index.js

const wildcard = '9007199254740991' // this will be injected as placeholder while calculating, before returning the classname we will remove those numbers

const is = (val, type) => {
  if (typeof val === 'function' && type === 'function') {
    return true
  } else {
    const objectType = Object.prototype.toString.call(val)
    return !!objectType.slice(8,(objectType.length - 1)).match(new RegExp(type, 'gi'))  
  }
}

const dashify = (str = '') => {
  if (typeof str !== 'string') return str
  return str.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase()
}

const removeNotSupportedTypes = val => {
  return is(val, 'array|string|object')
}

const handleBlocks = (block, val) => {
  if (is(val, 'string') && val.length > 0) {
    return `${block}__${val}`
  } else {
    return val
  }
}

const handleModifiers = (block, val) => {
  if(is(val, 'array')) {
    return val.length === 0 ?  wildcard : val.map(a => `${block}--${a}`)
  }

  if(is(val, 'object')) {
    const keys = Object.keys(val)

    return keys.length === 0 ? wildcard : Object.keys(val).map(key => {
      if(is(val[key], 'boolean')) {
        return !!val[key] ? `${block}--${dashify(key)}` : wildcard
      } else {
        return `${block}--${dashify(key)}-${dashify(val[key])}`
      }
    })
  }

  if(is(val, 'string')) {
    return val.length === 0 ? wildcard : val
  }

  return val
}

module.exports = block => (...args) => (args
    .filter(removeNotSupportedTypes)
    .map(handleBlocks.bind(null, block))
    .map(handleModifiers.bind(null, block))
    .join(' ')
    .replace(/,/g, ' ') || block
  ).replace(new RegExp(wildcard, 'g'),'').trim()