#!/bin/sh
# Edit a temporary copy of the doas.conf file and check it for syntax
# errors before installing it as the actual doas.conf file.

set -eu

PATH=/bin:/usr/bin:/usr/local/bin
export PATH

PROG="${0##*/}"

umask 022

DOAS_CONF=@DOAS_CONF@
doas_lock_file="${DOAS_CONF}.lck"

die()
{
    echo "${PROG}: ${@}" 1>&2
    exit 1
}

warn()
{
    echo "${PROG}: ${@}" 1>&2
}

get_intr()
{
    stty -a \
    | sed -En '
	/^(.* )?intr = / {
	    s///
	    s/;.*$//
	    p
	}
    '
}

set_trap_rm()
{
    local file file_list
    file_list=
    for file
    do
	file_list="${file_list} '${file}'"
    done
    if [ -n "${file_list}" ]
    then
	trap "rm -f ${file_list}" 0 1 2 15
    fi
}

tmp_doas="$(mktemp "${DOAS_CONF}.XXXXXXXXXX")" \
|| die "You probably need to run ${PROG} as root"
set_trap_rm "${tmp_doas}"

# It is important that the ln(1) command fails if the target already
# exists.  Some versions are known to behave like "ln -f" by default
# (removing any existing target).  Adjust PATH to avoid such ln(1)
# implementations.

tmp_test_ln="$(mktemp "${DOAS_CONF}.XXXXXXXXXX")"
set_trap_rm "${tmp_doas}" "${tmp_test_ln}"

if ln "${tmp_doas}" "${tmp_test_ln}" 2>/dev/null
then
    die 'ln(1) is not safe for lock files, bailing'
fi

# If a doas.conf file exists, copy it into the temporary file for
# editing.  If none exist, the editor will open with an empty file.

if [ -f "${DOAS_CONF}" ]
then
    if [ -r "${DOAS_CONF}" ]
    then
	cp "${DOAS_CONF}" "${tmp_doas}"
    else
	die "Cannot read ${DOAS_CONF}"
    fi
fi

# Link the temporary file to the lock file.

if ln "${tmp_doas}" "${doas_lock_file}"
then
    set_trap_rm "${tmp_doas}" "${tmp_test_ln}" "${doas_lock_file}"
else
    die "${DOAS_CONF} is already locked"
fi

# Some versions of vi(1) exit with a code that reflects the number of
# editing errors made.  This is why we ignore the exit code from the
# editor.

"${EDITOR:-vi}" "${tmp_doas}" || true

while ! doas -C "${tmp_doas}"
do
    warn "Press enter to edit doas.conf again to fix it,"
    warn "or interrupt ($(get_intr)) to cancel."
    read status
    "${EDITOR:-vi}" "${tmp_doas}" || true
done

# Use mv(1) to rename the temporary file to doas.conf as it is atomic.
# This avoids any problems from another process reading doas.conf while
# it is being written.

if [ -s "${tmp_doas}" ]
then
    if cmp -s "${tmp_doas}" "${DOAS_CONF}"
    then
	warn "No changes made"
	warn "${DOAS_CONF} unchanged"
    else
	mv "${tmp_doas}" "${DOAS_CONF}" \
	&& warn "${DOAS_CONF} updated"
    fi
else
    warn "Not installing an empty doas.conf file"
    warn "${DOAS_CONF} unchanged"
fi