#434

frontend/src/lib/countsClipboard.ts

@@ -0,0 +1,70 @@
+export type CountsClipboard = { text: string; html: string }
+
+
+const escapeHTML = (value: string): string => value.replace (/[&<>"']/g, character =>
+    ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' })[character]!)
+
+
+export const countsClipboard = (rows: string[][], headers = false): CountsClipboard => {
+  // Excel accepts quoted TSV fields only when delimiters or quotes require them.
+  // Prefix formula-like text in both representations, including leading whitespace.
+  const safe = rows.map (row => row.map (value => /^\s*[=+@-]/.test (value)
+      ? `'${value}` : value))
+  const text = safe.map (row => row.map (value => /[\t\r\n"]/.test (value)
+      ? `"${value.replaceAll ('"', '""')}"` : value).join ('\t')).join ('\r\n')
+  const html = '<html><body><table>' + safe.map ((row, index) => '<tr>' + row.map (value => {
+    const tag = headers && index === 0 ? 'th' : 'td'
+    // Preserve time strings, leading zeroes, and user text instead of inferring dates/formulae.
+    const numeric = value.length <= 15 && /^(?:0|[1-9]\d*)(?:\.\d+)?$/.test (value)
+    const style = numeric ? 'white-space:pre-wrap' : 'white-space:pre-wrap;mso-number-format:"\\@"'
+    return `<${tag} style="${escapeHTML (style)}">${escapeHTML (value)
+	.replace (/\r\n|\r|\n/g, '<br>')}</${tag}>`
+  }).join ('') + '</tr>').join ('') + '</table></body></html>'
+  return { text, html }
+}
+
+
+export const writeCountsClipboard = async (payload: CountsClipboard): Promise<void> => {
+  if (navigator.clipboard?.write != null && typeof ClipboardItem !== 'undefined')
+  {
+    try
+    {
+      await navigator.clipboard.write ([new ClipboardItem ({
+	  'text/plain': new Blob ([payload.text], { type: 'text/plain' }),
+	  'text/html': new Blob ([payload.html], { type: 'text/html' }) })])
+      return
+    }
+    catch
+    {
+      // Browsers without HTML clipboard support may still permit plain TSV.
+    }
+  }
+  if (navigator.clipboard?.writeText != null)
+  {
+    try
+    {
+      await navigator.clipboard.writeText (payload.text)
+      return
+    }
+    catch
+    {
+      // Try the synchronous copy event when clipboard permission is unavailable.
+    }
+  }
+  // The synchronous copy event fallback is also used on non-secure local origins.
+  const listener = (event: ClipboardEvent) => {
+    event.preventDefault ()
+    event.stopImmediatePropagation ()
+    event.clipboardData?.setData ('text/plain', payload.text)
+    event.clipboardData?.setData ('text/html', payload.html)
+  }
+  document.addEventListener ('copy', listener, true)
+  try
+  {
+    if (!document.execCommand ('copy')) throw new Error ('Clipboard unavailable')
+  }
+  finally
+  {
+    document.removeEventListener ('copy', listener, true)
+  }
+}