Link previews: show full size image less often

ts/linkPreviews/shouldUseFullSizeLinkPreviewImage.ts

@@ -0,0 +1,34 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { LinkPreviewType } from '../types/message/LinkPreviews';
+import { isImageAttachment } from '../types/Attachment';
+
+const MINIMUM_FULL_SIZE_DIMENSION = 200;
+
+export function shouldUseFullSizeLinkPreviewImage({
+  isStickerPack,
+  image,
+}: Readonly<LinkPreviewType>): boolean {
+  if (isStickerPack || !isImageAttachment(image)) {
+    return false;
+  }
+
+  const { width, height } = image;
+
+  return (
+    isDimensionFullSize(width) &&
+    isDimensionFullSize(height) &&
+    !isRoughlySquare(width, height)
+  );
+}
+
+function isDimensionFullSize(dimension: unknown): dimension is number {
+  return (
+    typeof dimension === 'number' && dimension >= MINIMUM_FULL_SIZE_DIMENSION
+  );
+}
+
+function isRoughlySquare(width: number, height: number): boolean {
+  return Math.abs(1 - width / height) < 0.05;
+}