#!/bin/sh

#set -x

# Places for flags:
# $HOME/.flag-cache <- Autogenerated flag (refreshed when hostname changes)
# /etc/flag <- Site admin's flag
# $HOME/.flag <- Local user's flag
# Check them in that order.

hash_string() {
  # Hash the passed string into 8 hex characters
  [ -z "${crc32_bin}" ] && find_crc32_bin
  if [ -z "${crc32_bin}" ]
  then
    echo "No crc32 algo found!" >&2
    echo "deadbeef"
  else
    echo -n "${*}" | eval "${crc32_bin}" | awk '{print $1}'
  fi
}

find_crc32_bin() {
  crc32=""
  for bin in crc32sum crc32sum-linux crc32sum-freebsd
  do
    bin="$(which "${bin}" 2>/dev/null)"
    if [ -x "${bin}" ]
    then
      export crc32_bin="${bin}"
      if [ "$(hash_string "meow" 2>/dev/null)" = "8a106afe" ]
      then
        crc32="${bin}"
        break
      fi
    fi
  done

  if [ -z "${crc32}" ]
  then
    for bin in ruby php perl
    do
      bin="$(which "${bin}" 2>/dev/null)"
      if [ -x "${bin}" ]
      then
        case "${bin}" in
        */ruby) bin="${bin} -e 'require \"zlib\"; printf(\"%08x\n\", Zlib.crc32(STDIN.readlines.join))'" ;;
        */php)  bin="${bin} -r 'printf(\"%08x\n\", crc32(file_get_contents(\"/dev/stdin\")));'" ;;
        */perl)        bin="${bin} -e 'use String::CRC32; printf(\"%08x\n\", crc32(*STDIN));'" ;;
        esac
        export crc32_bin="${bin}"
        if [ "$(hash_string "meow" 2>/dev/null)" = "8a106afe" ]
        then
          crc32="${bin}"
          break
        fi
      fi
    done
  fi
  if [ -n "${crc32}" ]
  then
    export crc32_bin="${crc32}"
  else
    echo "Failed to locate usable crc32 algo" >&2
    unset crc32_bin
    return 1
  fi
}

flagcache(){
  myhost="$(/bin/hostname -f)"
  cache="${HOME}/.flag-cache"
  if [ -f "${cache}" ]
  then
    flag_hex="$(awk '/^'${myhost}'/{print $2}' "${cache}")"
  fi
  if [ -z "${flag_hex}" ]
  then
    flag_hex="$(hash_string "${myhost}")"
    echo -e "${myhost}\t${flag_hex}" >> "${cache}"
  fi
}

if [ -f "${HOME}/.flag" ]
then
  flag_hex="$(cat "${HOME}/.flag")"
fi

if [ -z "${flag_hex}" -a -f "/etc/flag" ]
then
  flag_hex="$(cat "/etc/flag")"
fi

if [ -z "${flag_hex}" ]
then
  flagcache
fi

# Now we definitely have flag_hex
firstchar() {
  eval $(echo -n "${data}" | sed -e 's/^\(.\)\(.*\)$/char="\1" data="\2"/g')
}

hexdec() {
  if [ -z "${1}" ]
  then
    echo "0"
    return
  fi
  echo $(( 0x${1} + 0 ))
}

flag() {
  if [ -z "${1}" ]
  then
    echo "Usage: flag 'hexcode' [symbol] [shellmode]" >&2
    echo "Generates an ANSI color flag using the specified hex codes" >&2
    echo "Uses the optional symbol (or ' ') to draw the flag" >&2
    echo "shellmode encapsulates all nonprintable codes in \[\] to" >&2
    echo " give the shell hints on how long the string is, for proper" >&2
    echo " wrapping of command prompts." >&2
    return
  fi
  data="${1}"
  sym="${2}"
  shm="${3}"
  [ -n "${shm}" ] && open='\\[' shut='\\]'
  while [ -n "${data}" ]
  do
    firstchar
    ord=$(hexdec "${char}")
    bright="0"
    [ "$(( ${ord} & 8 ))" -gt 0 ] && bright="1;7"
    colour="$(( ${ord} & 7 ))"
    printf "${open}\033[%s;3%s;4%sm${shut}%s" "${bright}" "${colour}" "${colour}" "${sym:-${char}}"
  done
  printf "${open}\033[0m${shut}"
}

pebkac() {
   echo "Usage: $(basename "${0}") [-s #] [-e]" >&2
   echo "Produces a neat little ansi colour 'flag' based off" >&2
   echo " a hash of the machine's hostname (or settable via" >&2
   echo " ~/.flag or /etc/flag) which can uniquely visually" >&2
   echo " identify a machine, at a glance. Useful for placing" >&2
   echo " into /etc/issue or your bash prompt, so that you" >&2
   echo " don't send stupid commands to the wrong machine." >&2
   echo " " >&2
   echo " -s #   Specify which character should be used to" >&2
   echo "         render the flag. If empty, use the hex code." >&2
   echo " -e     Turn on bash encapsulation mode, to provide" >&2
   echo "         hints to Bash on what is or is not printable" >&2
   echo "         so it can wrap your commands appropriately" >&2
   echo "         when used in your prompt" >&2
   echo " " >&2
   echo "This machine's flag is as such: ($(flag "${flag_hex}"))" >&2
   exit 1
}

symbol=""
shellmode=""

while [ -n "${1}" ]
do
  case "${1}" in
  -s)  shift; symbol="${1}" ;;
  -e)  shellmode="yes" ;;
  *)   pebkac ;;
  esac
  shift
done
flag "${flag_hex}" "${symbol}" "${shellmode}"