#! /bin/sh

generate_key() {
    local FILE=$1
    local TYPE=$2
    local DIR="$(dirname "$FILE")"

    mkdir -p "$DIR"
    ssh-keygen -q -f "${FILE}.tmp" -N '' -t $TYPE

    # Atomically rename file public key
    mv -f "${FILE}.tmp.pub" "${FILE}.pub"

    # This sync does double duty: Ensuring that the data in the temporary
    # private key file is on disk before the rename, and ensuring that the
    # public key rename is completed before the private key rename, since we
    # switch on the existence of the private key to trigger key generation.
    # This does mean it is possible for the public key to exist, but be garbage
    # but this is OK because in that case the private key won't exist and the
    # keys will be regenerated.
    #
    # In the event that sync understands arguments that limit what it tries to
    # fsync(), we provided them. If it does not, it will simply call sync()
    # which is just as well
    sync "${FILE}.pub" "$DIR" "${FILE}.tmp"

    mv "${FILE}.tmp" "$FILE"

    # sync to ensure the atomic rename is committed
    sync "$DIR"
}

# /etc/default/ssh may set SYSCONFDIR and SSHD_OPTS
if test -f /etc/default/ssh; then
    . /etc/default/ssh
fi

[ -z "$SYSCONFDIR" ] && SYSCONFDIR=/etc/ssh
mkdir -p $SYSCONFDIR

# parse sshd options
set -- ${SSHD_OPTS} --
sshd_config=/etc/ssh/sshd_config
while true ; do
    case "$1" in
    -f*) if [ "$1" = "-f" ] ; then
            sshd_config="$2"
            shift
        else
            sshd_config="${1#-f}"
        fi
        shift
        ;;
    --) shift; break;;
    *) shift;;
    esac
done

HOST_KEYS=$(sed -n 's/^[ \t]*HostKey[ \t]\+\(.*\)/\1/p' "${sshd_config}")
[ -z "${HOST_KEYS}" ] && HOST_KEYS="$SYSCONFDIR/ssh_host_rsa_key $SYSCONFDIR/ssh_host_ecdsa_key $SYSCONFDIR/ssh_host_ed25519_key"

for key in ${HOST_KEYS} ; do
    [ -f $key ] && continue
    case $key in
    *_rsa_key)
        echo "  generating ssh RSA host key..."
        generate_key $key rsa
        ;;
    *_ecdsa_key)
        echo "  generating ssh ECDSA host key..."
        generate_key $key ecdsa
        ;;
    *_ed25519_key)
        echo "  generating ssh ED25519 host key..."
        generate_key $key ed25519
        ;;
    esac
done