#!/bin/bash

# SPDX-License-Identifier: CC0-1.0
# 2023 Thilo-Alexander Ginkel <thilo@ginkel.com>
#
# Lenovo-shipped Fibocom FM350-GL (14c3:4d75) 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-fm350-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
}

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" "$CHALLENGE")
        COMBINED_CHALLENGE="${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")

        if [[ "$UNLOCK_RESPONSE" == "+GTFCCLOCKVER:"* ]]; then
            UNLOCK_RESULT=$(echo "$UNLOCK_RESPONSE" | grep -o '[0-9]\+')
            if [[ "$UNLOCK_RESULT" == "1" ]]; then
                log "FCC unlock succeeded"
                exit 0
            else
                error "FCC unlock failed. Got result: $UNLOCK_RESULT"
            fi
        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