add function diffArraysSimple for more efficient change detection

1 files changed, 44 insertions, 0 deletions

diff --git a/packages/backend/src/misc/diff-arrays.ts b/packages/backend/src/misc/diff-arrays.ts
index b3879cc996..b50ca1d4f7 100644
--- a/packages/backend/src/misc/diff-arrays.ts
+++ b/packages/backend/src/misc/diff-arrays.ts
@@ -56,3 +56,47 @@ export function diffArrays<T>(dataBefore: T[] | null | undefined, dataAfter: T[]
 	// data NEITHER before nor after => no change
 	return { added: [], removed: [] };
 }
+
+/**
+ * Checks for any difference between two snapshots of data.
+ * Null, undefined, and empty arrays are supported, and duplicate values are ignored.
+ * The inputs are treated as un-ordered, so a re-ordering of the same data will NOT be considered a change.
+ * @param dataBefore Array containing data before the change
+ * @param dataAfter Array containing data after the change
+ */
+export function diffArraysSimple<T>(dataBefore: T[] | null | undefined, dataAfter: T[] | null | undefined): boolean {
+	const before = dataBefore ? new Set(dataBefore) : null;
+	const after = dataAfter ? new Set(dataAfter) : null;
+
+	if (before?.size && after?.size) {
+		// different size => changed
+		if (before.size !== after.size) return true;
+
+		// removed => changed
+		for (const host of before) {
+			// delete operation removes duplicates to speed up the "after" loop
+			if (!after.delete(host)) {
+				return true;
+			}
+		}
+
+		// added => changed
+		for (const host of after) {
+			if (!before.has(host)) {
+				return true;
+			}
+		}
+
+		// identical values => no change
+		return false;
+	}
+
+	// before and NOT after => change
+	if (before?.size) return true;
+
+	// after and NOT before => change
+	if (after?.size) return true;
+
+	// NEITHER before nor after => no change
+	return false;
+}