Building Slack integration

backend/lib/slackText.ts

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+/**
+ * Slack delivers mrkdwn, not plain text. Link syntax and HTML entities that
+ * survive into a note degrade embedding quality and read as noise on a sticky,
+ * so they are unwrapped here. Pure and dependency-free so both the normalizer
+ * and the API client can use it.
+ */
+
+const ENTITIES: Record<string, string> = {
+  '&amp;': '&',
+  '&lt;': '<',
+  '&gt;': '>',
+};
+
+const unescapeEntities = (text: string): string =>
+  text.replace(/&(?:amp|lt|gt);/g, (match) => ENTITIES[match] ?? match);
+
+const splitOnce = (value: string, separator: string): [string, string | undefined] => {
+  const index = value.indexOf(separator);
+  if (index === -1) return [value, undefined];
+  return [value.slice(0, index), value.slice(index + separator.length)];
+};
+
+const BROADCASTS: readonly string[] = ['here', 'channel', 'everyone'];
+
+const MARKUP = /<([^<>]*)>/g;
+
+const unwrap = (inner: string): string => {
+  const [target, rawLabel] = splitOnce(inner, '|');
+  const label = rawLabel !== undefined && rawLabel.length > 0 ? rawLabel : undefined;
+
+  if (target.startsWith('@')) return `@${label ?? target.slice(1)}`;
+  if (target.startsWith('#')) return `#${label ?? target.slice(1)}`;
+
+  if (target.startsWith('!')) {
+    const special = target.slice(1);
+    if (BROADCASTS.includes(special)) return `@${special}`;
+    return label ?? `@${special}`;
+  }
+
+  if (target.startsWith('mailto:')) return label ?? target.slice('mailto:'.length);
+
+  return label ?? target;
+};
+
+/**
+ * Entities are unescaped only after markup is unwrapped. Slack escapes a
+ * literal `<` as `&lt;` precisely so it is not read as markup, and reversing
+ * that order would turn user text into parsed link syntax.
+ */
+export const cleanSlackText = (input: string): string =>
+  unescapeEntities(input.replace(MARKUP, (_match, inner: string) => unwrap(inner)))
+    .replace(/[ \t]+$/gm, '')
+    .trim();