#!/bin/bash
# Make sure stdin and stdout are a tty.
if [ ! -t 0 ] ; then
  exit 1
fi
if [ ! -t 1 ] ; then
  exit 1
fi

# Read some bytes from stdin. Pass the number of bytes to read as the first argument.
function read_bytes()
{
  numbytes=$1
  dd bs=1 count=$numbytes 2>/dev/null
}

# read_until c
# Returns bytes read from stdin up to but not including the fist one equal to c
function read_until() {
  result=""
  while :
  do
    b=$(read_bytes 1)
    if [[ $b == $1 ]]
    then
      echo "$result"
      return
    fi
    result="$result$b"
  done
}

function read_first_response() {
  # If this is an OSC read until terminating BEL and output payload.
  # If this is a CSI then read until 'n' and output nothing.
  read_bytes 1 > /dev/null
  c=$(read_bytes 1)
  if [ "${c}" = "]" ]; then
    # OSC
    bel=$(printf "\a")
    read_until ${bel}
  else
    # CSI
    read_until n > /dev/null
  fi
}

trap clean_up EXIT
_STTY=$(stty -g)      ## Save current terminal setup

function clean_up() {
  stty "$_STTY"            ## Restore terminal settings
}

# Enter raw mode and turn off echo so the terminal and I can chat quietly.
stty -echo -icanon raw

# Send iTerm2-proprietary code. Other terminals ought to ignore it (but are
# free to use it respectfully). iTerm2 will respond with an OSC code.
printf "\e]1337;Capabilities\a" >& 2

# Report device status. Responds with esc [ 0 n. All terminals support this. We
# do this because if the terminal will not respond to iTerm2's custom escape
# sequence, we can still read from stdin without blocking indefinitely.
echo -n '' >& 2

response=$(read_first_response)
if [[ "$response" == *"Capabilities"* ]]; then
  read_until n > /dev/null
  payload=$(sed -re "s/.*Capabilities=([A-Za-z0-9]+).*/\1/" <<< $response)
  clean_up
  # Format capabilities as one per line. If there is a numeric param, add a
  # space between the capability name and the parameter.
  grep -Eo '[A-Z][a-z0-9]*' <<< "$payload"  | sed -re 's/([0-9]+)/ \1/'
else
  clean_up
fi