#!/bin/sh

# SPDX-License-Identifier: CC0-1.0
# 2023 Thilo-Alexander Ginkel <thilo@ginkel.com>
# 2025 Jongmin Kim <jmkim@debian.org>
#
# Lenovo-shipped Fibocom FM350-GL (14c3:4d75) FCC unlock

[ "$FCC_UNLOCK_DEBUG_LOG" = '1' ] && {
    exec 3>&1 4>&2
    trap 'exec 2>&4 1>&3' 0 1 2 3
    exec 1>>'/var/log/mm-fm350-fcc.log' 2>&1
}

# 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 ||
  # match port name in Linux 5.13
  echo "$PORT" | grep -qi AT && {
    AT_PORT="$PORT"
    break
  }
done

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

DEVICE="/dev/$AT_PORT"

at_command() {
    exec 9<>"$DEVICE"
    printf "%s\r" "$1" >&9
    read answer <&9
    read answer <&9
    echo "$answer"
    exec 9>&-
}

log() {
    echo "$1"
}

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

VENDOR_ID_HASH='3df8c719'

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

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

        log "Sending response to WWAN modem: $RESPONSE"
        UNLOCK_RESPONSE="$(at_command "at+gtfcclockver=$RESPONSE")"

        echo "$UNLOCK_RESPONSE" | grep -q '^+GTFCCLOCKVER:' && {
            UNLOCK_RESULT="$(echo "$UNLOCK_RESPONSE" | grep -o '[0-9]*')"
            [ "$UNLOCK_RESULT" = '1' ] && {
                log "FCC unlock succeeded"
                exit 0
            } || error "FCC unlock failed. Got result: $UNLOCK_RESULT"
        } || error "Unlock failed. Got response: $UNLOCK_RESPONSE"
    } || error "Failed to obtain FCC challenge. Got: $RAW_CHALLENGE"

    sleep 0.5
    i="$((i + 1))"
done

exit 2