#!/bin/bash
set -e
set -o pipefail

# x11vnc option '-noxrecord' added as workaround for crashing bug
# See https://github.com/LibVNC/x11vnc/issues/61
#
# The option is not be needed with latest x11vnc from source, but we don't rely
# on the remote side being up to date.

ssh()
{
    command ssh "$@" 2>&1 | sed 's/^/REMOTE> /'
}

direct_connection()
{
    rando=$(tr -dc A-Za-z0-9 < /dev/urandom | head -c15) && [ "$rando" ]
    remote_socket_file=/tmp/x11vnc.$rando.socket
    port=$((5500 + $(tr -dc 1-9 </dev/urandom | head -c3 || true)))

    ssh -n \
        -o ControlPath=none \
        -o ExitOnForwardFailure=yes \
        -L "$port:$remote_socket_file" \
        ${remote_port:+-p "$remote_port"} \
        "$remote_host" \
        "x11vnc -noxrecord -nopw -ncache -ncache_cr -display $local_display -unixsock $remote_socket_file -rfbport 0" &
    X11VNC=$!
    while ! fuser $port/tcp
    do
        sleep 0.3
    done
    xtightvncviewer -encodings 'copyrect tight zrle hextile' localhost:$port
    kill $X11VNC
}

atexit()
{
    [ "$DEBUG" ] || exec 2>/dev/null || true
    set +e
    set -- "$X11VNC" "$SSH"
    ps hu "$@"
    kill "$@"
    rm -rf "$OUR_TMP"
}

share_display()
{
    if [ "$DEBUG" ]
    then
        set -x
    fi

    port=$((5500 + $(tr -dc 1-9 </dev/urandom | head -c3 || true)))
    OUR_TMP=$(mktemp -d) || exit
    local_socket_file=$OUR_TMP/x11vnc.socket
    ssh_control=$OUR_TMP/ssh.socket

    x11vnc -noxrecord -q -nopw -ncache -ncache_cr -display "${local_display}" -unixsock "$local_socket_file" -rfbport 0 &
    X11VNC=$!
    trap atexit EXIT

    ssh -n \
        -o ControlPath=none \
        -o ExitOnForwardFailure=yes \
        -R "$port:$local_socket_file" \
        ${remote_port:+ -p "$remote_port" } \
        "$remote_host" \
        "${DEBUG:+ set -x; } trap 'DISPLAY=$remote_display xtightvncviewer -encodings 'copyrect tight zrle hextile' localhost:$port" &
    SSH=$!
    wait -n
}

if [ "$1" = -r ]
then
    shift
    cmd=share_display
elif [ "$1" = -d ]
then
    shift
    cmd=direct_connection
else
    cmd=direct_connection
fi

remote_host=${1:-blackboard}

case "$remote_host" in
    *:*) remote_port=${remote_host##*:}
         remote_host=${remote_host%:*}
         ;;
    *) remote_port=
       ;;
esac
remote_display=${2:-:0}
local_display=${3:-:0}

$cmd