#!/usr/bin/env bash
set -e
myname="${0##*/}"

#----------------------------------------------------------------------------
# Configurable items
MIN_UID=1000
MAX_UID=1999
MIN_GID=1000
MAX_GID=1999
# No more is configurable below this point
#----------------------------------------------------------------------------

#----------------------------------------------------------------------------
error() {
    local fmt="${1}"
    shift

    printf "%s: " "${myname}" >&2
    printf "${fmt}" "${@}" >&2
}
fail() {
    error "$@"
    exit 1
}

#----------------------------------------------------------------------------
if [ ${#} -ne 2 ]; then
    fail "usage: %s USERS_TABLE TARGET_DIR\n"
fi
USERS_TABLE="${1}"
TARGET_DIR="${2}"
shift 2
PASSWD="${TARGET_DIR}/etc/passwd"
SHADOW="${TARGET_DIR}/etc/shadow"
GROUP="${TARGET_DIR}/etc/group"
# /etc/gshadow is not part of the standard skeleton, so not everybody
# will have it, but some may have it, and its content must be in sync
# with /etc/group, so any use of gshadow must be conditional.
GSHADOW="${TARGET_DIR}/etc/gshadow"

# We can't simply source ${BR2_CONFIG} as it may contains constructs
# such as:
#    BR2_DEFCONFIG="$(CONFIG_DIR)/defconfig"
# which when sourced from a shell script will eventually try to execute
# a command named 'CONFIG_DIR', which is plain wrong for virtually every
# systems out there.
# So, we have to scan that file instead. Sigh... :-(
PASSWD_METHOD="$( sed -r -e '/^BR2_TARGET_GENERIC_PASSWD_METHOD="(.*)"$/!d;'    \
                         -e 's//\1/;'                                           \
                         "${BR2_CONFIG}"                                        \
                )"

#----------------------------------------------------------------------------
get_uid() {
    local username="${1}"

    awk -F: -v username="${username}"                           \
        '$1 == username { printf( "%d\n", $3 ); }' "${PASSWD}"
}

#----------------------------------------------------------------------------
get_ugid() {
    local username="${1}"

    awk -F: -v username="${username}"                          \
        '$1 == username { printf( "%d\n", $4 ); }' "${PASSWD}"
}

#----------------------------------------------------------------------------
get_gid() {
    local group="${1}"

    awk -F: -v group="${group}"                             \
        '$1 == group { printf( "%d\n", $3 ); }' "${GROUP}"
}

#----------------------------------------------------------------------------
get_username() {
    local uid="${1}"

    awk -F: -v uid="${uid}"                                 \
        '$3 == uid { printf( "%s\n", $1 ); }' "${PASSWD}"
}

#----------------------------------------------------------------------------
get_group() {
    local gid="${1}"

    awk -F: -v gid="${gid}"                             \
        '$3 == gid { printf( "%s\n", $1 ); }' "${GROUP}"
}

#----------------------------------------------------------------------------
get_ugroup() {
    local username="${1}"
    local ugid

    ugid="$( get_ugid "${username}" )"
    if [ -n "${ugid}" ]; then
        get_group "${ugid}"
    fi
}

#----------------------------------------------------------------------------
# Sanity-check the new user/group:
#   - check the gid is not already used for another group
#   - check the group does not already exist with another gid
#   - check the user does not already exist with another gid
#   - check the uid is not already used for another user
#   - check the user does not already exist with another uid
#   - check the user does not already exist in another group
check_user_validity() {
    local username="${1}"
    local uid="${2}"
    local group="${3}"
    local gid="${4}"
    local _uid _ugid _gid _username _group _ugroup

    _group="$( get_group "${gid}" )"
    _gid="$( get_gid "${group}" )"
    _ugid="$( get_ugid "${username}" )"
    _username="$( get_username "${uid}" )"
    _uid="$( get_uid "${username}" )"
    _ugroup="$( get_ugroup "${username}" )"

    if [ "${username}" = "root" ]; then
        fail "invalid username '%s\n'" "${username}"
    fi

    if [ ${gid} -lt -1 -o ${gid} -eq 0 ]; then
        fail "invalid gid '%d' for '%s'\n" ${gid} "${username}"
    elif [ ${gid} -ne -1 ]; then
        # check the gid is not already used for another group
        if [ -n "${_group}" -a "${_group}" != "${group}" ]; then
            fail "gid '%d' for '%s' is already used by group '%s'\n" \
                 ${gid} "${username}" "${_group}"
        fi

        # check the group does not already exists with another gid
        # Need to split the check in two, otherwise '[' complains it
        # is missing arguments when _gid is empty
        if [ -n "${_gid}" ] && [ ${_gid} -ne ${gid} ]; then
            fail "group '%s' for '%s' already exists with gid '%d' (wants '%d')\n" \
                 "${group}" "${username}" ${_gid} ${gid}
        fi

