#!/bin/bash
set -e
PROGNAME=$(basename $0)

#  Globals
VERBOSELEVEL=20

main()
{
    ERRMSG_MODE=echo

    debug 10 "main: sanity checks ..."
    [ "X$DISPLAY" != X ] || error "DISPLAY: not set (are you logged in on the console?)"
    type -p gxmessage || error "gxmessage: not found (do you need to install it?)"
    ERRMSG_MODE=gxmessage
    type -p Xvnc      || error "Xvnc: not found (do you need to install it?)"
    type -p vncviewer || error "vncviewer: not found (do you need to install it?)"
    
    debug 10 "main: determining if VNC server is running ..."
    #  Assign a different VNC server ID for each user (probably)
    VNC_DISPLAY_ID=$(echo "$(echo $LOGNAME | sum | awk '{ print $1 }') % 64" | bc -q)
    #  Lock files for existing servers and viewers
    XVNC_SERVER_LOCK_FILE=/tmp/$PROGNAME.vnc-server-$VNC_DISPLAY_ID.lock
    XVNC_VIEWER_LOCK_FILE=/tmp/$PROGNAME.vnc-viewer-$VNC_DISPLAY_ID.lock
    #  Is a server running?
    if ! XVNC_SERVER_PID=`cat $XVNC_SERVER_LOCK_FILE 2>/dev/null`; then
        VNC_SERVER_IS_RUNNING_FLAG=false
    elif [ ! -d /proc/$XVNC_SERVER_PID ]; then
        VNC_SERVER_IS_RUNNING_FLAG=false
    else
        VNC_SERVER_IS_RUNNING_FLAG=true
    fi
    debug 10 "main: VNC_SERVER_IS_RUNNING_FLAG=$VNC_SERVER_IS_RUNNING_FLAG"
    
    #  If a server is not running then start one, with the same
    #  geometry as a reference window (firefox).
    if $VNC_SERVER_IS_RUNNING_FLAG; then
        debug 10 "main: VNC is running, no action necessary"
    #  'xlsclients -al' returns the wrong window ID for Firefox. The best
    #  I've found is run 'xwininfo -root -tree' and search for 'Navigator'.
    elif ! XWININFO_ROOT_TREE_OUTPUT="$(xwininfo -root -tree)"; then
        debug 10 "main: xwininfo -root -tree: failed"
        error "failed to run 'xwininfo -root -tree' (please seek developer assistance)"
    elif ! REFERENCE_WINDOW_ID=$(echo "$XWININFO_ROOT_TREE_OUTPUT" | sed -n 's/ *\(0x[^ ]*\).*"Navigator".*/\1/p'); then
        debug 10 "main: sed: failed"
        error "failed run 'sed ...' (please seek developer assistance)"
    elif [ "X$REFERENCE_WINDOW_ID" = X ]; then
        debug 10 "main: no window ID found"
        error "failed to get Firefox's window ID (do you need to run firefox?)"
    elif ! REFERENCE_WINDOW_XWININFO_OUTPUT=$(xwininfo -id $REFERENCE_WINDOW_ID); then
        debug 10 "main: xwininfo -id $REFERENCE_WINDOW_ID: failed"
        error "failed to run 'xwininfo -id $REFERENCE_WINDOW_ID' ((please seek developer assistance)"
    else
        info "starting vnc server ..."
        REFERENCE_WINDOW_GEOMETRY=$(echo "$REFERENCE_WINDOW_XWININFO_OUTPUT" | sed -n 's/.*-geometry \([^+]*\).*/\1/p')
        sh -c "echo \$\$ > $XVNC_SERVER_LOCK_FILE; exec Xvnc :$VNC_DISPLAY_ID -localhost -geometry $REFERENCE_WINDOW_GEOMETRY -query localhost 2>/dev/null" &
    fi
    
    debug 10 "main: determining if VNC viewer is running ..."
    #  Is a viewer running? (We will *always*
    #  start a new viewer, but we need to know
    #  if a viewer is already running in order
    #  to know if we need to kill it or not).
    if ! XVNC_VIEWER_PID=`cat $XVNC_VIEWER_LOCK_FILE 2>/dev/null`; then
        VNC_VIEWER_IS_RUNNING_FLAG=false
    elif [ ! -d /proc/$XVNC_VIEWER_PID ]; then
        VNC_VIEWER_IS_RUNNING_FLAG=false
    else
        VNC_VIEWER_IS_RUNNING_FLAG=true
    fi
    debug 10 "main: VNC_VIEWER_IS_RUNNING_FLAG=$VNC_VIEWER_IS_RUNNING_FLAG"
    
    #  If a viewer is running then kill it.
    if $VNC_VIEWER_IS_RUNNING_FLAG; then
       debug 10 "main: killing existing vnc viewer ..."
       kill $XVNC_VIEWER_PID
       sleep 1
    fi
    
    #  Start a new viewer.
    debug 10 "main: starting vnc viewer ..."
    sh -c "echo \$\$ > $XVNC_VIEWER_LOCK_FILE; exec vncviewer -FullColour localhost:$VNC_DISPLAY_ID 2>/dev/null" &
}

#  Standard message functions
debug()    { [ $VERBOSELEVEL -lt $1 ] || echo "$PROGNAME: DEBUG[$1]: $2"      >&2;         }
info()     { [ $VERBOSELEVEL -lt 3  ] || echo "$PROGNAME: INFO: $1"           >&2;         }
warning()  { [ $VERBOSELEVEL -lt 2  ] || echo "$PROGNAME: WARNING: $1"        >&2;         }
error()    { [ $VERBOSELEVEL -lt 1  ] || if [ $ERRMSG_MODE = echo ]; then echo "$PROGNAME: ERROR: $1" >&2; else gxmessage -name $PROGNAME -buttons "GTK_STOCK_OK:0" "ERROR: $1"; fi; exit 1; }
internal() {                             echo "$PROGNAME: INTERNAL ERROR: $1" >&2; exit 2; }

main "$@"