dtsh

#!/bin/sh

#---
# Wrapper around the 'dtach' utility to manage multiple sessions
# stored in the same directory, creating/switching to them easily.
#---

DIR=$HOME/.config/dtsh

DEFAULT_NAME=s
DEFAULT_CMD=$SHELL

DTACH_ESCAPE='^\'
DTACH_OPTS="-e $DTACH_ESCAPE -z"

usage() {
    cat <<EOF
  Usage: ${0##*/} <session name>
         ${0##*/} -c [<session name>] [<command>]
  Open sessions:
EOF
    get_sessions

    if [ "$DTSH_SESSION" ]
    then
	echo "  Currently attached: $(basename $DTSH_SESSION)"
    fi
}

# print list of current sessions
get_sessions() {
    for s in "$DIR"/*
    do
	[ -S "$s" ] || continue
	printf " $(basename $s)\n"	
    done 
}

# Find and print the filename for the new session
# arguments will be used as name
new_session_name() {
    local name=${*:-$DEFAULT_NAME}
    local fname;
    while true
    do
	fname="${DIR}/${name}${i}"
	[ -S "$fname" ] || break
	i=$((i+1))
    done
    printf "$fname"
}

# Shell commands to run after a new deattached session
# is created.
# 
new_session_command() {
    cat <<EOF
 printf "This is a dtsh session: '$(basename "$DTSH_SESSION")'\n"
 printf "To detach it from the terminal press: %s\n" "${DTACH_ESCAPE/\\/\\\\}"
 exec ${@:-$DEFAULT_CMD}
EOF
}

if ! [ "$1" ]
then
    usage
    exit 1

elif [ "$1" = "-c" ]
then
    shift
    DTSH_SESSION=$(new_session_name $1)
    shift
    DTSH_CMD=$(new_session_command $@)
    mkdir -p "$DIR"
    export DTSH_SESSION
    exec dtach -c "$DTSH_SESSION" $DTACH_OPTS sh -c "$DTSH_CMD"

else
    s="$DIR/$*"
    if [ "$DTSH_SESSION" = "$s" ]
    then
	echo "err: the session is already attached to the current terminal"
	exit 2
	
    elif ! [ -S "$s" ]
    then
	echo "The given session doesn't exist: '$*'"
	echo "Use the -c flag to create it, or pick an existing session:"
	get_sessions	
	exit 2

    else
	exec dtach -a "$s" $DTACH_OPTS
    fi
fi