Initial commit: PriceGhost price tracking application

Full-stack application for tracking product prices:
- Backend: Node.js + Express + TypeScript
- Frontend: React + Vite + TypeScript
- Database: PostgreSQL
- Price scraping with Cheerio
- JWT authentication
- Background price checking with node-cron
- Price history charts with Recharts
- Docker support with docker-compose

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/services/scheduler.ts

@@ -0,0 +1,76 @@
+import cron from 'node-cron';
+import { productQueries, priceHistoryQueries } from '../models';
+import { scrapePrice } from './scraper';
+
+let isRunning = false;
+
+async function checkPrices(): Promise<void> {
+  if (isRunning) {
+    console.log('Price check already in progress, skipping...');
+    return;
+  }
+
+  isRunning = true;
+  console.log('Starting scheduled price check...');
+
+  try {
+    // Find all products that are due for a refresh
+    const products = await productQueries.findDueForRefresh();
+    console.log(`Found ${products.length} products to check`);
+
+    for (const product of products) {
+      try {
+        console.log(`Checking price for product ${product.id}: ${product.url}`);
+
+        const priceData = await scrapePrice(product.url);
+
+        if (priceData) {
+          // Get the latest recorded price to compare
+          const latestPrice = await priceHistoryQueries.getLatest(product.id);
+
+          // Only record if price has changed or it's the first entry
+          if (!latestPrice || latestPrice.price !== priceData.price) {
+            await priceHistoryQueries.create(
+              product.id,
+              priceData.price,
+              priceData.currency
+            );
+            console.log(
+              `Recorded new price for product ${product.id}: ${priceData.currency} ${priceData.price}`
+            );
+          } else {
+            console.log(`Price unchanged for product ${product.id}`);
+          }
+        } else {
+          console.warn(`Could not extract price for product ${product.id}`);
+        }
+
+        // Update last_checked even if price extraction failed
+        await productQueries.updateLastChecked(product.id);
+
+        // Add a small delay between requests to avoid rate limiting
+        await new Promise((resolve) => setTimeout(resolve, 2000));
+      } catch (error) {
+        console.error(`Error checking product ${product.id}:`, error);
+        // Continue with next product even if one fails
+      }
+    }
+  } catch (error) {
+    console.error('Error in scheduled price check:', error);
+  } finally {
+    isRunning = false;
+    console.log('Scheduled price check complete');
+  }
+}
+
+export function startScheduler(): void {
+  // Run every minute
+  cron.schedule('* * * * *', () => {
+    checkPrices().catch(console.error);
+  });
+
+  console.log('Price check scheduler started (runs every minute)');
+}
+
+// Allow manual trigger for testing
+export { checkPrices };