# Increment or decrement a number on the current line.
function __readline_incdec {
	local increment_by="$1"
	local backward="$2"

	line=$(perl -s -e '
sub incdec {
	my ($line, $increment_by, $point_position, $is_backward) = @_;

	$point_position ||= 0;
	$is_backward ||= 0;

	my $start_position = 0;
	my $previous_match_start = 0;
	while ($line =~ /(-?\d+)/g) {
		if ($is_backward) {
			# Set start position to the current match start. This gives us the
			# correct start position when incrementing the last number in a
			# line.
			$start_position = $-[0];

			# If point is not at the end, set start position to the number
			# closest to the point position.
			if ($point_position < $-[0]) {
				$start_position = $previous_match_start;

				last;
			}

			$previous_match_start = $-[0];
		}
		else {
			if ($point_position < $+[0]) {
				$start_position = $-[0];

				last;
			}
		}
	}

	pos($line) = $start_position;
	$line =~ s/\G([^-\d]*)(-?\d+)/$1 . ($2 + $increment_by)/e;

	return $line;
}

my $output = incdec($line, $increment_by, $point_position, $backward);
print $output;
' \
		-- \
		-line="$READLINE_LINE" \
		-increment_by="$increment_by" \
		-point_position="$READLINE_POINT" \
		-backward="$backward"
	)

	READLINE_LINE="$line"
}

# Increment the nearest number to the left of point by 1.
function __readline_incdec_increment {
	local old_line_length="${#READLINE_LINE}"

	__readline_incdec 1 1

	local new_line_length="${#READLINE_LINE}"

	# If a negative sign was removed, keep point where it was.
	if [ "$old_line_length" -gt "$new_line_length" ]; then
		READLINE_POINT="$(($READLINE_POINT - 1))"
	fi
}

# Decrement the nearest number to the left of point by 1.
function __readline_incdec_decrement {
	local old_line_length="${#READLINE_LINE}"

	__readline_incdec -1 1

	local new_line_length="${#READLINE_LINE}"

	# If a negative sign was added, keep point where it was.
	if [ "$old_line_length" -lt "$new_line_length" ]; then
		READLINE_POINT="$(($READLINE_POINT + 1))"
	fi
}

bind -x '"\C-x-": __readline_incdec_decrement'
bind -x '"\C-x+": __readline_incdec_increment'