#!/bin/sh -e

# rhesus: monkeysphere authorized_keys/known_hosts generating script
#
# Written by
# Jameson Rollins <jrollins@fifthhorseman.net>
#
# Copyright 2008, released under the GPL, version 3 or later

CMD=$(basename $0)

########################################################################
# FUNCTIONS
########################################################################

usage() {
cat <<EOF
usage: $CMD -k|--known_hosts
       $CMD -a|--authorized_keys
EOF
}

failure() {
    echo "$1" >&2
    exit ${2:-'1'}
}

log() {
    echo -n "ms: "
    echo "$@"
}

# cut out all comments(#) and blank lines from standard input
meat() {
    grep -v -e "^[[:space:]]*#" -e '^$'
}

# cut a specified line from standard input
cutline() {
    head --line="$1" | tail -1
}

# retrieve all keys with given user id from keyserver
# FIXME: need to figure out how to retrieve all matching keys
# (not just first 5)
gpg_fetch_keys() {
    local id="$1"
    echo 1,2,3,4,5 | \
	gpg --quiet --batch --command-fd 0 --with-colons \
	--keyserver "$KEYSERVER" \
	--search ="$id" >/dev/null 2>&1
}

# convert escaped characters from gpg output back into original
# character
# FIXME: undo all escape character translation in with-colons gpg output
unescape() {
    echo "$1" | sed 's/\\x3a/:/'
}

# stand in until we get dkg's gpg2ssh program
gpg2ssh_tmp() {
    local mode
    local keyID

    mode="$1"
    keyID="$2"
    userID="$3"

    if [ "$mode" = '--authorized_keys' -o "$mode" = '-a' ] ; then
	gpgkey2ssh "$keyID" | sed -e "s/COMMENT/$userID/"
    elif [ "$mode" = '--known_hosts' -o "$mode" = '-k' ] ; then
	echo -n "$userID "; gpgkey2ssh "$keyID" | sed -e 's/ COMMENT//'
    fi
}

# userid and key policy checking
# the following checks policy on the returned keys
# - checks that full key has appropriate valididy (u|f)
# - checks key has appropriate capability (E|A)
# - checks that particular desired user id has appropriate validity
# see /usr/share/doc/gnupg/DETAILS.gz
# FIXME: add some more status output
# expects global variable: "mode"
process_user_id() {
    local userID
    local cacheDir
    local keyOK
    local keyCapability
    local keyFingerprint
    local userIDHash

    userID="$1"
    cacheDir="$2"

    # fetch all keys from keyserver
    # if none found, break
    if ! gpg_fetch_keys "$userID" ; then
	echo "    no keys found."
	return
    fi

    # some crazy piping here that takes the output of gpg and
    # pipes it into a "while read" loop that reads each line
    # of standard input one-by-one.
    gpg --fixed-list-mode --list-key --with-colons \
	--with-fingerprint ="$userID" 2> /dev/null | \
    cut -d : -f 1,2,5,10,12 | \
    while IFS=: read -r type validity keyid uidfpr capability ; do
	# process based on record type
	case $type in
	    'pub')
		# new key, wipe the slate
		keyOK=
		keyCapability=
		keyFingerprint=
		# check primary key validity
		if [ "$validity" != 'u' -a "$validity" != 'f' ] ; then
		    continue
		fi
		# check capability is not Disabled...
		if echo "$capability" | grep -q 'D' ; then
		    continue
		fi
		# check capability is Encryption and Authentication
		# FIXME: make more flexible capability specification
		# (ie. in conf file)
		if echo "$capability" | grep -q -v 'E' ; then
		    if echo "$capability" | grep -q -v 'A' ; then
			continue
		    fi
		fi
		keyCapability="$capability"
		keyOK=true
		keyID="$keyid"
		;;
	    'fpr')
		# if key ok, get fingerprint
		if [ "$keyOK" ] ; then
		    keyFingerprint="$uidfpr"
		fi
		;;
	    'uid')
		# check key ok and we have key fingerprint
		if [ -z "$keyOK" -o  -z "$keyFingerprint" ] ; then
		    continue
		fi
		# check key validity
		if [ "$validity" != 'u' -a "$validity" != 'f' ] ; then
		    continue
		fi
		# check the uid matches
		if [ "$(unescape "$uidfpr")" != "$userID" ] ; then
		    continue
		fi
		# convert the key
		# FIXME: needs to apply extra options if specified
		echo -n "    valid key found; generating ssh key(s)... "
		userIDHash=$(echo "$userID" | sha1sum | awk '{ print $1 }')
		# export the key with gpg2ssh
		#gpg --export "$keyFingerprint" | gpg2ssh "$mode" > "$cacheDir"/"$userIDHash"."$keyFingerprint"
		# stand in until we get dkg's gpg2ssh program
		gpg2ssh_tmp "$mode" "$keyID" "$userID" > "$cacheDir"/"$userIDHash"."$keyFingerprint"
		if [ "$?" = 0 ] ; then
		    echo "done."
		else
		    echo "error."
		fi
		;;
	esac
    done
}

