Add copy buttons to markdown code blocks

src/client/src/components/FormattedText.ts

@@ -9,8 +9,55 @@ export class FormattedText extends LitElement {
   @property() text = "";
 
   override render() {
-    return html`<div class="formatted">${unsafeHTML(toSafeMarkdownHtml(this.text))}</div>`;
+    return html`<div class="formatted" @click=${this.onFormattedClick}>${unsafeHTML(toSafeMarkdownHtml(this.text))}</div>`;
+  }
+
+  override updated(): void {
+    this.enhanceCodeBlocks();
+  }
+
+  private enhanceCodeBlocks(): void {
+    this.renderRoot.querySelectorAll("pre").forEach((element) => {
+      if (!(element instanceof HTMLPreElement) || element.parentElement?.classList.contains("code-block-wrapper") === true) return;
+      const code = element.querySelector("code");
+      if (!(code instanceof HTMLElement)) return;
+      const wrapper = document.createElement("div");
+      wrapper.className = "code-block-wrapper";
+      const button = document.createElement("button");
+      button.type = "button";
+      button.className = "code-copy-button";
+      button.textContent = "Copy";
+      button.setAttribute("aria-label", "Copy code block");
+      element.before(wrapper);
+      wrapper.append(element, button);
+    });
+  }
+
+  private readonly onFormattedClick = (event: MouseEvent): void => {
+    if (!(event.target instanceof HTMLButtonElement) || !event.target.classList.contains("code-copy-button")) return;
+    const wrapper = event.target.closest(".code-block-wrapper");
+    if (!(wrapper instanceof HTMLElement)) return;
+    const code = wrapper.querySelector("pre code");
+    if (!(code instanceof HTMLElement)) return;
+    void this.copyCode(code.textContent, event.target);
+  };
+
+  private async copyCode(text: string, button: HTMLButtonElement): Promise<void> {
+    const ok = await writeClipboard(text);
+    button.textContent = ok ? "Copied" : "Failed";
+    window.setTimeout(() => {
+      button.textContent = "Copy";
+    }, 1200);
   }
 
   static override styles = formattedTextStyles;
 }
+
+async function writeClipboard(text: string): Promise<boolean> {
+  try {
+    await navigator.clipboard.writeText(text);
+    return true;
+  } catch {
+    return false;
+  }
+}

src/client/src/components/shared.ts

@@ -162,13 +162,17 @@ export const chatStyles = css`
 export const formattedTextStyles = css`
   :host { display: block; }
   .formatted { white-space: normal; overflow-wrap: anywhere; line-height: 1.45; }
-  p, ul, ol, pre, blockquote, table { margin: 0 0 10px; }
-  :is(p, ul, ol, pre, blockquote, table):last-child { margin-bottom: 0; }
+  p, ul, ol, pre, blockquote, table, .code-block-wrapper { margin: 0 0 10px; }
+  :is(p, ul, ol, pre, blockquote, table, .code-block-wrapper):last-child { margin-bottom: 0; }
   ul, ol { padding-left: 22px; }
   li + li { margin-top: 3px; }
   code { border: 1px solid #30363d; border-radius: 4px; background: #0d1117; padding: 1px 4px; font: 13px ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
+  .code-block-wrapper { position: relative; }
+  .code-block-wrapper pre { margin: 0; padding-right: 58px; }
   pre { border: 1px solid #30363d; border-radius: 8px; background: #0d1117; padding: 10px; overflow: auto; }
   pre code { border: 0; padding: 0; background: transparent; }
+  .code-copy-button { position: absolute; top: 6px; right: 6px; z-index: 1; border: 1px solid #30363d; border-radius: 6px; background: #161b22; color: #8b949e; padding: 3px 7px; font: 12px system-ui, sans-serif; cursor: pointer; }
+  .code-copy-button:hover { color: #e6edf3; border-color: #58a6ff; }
   blockquote { border-left: 3px solid #30363d; padding-left: 10px; color: #8b949e; }
   a { color: #58a6ff; }
   h1, h2, h3, h4 { margin: 14px 0 8px; line-height: 1.2; }