#!/bin/sh
#
# backlinks - check for backlinks in extension-less Gemini files
#
# SPDX-FileCopyrightText: 2023 Daniel Kalak
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This script loops through all files in the current directory that
# don't have a file ending and prints:
#
#   "f1 <=> f2" if f1 and f2 link to each other,
#
#   "f1 => f2" if f1 links to f2, but f2 not to f1,
#
#   "=> f1" if no other file links to f1.

# Sort $1 and $2 alphabetically and print the first to stdout.
alpha_first() {
	printf '%s\n%s\n' "$1" "$2" | sort | head -n1
}

# List all files in the current dir that contain no dots in their names.
# Loop over them and call them f1.
find -type f -regex '\./[^/.]*' | cut -c3- |
while read -r f1
do
	# List all paths that f1 links to that contain no ":" (i.e. they
	# are on the same server), no "/" (i.e. they are in the same
	# dir), and no ".". Loop over them and call them f2.
	grep -o '^=> [^:/. ]*\( \|$\)' "$f1" | cut -c4- |
	while read -r f2
	do
		# Does f2 link back to f1? If no, print "f1 => f2". If
		# yes, print "f1 <=> f2", but only if f1 comes before f2
		# in the alphabet. This prevents printing both "f1 <=>
		# f2" and "f2 <=> f1".
		if grep -q '^=> '"$f1"'\( \|$\)' "$f2"
		then
			[ "$(alpha_first "$f1" "$f2")" = "$f1" ] &&
			printf '%s <=> %s\n' "$f1" "$f2"
		else printf '%s => %s\n' "$f1" "$f2"
		fi
	done

	# List all files in the current dir that contain no dots in
	# their names, again. Loop over them and call them f2. If none
	# of these f2 link to f1, print "=> f1".
	find -type f -regex '\./[^/.]*' | cut -c3- |
	{
		while read -r f2
		do
			grep -q '^=> '"$f1"'\( \|$\)' "$f2" && exit 0
		done
		exit 1
	} || printf '=> %s\n' "$f1"

done | sort