fix: backlight consider bright not multiple of step

backlight consider after long time no use, screen go black then me wake
it and go bright, the brightness is not a multiple of step, so it can
not decrease to 1 or 0 or increase to max

Also consider no write if decrease when 0 or increase when max

1 files changed, 16 insertions, 2 deletions

diff --git a/sh/backlight b/sh/backlight
index 3de87f5..b9fdbfb 100755
--- a/sh/backlight
+++ b/sh/backlight
@@ -9,14 +9,28 @@ case "$1" in
 		case "$brightness" in
 			0) echo 1;;
 			1) echo "$step";;
-			*) echo "$((brightness+step))";;
+			"$max_brightness") exit 0;;
+			*)
+				if [ "$brightness" -gt "$((max_brightness-step))" ]; then
+					echo "$max_brightness"
+				else
+					echo "$((brightness+step))"
+				fi
+				;;
 		esac
 	;;
 	'-d')
 		case "$brightness" in
+			0) exit 0;;
 			1) echo 0;;
 			"$step") echo 1;;
-			*) echo "$((brightness-step))";;
+			*)
+				if [ "$brightness" -le "$step" ]; then
+					echo 1
+				else
+					echo "$((brightness-step))"
+				fi
+				;;
 		esac
 	;;
 	*) exit 1;;