Convert comics (.rar, .zip, .cbz, .cbx) to pdfs based on their internal file structure

Makefile

# remember to not use the old builtin gnu make on macos
ifeq ($(word 1,$(subst ., ,$(MAKE_VERSION))),3)
  _ := $(error use a newer gnu make)
endif

SHELL        := bash
manga_dir    := $(HOME)/Documents/manga
escape       =  '$(subst ','\'',$1)'
img2pdf_opts := --rotation=ifvalid --engine=internal

find_image_files = \
	find $1 -type f -exec file --mime-type --no-pad --separator / -- '{}' '+' \
	| sed -n 's|/ image/[^ ]*$$||p' \
	| grep -vF /__MACOSX/ \
	| grep -vF /.DS_Store/

define pdfize
	mkdir -p $(call escape,$@)/_unpack
	cd $(call escape,$@)/_unpack && \
		$1 $(call escape,$^)
	cd $(call escape,$@) && \
		$(call find_image_files,.) \
		| sed 's|/[^/]*$$||' \
		| sort --version-sort \
		| uniq \
		| while read -r comic_dir; do \
			echo "Processing $$comic_dir"; \
			$(call find_image_files,"$$comic_dir" -maxdepth 1) \
				| sort --version-sort \
				| tr '\n' '\0' \
				| img2pdf \
					--from-file - \
					$(img2pdf_opts) \
					-o ./"$$(echo "$$comic_dir" | tr / - | sed 's|^\.-_unpack-||')".pdf -- "$${files[@]}"; \
		done
	rm -r $(call escape,$@)/_unpack
endef

.PHONY: all
all:
	shopt -s nullglob \
		&& pushd $(call escape,$(manga_dir)) \
		&& all=( \
			*.zip */*.zip \
			*.rar */*.rar \
			*.cbz */*.cbz \
			*.cbr */*.cbr \
		) \
		&& popd \
		&& $(MAKE) "$${all[@]/%//}"

%.rar/: $(manga_dir)/%.rar; $(call pdfize,unrar x)
%.cbr/: $(manga_dir)/%.cbr; $(call pdfize,unrar x)
%.zip/: $(manga_dir)/%.zip; $(call pdfize,unar)
%.cbz/: $(manga_dir)/%.cbz; $(call pdfize,unar)