feat: add creative work position props for series

packages/contentlayer/src/fields/creative-work.ts

@@ -10,4 +10,5 @@ export const creativeWorkFields: FieldDefs = {
   datePublished: { type: 'date', required: false },
   isPartOf: { type: 'string', required: false },
   keywords: { type: 'list', required: false, of: { type: 'string' } },
+  position: { type: 'number', required: false },
 };

packages/explorer/src/content/repositories/index.ts

@@ -91,3 +91,46 @@ export const getIndexPage = async (): Promise<Content | undefined> => {
 
   return getHomePage({ inLanguage });
 };
+
+type ContentWithIsPartOf = Content & Required<Pick<Content, 'isPartOf'>>;
+
+export const getSerieWorks = async (content: ContentWithIsPartOf) => (
+  (
+    await getPagesPartOf(content.isPartOf, {
+      type: content.type,
+      inLanguage: content.inLanguage,
+    })
+  ).filter(w => 'position' in w && typeof w.position === "number")
+    .sort((a, b) => (a.position as number) - (b.position as number)) as Array<Content & Required<Pick<Content, 'position'>>>
+);
+
+export const getPreviousWorkSeries = async (content: Content): Promise<Content | undefined> => {
+  if (!(content.isPartOf && typeof content.position === 'number')) {
+    return undefined;
+  }
+
+  const serieWorks = await getSerieWorks(content as ContentWithIsPartOf);
+  let previousWork = undefined;
+  for (const work of serieWorks) {
+    if (work.position === content.position) {
+      return previousWork;
+    }
+
+    previousWork = work;
+  }
+
+  return previousWork;
+}
+
+export const getNextWorkSeries = async (content: Content): Promise<Content | undefined> => {
+  if (!(content.isPartOf && typeof content.position === 'number')) {
+    return undefined;
+  }
+
+  const serieWorks = await getSerieWorks(content as ContentWithIsPartOf);
+  for (const work of serieWorks) {
+    if (work.position > content.position) {
+      return work;
+    }
+  }
+}