeadElement([tag, attrs, innerHTML]: HeadConfig) {
+  const el = document.createElement(tag)
+  for (const key in attrs) {
+    el.setAttribute(key, attrs[key])
+  }
+  if (innerHTML) {
+    el.innerHTML = innerHTML
+  }
+  return el
+}
diff --git a/src/client/app/index.ts b/src/client/app/index.ts
index 923ebb37..3065c813 100644
--- a/src/client/app/index.ts
+++ b/src/client/app/index.ts
@@ -10,6 +10,7 @@ import {
 import { inBrowser, pathToFile } from './utils'
 import { Router, RouterSymbol, createRouter } from './router'
 import { siteDataRef, useData } from './data'
+import { useUpdateHead } from './composables/head'
 import Theme from '/@theme/index'
 import { usePrefetch } from './composables/preFetch'
 import { dataSymbol, initData } from './data'
@@ -54,6 +55,11 @@ export function createApp() {
   const data = initData(router.route)
   app.provide(dataSymbol, data)
 
+  if (inBrowser) {
+    // dynamically update head tags
+    useUpdateHead(router.route, data.site)
+  }
+
   // install global components
   app.component('Content', Content)
   app.component('ClientOnly', ClientOnly)