#!/usr/bin/env bash

# SPDX-License-Identifier: CC0-1.0
# 2024 Stoica Floris <floris@nusunt.eu>
#
# Lenovo-shipped XMM7560 (8086:7560) FCC unlock

if [[ "$FCC_UNLOCK_DEBUG_LOG" == '1' ]]; then
	exec 3>&1 4>&2
	trap 'exec 2>&4 1>&3' 0 1 2 3
	exec 1>>/var/log/mm-xmm7560-fcc.log 2>&1
fi

# require program name and at least 2 arguments
[ $# -lt 2 ] && exit 1

# first argument is DBus path, not needed here
shift

# second and next arguments are control port names
for PORT in "$@"; do
	# match port type in Linux 5.14 and newer
	grep -q AT "/sys/class/wwan/$PORT/type" 2>/dev/null && {
		AT_PORT=$PORT
		break
	}
	# match port name in Linux 5.13
	echo "$PORT" | grep -q AT && {
		AT_PORT=$PORT
		break
	}
done

# fail if no AT port exposed
[ -n "$AT_PORT" ] || exit 2

DEVICE=/dev/${AT_PORT}

at_command() {
	exec 99<>"$DEVICE"
	echo -e "$1\r" >&99
	read answer <&99
	read answer <&99
	echo "$answer"
	exec 99>&-
}

log() {
	echo "$1"
}

error() {
	echo "$1" >&2
}

reverseWithLittleEndian() {
	num="$1"
	printf "%x" $(("0x${num:6:2}${num:4:2}${num:2:2}${num:0:2}"))
}

VENDOR_ID_HASH="3df8c719"

for i in {1..9}; do
	log "Requesting challenge from WWAN modem (attempt #${i})"
	RAW_CHALLENGE=$(at_command "at+gtfcclockgen")
	CHALLENGE=$(echo "$RAW_CHALLENGE" | grep -o '0x[0-9a-fA-F]\+' | awk '{print $1}')

	if [ -n "$CHALLENGE" ]; then
		log "Got challenge from modem: $CHALLENGE"
		HEX_CHALLENGE=$(printf "%08x" "$CHALLENGE")
		REVERSE_HEX_CHALLENGE=$(reverseWithLittleEndian "${HEX_CHALLENGE}")
		COMBINED_CHALLENGE="${REVERSE_HEX_CHALLENGE}${VENDOR_ID_HASH}"
		RESPONSE_HASH=$(printf "%s" "$COMBINED_CHALLENGE" | xxd -r -p | sha256sum | cut -d ' ' -f 1)
		TRUNCATED_RESPONSE=$(printf "%.8s" "${RESPONSE_HASH}")
		REVERSED_RESPONSE=$(reverseWithLittleEndian "$TRUNCATED_RESPONSE")
		RESPONSE=$(printf "%d" "0x${REVERSED_RESPONSE}")

		log "Sending hash modem: $RESPONSE"
		UNLOCK_RESPONSE=$(at_command "at+gtfcclockver=$RESPONSE")
		log "at+gtfcclockver response = $UNLOCK_RESPONSE"
		UNLOCK_RESPONSE=$(at_command "at+gtfcclockmodeunlock")
		log "at+gtfcclockmodeunlock response = $UNLOCK_RESPONSE"
		UNLOCK_RESPONSE=$(at_command "at+cfun=1")
		log "at+cfun response = $UNLOCK_RESPONSE"
		UNLOCK_RESPONSE=$(at_command "at+gtfcclockstate")
		log "at+gtfcclockstate response = $UNLOCK_RESPONSE"
		UNLOCK_RESPONSE=$(echo "$UNLOCK_RESPONSE" | tr -d '\r')

		if [ "$UNLOCK_RESPONSE" = "1" ]; then
			log "FCC was unlocked previously"
			exit 0
		fi

		if [ "$UNLOCK_RESPONSE" = "OK" ]; then
			log "FCC unlock success"
			exit 0
		else
			error "Unlock failed. Got response: $UNLOCK_RESPONSE"
		fi
	else
		error "Failed to obtain FCC challenge. Got: ${RAW_CHALLENGE}"
	fi

	sleep 0.5
done

exit 2