Improve backend media readiness for mobile clients

src/common/utils/post-media-response.util.ts

@@ -0,0 +1,105 @@
+import { PostType } from '../enums/post-type.enum';
+
+type VariantSet = {
+  originalUrl?: string;
+  lowUrl?: string;
+  mediumUrl?: string;
+  highUrl?: string;
+} | null;
+
+type PostMediaInput = {
+  postType?: PostType | string;
+  imageUrls?: string[];
+  imageItems?: Array<{ url?: string; caption?: string; altText?: string; order?: number }>;
+  imageVariants?: VariantSet[];
+  videoUrl?: string;
+  hlsUrl?: string;
+  audioUrl?: string;
+  thumbnailUrl?: string;
+  thumbnailVariants?: VariantSet;
+  waveformPeaks?: number[];
+  durationSeconds?: number | null;
+};
+
+const firstNonEmpty = (...values: Array<string | undefined | null>): string =>
+  values.find((value): value is string => typeof value === 'string' && value.trim().length > 0) ?? '';
+
+const normalizeVariantSet = (variants: VariantSet) => {
+  if (!variants) {
+    return null;
+  }
+
+  return {
+    originalUrl: variants.originalUrl ?? '',
+    lowUrl: variants.lowUrl ?? variants.mediumUrl ?? variants.highUrl ?? variants.originalUrl ?? '',
+    mediumUrl: variants.mediumUrl ?? variants.highUrl ?? variants.lowUrl ?? variants.originalUrl ?? '',
+    highUrl: variants.highUrl ?? variants.mediumUrl ?? variants.originalUrl ?? variants.lowUrl ?? '',
+  };
+};
+
+const preferredImageUrl = (variants: ReturnType<typeof normalizeVariantSet>, fallback = ''): string =>
+  firstNonEmpty(variants?.mediumUrl, variants?.highUrl, variants?.lowUrl, variants?.originalUrl, fallback);
+
+export const buildPostMediaResponse = (post: PostMediaInput) => {
+  const imageUrls = Array.isArray(post.imageUrls) ? post.imageUrls : [];
+  const imageItems = Array.isArray(post.imageItems) ? post.imageItems : [];
+  const imageVariants = Array.isArray(post.imageVariants) ? post.imageVariants : [];
+  const thumbnailVariants = normalizeVariantSet(post.thumbnailVariants ?? null);
+  const fallbackImageItems: NonNullable<PostMediaInput['imageItems']> = imageUrls.map((url, index) => ({
+    url,
+    caption: '',
+    altText: '',
+    order: index,
+  }));
+  const images = (imageItems.length ? imageItems : fallbackImageItems).map(
+    (item, index) => {
+      const variants = normalizeVariantSet(imageVariants[index] ?? null);
+      const url = item.url || imageUrls[index] || '';
+      return {
+        url: preferredImageUrl(variants, url),
+        originalUrl: firstNonEmpty(variants?.originalUrl, url),
+        variants,
+        caption: item.caption ?? '',
+        altText: item.altText ?? '',
+        order: typeof item.order === 'number' ? item.order : index,
+      };
+    },
+  );
+
+  const mediaType =
+    post.postType === PostType.IMAGE && images.length
+      ? PostType.IMAGE
+      : post.postType === PostType.VIDEO || post.videoUrl || post.hlsUrl
+        ? PostType.VIDEO
+        : post.postType === PostType.AUDIO || post.audioUrl
+          ? PostType.AUDIO
+          : PostType.TEXT;
+  const thumbnailUrl = preferredImageUrl(thumbnailVariants, post.thumbnailUrl ?? '');
+  const preferredPlaybackUrl =
+    mediaType === PostType.VIDEO
+      ? firstNonEmpty(post.hlsUrl, post.videoUrl)
+      : mediaType === PostType.AUDIO
+        ? post.audioUrl ?? ''
+        : '';
+  const displayUrl =
+    mediaType === PostType.IMAGE
+      ? images[0]?.url ?? ''
+      : mediaType === PostType.VIDEO || mediaType === PostType.AUDIO
+        ? thumbnailUrl
+        : '';
+
+  return {
+    mediaType,
+    displayUrl,
+    thumbnailUrl,
+    thumbnailVariants,
+    preferredPlaybackUrl,
+    hlsUrl: post.hlsUrl ?? '',
+    videoUrl: post.videoUrl ?? '',
+    audioUrl: post.audioUrl ?? '',
+    images,
+    durationSeconds: post.durationSeconds ?? null,
+    waveformPeaks: Array.isArray(post.waveformPeaks) ? post.waveformPeaks : [],
+    isPlayable: mediaType === PostType.VIDEO ? !!preferredPlaybackUrl : mediaType === PostType.AUDIO ? !!post.audioUrl : false,
+  };
+};