add oxiora script for handling OpenRaster files

Ref https://openraster.org/

scripts/oxiora.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+
+set -e;
+
+###
+## Input handling
+###
+
+# Set flags for calling oxipng later
+if [[ -n "${UNSAFE}" ]]; then FLAGS="${FLAGS} -a"; fi
+
+if [[ -z "${1}" ]]; then
+	echo "Wrapper for oxipng for handling OpenRaster files
+
+Usage:
+    oxiora file_a.ora file_b.ora ... file_n.ora
+
+Environment variables:
+    UNSAFE
+        Set to any value to send the -a flag to oxipng, which allows altering the colour of completely transparent pixels. Alters the content of images, so disabled by default.
+    
+    FLAGS
+        Any additional flags to pass to oxipng.
+";
+	exit 0;
+fi
+
+###
+## Preamble
+###
+
+# Create temporary directory and clean it up afterwards no matter what
+temp_dir="$(mktemp --tmpdir -d "oxiora-XXXXXXX")";
+
+on_exit() {
+	rm -rf "${temp_dir}";
+}
+trap on_exit EXIT;
+
+###
+## Main loop
+###
+
+# We process serially here, because oxipng does a good job of using all available CPU cores already
+for filepath in "$@"; do
+	echo ">>> Processing ${filepath}";
+	
+	filesize_before="$(wc -c <"${filepath}")";
+	
+	unzip "${filepath}" -d "${temp_dir}";
+	chmod u+w -R "${temp_dir}"
+	
+	# no -a here 'cause this is technically an editing file to fully-transparent pixel colours could have meaning
+	#shellcheck disable=SC2086
+	find "${temp_dir}" -iname '*.png' -print0 | xargs -0 oxipng ${FLAGS} -somax;
+	
+	filepath_target="${filepath%.*}-small.${filepath##*.}";
+	filepath_target="$(realpath "${filepath_target}")";
+	
+	# The OpenRaster spec says the mimetype file has to be uncompressed
+	# Ref https://www.openraster.org/baseline/file-layout-spec.html#mimetype
+	# unzip style ref https://askubuntu.com/a/1399484/139735
+	(cd "${temp_dir}" && find . -type f -name 'mimetype' | zip -0 -r "${filepath_target}" --names-stdin)
+	(cd "${temp_dir}" && find . -type f -not -name 'mimetype' | zip -9 -r "${filepath_target}" --names-stdin)
+	
+	# Only write the .ora back if it is smaller than the original
+	filesize_after="$(wc -c <"${filepath_target}")";
+	difference="$((filesize_before-filesize_after))";
+	
+	echo ">>> BEFORE $(echo "${filesize_before}" | numfmt --to=iec)iB";
+	echo ">>> AFTER  $(echo "${filesize_after}" | numfmt --to=iec)iB";
+	
+	if [[ "${filesize_after}" -lt "${filesize_before}" ]]; then
+		echo ">>> Compressed by $(echo "${difference}" | numfmt --to=iec)iB";
+		mv -f "${filepath_target}" "${filepath}";
+	else
+		echo ">>> Compressed file was $(echo "$((-difference))" | numfmt --to=iec)iB larger, discarding";
+		rm "${filepath_target}";
+	fi
+	
+	find "${temp_dir}" -mindepth 1 -delete
+done