#! /bin/sh
#
# ircsink - send stdin to IRC
#
# SYNOPSIS
#   ircsink [--nick=NICK] [--port=PORT] [--secure]
#           --server=SERVER --target=TARGET
#
#   ircsink --help
#
# DESCRIPTION
#   ircsink sends lines from standard input to the specified IRC target.
#
#   --command=NOTICE (default: PRIVMSG)
#     Whether a PRIVMSG or NOTICE is sent.
#
#   --help
#
#   --nick=NICK (default: the system's host name)
#
#   --port=PORT (default: 6667, or 6697 if --secure is specified)
#
#   --sasl=plain
#     If specified, then use the PLAIN SASL mechanism.
#
#   --sasl-pass=@FILE
#   --sasl-pass=$VAR
#   --sasl-pass="PASS
#     Password to be used for SASL authentication, which can be read either
#     from a file, an environment variable, or passed in as argument.
#
#     Note: the characters @, $, and " have to be verbatim and might need to be
#     quoted in the shell, e.g. ircsink --sasl-pass=\$SASL_PASS
#
#   --sasl-user=USER (default: NICK)
#     User to be used for SASL authentication.
#
#   --secure
#     If specified, then the connection will be made using openssl.
#     Otherwise netcat will be used.
#
#   --server=SERVER
#
#   --target=TARGET
#     The target for receiving messages.
#     Can be either a channel's or a user's name.
#

set -efu

main() {(

  exec 3<&0

  _args=$(getopt -n "$0" -s sh \
      -l command:,help,nick:,port:,sasl:,sasl-pass:,sasl-user:,secure,server:,target: \
      -- "$0" "$@")
  eval set -- "$_args"
  unset _args

  command=
  help=
  nick=
  port=
  sasl_mech=
  sasl_pass=
  sasl_user=
  secure=
  server=
  target=
  while :; do
    case $1 in
      --command) command=$2; shift 2;;
      --help) help=1; shift;;
      --nick) nick=$2; shift 2;;
      --port) port=$2; shift 2;;
      --sasl)
        case $2 in
          plain) sasl_mech=$2; shift 2;;
          *) echo "$0: unsupported SASL mechanism: $2" >&2; exit 1;;
        esac
        ;;
      --sasl-pass)
        case $2 in
          \@*) sasl_pass=$(cat "${2:1}"); shift 2;;
          \$*) sasl_pass=$(env | awk -F= -v name="${2:1}" '$1==name{print$2}'); shift 2;;
          \"*) sasl_pass=${2:1}; shift 2;;
          *) echo "$0: don't know how to get SASL password: $2" >&2; exit 1;;
        esac
        ;;
      --sasl-user) sasl_user=$2; shift 2;;
      --secure) secure=1; shift;;
      --server) server=$2; shift 2;;
      --target) target=$2; shift 2;;
      --) shift; break;;
    esac
  done
  case $# in
    0) :;;
    1) echo "$0: bad argument: $*" >&2; exit 1;;
    *) echo "$0: bad arguments: $*" >&2; exit 1;;
  esac

  if test "$help" = 1; then
    print_help
    exit
  fi

  if test -t 3; then
    echo "$0: error: ircsink cannot be used interactively" >&2
    exit 1
  fi

  if test -z "$command"; then
    command=PRIVMSG
  fi

  if test -z "$nick"; then
    nick=$(hostname)
  fi

  if test -n "$sasl_mech" && test -z "$sasl_user"; then
    sasl_user=$nick
  fi

  if test -n "$sasl_mech" && test -z "$secure"; then
    echo "$0: error: cannot use --sasl without --secure" >&2
    exit 1
  fi

  if test -z "$port"; then
    case $secure in
      '') port=6667;;
      1) port=6697;;
      *)
        echo "$0: missing argument: --port" >&2
        exit 1
        ;;
    esac
  fi

  if test -z "$server"; then
    echo "$0: missing argument: --server" >&2
    exit 1
  fi

  if test -z "$target"; then
    echo "$0: missing argument: --target" >&2
    exit 1
  fi

  is_channel() {
    case $1 in
      \#*) :;;
      *) ! :;;
    esac
  }

  # echo2 and cat2 are used output to both, stdout and stderr
  # This is used to see what we send to the irc server. (debug output)
  echo2() { echo "$*"; echo "$*" >&2; }
  cat2() {
    awk '{
      print $0
      print $0 > "/dev/stderr"
    }'
  }

  # command_cat transforms stdin to a privmsg or notice
  command_cat() {
    awk -v command="$command" -v target="$target" '{ print command" "target" :"$0 }'
  }

  ircat() {
    if test "$secure" = 1; then
      openssl s_client -connect "$server:$port"
    else
      nc "$server" "$port"
    fi
  }

  # ircin is used to feed the output of netcat back to the "irc client"
  # so we can implement expect-like behavior with sed^_^
  # XXX mkselfdestructingtmpfifo would be nice instead of this cruft
  tmpdir=$(mktemp --tmpdir -d ircsink_XXXXXXXX)
  cd "$tmpdir"
  mkfifo ircin
  trap cleanup EXIT
  cleanup() {
    trap - EXIT
    rm ircin
    cd "$OLDPWD"
    rmdir "$tmpdir"
  }

  {
    LOGNAME=${LOGNAME-$USER}
    echo2 "USER $LOGNAME 0 * :$LOGNAME@$(hostname)"
    echo2 "NICK $nick"

    sed -nru '
      # wait for messages that indicate that the connection is ready
      #   RPL_UMODEIS (221)
      #   RPL_ENDOFMOTD (376)
      #   ERR_NOMOTD (422)
      /^:[^ ]* (MODE|221|376|422) /q

      # answer any PING messages while waiting
      s/^PING (:.*)/PONG \1/p
    '

    case $sasl_mech in
      plain)
        echo2 "CAP REQ :sasl"
        sed -nru '/^:[^ ]* CAP [0-9A-Za-z]+ ACK :?sasl/q'

        echo2 "AUTHENTICATE PLAIN"
        sed -nru '/AUTHENTICATE +/q'

        echo sasl user: $sasl_user >&2
        message=$(printf '\0%s\0%s' "$sasl_user" "$sasl_pass" | base64 -w0)
        echo "AUTHENTICATE $message"
        echo "AUTHENTICATE ***REDACTED***" >&2

        sed -nru '/^(.*?):SASL authentication successful/q'
        ;;
    esac

    if is_channel "$target"; then
      echo2 "JOIN $target"
    fi

    command_cat <&3 \
      | cat2

    if is_channel "$target"; then
      echo2 "PART $target"

      # wait for PART confirmation
      sed -n '/:'"$nick"'![^ ]* PART /q'
    fi

    echo2 'QUIT :Gone to have lunch'
  } < ircin \
    | ircat | tee -a ircin
)}

print_help() {
  sed -nr '
    0,/^$/{
      /^#!/d
      s/^#($| )//p
    }
  ' "$0"
}

main "$@"