nizika/broadcast/common_module.js

export default class
CommonModule
{
  static
  isWide (chr)
  {
    return chr.match (/[^\x01-\x7f]/) !== null;
  }

  static
  lenByFull (str)
  {
    return str.split ('').map (c => this.isWide (c) ? 1 : .5)
                         .reduce ((a, c) => a + c);
  }

  static
  indexByFToC (str, index)
  {
    let i = 0;
    let work = '';

    for (let c of str)
      {
        work += c;

        if (this.lenByFull (work) > index)
          break;

        i += 1;
      }

    return i;
  }

  static
  midByFull (str, start, length)
  {
    const trimmedLeft = str.slice (this.indexByFToC (str, start));

    return trimmedLeft.slice (0, this.indexByFToC (trimmedLeft, length));
  }
}