/**
 * 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();