do not spit url between Read More chunks by expanding chunk to end of url

ts/util/graphemeAndLinkAwareSlice.ts

@@ -0,0 +1,68 @@
+// Copyright 2021-2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import LinkifyIt from 'linkify-it';
+
+export function graphemeAndLinkAwareSlice(
+  str: string,
+  length: number,
+  buffer = 100
+): {
+  hasReadMore: boolean;
+  text: string;
+} {
+  if (str.length <= length + buffer) {
+    return { text: str, hasReadMore: false };
+  }
+
+  let text: string | undefined;
+
+  for (const { index } of new Intl.Segmenter().segment(str)) {
+    if (!text && index >= length) {
+      text = str.slice(0, index);
+    }
+
+    if (text && index > length) {
+      text = expandToIncludeEntireLink(str, text);
+
+      return {
+        text,
+        hasReadMore: text.length < str.length,
+      };
+    }
+  }
+
+  return {
+    text: str,
+    hasReadMore: false,
+  };
+}
+
+const expandToIncludeEntireLink = (
+  original: string,
+  truncated: string
+): string => {
+  const linksInText = new LinkifyIt().match(original);
+
+  if (!linksInText) {
+    return truncated;
+  }
+
+  const invalidTruncationRanges: Array<LinkRange> = linksInText.map(
+    ({ index: startIndex, lastIndex }) => ({ startIndex, lastIndex })
+  );
+
+  const truncatedLink: Array<LinkRange> = invalidTruncationRanges.filter(
+    ({ startIndex, lastIndex }) =>
+      startIndex < truncated.length && lastIndex > truncated.length
+  );
+
+  if (truncatedLink.length === 0) return truncated;
+
+  return original.slice(0, truncatedLink[0].lastIndex);
+};
+
+type LinkRange = {
+  startIndex: number;
+  lastIndex: number;
+};