const encodeTable = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'.split('')
const decodeTable = {}
for (const idx in encodeTable) {
  decodeTable[encodeTable[idx]] = idx
}

const base32 = {}
module.exports = base32

/**
 * encode byte data to string
 * @param {ArrayBuffer} b buffer data
 * @return {string}
 */
base32.encodeToString = (b) => {
  if (!(b instanceof Buffer)) throw new Error('input not Buffer')
  if (b.length === 0) return ''

  let str = ''
  const len = b.length
  let v1, v2, v3, v4, v5

  const count = parseInt(len / 5) * 5
  let i = 0
  while (i < count) {
    v1 = b[i++]
    v2 = b[i++]
    v3 = b[i++]
    v4 = b[i++]
    v5 = b[i++]
    str += encodeTable[v1 >>> 3] +
      encodeTable[(v1 << 2 | v2 >>> 6) & 31] +
      encodeTable[(v2 >>> 1) & 31] +
      encodeTable[(v2 << 4 | v3 >>> 4) & 31] +
      encodeTable[(v3 << 1 | v4 >>> 7) & 31] +
      encodeTable[(v4 >>> 2) & 31] +
      encodeTable[(v4 << 3 | v5 >>> 5) & 31] +
      encodeTable[v5 & 31]
  }

  const remain = len - count
  switch (remain) {
    case 1:
      v1 = b[i]
      str += encodeTable[v1 >>> 3] +
        encodeTable[(v1 << 2) & 31] + '======'
      break
    case 2:
      v1 = b[i++]
      v2 = b[i]
      str += encodeTable[v1 >>> 3] +
        encodeTable[(v1 << 2 | v2 >>> 6) & 31] +
        encodeTable[(v2 >>> 1) & 31] +
        encodeTable[(v2 << 4) & 31] + '===='
      break
    case 3:
      v1 = b[i++]
      v2 = b[i++]
      v3 = b[i]
      str += encodeTable[v1 >>> 3] +
        encodeTable[(v1 << 2 | v2 >>> 6) & 31] +
        encodeTable[(v2 >>> 1) & 31] +
        encodeTable[(v2 << 4 | v3 >>> 4) & 31] +
        encodeTable[(v3 << 1) & 31] + '==='
      break
    case 4:
      v1 = b[i++]
      v2 = b[i++]
      v3 = b[i++]
      v4 = b[i]
      str += encodeTable[v1 >>> 3] +
        encodeTable[(v1 << 2 | v2 >>> 6) & 31] +
        encodeTable[(v2 >>> 1) & 31] +
        encodeTable[(v2 << 4 | v3 >>> 4) & 31] +
        encodeTable[(v3 << 1 | v4 >>> 7) & 31] +
        encodeTable[(v4 >>> 2) & 31] +
        encodeTable[(v4 << 3) & 31] + '='
      break
  }

  return str
}

/**
 * decode base32 string to byte
 * @param {string} str
 * @return {ArrayBuffer}
 */
base32.decodeFromString = (str) => {
  if (typeof str !== 'string' || str.length === 0) throw new Error('input not string or empty')
  if (!/^[A-Z2-7=]+$/.test(str)) throw new Error('Invalid base32 characters')
  str = str.toUpperCase().replace(/=/g, '')

  let v = []
  const buf = []
  const len = str.length
  const count = len >> 3 << 3
  let i = 0

  while (i < count) {
    v[0] = decodeTable[str.charAt(i++)]
    v[1] = decodeTable[str.charAt(i++)]
    v[2] = decodeTable[str.charAt(i++)]
    v[3] = decodeTable[str.charAt(i++)]
    v[4] = decodeTable[str.charAt(i++)]
    v[5] = decodeTable[str.charAt(i++)]
    v[6] = decodeTable[str.charAt(i++)]
    v[7] = decodeTable[str.charAt(i++)]
    buf.push(
      (v[0] << 3 | v[1] >>> 2) & 0xff,
      (v[1] << 6 | v[2] << 1 | v[3] >>> 4) & 0xff,
      (v[3] << 4 | v[4] >>> 1) & 0xff,
      (v[4] << 7 | v[5] << 2 | v[6] >>> 3) & 0xff,
      (v[6] << 5 | v[7]) & 0xff
    )
  }

  switch (len - count) {
    case 2:
      v[0] = decodeTable[str.charAt(i++)]
      v[1] = decodeTable[str.charAt(i++)]
      buf.push(
        (v[0] << 3 | v[1] >>> 2) & 0xff
      )
      break
    case 4:
      v[0] = decodeTable[str.charAt(i++)]
      v[1] = decodeTable[str.charAt(i++)]
      v[2] = decodeTable[str.charAt(i++)]
      v[3] = decodeTable[str.charAt(i++)]
      buf.push(
        (v[0] << 3 | v[1] >>> 2) & 0xff,
        (v[1] << 6 | v[2] << 1 | v[3] >>> 4) & 0xff
      )
      break
    case 5:
      v[0] = decodeTable[str.charAt(i++)]
      v[1] = decodeTable[str.charAt(i++)]
      v[2] = decodeTable[str.charAt(i++)]
      v[3] = decodeTable[str.charAt(i++)]
      v[4] = decodeTable[str.charAt(i++)]
      buf.push(
        (v[0] << 3 | v[1] >>> 2) & 0xff,
        (v[1] << 6 | v[2] << 1 | v[3] >>> 4) & 0xff,
        (v[3] << 4 | v[4] >>> 1) & 0xff
      )
      break
    case 7:
      v[0] = decodeTable[str.charAt(i++)]
      v[1] = decodeTable[str.charAt(i++)]
      v[2] = decodeTable[str.charAt(i++)]
      v[3] = decodeTable[str.charAt(i++)]
      v[4] = decodeTable[str.charAt(i++)]
      v[5] = decodeTable[str.charAt(i++)]
      v[6] = decodeTable[str.charAt(i++)]
      buf.push(
        (v[0] << 3 | v[1] >>> 2) & 0xff,
        (v[1] << 6 | v[2] << 1 | v[3] >>> 4) & 0xff,
        (v[3] << 4 | v[4] >>> 1) & 0xff,
        (v[4] << 7 | v[5] << 2 | v[6] >>> 3) & 0xff
      )
      break
  }

  return Buffer.from(buf)
}