protomaps-leaflet/src/text.ts

Vector tile rendering and labeling for [Leaflet](https://github.com/Leaflet/Leaflet).

// TODO should be visual length in pixels, not strlen
export function linebreak(str: string, maxUnits: number): string[] {
  if (str.length <= maxUnits) return [str];
  const endIndex = maxUnits - 1;
  const spaceBefore = str.lastIndexOf(" ", endIndex);
  const spaceAfter = str.indexOf(" ", endIndex);
  if (spaceBefore === -1 && spaceAfter === -1) {
    return [str];
  }
  let first: string;
  let after: string;
  if (
    spaceAfter === -1 ||
    (spaceBefore >= 0 && endIndex - spaceBefore < spaceAfter - endIndex)
  ) {
    first = str.substring(0, spaceBefore);
    after = str.substring(spaceBefore + 1, str.length);
  } else {
    first = str.substring(0, spaceAfter);
    after = str.substring(spaceAfter + 1, str.length);
  }
  return [first, ...linebreak(after, maxUnits)];
}

const CJK_CHARS =
  "\u3005-\u3007\u3021-\u3029\u3031-\u3035\u3038-\u303C\u3220-\u3229\u3248-\u324F\u3251-\u325F\u3280-\u3289\u32B1-\u32BF\u3400-\u4DB5\u4E00-\u9FEA\uF900-\uFA6D\uFA70-\uFAD9\u2000";
const cjkTest = new RegExp(`^[${CJK_CHARS}]+$`);

export function isCjk(s: string) {
  return cjkTest.test(s);
}