interface Options {
  block: string
  blockSuffix?: string
  element?: string
  modifier?: string
}

function _bem(options: Options) {
  const { block, blockSuffix, element, modifier } = options

  let cls = block

  if (blockSuffix)
    cls += `-${blockSuffix}`

  if (element)
    cls += `__${element}`

  if (modifier)
    cls += `--${modifier}`

  return cls
}

function isTruthy(value: unknown): boolean {
  if (Array.isArray(value)) {
    return value.length > 0
  }
  else if (typeof value === 'object' && value !== null) {
    return Object.keys(value).length > 0
  }

  return !!value
}

export default (block: string) => {
  const b = (blockSuffix?: string) => _bem({ block, blockSuffix })
  const e = (element: string) => _bem({ block, element })
  const m = (modifier: string) => _bem({ block, modifier })

  const be = (blockSuffix: string, element: string) => _bem({ block, blockSuffix, element })
  const em = (element: string, modifier: string) => _bem({ block, element, modifier })
  const bm = (blockSuffix: string, modifier: string) => _bem({ block, blockSuffix, modifier })

  const bem = (blockSuffix: string, element: string, modifier: string) => _bem({ block, blockSuffix, element, modifier })

  const is = (name: string, state: unknown) => isTruthy(state) ? `is-${name}` : ''
  const has = (name: string, state: unknown) => isTruthy(state) ? `has-${name}` : ''

  const exp = (condition: boolean, trueState: string, falseState: string = '') => condition ? trueState : falseState

  return {
    b,
    e,
    m,

    be,
    em,
    bm,

    bem,

    is,
    has,

    exp,
  }
}