#!/bin/sh
#
# multissh.sh, Copyright © 2013, 2019 Matteo Cypriani <mcy@lm7.fr>
# (Formerly named cluster-run.sh)
#
# This program is free software. It comes without any warranty, to
# the extent permitted by applicable law. You can redistribute it
# and/or modify it under the terms of the Do What The Fuck You Want
# To Public License, Version 2, as published by Sam Hocevar. See
# http://sam.zoy.org/wtfpl/COPYING for more details.
#
# Run a command on a list of remote hosts using Parallel SSH.

#set -x
set -u

# Exit codes
readonly EXIT_SUCCESS=0
readonly EXIT_USAGE=127
readonly EXIT_HOSTS_LIST=6

print_usage()
{
  echo "Usage: $0 [-l login] <hosts_list> <command>"
}

bad_usage()
{
  err "$@"
  echo >&2
  print_usage >&2
  exit $EXIT_USAGE
}

err()
{
  printf 'Error! ' >&2
  printf '%s\n' "$@" >&2
}

warn()
{
  printf 'Warning! ' >&2
  printf '%s\n' "$@" >&2
}

ssh_command()
{
  grep -v '^#' "$HOSTS" | while read -r host ; do
    [ -z "$host" ] && continue
    echo "Executing command on '$host'..."
    # shellcheck disable=SC2086
    ssh ${LOGIN} "${host}" -- "$@" </dev/null
    # Note: </dev/null is to prevent ssh from swallowing stdin (see SC2095).
  done
}

# Do we have at least a host list and a command?
[ $# -lt 2 ] && bad_usage "Wrong number of arguments."

# Parse the optional arguments
LOGIN=
if [ "$1" = "-l" ] ; then
  LOGIN="$2"
  shift
  shift

  # Do we still have at least a host list and a command?
  [ $# -lt 2 ] && bad_usage "Wrong number of arguments."
fi

# Check dependencies
PSSH=$(command -v parallel-ssh || command -v pssh)
if [ -z "$PSSH" ] ; then
  warn "Parallel SSH (pssh) is not available. Install it for best results."
fi

# Hosts list file
[ -z ${XDG_CONFIG_HOME+x} ] && XDG_CONFIG_HOME="$HOME/.config"
HOSTS_LIST_NAME="$1"
shift
HOSTS="$XDG_CONFIG_HOME/ssh_tools/${HOSTS_LIST_NAME}.lst"
echo "Using file '$HOSTS' as hosts list."
if [ ! -f "$HOSTS" ] ; then
  err "The hosts list file doesn't exist or is not a regular file."
  exit $EXIT_HOSTS_LIST
fi

# Login
if [ -n "$LOGIN" ] ; then
  echo "Login: $LOGIN"
  LOGIN="-l $LOGIN"
fi

echo "Command:" "$@"

if [ -n "$PSSH" ] ; then
  # shellcheck disable=SC2086
  exec $PSSH --print $LOGIN -h "$HOSTS" -- "$@"
else
  ssh_command "$@"
fi