#!/bin/bash
help() {
  self=`basename $0`
  cat <<END >&2
Reconnect to remote host after connection broken -- 3/22/21 brent@mbari.org
All args through user@hostname are passed to ssh
Any remaining args are interpreteed as a shell command
to be run in a new GNU screen session as user@hostname
If no command is specified, try reconnecting with the previous screen session
Any -options between user@hostname and the command are passed through to screen

Examples:
\$ $self esp@koa.tun esp                #new interactive esp server session
\$ $self esp@koa.tun espclient chris    #new esp client session named 'chris'
\$ $self esp@koa.tun                    #reconnect to most recent session

\$ $self esp@koa.tun espclient bob      #new esp client session named 'bob'
\$ session=chris $self esp@koa.tun      #reconnect to session 'chris'

\$ $self esp@koa.tun -list      #list all esp@koa.tun screen sessions

If the network disconnects, try to reconnect every 30 seconds,
or whenever <ENTER> key pressed at the '...' prompt

Environment Variable:
session=name  #names the session being started or reconnected
If session is unset when starting a new one, the name of the new session
is the last non-option word in the command used to start it.
If session is set to the null string, no attempt is made to guess at
the new session name.

Bugs:
ssh command errors are mistaken for disconnections
Use Ctrl-C to exit at the '...' prompt.
END
  exit 2
}

ssh="ssh -t"
userHost=
set -f  #no globbing

while [ "$1" ]; do
  ssh="$ssh $1"
  case "$1" in
    -*) shift; continue
  esac
  userHost="$1"
  break  #assume 1st non-opt is user@host
done
[ "$userHost" ] || help
shift
[ "$1" -a -z ${session+x} ] && for arg; do
  case "$arg" in
    -*) continue
  esac
  session=${arg//\//+}  #change slashes into plus signs
done
if [ "$session" ]; then
screen="-S $session $@"
resume="-xr $session"
else
screen="$@"
resume="-xRR"
fi
[ "$1" ] || screen=$resume

#echo "$ssh screen $screen ($resume)"; exit  #uncomment for debugging

while $ssh screen $screen; err=$?; [ $err = 255 ]; do
  read -t30 -p"`date`: Reconnecting to $userHost in 30 seconds ..." || echo >&2
  screen=$resume
done
exit $err