const CJK_CHAR_PATTERN = /[\u3400-\u4DBF\u4E00-\u9FFF\uF900-\uFAFF]/gu;
const LATIN_WORD_PATTERN = /[A-Za-z][A-Za-z'’-]{1,}/g;
const LATIN_FRAGMENT_PATTERN =
  /[A-Za-z][A-Za-z0-9'"“”‘’()\-,:;!?/]*(?:\s+[A-Za-z0-9'"“”‘’()\-,:;!?/]+)+/gu;
const SAFE_LATIN_TOKENS = new Set([
  'act',
  'ai',
  'boss',
  'cd',
  'hp',
  'json',
  'llm',
  'mp',
  'npc',
  'qa',
  'rpg',
]);

function getCjkCharCount(text: string) {
  return text.match(CJK_CHAR_PATTERN)?.length ?? 0;
}

function getSignificantLatinWords(text: string) {
  return (text.match(LATIN_WORD_PATTERN) ?? [])
    .map((word) => word.toLowerCase())
    .filter((word) => word.length >= 4 && !SAFE_LATIN_TOKENS.has(word));
}

export function hasMixedNarrativeLanguage(text: string) {
  const trimmed = text.trim();
  if (!trimmed) {
    return false;
  }

  const cjkCharCount = getCjkCharCount(trimmed);
  const latinSentenceFragments = (trimmed.match(LATIN_FRAGMENT_PATTERN) ?? [])
    .map((fragment) => fragment.trim())
    .filter((fragment) => fragment.split(/\s+/u).length >= 2);
  const significantLatinWords = getSignificantLatinWords(trimmed);

  if (latinSentenceFragments.length > 0) {
    return true;
  }

  if (cjkCharCount > 0 && significantLatinWords.length >= 2) {
    return true;
  }

  return cjkCharCount === 0 && significantLatinWords.length >= 3;
}

export function sanitizePromptNarrativeText(
  text: string | null | undefined,
  fallback: string | null = null,
) {
  if (typeof text !== 'string') {
    return fallback;
  }

  const trimmed = text.trim();
  if (!trimmed) {
    return fallback;
  }

  return hasMixedNarrativeLanguage(trimmed) ? fallback : trimmed;
}