ramsayleung
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+title = "Hugo评论系统自适应博客主题: 支持dark与light theme"
+date = 2024-12-04T13:25:00+08:00
+lastmod = 2024-12-04T14:27:41+08:00
+tags = ["blog", "hugo"]
+categories = ["blog", "hugo"]
+draft = false
+toc = true
++++
+
+## <span class="section-num">1</span> 问题 {#问题}
+
+评论系统是博客的关键组件，Hugo 支持若干个评论系统，包括流行的 [Disqus](https://disqus.com/), 基于 GitHub 的 [Giscus](https://giscus.app) 和 [Utteranc](https://utteranc.es/), 以及其他[评论系统](https://gohugo.io/content-management/comments/)
+
+我[博客](https://ramsayleung.github.io/)使用的评论系统是 Utteranc, 主题是 [PaperMod](https://github.com/adityatelange/hugo-PaperMod/), PaperMod 支持 dark 和 light 两种主题, 在初始化 Utteranc 时可以指定 theme, 如 `Github-Light`
+
+```html
+<script src="https://utteranc.es/client.js"
+        repo="ramsayleung/comment"
+        issue-term="title"
+        theme="github-light"
+        crossorigin="anonymous"
+        async>
+</script>
+```
+
+但是 theme 在初始化时就指定好了，那么在博客切换到 dark theme 的时候， Utteranc 也不会自适应 dark theme，博客的theme与评论theme就不一致：
+
+{{< figure src="/ox-hugo/responsive_comment_theme.jpg" >}}
+
+
+## <span class="section-num">2</span> 解决思路 {#解决思路}
+
+解决思路其实很简单，就获取当前的 theme, 然后再初始化 Utteranc 对应的 theme; 再在用户切换 theme 之后，再重新初始化 `Utteranc`.
+
+
+### <span class="section-num">2.1</span> 获取当前Theme {#获取当前theme}
+
+Hugo 并没有提供标准接口来获取当前主题， 虽然可以通过以下的方式来获取的 theme:
+
+```js
+const isDarkMode = window.matchMedia('(prefers-color-scheme: dark)').matches;
+console.log(isDarkMode ? 'dark' : 'light');
+```
+
+但是这个是通过编译出来的CSS来判断当前theme，用户一旦手动切换了 theme, 上面的代码就无法生效了.
+
+每个Hugo主题定义的方式可能还不一样, 以 PaperMod 为例，观察之后发现，light theme的时候body的html 为:
+
+```css
+<body id = "top" class="">
+</body>
+```
+
+dark theme 的时候 `class` 就变为了 `class`"dark"=:
+
+```css
+<body id = "top" class="">
+</body>
+```
+
+所以可以通过判断 `body` 是否包含 `dark` 的 class 来判断当前是否为 dark theme.
+
+```js
+// 不同的Hugo theme可能会需要不同的判断方式
+function getCurrentTheme() {
+    return document.body.classList.contains('dark') ? 'dark' : 'light';
+}
+```
+
+
+### <span class="section-num">2.2</span> 初始化评论系统 {#初始化评论系统}
+
+[Utteranc](https://utteranc.es/) 文档提供的启用评价系统代码如下：
+
+```html
+<script src="https://utteranc.es/client.js"
+        repo="[ENTER REPO HERE]"
+        issue-term="pathname"
+        theme="github-light"
+        crossorigin="anonymous"
+        async>
+</script>
+```
+
+因为我们需要在切换 Theme 时重新加载 Utteranc, 所以就需要通过 Javascript 来实现上面的HTML功能:
+
+```js
+function loadUtterances(darkMode=false) {
+    const commentContainer = document.getElementById("comments-utteranc");
+    if (commentContainer !== null) {
+        commentContainer.innerHTML = ''
+        const commentScript = document.createElement("script");
+        commentScript.setAttribute("id", "utteranc");
+        commentScript.setAttribute("src", "https://utteranc.es/client.js");
+        commentScript.setAttribute("data-repo", "ramsayleung/comment");
+        commentScript.setAttribute("data-theme", darkMode ? "github-dark" : "github-light");
+        commentScript.setAttribute("data-issue-term", "title");
+        commentScript.setAttribute("crossorigin", "anonymous");
+        commentScript.setAttribute("async", "true");
+        commentContainer.appendChild(commentScript);
+    }
+}
+```
+
+
+### <span class="section-num">2.3</span> 监听主题变动 {#监听主题变动}
+
+用户可以在博客界面手动选择他们喜欢的主题，可以从 `dark` -&gt; `light`, `light` -&gt; `dark`, 我们需要做的就是监听主题的变动，在切换主题之后，重新加载评论系统。
+
+```js
+// Watch for theme changes
+const themeObserver = new MutationObserver((mutations) => {
+    mutations.forEach((mutation) => {
+        if (mutation.type === 'attributes' && mutation.attributeName === 'class') {
+            const isDarkMode = getCurrentTheme() === 'dark';
+            loadUtterances(isDarkMode);
+            console.log(`changing theme`);
+        }
+    });
+});
+
+// Start observing the body element for class changes
+themeObserver.observe(document.body, {
+    attributes: true,
+    attributeFilter: ['class']
+});
+```
+
+
+## <span class="section-num">3</span> 总结 {#总结}
+
+自适应评论系统的代码[在这里](https://github.com/ramsayleung/ramsayleung.github.io/blob/master/layouts/partials/comments.html), 实现的效果如下:
+
+{{< figure src="/ox-hugo/responsive_comment_theme_2.jpg" >}}
+
+{{< figure src="/ox-hugo/responsive_comment_theme_3.jpg" >}}