#!/bin/sh -e
#
# 2020 Dennis Camera (dennis.camera at ssrq-sds-fds.ch)
#
# This file is part of cdist.
#
# cdist is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# cdist is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with cdist. If not, see <http://www.gnu.org/licenses/>.
#
# This explorer determines the "prefix" of the --type section matching --match
# if set, or __object_id otherwise.

RS=$(printf '\036')
NL=$(printf '\n '); NL=${NL% }

squote_values() {
	sed -e '/=".*"$/{s/="/='\''/;s/"$/'\''/}' \
	    -e "/='.*'$/"'!{s/=/='\''/;s/$/'\''/}'
}
count_lines() (
	IFS=${NL?}
	# shellcheck disable=SC2048,SC2086
	set -f -- $*; echo $#
)

echo "${__object_id:?}" | grep -q -e '^[^.]\{1,\}\.[^.]\{1,\}$' || {
	echo 'Section identifiers are a package and section name separated by a "." (period).' >&2
	exit 1
}

test -s "${__object:?}/parameter/match" || {
	# If no --match is given, we take the __object_id as the section identifier.
	echo "${__object_id:?}"
	exit 0
}
test -s "${__object:?}/parameter/type" || {
	echo 'Parameters --match and --type must be used together.' >&2
	exit 1
}

sect_type_param=$(cat "${__object:?}/parameter/type")
expr "${sect_type_param}" : '[^.]\{1,\}\.[^.]\{1,\}$' >/dev/null 2>&1 || {
	echo 'Section types are a package name and section type separated by a "." (period).' >&2
	exit 1
}
package_filter=${sect_type_param%%.*}
section_filter=${sect_type_param#*.}

# Find by --match
# NOTE: Apart from section types all values are printed in single quotes by uci show.
match=$(head -n 1 "${__object:?}/parameter/match" | squote_values)

if uci -s -N get "${__object_id:?}" >/dev/null 2>&1
then
	# Named section exists: ensure if --match applies to it
	# if the "matched" option does not exist (e.g. empty section) we use the
	# section unconditionally.
	if match_value_is=$(uci -s -N get "${__object_id:?}.${match%%=*}" 2>/dev/null)
	then
		match_value_should=$(expr "${match}" : ".*='\\(.*\\)'$")

		test "${match_value_is}" = "${match_value_should}" || {
			printf 'Named section "%s" does not match --match "%s"\n' \
				   "${__object_id:?}" "${match}" >&2
			exit 1
		}
	fi

	echo "${__object_id:?}"
	exit 0
fi

# No correctly named section exists already: find one to which --match applies
regex="^${package_filter}\\.@${section_filter}\\[[0-9]\\{1,\\}\\]\\.${match%%=*}="

matched_sections=$(
	uci -s -N -d "${RS}" show "${package_filter}" 2>/dev/null \
	| grep -e "${regex}" \
	| while read -r _line
	  do
		  if test "${_line#*=}" = "${match#*=}"
		  then
			  echo "${_line}"
		  fi
	  done \
	| sed -e 's/\.[^.]*=.*$//')

test "$(count_lines "${matched_sections}")" -le 1 || {
	printf 'Found multiple matching sections:\n%s\n' "${matched_sections}" >&2
	exit 1
}

echo "${matched_sections}"