Studies: add a Download Study Guide button to the study page, automatic from the linked series/book or chosen per study in admin; v2.35.0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/content.ts

@@ -14,6 +14,9 @@ export interface StudyProgram {
   showOnHomepage?: boolean
   showNewTag?: boolean
   newTagLabel?: string
+  // Which companion guide the study offers for download: '' = automatic (the guide of the series or
+  // finished book linked to this study), 'none', 'primary', 'second', or 'book:<finished book id>'
+  guideSource?: string
   // 'complete' = finished and self-paced (still open for enrollment). A study whose lessons
   // have all been released is treated as complete even if left as 'active'.
   status: 'active' | 'planned' | 'complete'
@@ -700,3 +703,39 @@ export function getAllHighlights(content: Pick<SiteContent, 'podcastFeaturedLink
     ...(content.finishedBooks ?? []).flatMap(book => book.highlights ?? []),
   ]
 }
+
+export interface StudyGuideLink {
+  // Page id under /downloads/ (primary-guide, second-guide, book-guide--<id>)
+  pageId: string
+  title: string
+}
+
+// The companion guide a study offers, either chosen explicitly in admin or found through the
+// series / finished book that is linked to the study.
+export function getStudyGuideLink(
+  content: Pick<SiteContent, 'seriesStudySlug' | 'studyGuideTitle' | 'studyGuideUrl' | 'studyGuideDownloadUrl' | 'studyGuideAppleBooksUrl' | 'secondSeries' | 'finishedBooks'>,
+  study: Pick<StudyProgram, 'slug' | 'guideSource'>,
+): StudyGuideLink | null {
+  const source = study.guideSource ?? ''
+  if (source === 'none') return null
+
+  const primary = (): StudyGuideLink | null =>
+    content.studyGuideTitle && (content.studyGuideUrl || content.studyGuideDownloadUrl || content.studyGuideAppleBooksUrl)
+      ? { pageId: 'primary-guide', title: content.studyGuideTitle }
+      : null
+  const second = (): StudyGuideLink | null =>
+    content.secondSeries?.guide?.title ? { pageId: 'second-guide', title: content.secondSeries.guide.title } : null
+  const book = (id: string): StudyGuideLink | null => {
+    const found = (content.finishedBooks ?? []).find(b => b.id === id)
+    return found?.guide?.title ? { pageId: `book-guide--${found.id}`, title: found.guide.title } : null
+  }
+
+  if (source === 'primary') return primary()
+  if (source === 'second') return second()
+  if (source.startsWith('book:')) return book(source.slice('book:'.length))
+
+  if (content.seriesStudySlug && content.seriesStudySlug === study.slug) return primary()
+  if (content.secondSeries?.studySlug && content.secondSeries.studySlug === study.slug) return second()
+  const linkedBook = (content.finishedBooks ?? []).find(b => b.studySlug === study.slug && b.guide?.title)
+  return linkedBook ? book(linkedBook.id) : null
+}