fix: filtering logic of flags [breaking]

When combining filters, the old logic assumed that every filter was
exclusive, unless that filter contained multiple items, in which
case it was added to a list of "or" filters that returned all
matching flags.

A fault was discovered in that if you passed in multiple "or"
states, it did not return flags with the expected filtering.

e.g. open flags, closed flags, flags of cid 1, flags of cid 2

This could return open flags of cid 3, since all of the filters
were "OR"'d.

This logic change updates the behaviour so disparate OR sets are
intersected (ANDed).

src/flags.js

@@ -39,7 +39,7 @@ Flags.init = async function () {
 			if (value.length === 1) {
 				sets.push(prefix + value[0]);
 			} else {
-				value.forEach(x => orSets.push(prefix + x));
+				orSets.push(value.map(x => prefix + x));
 			}
 		}
 	}
@@ -154,7 +154,12 @@ Flags.getFlagIdsWithFilters = async function ({ filters, uid }) {
 	}
 
 	if (orSets.length) {
-		const _flagIds = await db.getSortedSetRevUnion({ sets: orSets, start: 0, stop: -1, aggregate: 'MAX' });
+		let _flagIds = await Promise.all(orSets.map(async orSet => await db.getSortedSetRevUnion({ sets: orSet, start: 0, stop: -1, aggregate: 'MAX' })));
+
+		// Each individual orSet is ANDed together to construct the final list of flagIds
+		_flagIds = _.intersection(..._flagIds);
+
+		// Merge with flagIds returned by sets
 		if (sets.length) {
 			// If flag ids are already present, return a subset of flags that are in both sets
 			flagIds = _.intersection(flagIds, _flagIds);