Fix local-time display bug, add Asia departure patterns, popularity extension

Major bug fix: formatTime/formatDate/dayDiff/departure-time-filter all used
new Date() which converts to browser timezone. Now extract time directly
from ISO strings to preserve airport local timezone.

Backend fixes:
- Add "asia_to_eu" departure weights (23:00-02:30 late-night pattern)
- Fix "asia_to_na" to peak in afternoon (12-3 PM) not evening
- Overnight-exempt routes skip popularity window and curfew
- Popularity latest-hour gets random +0-1.5h extension

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/config.py

@@ -97,14 +97,18 @@ DEPARTURE_WEIGHTS: dict[str, list[int]] = {
     "na_to_asia": [
         0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 5, 12, 15, 14, 10, 7, 4, 2, 1, 0, 0, 0, 0, 0,
     ],
-    # Asia → NA: Evening departures, arrive same day NA
+    # Asia → NA: Afternoon departures, arrive same day NA
     "asia_to_na": [
-        0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 3, 3, 3, 3, 3, 4, 6, 10, 14, 13, 9, 6, 3, 1,
+        0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 5, 7, 10, 14, 14, 10, 7, 4, 2, 1, 0, 0, 0, 0,
     ],
-    # EU → Asia / AS → EU: afternoon–evening lean
+    # EU → Asia: afternoon–evening lean
     "eu_to_asia": [
         0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 5, 5, 6, 7, 8, 8, 7, 5, 3, 2, 1, 0,
     ],
+    # Asia → EU: late-night departures (23:00–02:30), arrive morning EU
+    "asia_to_eu": [
+        5, 3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 8, 14,
+    ],
     # Domestic / same-continent: morning rush + evening rush
     "domestic": [
         0, 0, 0, 0, 0, 1, 4, 8, 10, 8, 6, 5, 5, 5, 5, 5, 6, 8, 8, 5, 3, 2, 1, 0,
@@ -143,6 +147,15 @@ HUB_FLIGHT_BONUS: list[tuple[int, int, int]] = [
     (50,  0, 2),
 ]
 
+# Route types with intentional late-night / early-morning departures.
+# These skip the popularity window and airport curfew so the overnight
+# pattern encoded in DEPARTURE_WEIGHTS is preserved.
+OVERNIGHT_EXEMPT_ROUTES: set[str] = {"asia_to_eu"}
+
+# Maximum random extension to the popularity latest-hour (in minutes).
+# Popular routes can have departures up to this much later than the base limit.
+POPULARITY_LATEST_EXTENSION_MAX = 90  # 1.5 hours
+
 # Departure-weight per-hour jitter range (±fraction applied to each hourly weight)
 DEPARTURE_WEIGHT_JITTER = 0.20
 

backend/flight_generator.py

@@ -21,6 +21,8 @@ from .config import (
     MAX_LAYOVER_MINUTES,
     MIN_FLIGHTS_PER_DAY,
     MIN_LAYOVER_MINUTES,
+    OVERNIGHT_EXEMPT_ROUTES,
+    POPULARITY_LATEST_EXTENSION_MAX,
     POPULARITY_TIME_LIMITS,
     POWER_AIRCRAFT,
     PREMIUM_CLASS_AMENITY_BOOST,
@@ -117,8 +119,7 @@ def _classify_route_type(origin_continent: str, dest_continent: str) -> str:
     if o == "EU" and d == "AS":
         return "eu_to_asia"
     if o == "AS" and d == "EU":
-        # Reverse of eu_to_asia: mirror the afternoon/evening pattern
-        return "eu_to_asia"
+        return "asia_to_eu"
     return "default"
 
 
@@ -131,29 +132,39 @@ def _build_departure_weights(
     """Build hourly departure weights adjusted for popularity, curfew, and jitter.
 
     Returns a 24-element list of non-negative floats (one weight per hour 0–23).
+
+    Overnight-exempt routes (e.g. asia_to_eu with 23:00–02:30 departures)
+    skip the popularity window and curfew so their late-night pattern is
+    preserved intact.
     """
     base = list(DEPARTURE_WEIGHTS.get(route_type, DEPARTURE_WEIGHTS["default"]))
     weights = [float(w) for w in base]
 
-    # 1. Popularity-based time window: zero out hours outside the allowed range
-    earliest, latest = 7, 21  # defaults
-    for min_carriers, eh, lh in POPULARITY_TIME_LIMITS:
-        if num_carriers >= min_carriers:
-            earliest, latest = eh, lh
-            break
-    for h in range(0, earliest):
-        weights[h] = 0.0
-    for h in range(latest + 1, 24):
-        weights[h] = 0.0
-
-    # 2. Airport curfew: reduce midnight–5 AM based on airport size
-    curfew_factor = 0.01
-    for min_routes, factor in CURFEW_FACTORS:
-        if origin_route_count >= min_routes:
-            curfew_factor = factor
-            break
-    for h in range(0, 6):
-        weights[h] *= curfew_factor
+    is_overnight = route_type in OVERNIGHT_EXEMPT_ROUTES
+
+    if not is_overnight:
+        # 1. Popularity-based time window: zero out hours outside the range
+        earliest, latest = 7, 21  # defaults
+        for min_carriers, eh, lh in POPULARITY_TIME_LIMITS:
+            if num_carriers >= min_carriers:
+                earliest, latest = eh, lh
+                break
+        # Random extension up to 1.5 h on the latest hour
+        if num_carriers >= 2:
+            latest = min(23, latest + rng.randint(0, POPULARITY_LATEST_EXTENSION_MAX) // 60)
+        for h in range(0, earliest):
+            weights[h] = 0.0
+        for h in range(latest + 1, 24):
+            weights[h] = 0.0
+
+        # 2. Airport curfew: reduce midnight–5 AM based on airport size
+        curfew_factor = 0.01
+        for min_routes, factor in CURFEW_FACTORS:
+            if origin_route_count >= min_routes:
+                curfew_factor = factor
+                break
+        for h in range(0, 6):
+            weights[h] *= curfew_factor
 
