board_status/to-wiki: Indicate age of test results by background color

A major issue with the board-status Wiki page is that it shows all
test results equally regardless of age.  As a test result ages it
becomes more likely that the board no longer works peroperly under
coreboot due to code churn.

Visually indicate board-test status "at a glance" by smoothly fading
the background color of the test result from green to yellow as the
test result ages.  This patch sets the full yellow transition to 255
days after test for programming convenience, however the number of
days required to fully "stale" a test result could be modified
relatively easily.

Change-Id: I5a076a6cc17d53fda8e4681e38074fc1f46c0e12
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: https://review.coreboot.org/14457
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Tested-by: build bot (Jenkins)

util/board_status/to-wiki/towiki.sh

@@ -412,7 +412,23 @@ EOF
 		if [ -z "$lastgood" ]; then
 			echo "| style=\"background:red\" | Unknown"
 		else
-			echo "| style=\"background:lime\" | [[#$vendor/$board|$lastgood]]"
+			lastgood_diff=0
+			lastgood_ts=$(date -d "$lastgood" "+%s")
+			if [ "$lastgood_ts" != "" ]; then
+				current_ts=$(date "+%s")
+				if [ "$lastgood_ts" -lt "$current_ts" ]; then
+					lastgood_diff=$(( current_ts - lastgood_ts ))
+					# Convert seconds to days
+					lastgood_diff=$(( lastgood_diff / 86400 ))
+					# Set maximum age at 255 days for convenience of code
+					if [ $lastgood_diff -gt 255 ]; then
+						lastgood_diff=255
+					fi
+				fi
+			fi
+			lastgood_diff_hex=$(echo "obase=16; $lastgood_diff" | bc)
+			cell_bgcolor="#${lastgood_diff_hex}ff00"
+			echo "| style=\"background:${cell_bgcolor}\" | [[#$vendor/$board|$lastgood]]"
 		fi
 
 		echo "| $northbridge_nice"