chbg: avoid the TOCTOU race

bin/chbg

@@ -1,12 +1,12 @@
 #!/bin/bash
 # to change wallpapers both niri workspace and niri tab view
 [ -z "$1" ] && {
-	echo "Usage: ${0##*/} <image-file>"
-	exit 1
+    echo "Usage: ${0##*/} <image-file>"
+    exit 1
 }
 fsize=$(magick identify -format "%w %h" -- "$1" 2>/dev/null) || {
-	echo "ERROR: unable to identify. is it an EXISTING ACCESSIBLE IMAGE file?"
-	exit 1
+    echo "ERROR: unable to identify. is it an EXISTING ACCESSIBLE IMAGE file?"
+    exit 1
 }
 
 WP_DIR="${XDG_DATA_HOME:-$HOME/.local/share}"
@@ -14,14 +14,14 @@ finput=$1
 
 read -r fw fh <<< "$fsize"
 (( fw > 3840 && fh > 2160 )) && {
-	finput="$(mktemp --dry-run).webp"
-	trap 'rm -f "$finput"' EXIT
-	echo "WARNING: image too large, resizing ..."
-	# echo "DEBUG: resized image at $finput"
-	magick "$1" -resize "3840x2160^" \
-		-quality 90 \
-		-define webp:method=6 \
-		-define webp:alpha-quality=100 "$finput"
+    finput=$(mktemp "${TMPDIR:-/tmp}/chbg.XXXXXXXX.webp")
+    trap 'rm -f "$finput"' EXIT
+    echo "WARNING: image too large, resizing ..."
+    # echo "DEBUG: resized image at $finput"
+    magick "$1" -resize "3840x2160^" \
+        -quality 90 \
+        -define webp:method=6 \
+        -define webp:alpha-quality=100 "$finput"
 }
 
 echo -n "making blurred version of ${1##*/} ... "