# process the auth_*_ids file
# go through line-by-line, extracting and processing each user id
# expects global variable: "mode"
process_auth_file() {
    local authIDsFile
    local cacheDir
    local nLines
    local line
    local userID

    authIDsFile="$1"
    cacheDir="$2"

    # find number of user ids in auth_user_ids file
    nLines=$(meat <"$authIDsFile" | wc -l)

    # make sure gpg home exists with proper permissions
    mkdir -p -m 0700 "$GNUPGHOME"

    # clean out keys file and remake keys directory
    rm -rf "$cacheDir"
    mkdir -p "$cacheDir"

    # loop through all user ids
    for line in $(seq 1 $nLines) ; do
        # get user id
	# FIXME: needs to handle extra options if necessary
	userID=$(meat <"$authIDsFile" | cutline "$line" )

	# process the user id and extract keys
	log "processing user id: '$userID'"
	process_user_id "$userID" "$cacheDir"
    done
}


########################################################################
# MAIN
########################################################################

if [ -z "$1" ] ; then
    usage
    exit 1
fi

# check mode
mode="$1"
shift 1

# check user
if ! id -u "$USER" > /dev/null 2>&1 ; then
    failure "invalid user '$USER'."
fi

# set user home directory
HOME=$(getent passwd "$USER" | cut -d: -f6)

# get ms home directory
MS_HOME=${MS_HOME:-"$HOME"/.config/monkeysphere}

# load configuration file
MS_CONF=${MS_CONF:-"$MS_HOME"/monkeysphere.conf}
[ -e "$MS_CONF" ] && . "$MS_CONF"

# set config variable defaults
STAGING_AREA=${STAGING_AREA:-"$MS_HOME"}
AUTH_HOST_FILE=${AUTH_HOST_FILE:-"$MS_HOME"/auth_host_ids}
AUTH_USER_FILE=${AUTH_USER_FILE:-"$MS_HOME"/auth_user_ids}
GNUPGHOME=${GNUPGHOME:-"$HOME"/.gnupg}
KEYSERVER=${KEYSERVER:-subkeys.pgp.net}

USER_KNOW_HOSTS="$HOME"/.ssh/known_hosts
USER_AUTHORIZED_KEYS="$HOME"/.ssh/authorized_keys

# export USER and GNUPGHOME variables, since they are used by gpg
export USER
export GNUPGHOME

# stagging locations
hostKeysCacheDir="$STAGING_AREA"/host_keys
userKeysCacheDir="$STAGING_AREA"/user_keys
msKnownHosts="$STAGING_AREA"/known_hosts
msAuthorizedKeys="$STAGING_AREA"/authorized_keys

# set mode variables
if [ "$mode" = '--known_hosts' -o "$mode" = '-k' ] ; then
    fileType=known_hosts
    authIDsFile="$AUTH_HOST_FILE"
    outFile="$msKnownHosts"
    cacheDir="$hostKeysCacheDir"
    userFile="$USER_KNOWN_HOSTS"
elif [ "$mode" = '--authorized_keys' -o "$mode" = '-a' ] ; then
    fileType=authorized_keys
    authIDsFile="$AUTH_USER_FILE"
    outFile="$msAuthorizedKeys"
    cacheDir="$userKeysCacheDir"
    userFile="$USER_AUTHORIZED_KEYS"
else
    failure "unknown command '$mode'."
fi

# check auth ids file
if [ ! -s "$authIDsFile" ] ; then
    echo $(basename "$authIDsFile") "file is empty or does not exist."
    exit
fi

log "user '$USER': monkeysphere $fileType generation..."

# process the auth file
process_auth_file "$authIDsFile" "$cacheDir"

# write output key file
log "writing ms $fileType file... "
> "$outFile"
if [ "$(ls "$cacheDir")" ] ; then
    log -n "adding gpg keys... "
    cat "$cacheDir"/* > "$outFile"
    echo "done."
else
    log "no gpg keys to add."
fi
if [ -s "$userFile" ] ; then
    log -n "adding user $fileType file... "
    cat "$userFile" >> "$outFile"
    echo "done."
fi
log "ms $fileType file generated:"
log "$outFile"