Add script to update comparison groups.

This should be run at regular intervals (via cron or so) to keep
the comparisons up to date.

It is not necessarily a good idea to run this as part of the
runner.sh script as it will delay other tasks trying to
update the active project every time.

Probably OK to put it on a cronjbo every 2‒24 hours. If two
copies are running concurrently that should not break anything
but it will increase the server load.

bin/update_comparisons.js

@@ -0,0 +1,60 @@
+#!/usr/bin/node
+
+const cmp = require('../lib/www/server/lib/comparisons');
+
+
+async function main () {
+	console.log("Retrieving project groups");
+	const groups = await cmp.groups();
+
+	if (!Object.keys(groups??{})?.length) {
+		console.log("No groups found");
+		return 0;
+	}
+
+	console.log(`Found ${groups.length} groups: ${Object.keys(groups).join(", ")}`);
+
+	for (const groupName of Object.keys(groups)) {
+		const projects = groups[groupName];
+
+		console.log(`Fetching saved comparisons for ${groupName}`);
+
+		const comparisons = await cmp.getGroup(groupName);
+
+		// Check if there are any projects that have been modified since last comparison
+		// or if there are any pairs that are no longer part of the group
+
+		const outdated = comparisons.filter( c => {
+			const baseline_tstamp = projects.find( p => p.pid === c.baseline_pid )?.tstamp;
+			const monitor_tstamp = projects.find( p => p.pid === c.monitor_pid )?.tstamp;
+			return (c.tstamp < baseline_tstamp) || (c.tstamp < monitor_tstamp) ||
+				baseline_tstamp == null || monitor_tstamp == null;
+		});
+
+		for (const comparison of outdated) {
+			console.log(`Removing stale comparison: ${comparison.baseline_pid} → ${comparison.monitor_pid}`);
+			await cmp.remove(comparison.baseline_pid, comparison.monitor_pid);
+		}
+
+		if (projects?.length < 2) {
+			console.log(`Group ${groupName} has less than two projects. No comparisons are possible`);
+			continue;
+		}
+
+		// Re-run the comparisons that are not in the database. They may
+		// be missing either beacause they were not there to start with
+		// or because we just removed them due to being stale
+
+		console.log(`Recalculating group ${groupName}`);
+		await cmp.saveGroup(groupName);
+	}
+
+	console.log("Comparisons update done");
+	return 0;
+}
+
+if (require.main === module) {
+	main();
+} else {
+	module.exports = main;
+}