flyer-crawler.projectium.com/src/services/db/deals.db.ts

// src/services/db/deals.db.ts
import { getPool } from './connection.db';
import { WatchedItemDeal } from '../../types';
import type { Pool, PoolClient } from 'pg';
import type { Logger } from 'pino';
import { logger as globalLogger } from '../logger.server';
import { handleDbError } from './errors.db';

export class DealsRepository {
  // The repository only needs an object with a `query` method, matching the Pool/PoolClient interface.
  // Using `Pick` makes this dependency explicit and simplifies testing by reducing the mock surface.
  private db: Pick<Pool | PoolClient, 'query'>;

  constructor(db: Pick<Pool | PoolClient, 'query'> = getPool()) {
    this.db = db;
  }

  /**
   * Finds the best current sale price for each of a user's watched items.
   * It considers only currently active flyers and handles ties by preferring the deal
   * that is valid for the longest time.
   *
   * @param userId - The ID of the user whose watched items are being checked.
   * @param logger - The logger instance for context-specific logging.
   * @returns A promise that resolves to an array of WatchedItemDeal objects.
   */
  async findBestPricesForWatchedItems(
    userId: string,
    logger: Logger = globalLogger,
  ): Promise<WatchedItemDeal[]> {
    logger.debug({ userId }, 'Finding best prices for watched items.');
    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,
          -- Rank prices for each item, lowest first. In case of a tie, the deal that ends later is preferred.
          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;
    `;
    try {
      const { rows } = await this.db.query<WatchedItemDeal>(query, [userId]);
      return rows;
    } catch (error) {
      handleDbError(error, logger, 'Database error in findBestPricesForWatchedItems', { userId }, {
        defaultMessage: 'Failed to find best prices for watched items.',
      });
    }
  }
}

export const dealsRepo = new DealsRepository();