package main

import (
  "bytes"
  "encoding/hex"
  "strings"
)

func CompactEncode(hexSlice []int) string {
  terminator := 0
  if hexSlice[len(hexSlice)-1] == 16 {
    terminator = 1
  }

  if terminator == 1 {
    hexSlice = hexSlice[:len(hexSlice)-1]
  }

  oddlen := len(hexSlice) % 2
  flags := 2 * terminator + oddlen
  if oddlen != 0 {
    hexSlice = append([]int{flags}, hexSlice...)
  } else {
    hexSlice = append([]int{flags, 0}, hexSlice...)
  }

  var buff bytes.Buffer
  for i := 0; i < len(hexSlice); i+=2 {
    buff.WriteByte(byte(16 * hexSlice[i] + hexSlice[i+1]))
  }

  return buff.String()
}

func CompactHexDecode(str string) []int {
  base := "0123456789abcdef"
  hexSlice := make([]int, 0)

  enc := hex.EncodeToString([]byte(str))
  for _, v := range enc {
    hexSlice = append(hexSlice, strings.IndexByte(base, byte(v)))
  }
  hexSlice = append(hexSlice, 16)

  return hexSlice
}