Add library function returning event changes after given epoch

lib/www/server/lib/db/event/changes.js

@@ -0,0 +1,61 @@
+const { setSurvey } = require('../connection');
+const { replaceMarkers } = require('../../utils');
+
+function parseValidity (row) {
+	if (row.validity) {
+		const rx = /^(.)("([\d :.+-]+)")?,("([\d :.+-]+)")?([\]\)])$/;
+		const m = row.validity.match(rx);
+		row.validity = [ m[1], m[3], m[5], m[6] ];
+	}
+	return row;
+}
+
+function transform (row) {
+	if (row.validity[2]) {
+		return {
+			uid: row.uid,
+			id: row.id,
+			is_deleted: true
+		}
+	} else {
+		row.is_deleted = false;
+		row.has_edits = row.id != row.uid;
+		row.modified_on = row.validity[1];
+		delete row.uid;
+		delete row.validity;
+		return row;
+	}
+}
+
+function unique (rows) {
+	const o = {};
+	rows.forEach(row => o[row.id] = row);
+	return Object.values(o);
+}
+
+/**
+ * Get the event change history from a given epoch (ts0),
+ * for all events.
+ */
+async function changes (projectId, ts0, opts = {}) {
+
+	if (!projectId || !ts0) {
+		throw {status: 400, message: "Invalid request" };
+		return;
+	}
+
+	const client = await setSurvey(projectId);
+
+	const text = `
+		SELECT *
+		FROM event_log_changes($1);
+	`;
+
+	const res = await client.query(text, [ts0]);
+	client.release();
+	return opts.unique
+		? unique(res.rows.map(i => transform(replaceMarkers(parseValidity(i)))))
+		: res.rows.map(i => transform(replaceMarkers(parseValidity(i))));
+}
+
+module.exports = changes;

lib/www/server/lib/db/event/index.js

@@ -5,5 +5,6 @@ module.exports = {
 	post: require('./post'),
 	put: require('./put'),
 	patch: require('./patch'),
-	del: require('./delete')
+	del: require('./delete'),
+	changes: require('./changes')
 }