const wout = (s) => {
  process.stdout.write(s)
}

const padStr = (s, len, ch) => {
  ch = ch || ' '
  while (s.length < len) {
    s = ch + s
  }
  return s
}

const hexDigit = (n, len) => {
  return padStr(n.toString(16), len || 2, '0')
}

const printableCh = (c) => {
  // [space to '~')
  if (c > 0x20 && c <= 0x7e) {
    return String.fromCharCode(c)
  } else {
    return '.'
  }
}

const hexdump = (buf, len) => {
  len = len || buf.length

  const maxline = 16
  let ascii = new Array(maxline)
  let i

  for (i = 0; i < len; i++) {
    if (i % maxline === 0) {
      if (i > 0) {
        wout(' ' + ascii.join(''))
        wout('\n')
      }
      wout(hexDigit(i, 4) + ': ')
    }

    // output the hex digit
    wout(hexDigit(buf[i]))
    wout(' ')
    ascii[i % maxline] = printableCh(buf[i])
  }
  if (i % maxline !== 0) {
    let diff = maxline - (i % maxline)
    wout('   '.repeat(diff))
  }

  wout(' ' + ascii.slice(0, (i % maxline)).join('') + '\n')
}

/*
let buf = Buffer.alloc(500)
for (let i = 0; i < buf.length; i++) {
  buf[i] = i & 0xff
}
hexdump(buf)
*/

module.exports = hexdump