feat: Implement deals repository and routes for fetching best watched item prices

- Added a new DealsRepository class to interact with the database for fetching the best sale prices of watched items.
- Created a new route `/api/users/deals/best-watched-prices` to handle requests for the best prices of items the authenticated user is watching.
- Enhanced logging in the FlyerDataTransformer and FlyerProcessingService for better traceability.
- Updated tests to ensure proper logging and functionality in the FlyerProcessingService.
- Refactored logger client to support structured logging for better consistency across the application.

src/services/db/deals.db.ts

@@ -0,0 +1,61 @@
+// src/services/db/deals.repository.ts
+import { getPool } from './connection.db';
+import { WatchedItemDeal } from '../../types';
+import { Pool } from 'pg';
+
+export class DealsRepository {
+  private pool: Pool;
+
+  constructor() {
+    this.pool = getPool();
+  }
+
+  /**
+   * Finds the best current sale price for each of a user's watched items.
+   *
+   * @param userId - The ID of the user whose watched items are being checked.
+   * @returns A promise that resolves to an array of WatchedItemDeal objects.
+   */
+  async findBestPricesForWatchedItems(userId: string): Promise<WatchedItemDeal[]> {
+    const query = `
+      WITH UserWatchedItems AS (
+        -- Select all items the user is watching
+        SELECT master_item_id FROM watched_items WHERE user_id = $1
+      ),
+      RankedPrices AS (
+        -- Find all current sale prices for those items and rank them
+        SELECT
+          fi.master_item_id,
+          mgi.name AS item_name,
+          fi.price_in_cents,
+          s.name AS store_name,
+          f.flyer_id,
+          f.valid_to,
+          ROW_NUMBER() OVER(PARTITION BY fi.master_item_id ORDER BY fi.price_in_cents ASC, f.valid_to DESC) as rn
+        FROM flyer_items fi
+        JOIN flyers f ON fi.flyer_id = f.flyer_id
+        JOIN stores s ON f.store_id = s.store_id
+        JOIN master_grocery_items mgi ON fi.master_item_id = mgi.master_grocery_item_id
+        WHERE
+          fi.master_item_id IN (SELECT master_item_id FROM UserWatchedItems)
+          AND f.valid_to >= CURRENT_DATE -- Only consider active flyers
+          AND fi.price_in_cents IS NOT NULL
+      )
+      -- Select only the #1 ranked (lowest) price for each item
+      SELECT
+        master_item_id,
+        item_name,
+        price_in_cents AS best_price_in_cents,
+        store_name,
+        flyer_id,
+        valid_to
+      FROM RankedPrices
+      WHERE rn = 1
+      ORDER BY item_name;
+    `;
+    const { rows } = await this.pool.query(query, [userId]);
+    return rows;
+  }
+}
+
+export const dealsRepo = new DealsRepository();