colorize usage

scripts/disk-health-check.sh

@@ -49,6 +49,28 @@ HTML_NVME=""
 HTML_ZFS=""
 HTML_SPACE=""
 
+# Map a usage percentage to a hex color: green at 0%, amber at 50%,
+# red at 100%, linearly interpolated per RGB channel. Endpoints are the
+# same dark shades used by state_html so they stay readable on white.
+# Done in bash because email clients can't compute colors in CSS.
+usage_color() {
+    local p=$1 r g b
+    [ "$p" -ge 0 ] 2>/dev/null || { printf '#222222'; return; }
+    [ "$p" -gt 100 ] && p=100
+    if [ "$p" -le 50 ]; then
+        # 1a7f37 (green) -> 9a6700 (amber)
+        r=$(( 26 + (154 - 26) * p / 50 ))
+        g=$(( 127 + (103 - 127) * p / 50 ))
+        b=$(( 55 + (0 - 55) * p / 50 ))
+    else
+        # 9a6700 (amber) -> cf222e (red)
+        r=$(( 154 + (207 - 154) * (p - 50) / 50 ))
+        g=$(( 103 + (34 - 103) * (p - 50) / 50 ))
+        b=$(( 0 + (46 - 0) * (p - 50) / 50 ))
+    fi
+    printf '#%02x%02x%02x' "$r" "$g" "$b"
+}
+
 # Green for healthy, red for anything else. UNKNOWN is amber because it
 # means smartctl couldn't read the device, not that the device failed.
 state_html() {
@@ -190,11 +212,12 @@ while IFS= read -r line; do
     used=$(echo "$line" | awk '{print $3}')
     avail=$(echo "$line" | awk '{print $4}')
     STATUS+="  $mount: ${usage}% (${used}/${size}, ${avail} free)\n"
-    usage_cell="${usage}%"
+    weight=""
     if [ "$usage" -gt "$SPACE_THRESHOLD" ] 2>/dev/null; then
         PROBLEMS+="[SPACE] $mount is ${usage}% full\n"
-        usage_cell="<span style=\"color:#cf222e;font-weight:bold\">${usage}%</span>"
+        weight=";font-weight:bold"
     fi
+    usage_cell="<span style=\"color:$(usage_color "$usage")$weight\">${usage}%</span>"
     HTML_SPACE+="<tr><td $TD>$mount</td><td $TDR>$usage_cell</td><td $TDR>$used</td><td $TDR>$size</td><td $TDR>$avail</td></tr>"$'\n'
 done < <(df -h --output=source,size,used,avail,pcent,target -x tmpfs -x devtmpfs -x overlay -x efivarfs 2>/dev/null | tail -n +2 || true)