Set random background image and i3lock wallpaper

#!/bin/sh

backgrounds="${HOME}/Pictures/backgrounds/"
BG_CMD="feh --no-xinerama --bg-center"

get_fitting_image () {
  # We check a directory that contains WIDTHxHEIGHT named subdirectories
  # So if your screen size is 1920x1080 you should have
  # "${backgrounds}/1920x1080"
  resolution=$(xdpyinfo | awk '/dimensions/{print $2}')
  find "${backgrounds}${resolution}" -type f | shuf -n1
}

set_screensaver () {
  # Convert images to png for i3lock if necessary
  # The image is only converted once and cached in the i3 directory
  img=$1
  echo "Set ${img} as i3lock wallpaper"
  png="${img%.*}.png"
  target="${HOME}/.config/i3/$(sha1sum "${img}" | awk '{ print $1 }').png"
  if [ ! -f "$target" ]; then
    if [ "$img" != "$png" ]; then
      echo "Converting source $img to $target"
      convert "$img" "$target"
    else
      cp "$img" "$target"
    fi
  fi
  ln -sf "$target" "${HOME}/.config/i3/i3lock.png"
}

set_background () {
  echo "Set ${1} as desktop wallpaper"
  $BG_CMD "$1"
}

for cmd in xdpyinfo feh convert; do
  if ! command -v "$cmd" >/dev/null 2>&1; then
    echo "$cmd is not installed, this won't work"
    exit 1
  fi
done

if ! xdpyinfo -display "$DISPLAY" >/dev/null 2>&1; then
  echo "I can't seem to connect to display '$DISPLAY'"
  exit 2
fi

img="$(get_fitting_image)"

case ${1:-background} in
  screensaver*)
    set_screensaver "$img"
    ;;
  background*)
    set_background "$img"
    ;;
  both*)
    set_background "$img"
    set_screensaver "$img"
    ;;
esac