Move top-level functions to Signal.Util

ts/util/GoogleChrome.ts

@@ -0,0 +1,39 @@
+/**
+ * @prettier
+ */
+import * as MIME from '../types/MIME';
+
+interface MIMETypeSupportMap {
+  [key: string]: boolean;
+}
+
+// See: https://en.wikipedia.org/wiki/Comparison_of_web_browsers#Image_format_support
+const SUPPORTED_IMAGE_MIME_TYPES: MIMETypeSupportMap = {
+  'image/bmp': true,
+  'image/gif': true,
+  'image/jpeg': true,
+  'image/svg+xml': true,
+  'image/webp': true,
+  'image/x-xbitmap': true,
+  // ICO
+  'image/vnd.microsoft.icon': true,
+  'image/ico': true,
+  'image/icon': true,
+  'image/x-icon': true,
+  // PNG
+  'image/apng': true,
+  'image/png': true,
+};
+
+export const isImageTypeSupported = (mimeType: MIME.MIMEType): boolean =>
+  SUPPORTED_IMAGE_MIME_TYPES[mimeType] === true;
+
+const SUPPORTED_VIDEO_MIME_TYPES: MIMETypeSupportMap = {
+  'video/mp4': true,
+  'video/ogg': true,
+  'video/webm': true,
+};
+
+// See: https://www.chromium.org/audio-video
+export const isVideoTypeSupported = (mimeType: MIME.MIMEType): boolean =>
+  SUPPORTED_VIDEO_MIME_TYPES[mimeType] === true;

ts/util/index.ts

@@ -0,0 +1,7 @@
+/**
+ * @prettier
+ */
+import * as GoogleChrome from './GoogleChrome';
+import { missingCaseError } from './missingCaseError';
+
+export { GoogleChrome, missingCaseError };

ts/util/missingCaseError.ts

@@ -0,0 +1,24 @@
+/**
+ * @prettier
+ */
+// `missingCaseError` is useful for compile-time checking that all `case`s in
+// a `switch` statement have been handled, e.g.
+//
+// type AttachmentType = 'media' | 'documents';
+//
+// const type: AttachmentType = selectedTab;
+// switch (type) {
+//   case 'media':
+//     return <ImageThumbnail/>;
+//   case 'documents':
+//     return <DocumentListEntry/>;
+//   default:
+//     return missingCaseError(type);
+// }
+//
+// If we extended `AttachmentType` to `'media' | 'documents' | 'links'` the code
+// above would trigger a compiler error stating that `'links'` has not been
+// handled by our `switch` / `case` statement which is useful for code
+// maintenance and system evolution.
+export const missingCaseError = (x: never): TypeError =>
+  new TypeError(`Unhandled case: ${x}`);