#!/bin/sh

# Copyright (c) 2022–2026 Thomas Voss <mail@thomasvoss.com>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
# WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
# AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
# DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA
# OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
# TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

# Copy an existing text file to a temporary location.  Then edit the file.
# Attempt to then transfer the temporary file back to the original location if
# the temprary file has been altered.  Conclude with a little clean-up.  Try to
# avoid deleting any changes.

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

err()
{
	warn "$1"
	exit 1
}

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

get_abspath()
(
	cd "$(dirname "$1")"
	echo "$(pwd)/$(basename "$1")"
)

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

if [ $# -ne 1 ]
then
	echo "Usage: $PROG file"
	exit 1
fi

[ ! -f "$1" ] && err "$1: file does not exist or is a special file/link"
[   -L "$1" ] && err "$1: file is a symbolic link; refusing to edit"
[ ! -r "$1" ] && err "$1: file cannot be read by the current user"

tmp="$(mktemp -t doasedit.XXXXXXXX)" || err 4 "could not create temporary file"
trap "rm -f \"$tmp\"" EXIT HUP INT TERM
cp "$1" $tmp || err "$1: unable to copy file"

abspath="$(get_abspath "$1")"
DOASEDIT_EDITING="$abspath" "${VISUAL:-${EDITOR:-vi}}" "$tmp" || exit $?

if cmp -s "$1" "$tmp"
then
	warn "file unchanged; not writing back to the original location"
	exit 0
fi

# At this point the file has been changed.  Make sure it still exists.
if [ -f "$tmp" ]
then
	doas cp "$tmp" "$1"
	until cmp -s "$tmp" "$1"
	do
		warn "$1: copying failed; press enter to try again, or $(get_intr) to cancel"
		read _
		doas cp "$tmp" "$1"
	done
fi