feat(30-01): add popular-items-by-tags query to discovery service

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server/services/discovery.service.ts

@@ -1,6 +1,14 @@
-import { and, count, desc, eq, isNotNull, lt, sql } from "drizzle-orm";
+import { and, count, desc, eq, inArray, isNotNull, lt, sql } from "drizzle-orm";
 import { db as prodDb } from "../../db/index.ts";
-import { globalItems, setupItems, setups, users } from "../../db/schema.ts";
+import {
+	globalItemTags,
+	globalItems,
+	items,
+	setupItems,
+	setups,
+	tags,
+	users,
+} from "../../db/schema.ts";
 
 type Db = typeof prodDb;
 
@@ -125,3 +133,53 @@ export async function getTrendingCategories(
 		itemCount: r.itemCount,
 	}));
 }
+
+/**
+ * Get popular global items filtered by tag names, ordered by owner count descending.
+ * Owner count = number of user items linked to each global item via globalItemId.
+ */
+export async function getPopularItemsByTags(
+	db: Db = prodDb,
+	tagNames: string[],
+	limit = 24,
+): Promise<
+	Array<{
+		id: number;
+		brand: string | null;
+		model: string;
+		category: string | null;
+		weightGrams: number | null;
+		priceCents: number | null;
+		imageFilename: string | null;
+		description: string | null;
+		ownerCount: number;
+	}>
+> {
+	if (tagNames.length === 0) return [];
+
+	const rows = await db
+		.select({
+			id: globalItems.id,
+			brand: globalItems.brand,
+			model: globalItems.model,
+			category: globalItems.category,
+			weightGrams: globalItems.weightGrams,
+			priceCents: globalItems.priceCents,
+			imageFilename: globalItems.imageFilename,
+			description: globalItems.description,
+			ownerCount: sql<number>`CAST(COUNT(DISTINCT ${items.id}) AS INT)`,
+		})
+		.from(globalItems)
+		.innerJoin(globalItemTags, eq(globalItemTags.globalItemId, globalItems.id))
+		.innerJoin(tags, eq(tags.id, globalItemTags.tagId))
+		.leftJoin(items, eq(items.globalItemId, globalItems.id))
+		.where(inArray(tags.name, tagNames))
+		.groupBy(globalItems.id)
+		.orderBy(
+			desc(sql<number>`COUNT(DISTINCT ${items.id})`),
+			desc(globalItems.id),
+		)
+		.limit(limit);
+
+	return rows;
+}