## Bash recognizess a variable called PROMPT_COMMAND and, if it is set,
## executes whatever it evaluates to. This script can be called from .bashrc or
## SOURCED (not executed) on demand. I define aliases "actcool" and actnormal"
## in my .alias file to facilitate turning this on and off.

## The first part defines a function, 'prompt_command', which
## evaluates the current working and directory, (and hostname and username if desired), 
## then writes it to the upper right corner of the display in contrasting color.
## The variable PROMPT_COMMAND is then set equal to 'prompt_command'.
## The second part provides a short prompt string indicating the current input device.

############################################################
## Step 1: Define PROMPT_COMMAND function and some variables.
############################################################
function prompt_command ()
{
  tput sc   # Save the current cursor position

  ## set background, forground color, bold
  if [ $UID = 0 ]
   then tput setab 1 ; tput setaf 3 ; tput bold  # yellow text on red background for root
   else tput setab 4 ; tput setaf 6 ; tput bold  # cyan text on blue background for users
  fi

  ## Define DIR as current directory, with current users home reduced to ~
  DIR=$(pwd | sed s?$(echo ~)?~?)
  
  ## OLDDIR is directory string most recently WRITTEN TO THE SCREEN.
  ## If $DIR is shorter than $OLDDIR it will be necessary to clean up
  ## artifacts which might remain to the left of the new one. This is
  ## done by over-writing with blank spaces. $OLDDIR must not be empty string.
  if [ -z "$OLDDIR" ]
   then OLDDIR=$DIR
  fi 

  DIFF=$(($(echo "$OLDDIR" | wc -m)-$(echo "$DIR" | wc -m)))
  if [ $DIFF -lt 0 ]
   then DIFF=0
  fi

  ## Define SPLASH_STRING - pick one
  # SPLASH_STRING="$DIR"
  # SPLASH_STRING="$HOSTNAME:$DIR"
  SPLASH_STRING="$(id -un)@$HOSTNAME:$DIR"

  ## Define PAD as the total width of the terminal minus the length
  ## of the splash string. Then position cursor to over write any 
  ## artifacts then print $SPLASH_STRING at the top left (Y=0, X=PAD)
 
  let PAD=$(( $(tput cols) -$(echo "$SPLASH_STRING" | wc -m) +1 -$DIFF ))
  tput cup 0 $PAD  # position cursor so the SPLASH_STRING will be left (Y=0, X=$PAD)
  for (($DIFF; DIFF>0; --DIFF)); do echo -n " "; done
  echo -n "$SPLASH_STRING"
 
  OLDDIR=$DIR   # Save directory string for DIFF in next execution.
  tput rc       # Return the cursor to the saved position
}

########################################
## Step 2: Set variable equal to function
########################################
PROMPT_COMMAND=prompt_command

############################################################
## Step 3: Set prompt string to display current input device
############################################################

## Evaluate current logged device from output of 'tty'
tty=$(echo $(tty) |sed s%/dev/%%)

PS1="$tty \\$ "

## Below is a nice idea, but it currently causes problems with display of command history.
## Set command prompt to show current console in UID apropriate colors.
## Colored prompts aid finding command lines among output lines in scrollback
#if [ $UID = 0 ]
#  then PS1="\e[31m\e[103m$tty \\$\e[0m "
#  else PS1="\e[34m\e[106m$tty \\$\e[0m "
#fi