Integrate utterances comments

_includes/comments/disqus.html

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+<!--
+  The Disqus lazy loading.
+-->
+<div id="disqus_thread" class="pt-2 pb-2">
+  <p class="text-center text-muted small">
+    Comments powered by <a href="https://disqus.com/">Disqus</a>.
+  </p>
+</div>
+
+<script type="text/javascript">
+
+  var disqus_config = function () {
+    this.page.url = '{{ page.url | absolute_url }}';
+    this.page.identifier = '{{ page.url }}';
+  };
+
+  /* Lazy loading */
+
+  var disqus_observer = new IntersectionObserver(function (entries) {
+    if(entries[0].isIntersecting) {
+        (function () {
+            var d = document, s = d.createElement('script');
+            s.src = 'https://{{ site.comments.disqus.shortname }}.disqus.com/embed.js';
+            s.setAttribute('data-timestamp', +new Date());
+            (d.head || d.body).appendChild(s);
+        })();
+
+        disqus_observer.disconnect();
+    }
+  }, { threshold: [0] });
+
+  disqus_observer.observe(document.querySelector('#disqus_thread'));
+
+  /* Auto switch theme */
+
+  function reloadDisqus() {
+    /* Disqus hasn't been loaded */
+    if (typeof DISQUS === "undefined") {
+      return;
+    }
+
+    if (document.readyState == 'complete') {
+      DISQUS.reset({ reload: true, config: disqus_config });
+    }
+  }
+
+  const modeToggle = document.querySelector(".mode-toggle");
+
+  if (typeof modeToggle !== "undefined") {
+    /*  modeToggle.addEventListener('click', reloadDisqus); // not pretty for 'color-scheme'  */
+    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', reloadDisqus);
+  }
+
+</script>

_includes/comments/utterances.html

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+<!-- https://utteranc.es/ -->
+<script src="https://utteranc.es/client.js"
+        repo="{{ site.comments.utterances.repo }}"
+        issue-term="{{ site.comments.utterances.issue_term }}"
+        crossorigin="anonymous"
+        async>
+</script>
+
+<script type="text/javascript">
+  $(function() {
+    const origin = "https://utteranc.es";
+    const iframe = "iframe.utterances-frame";
+    const lightTheme = "github-light";
+    const darkTheme = "github-dark";
+    let initTheme = lightTheme;
+
+    if ($("html[mode=dark]").length > 0
+        || ($("html[mode]").length == 0
+            && window.matchMedia("(prefers-color-scheme: dark)").matches)) {
+      initTheme = darkTheme;
+    }
+
+    addEventListener("message", (event) => {
+      let theme;
+
+      /* credit to <https://github.com/utterance/utterances/issues/170#issuecomment-594036347> */
+      if (event.origin === origin) {
+        /* page initial */
+        theme = initTheme;
+
+      } else if (event.source === window && event.data &&
+            event.data.direction === ModeToggle.ID) {
+        /* global theme mode changed */
+        const mode = event.data.message;
+        theme = (mode === ModeToggle.DARK_MODE ? darkTheme : lightTheme);
+
+      } else {
+        return;
+      }
+
+      const message = {
+        type: "set-theme",
+        theme: theme
+      };
+
+      const utterances = document.querySelector(iframe).contentWindow;
+      utterances.postMessage(message, origin);
+    });
+
+  });
+</script>