Fix isInternalUrl for subdomain support

Refactor / reduce plumbing

app/components/Highlight.js

@@ -0,0 +1,44 @@
+// @flow
+import * as React from 'react';
+import replace from 'string-replace-to-array';
+import styled from 'styled-components';
+
+type Props = {
+  highlight: ?string | RegExp,
+  processResult?: (tag: string) => string,
+  text: string,
+  caseSensitive?: boolean,
+};
+
+function Highlight({
+  highlight,
+  processResult,
+  caseSensitive,
+  text,
+  ...rest
+}: Props) {
+  let regex;
+  if (highlight instanceof RegExp) {
+    regex = highlight;
+  } else {
+    regex = new RegExp(
+      (highlight || '').replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&'),
+      caseSensitive ? 'g' : 'gi'
+    );
+  }
+  return (
+    <span {...rest}>
+      {highlight
+        ? replace(text, regex, (tag, index) => (
+            <Mark key={index}>{processResult ? processResult(tag) : tag}</Mark>
+          ))
+        : text}
+    </span>
+  );
+}
+
+const Mark = styled.mark`
+  background: ${props => props.theme.yellow};
+`;
+
+export default Highlight;