const binLookup = (key) => ({
  0: '0000',
  1: '0001',
  2: '0010',
  3: '0011',
  4: '0100',
  5: '0101',
  6: '0110',
  7: '0111',
  8: '1000',
  9: '1001',
  a: '1010',
  b: '1011',
  c: '1100',
  d: '1101',
  e: '1110',
  f: '1111'
}[key.toLowerCase()]) // select the binary number by valid hex key with the help javascript object

const hexToBinary = (hexString) => {
  if (typeof hexString !== 'string') {
    throw new TypeError('Argument is not a string type')
  }

  if (/[^\da-f]/gi.test(hexString)) {
    throw new Error('Argument is not a valid HEX code!')
  }
  /*
    Function for converting Hex to Binary

    1. We convert every hexadecimal bit to 4 binary bits
    2. Conversion goes by searching in the lookup table
  */

  return hexString.replace(
    /[0-9a-f]/gi,
    lexeme => binLookup(lexeme)
  )
}

export default hexToBinary