        # check the user does not already exists with another gid
        # Need to split the check in two, otherwise '[' complains it
        # is missing arguments when _ugid is empty
        if [ -n "${_ugid}" ] && [ ${_ugid} -ne ${gid} ]; then
            fail "user '%s' already exists with gid '%d' (wants '%d')\n" \
                 "${username}" ${_ugid} ${gid}
        fi
    fi

    if [ ${uid} -lt -1 -o ${uid} -eq 0 ]; then
        fail "invalid uid '%d' for '%s'\n" ${uid} "${username}"
    elif [ ${uid} -ne -1 ]; then
        # check the uid is not already used for another user
        if [ -n "${_username}" -a "${_username}" != "${username}" ]; then
            fail "uid '%d' for '%s' already used by user '%s'\n" \
                 ${uid} "${username}" "${_username}"
        fi

        # check the user does not already exists with another uid
        # Need to split the check in two, otherwise '[' complains it
        # is missing arguments when _uid is empty
        if [ -n "${_uid}" ] && [ ${_uid} -ne ${uid} ]; then
            fail "user '%s' already exists with uid '%d' (wants '%d')\n" \
                 "${username}" ${_uid} ${uid}
        fi
    fi

    # check the user does not already exist in another group
    if [ -n "${_ugroup}" -a "${_ugroup}" != "${group}" ]; then
        fail "user '%s' already exists with group '%s' (wants '%s')\n" \
             "${username}" "${_ugroup}" "${group}"
    fi

    return 0
}

#----------------------------------------------------------------------------
# Generate a unique GID for given group. If the group already exists,
# then simply report its current GID. Otherwise, generate the lowest GID
# that is:
#   - not 0
#   - comprised in [MIN_GID..MAX_GID]
#   - not already used by a group
generate_gid() {
    local group="${1}"
    local gid

    gid="$( get_gid "${group}" )"
    if [ -z "${gid}" ]; then
        for(( gid=MIN_GID; gid<=MAX_GID; gid++ )); do
            if [ -z "$( get_group "${gid}" )" ]; then
                break
            fi
        done
        if [ ${gid} -gt ${MAX_GID} ]; then
            fail "can not allocate a GID for group '%s'\n" "${group}"
        fi
    fi
    printf "%d\n" "${gid}"
}

#----------------------------------------------------------------------------
# Add a group; if it does already exist, remove it first
add_one_group() {
    local group="${1}"
    local gid="${2}"
    local _f

    # Generate a new GID if needed
    if [ ${gid} -eq -1 ]; then
        gid="$( generate_gid "${group}" )"
    fi

    # Remove any previous instance of this group, and re-add the new one
    sed -i --follow-symlinks -e '/^'"${group}"':.*/d;' "${GROUP}"
    printf "%s:x:%d:\n" "${group}" "${gid}" >>"${GROUP}"

    # Ditto for /etc/gshadow if it exists
    if [ -f "${GSHADOW}" ]; then
        sed -i --follow-symlinks -e '/^'"${group}"':.*/d;' "${GSHADOW}"
        printf "%s:*::\n" "${group}" >>"${GSHADOW}"
    fi
}

#----------------------------------------------------------------------------
# Generate a unique UID for given username. If the username already exists,
# then simply report its current UID. Otherwise, generate the lowest UID
# that is:
#   - not 0
#   - comprised in [MIN_UID..MAX_UID]
#   - not already used by a user
generate_uid() {
    local username="${1}"
    local uid

    uid="$( get_uid "${username}" )"
    if [ -z "${uid}" ]; then
        for(( uid=MIN_UID; uid<=MAX_UID; uid++ )); do
            if [ -z "$( get_username "${uid}" )" ]; then
                break
            fi
        done
        if [ ${uid} -gt ${MAX_UID} ]; then
            fail "can not allocate a UID for user '%s'\n" "${username}"
        fi
    fi
    printf "%d\n" "${uid}"
}

#----------------------------------------------------------------------------
# Add given user to given group, if not already the case
add_user_to_group() {
    local username="${1}"
    local group="${2}"
    local _f

    for _f in "${GROUP}" "${GSHADOW}"; do
        [ -f "${_f}" ] || continue
        sed -r -i --follow-symlinks \
                  -e 's/^('"${group}"':.*:)(([^:]+,)?)'"${username}"'(,[^:]+*)?$/\1\2\4/;'  \
                  -e 's/^('"${group}"':.*)$/\1,'"${username}"'/;'                           \
                  -e 's/,+/,/'                                                              \
                  -e 's/:,/:/'                                                              \
                  "${_f}"
    done
}

#----------------------------------------------------------------------------
# Encode a password
encode_password() {
    local passwd="${1}"

    mkpasswd -m "${PASSWD_METHOD}" "${passwd}"
}

#----------------------------------------------------------------------------
# Add a user; if it does already exist, remove it first
add_one_user() {
    local username="${1}"
    local uid="${2}"
    local group="${3}"
    local gid="${4}"
    local passwd="${5}"
    local home="${6}"
    local shell="${7}"
    local groups="${8}"
    local comment="${9}"
    local _f _group _home _shell _gid _passwd

