makeicns

#!/bin/bash

readonly program="$(basename "${0}")"

function usage {
  echo "
    Generate an icns icon from a png.

    Usage:
      ${program} [options] <file>

    Options:
      -i, --input <file>    File to convert.
      -o, --output <file>   File to save.
      -h, --help                 Show this message.
  " | sed -E 's/^ {4}//'

  exit "${1}"
}

# Options
args=()
while [[ "${1}" ]]
do
  case "${1}" in
    -h | --help)
      usage 0
      ;;
    -i | --input)
      readonly input="$(realpath "${2}")"
      shift
      ;;
    -o | --output)
      readonly output="${2%.icns}.icns" # Add extension if missing
      shift
      ;;
    --)
      shift
      args+=("${@}")
      break
      ;;
    -*)
      echo "Unrecognised option: ${1}"
      exit 1
      ;;
    *)
      args+=("${1}")
      ;;
  esac
  shift
done
set -- "${args[@]}"

# Checks
[[ -f "${input}" && -n "${output}" ]] || usage 1

# Main
readonly iconset="$(mktemp -d)"

if [[ "$(/usr/bin/file --mime-type --brief "${input}")" != 'image/png' ]]
then
  echo 'Image needs to be a png.' >&2
  exit 1
fi

for size in {16,32,64,128,256,512}
do
  /usr/bin/sips --resampleHeightWidth "${size}" "${size}" "${input}" --out "${iconset}/icon_${size}x${size}.png" &> /dev/null
  /usr/bin/sips --resampleHeightWidth "$((size * 2))" "$((size * 2))" "${input}" --out "${iconset}/icon_${size}x${size}@2x.png" &> /dev/null
done

/bin/mv "${iconset}" "${iconset}.iconset"
/usr/bin/iconutil --convert icns "${iconset}.iconset" --output "${output}"