     # 3. Per-route jitter: ±DEPARTURE_WEIGHT_JITTER on each hour
     for h in range(24):

frontend/src/components/results/FlightCard.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react';
 import type { FlightOffer } from '../../api/types';
-import { formatDuration, formatPrice, formatStops, formatTime } from '../../utils/format';
+import { daysBetween, formatDuration, formatPrice, formatStops, formatTime } from '../../utils/format';
 
 interface Props {
   flight: FlightOffer;
@@ -14,9 +14,8 @@ export default function FlightCard({ flight }: Props) {
   const [expanded, setExpanded] = useState(false);
   const firstSeg = flight.segments[0];
 
-  const depDate = new Date(flight.departure).toDateString();
-  const arrDate = new Date(flight.arrival).toDateString();
-  const dayDiff = depDate !== arrDate;
+  // Compare calendar dates in their respective local timezones (not browser TZ)
+  const daysDiff = daysBetween(flight.departure, flight.arrival);
 
   // All airlines in this itinerary
   const airlineNames = [...new Set(flight.segments.map(s => s.airline_name))];
@@ -46,7 +45,7 @@ export default function FlightCard({ flight }: Props) {
             </span>
             <span className="text-gray-400 text-sm">&ndash;</span>
             <span className="text-[15px] font-medium whitespace-nowrap" data-testid="arrival-time">
-              {formatTime(flight.arrival)}{dayDiff && <sup className="text-[10px] text-red-500 ml-px">+1</sup>}
+              {formatTime(flight.arrival)}{daysDiff > 0 && <sup className="text-[10px] text-red-500 ml-px">+{daysDiff}</sup>}
             </span>
           </div>
 

frontend/src/pages/ResultsPage.tsx

@@ -1,6 +1,7 @@
 import { useCallback, useEffect, useMemo, useState } from 'react';
 import { useSearchParams } from 'react-router-dom';
 import type { CabinClass, Filters, Passengers, SortBy, TripType } from '../api/types';
+import { getLocalMinuteOfDay } from '../utils/format';
 import SearchForm from '../components/search/SearchForm';
 import type { SearchFormData } from '../components/search/SearchForm';
 import FlightCard from '../components/results/FlightCard';
@@ -68,18 +69,12 @@ export default function ResultsPage() {
     if (filters.departure_time_min) {
       const [h, m] = filters.departure_time_min.split(':').map(Number);
       const min = h * 60 + m;
-      flights = flights.filter(f => {
-        const d = new Date(f.departure);
-        return d.getHours() * 60 + d.getMinutes() >= min;
-      });
+      flights = flights.filter(f => getLocalMinuteOfDay(f.departure) >= min);
     }
     if (filters.departure_time_max) {
       const [h, m] = filters.departure_time_max.split(':').map(Number);
       const max = h * 60 + m;
-      flights = flights.filter(f => {
-        const d = new Date(f.departure);
-        return d.getHours() * 60 + d.getMinutes() <= max;
-      });
+      flights = flights.filter(f => getLocalMinuteOfDay(f.departure) <= max);
     }
 
     // Sort

frontend/src/utils/format.ts

@@ -11,17 +11,41 @@ export function formatDuration(minutes: number): string {
 }
 
 export function formatTime(isoString: string): string {
-  const d = new Date(isoString);
-  return d.toLocaleTimeString('en-US', {
-    hour: 'numeric',
-    minute: '2-digit',
-    hour12: true,
-  });
+  // Extract HH:MM directly from ISO string to preserve the airport's
+  // local timezone. new Date() would convert to the browser's timezone.
+  const match = isoString.match(/T(\d{2}):(\d{2})/);
+  if (!match) {
+    return isoString;
+  }
+  const hours = parseInt(match[1], 10);
+  const minutes = match[2];
+  const ampm = hours >= 12 ? 'PM' : 'AM';
+  const displayHour = hours % 12 || 12;
+  return `${displayHour}:${minutes} ${ampm}`;
+}
+
+/** Minutes since midnight extracted from ISO string (airport local time). */
+export function getLocalMinuteOfDay(isoString: string): number {
+  const match = isoString.match(/T(\d{2}):(\d{2})/);
+  if (!match) return 0;
+  return parseInt(match[1], 10) * 60 + parseInt(match[2], 10);
+}
+
+/** Number of calendar days between two ISO date-times (in their local timezones). */
+export function daysBetween(isoA: string, isoB: string): number {
+  const dateA = isoA.split('T')[0];
+  const dateB = isoB.split('T')[0];
+  return Math.round(
+    (new Date(dateB).getTime() - new Date(dateA).getTime()) / 86400000,
+  );
 }
 
 export function formatDate(isoString: string): string {
-  const d = new Date(isoString);
-  return d.toLocaleDateString('en-US', {
+  // Parse from the date portion of the ISO string (airport local date)
+  const datePart = isoString.split('T')[0];
+  const [y, m, d] = datePart.split('-').map(Number);
+  const dt = new Date(y, m - 1, d); // local-date-only, no TZ conversion
+  return dt.toLocaleDateString('en-US', {
     weekday: 'short',
     month: 'short',
     day: 'numeric',