#!/bin/bash

# toggle display arrangements.

# If there is only one monitor, then run xrandr --auto

# Otherwise assume there are two displays. A small one (e.g. laptop)
# and a big one (e.g. monitor). Identify the displays, and toggle
# between 3 states: small one only -> both with the big one to the
# left of the small one -> big one only small one: <20 inch big one:
# >20 inch

# Make sure the variables from pipe can be assigned
# https://stackoverflow.com/questions/42963395/bash-assign-variable-from-pipe
shopt -s lastpipe
i=0
regex="^([^ ]+).* .*$"

# Read the output of xrandr for connected display names and sizes
xrandr | grep " connected " | while IFS=$'\n' read -r line; do
  if [[ $line =~ $regex ]]; then
    name["$i"]="${BASH_REMATCH[1]}"
    (( i++ ))
  fi
done

# Only one monitor: run xrandr --auto
if (( i == 1 )); then
  xrandr --auto
  exit 0
fi

regex="^.*/([0-9]+)x.*/([0-9]+).* ([^ ]+)$"
xrandr --listactivemonitors | while IFS=$'\n' read -r line; do
  if [[ $line =~ $regex ]]; then
    if (( "${BASH_REMATCH[1]}" > 500 )); then
      bigger="${BASH_REMATCH[3]}"
      if [[ $bigger == "${name[0]}" ]]; then
        smaller=${name[1]}
      else
        smaller=${name[0]}
      fi
    else
      smaller="${BASH_REMATCH[3]}"
      if [[ $smaller == "${name[0]}" ]]; then
        bigger=${name[1]}
      else
        bigger=${name[0]}
      fi
    fi
  fi
done

# If only smaller on, then have both on
if ! xrandr --listactivemonitors | grep -q "$bigger"; then
  xrandr --output "$bigger" --primary --auto --output "$smaller" --right-of "$bigger" --auto
  # if only bigger on, then only smaller on
elif ! xrandr --listactivemonitors | grep -q "$smaller"; then
  xrandr --output "$bigger" --auto --left-of "$smaller" --output "$smaller" --primary --auto
  xrandr --output "$bigger" --off
  # if both are on, then only bigger on
else
  xrandr --output "$bigger" --primary --auto --left-of "$smaller" --output "$smaller" --auto
  xrandr --output "$smaller" --off
fi