#!/bin/sh

BIB_FILE="${HOME}/latex/uni.bib"
[ -f "${BIB_FILE}" ] || BIB_FILE="${2:-$(find "${HOME}" -path "${HOME}/.*" \
	-prune -o -type "f" -name "*.bib" -print -quit)}"

{ [ -f "${BIB_FILE}" ] || [ "${2}" ]; } || {
	printf "%s\n" "Create a .bib file or provide as \$2." && exit "1"
}

filter() {
	sed -n -E 's/.*((DOI|doi)((\.(org))?\/?|:? *))([^: ]+[^ .]).*/\6/p; T; q'
}

fpdf() {
        pdf="${1}"
	doi="$(pdfinfo "${pdf}" 2> "/dev/null" | filter)"

	[ "${doi}" ] || doi="$(pdftotext -q -l "2" "${pdf}" - 2> "/dev/null" | filter)"

	[ "${doi}" ] || printf "%s\n" "No DOI found for PDF: ${pdf}" >&2

	printf "%s\n" "${doi}"
}

arrange() {
	sed 's/\}, /\},\n	/g
		s/, /,\n	/
		s/ }/\n}/
		s/,\s*pages=/,\n\tpages=/' |
        sed '1s/^ *//
        	1s/[0-9]*\([0-9]\{2\}\)/\1/
        	1s/_//
        	1s/.*/\L&/
		s/.*=/\L&/
		s/=/ = /'
}

doi2bib() {
        doi="${1#doi:}"
	url="https://api.crossref.org/works/${doi}/transform/application/x-bibtex"
        entry="$(curl -kLsS --no-fail "${url}" | arrange)"
        red='\033[0;31m'
        reset='\033[0m'

        printf "${red}%s${reset}\n" "${entry}"

	[ "${entry%"${entry#?}"}" != "@" ] && {
		printf "%s\n" "Failed to fetch bibtex entry for DOI: ${doi}"
		return "1"
	}

	rg -iFq "doi = {${doi}}" "${BIB_FILE}" 2> "/dev/null" && {
		printf "%s\n" "Bibtex entry for DOI: ${doi} already exists in the file."
	} || {
		[ -s "${BIB_FILE}" ] && printf "\n" >> "${BIB_FILE}"
		printf "%s\n" "${entry}" >> "${BIB_FILE}"
		printf "%s\n" "Added bibtex entry for DOI: ${doi}"
        }
}

[ "${1}" ] || {
	printf "%s\n" "Give either a pdf file or a DOI or a directory path that has PDFs as an argument."
	exit "1"
}

[ -f "${1}" ] && doi="$(fpdf "${1}")" && doi2bib "${doi}" && exit "0"

[ -d "${1}" ] && for i in "${1}"/*.pdf; do doi="$(fpdf "${i}")" && doi2bib "${doi}"; done && exit "0"

doi="$(printf "%s\n" "${1}" | filter)" && doi2bib "${doi}"