Add streak counter to flashcards

src/lib/shareMetadata.ts

@@ -0,0 +1,159 @@
+import type { Metadata } from "next";
+
+/**
+ * Builds the link-preview metadata (Discord, Slack, iMessage, ...) for a public
+ * share URL, so every shared deck, quiz and group describes itself rather than
+ * falling back to the generic site description.
+ */
+
+const SITE_NAME = "Study Desk";
+const SITE_DESCRIPTION = "A focused workspace for flashcards and practice quizzes";
+
+interface MetaClass {
+  slug: string;
+  name: string;
+}
+
+interface MetaItem {
+  id: string;
+  name: string;
+  description: string | null;
+  count: number;
+}
+
+export interface ShareMetaLink {
+  deck: {
+    name: string;
+    description: string | null;
+    class: MetaClass;
+    _count: { cards: number };
+  } | null;
+  quizSet: {
+    name: string;
+    description: string | null;
+    class: MetaClass;
+    _count: { questions: number };
+  } | null;
+  group: {
+    name: string;
+    type: string;
+    class: MetaClass;
+    decks: { id: string; name: string; description: string | null; _count: { cards: number } }[];
+    quizSets: { id: string; name: string; description: string | null; _count: { questions: number } }[];
+  } | null;
+}
+
+function count(n: number, singular: string, plural: string) {
+  return `${n} ${n === 1 ? singular : plural}`;
+}
+
+/** Collapses Markdown-ish whitespace and keeps previews to a sane length. */
+function tidy(text: string, maxLength = 200) {
+  const flat = text.replace(/\s+/g, " ").trim();
+  if (flat.length <= maxLength) return flat;
+  return `${flat.slice(0, maxLength - 1).trimEnd()}…`;
+}
+
+function toMetadata(title: string, description: string): Metadata {
+  return {
+    title,
+    description,
+    openGraph: {
+      title,
+      description,
+      siteName: SITE_NAME,
+      type: "website",
+    },
+    twitter: {
+      card: "summary",
+      title,
+      description,
+    },
+  };
+}
+
+function itemMetadata(
+  item: MetaItem,
+  className: string,
+  kind: "flashcards" | "quiz",
+  groupName?: string,
+) {
+  const title = `${item.name} · ${className}`;
+  const context = groupName ? `${className} ${groupName}` : className;
+  const fallback =
+    kind === "flashcards"
+      ? `${context} flashcard deck · ${count(item.count, "card", "cards")}`
+      : `${context} practice quiz · ${count(item.count, "question", "questions")}`;
+
+  const described = item.description?.trim();
+  return toMetadata(title, described ? tidy(described) : fallback);
+}
+
+/**
+ * `itemId` mirrors the `?itemId=` deep link into a shared group, which shows a
+ * single deck or quiz instead of the group index.
+ */
+export function buildShareMetadata(
+  link: ShareMetaLink | null,
+  options: { classSlug?: string; itemId?: string } = {},
+): Metadata {
+  const { classSlug, itemId } = options;
+
+  if (!link) return toMetadata(SITE_NAME, SITE_DESCRIPTION);
+
+  // Never describe content whose URL does not agree with the stored class, so
+  // previews stay silent for the same requests the page itself rejects.
+  const target = link.deck ?? link.quizSet ?? link.group;
+  if (!target || (classSlug && target.class.slug !== classSlug)) {
+    return toMetadata(SITE_NAME, SITE_DESCRIPTION);
+  }
+
+  if (link.deck) {
+    return itemMetadata(
+      { id: "", name: link.deck.name, description: link.deck.description, count: link.deck._count.cards },
+      link.deck.class.name,
+      "flashcards",
+    );
+  }
+
+  if (link.quizSet) {
+    return itemMetadata(
+      { id: "", name: link.quizSet.name, description: link.quizSet.description, count: link.quizSet._count.questions },
+      link.quizSet.class.name,
+      "quiz",
+    );
+  }
+
+  const group = link.group!;
+  const className = group.class.name;
+  const isDeckGroup = group.type === "DECK";
+
+  if (itemId) {
+    const deck = isDeckGroup ? group.decks.find((d) => d.id === itemId) : undefined;
+    const quizSet = isDeckGroup ? undefined : group.quizSets.find((q) => q.id === itemId);
+
+    if (deck) {
+      return itemMetadata(
+        { id: deck.id, name: deck.name, description: deck.description, count: deck._count.cards },
+        className,
+        "flashcards",
+        group.name,
+      );
+    }
+
+    if (quizSet) {
+      return itemMetadata(
+        { id: quizSet.id, name: quizSet.name, description: quizSet.description, count: quizSet._count.questions },
+        className,
+        "quiz",
+        group.name,
+      );
+    }
+  }
+
+  const members = isDeckGroup
+    ? count(group.decks.length, "flashcard deck", "flashcard decks")
+    : count(group.quizSets.length, "quiz", "quizzes");
+
+  return toMetadata(`${group.name} · ${className}`, `${className} ${group.name} — ${members}`);
+}