use https://github.com/nunocoracao/blowfish.git

themes/blowfish/assets/js/code.js

@@ -0,0 +1,66 @@
+var scriptBundle = document.getElementById("script-bundle");
+var copyText = scriptBundle && scriptBundle.getAttribute("data-copy")? scriptBundle.getAttribute("data-copy") : "Copy";
+var copiedText = scriptBundle && scriptBundle.getAttribute("data-copied")? scriptBundle.getAttribute("data-copied") : "Copied";
+
+function createCopyButton(highlightDiv) {
+  const button = document.createElement("button");
+  button.className = "copy-button";
+  button.type = "button";
+  button.ariaLabel = copyText;
+  button.innerText = copyText;
+  button.addEventListener("click", () => copyCodeToClipboard(button, highlightDiv));
+  addCopyButtonToDom(button, highlightDiv);
+}
+
+async function copyCodeToClipboard(button, highlightDiv) {
+  const codeToCopy = highlightDiv.querySelector(":last-child").innerText;
+  try {
+    result = await navigator.permissions.query({ name: "clipboard-write" });
+    if (result.state == "granted" || result.state == "prompt") {
+      await navigator.clipboard.writeText(codeToCopy);
+    } else {
+      copyCodeBlockExecCommand(codeToCopy, highlightDiv);
+    }
+  } catch (_) {
+    copyCodeBlockExecCommand(codeToCopy, highlightDiv);
+  } finally {
+    codeWasCopied(button);
+  }
+}
+
+function copyCodeBlockExecCommand(codeToCopy, highlightDiv) {
+  const textArea = document.createElement("textArea");
+  textArea.contentEditable = "true";
+  textArea.readOnly = "false";
+  textArea.className = "copy-textarea";
+  textArea.value = codeToCopy;
+  highlightDiv.insertBefore(textArea, highlightDiv.firstChild);
+  const range = document.createRange();
+  range.selectNodeContents(textArea);
+  const sel = window.getSelection();
+  sel.removeAllRanges();
+  sel.addRange(range);
+  textArea.setSelectionRange(0, 999999);
+  document.execCommand("copy");
+  highlightDiv.removeChild(textArea);
+}
+
+function codeWasCopied(button) {
+  button.blur();
+  button.innerText = copiedText;
+  setTimeout(function () {
+    button.innerText = copyText;
+  }, 2000);
+}
+
+function addCopyButtonToDom(button, highlightDiv) {
+  highlightDiv.insertBefore(button, highlightDiv.firstChild);
+  const wrapper = document.createElement("div");
+  wrapper.className = "highlight-wrapper";
+  highlightDiv.parentNode.insertBefore(wrapper, highlightDiv);
+  wrapper.appendChild(highlightDiv);
+}
+
+window.addEventListener("DOMContentLoaded", (event) => {
+  document.querySelectorAll(".highlight").forEach((highlightDiv) => createCopyButton(highlightDiv));
+});