feat(notification): format prices with thousands separators

lib/utils/formatListing.js

@@ -30,6 +30,20 @@ const ROOMS_LABEL = {
   tr: 'Odalar',
 };
 
+/**
+ * German digit grouping for every price, whatever the UI language: the amount is always in euros,
+ * and "1200000 €" is hard to read at a glance in a push notification.
+ */
+const PRICE_FORMAT = new Intl.NumberFormat('de-DE', { maximumFractionDigits: 2 });
+
+/**
+ * Formats a price in euros with thousands separators, e.g. `1000000` becomes `1.000.000 €`.
+ *
+ * @param {number} price
+ * @returns {string}
+ */
+export const formatPrice = (price) => `${PRICE_FORMAT.format(price)} €`;
+
 /**
  * Formats a listing's numerical fields (price, size, rooms) into strings with their respective units.
  *
@@ -41,7 +55,7 @@ export const formatListing = (listing, language = 'en') => {
   const rooms = ROOMS_LABEL[language] ?? ROOMS_LABEL.en;
   return {
     ...listing,
-    price: listing.price != null ? `${listing.price} €` : null,
+    price: listing.price != null ? formatPrice(listing.price) : null,
     size: listing.size != null ? `${listing.size} m²` : null,
     rooms: listing.rooms != null ? `${listing.rooms} ${rooms}` : null,
     // Null unless a router actually answered for this listing. Adapters drop it with the same
@@ -101,8 +115,8 @@ export const formatPriceChange = (change, language = 'en') => {
   const percent = Math.abs(change.changePercent).toFixed(1);
   return {
     ...formatListing(change.listing, language),
-    oldPrice: `${change.oldPrice} €`,
-    newPrice: `${change.newPrice} €`,
+    oldPrice: formatPrice(change.oldPrice),
+    newPrice: formatPrice(change.newPrice),
     // Signed and with the unit, so an adapter can drop it straight into a line of text.
     changePercent: `${change.changePercent < 0 ? '-' : '+'}${percent} %`,
     direction: change.direction,

test/services/listings/priceHistoryService.test.js

@@ -165,8 +165,8 @@ describe('services/listings/priceHistoryService', () => {
       await notifyPriceChanges([change('job1')]);
 
       expect(state.sent[0][1][0]).toMatchObject({
-        oldPrice: '1200 €',
-        newPrice: '1100 €',
+        oldPrice: '1.200 €',
+        newPrice: '1.100 €',
         changePercent: '-8.3 %',
         changeHeadline: 'Price reduced',
       });

test/utils/formatListing.test.js

@@ -4,7 +4,7 @@
  */
 
 import { describe, it, expect } from 'vitest';
-import { formatListing } from '../../lib/utils/formatListing.js';
+import { formatListing, formatPrice, formatPriceChange } from '../../lib/utils/formatListing.js';
 
 /**
  * Notification text used to be German whatever the user had set the interface to, because the
@@ -29,7 +29,7 @@ describe('formatListing', () => {
 
   it('formats price and size with their language-neutral units', () => {
     const formatted = formatListing(listing, 'de');
-    expect(formatted.price).toBe('1200 €');
+    expect(formatted.price).toBe('1.200 €');
     expect(formatted.size).toBe('74 m²');
   });
 
@@ -54,3 +54,44 @@ describe('formatListing', () => {
     expect(listing).toEqual(original);
   });
 });
+
+describe('formatPrice', () => {
+  it('groups thousands with dots so large prices stay readable', () => {
+    expect(formatPrice(1000000)).toBe('1.000.000 €');
+    expect(formatPrice(100000)).toBe('100.000 €');
+    expect(formatPrice(1200)).toBe('1.200 €');
+  });
+
+  it('leaves small prices alone', () => {
+    expect(formatPrice(800)).toBe('800 €');
+    expect(formatPrice(0)).toBe('0 €');
+  });
+
+  it('uses a decimal comma and keeps at most two decimals', () => {
+    expect(formatPrice(1234.5)).toBe('1.234,5 €');
+    expect(formatPrice(999.999)).toBe('1.000 €');
+  });
+
+  it('uses German grouping even when the interface is English', () => {
+    expect(formatListing({ id: 'l3', title: 'House', price: 450000 }, 'en').price).toBe('450.000 €');
+  });
+});
+
+describe('formatPriceChange', () => {
+  it('formats old and new price the same way as a new listing', () => {
+    const formatted = formatPriceChange(
+      {
+        listing: { id: 'l4', title: 'House', price: 475000 },
+        oldPrice: 499000,
+        newPrice: 475000,
+        changePercent: -4.81,
+        direction: 'down',
+      },
+      'de',
+    );
+    expect(formatted.oldPrice).toBe('499.000 €');
+    expect(formatted.newPrice).toBe('475.000 €');
+    expect(formatted.price).toBe('475.000 €');
+    expect(formatted.changePercent).toBe('-4.8 %');
+  });
+});