    # First, sanity-check the user
    check_user_validity "${username}" "${uid}" "${group}" "${gid}"

    # Generate a new UID if needed
    if [ ${uid} -eq -1 ]; then
        uid="$( generate_uid "${username}" )"
    fi

    # Remove any previous instance of this user
    for _f in "${PASSWD}" "${SHADOW}"; do
        sed -r -i --follow-symlinks -e '/^'"${username}"':.*/d;' "${_f}"
    done

    _gid="$( get_gid "${group}" )"
    _shell="${shell}"
    if [ "${shell}" = "-" ]; then
        _shell="/bin/false"
    fi
    case "${home}" in
        -)  _home="/";;
        /)  fail "home can not explicitly be '/'\n";;
        /*) _home="${home}";;
        *)  fail "home must be an absolute path\n";;
    esac
    case "${passwd}" in
        -)
            _passwd=""
            ;;
        !=*)
            _passwd='!'"$( encode_password "${passwd#!=}" )"
            ;;
        =*)
            _passwd="$( encode_password "${passwd#=}" )"
            ;;
        *)
            _passwd="${passwd}"
            ;;
    esac

    printf "%s:x:%d:%d:%s:%s:%s\n"              \
           "${username}" "${uid}" "${_gid}"     \
           "${comment}" "${_home}" "${_shell}"  \
           >>"${PASSWD}"
    printf "%s:%s:::::::\n"      \
           "${username}" "${_passwd}"   \
           >>"${SHADOW}"

    # Add the user to its additional groups
    if [ "${groups}" != "-" ]; then
        for _group in ${groups//,/ }; do
            add_user_to_group "${username}" "${_group}"
        done
    fi

    # If the user has a home, chown it
    # (Note: stdout goes to the fakeroot-script)
    if [ "${home}" != "-" ]; then
        mkdir -p "${TARGET_DIR}/${home}"
        printf "chown -h -R %d:%d '%s'\n" "${uid}" "${_gid}" "${TARGET_DIR}/${home}"
    fi
}

#----------------------------------------------------------------------------
main() {
    local username uid group gid passwd home shell groups comment
    local line
    local -a ENTRIES

    # Some sanity checks
    if [ ${MIN_UID} -le 0 ]; then
        fail "MIN_UID must be >0 (currently %d)\n" ${MIN_UID}
    fi
    if [ ${MIN_GID} -le 0 ]; then
        fail "MIN_GID must be >0 (currently %d)\n" ${MIN_GID}
    fi

    # Read in all the file in memory, exclude empty lines and comments
    while read line; do
        ENTRIES+=( "${line}" )
    done < <( sed -r -e 's/#.*//; /^[[:space:]]*$/d;' "${USERS_TABLE}" )

    # We first create groups whose gid is not -1, and then we create groups
    # whose gid is -1 (automatic), so that, if a group is defined both with
    # a specified gid and an automatic gid, we ensure the specified gid is
    # used, rather than a different automatic gid is computed.

    # First, create all the main groups which gid is *not* automatic
    for line in "${ENTRIES[@]}"; do
        read username uid group gid passwd home shell groups comment <<<"${line}"
        [ ${gid} -ge 0 ] || continue    # Automatic gid
        add_one_group "${group}" "${gid}"
    done

    # Then, create all the main groups which gid *is* automatic
    for line in "${ENTRIES[@]}"; do
        read username uid group gid passwd home shell groups comment <<<"${line}"
        [ ${gid} -eq -1 ] || continue    # Non-automatic gid
        add_one_group "${group}" "${gid}"
    done

    # Then, create all the additional groups
    # If any additional group is already a main group, we should use
    # the gid of that main group; otherwise, we can use any gid
    for line in "${ENTRIES[@]}"; do
        read username uid group gid passwd home shell groups comment <<<"${line}"
        if [ "${groups}" != "-" ]; then
            for g in ${groups//,/ }; do
                add_one_group "${g}" -1
            done
        fi
    done

    # When adding users, we do as for groups, in case two packages create
    # the same user, one with an automatic uid, the other with a specified
    # uid, to ensure the specified uid is used, rather than an incompatible
    # uid be generated.

    # Now, add users whose uid is *not* automatic
    for line in "${ENTRIES[@]}"; do
        read username uid group gid passwd home shell groups comment <<<"${line}"
        [ "${username}" != "-" ] || continue # Magic string to skip user creation
        [ ${uid} -ge 0         ] || continue # Automatic uid
        add_one_user "${username}" "${uid}" "${group}" "${gid}" "${passwd}" \
                     "${home}" "${shell}" "${groups}" "${comment}"
    done

    # Finally, add users whose uid *is* automatic
    for line in "${ENTRIES[@]}"; do
        read username uid group gid passwd home shell groups comment <<<"${line}"
        [ "${username}" != "-" ] || continue # Magic string to skip user creation
        [ ${uid} -eq -1        ] || continue # Non-automatic uid
        add_one_user "${username}" "${uid}" "${group}" "${gid}" "${passwd}" \
                     "${home}" "${shell}" "${groups}" "${comment}"
    done
}

#----------------------------------------------------------------------------
main "${@}"