Fix DST timezone selection: Add "+" buttons to search, expand modal for timezone choice, and modernize with Temporal API

src/scripts/index.ts

@@ -85,7 +85,7 @@ export function getUserTimezone(date?: Date): TimeZone {
   // Get user's timezone ID using Temporal (polyfill ensures availability)
   const userTimezone = Temporal.Now.timeZoneId();
 
-  const now = date || new Date();
+  const now = date || new Date(Temporal.Now.instant().epochMilliseconds);
 
   // Use Intl for offset calculation (proven compatibility)
   const formatter = new Intl.DateTimeFormat('en', {
@@ -421,7 +421,7 @@ function getTimezoneAbbreviation(displayName: string, iana: string, date?: Date)
     });
 
     // Format the provided date (or current date) and extract the timezone abbreviation
-    const parts = formatter.formatToParts(date || new Date());
+    const parts = formatter.formatToParts(date || new Date(Temporal.Now.instant().epochMilliseconds));
     const timeZonePart = parts.find(part => part.type === 'timeZoneName');
 
     if (timeZonePart && timeZonePart.value && timeZonePart.value.length <= 5) {
@@ -469,7 +469,7 @@ function createTimezoneDisplayName(iana: string, offset: number, date?: Date): s
     });
 
     // Get the timezone name from the provided date (or current date)
-    const parts = formatter.formatToParts(date || new Date());
+    const parts = formatter.formatToParts(date || new Date(Temporal.Now.instant().epochMilliseconds));
     const timeZonePart = parts.find(part => part.type === 'timeZoneName');
 
     if (timeZonePart && timeZonePart.value) {
@@ -513,7 +513,7 @@ function formatOffset(offset: number): string {
  * @returns Array of timeline hours with daylight information and date transitions
  */
 export function generateTimelineHours(numHours: number, timezone: TimeZone, baseDate?: Date): TimelineHour[] {
-  const now = baseDate || new Date();
+  const now = baseDate || new Date(Temporal.Now.instant().epochMilliseconds);
   const userTz = getUserTimezone();
 
   // Get current hour in user's timezone and round down
@@ -924,7 +924,7 @@ export class TimelineManager {
   private modal: TimezoneModal;
   private dateTimeModal: DateTimeModal;
   private selectedTimezones: TimeZone[] = [];
-  private selectedDate: Date = new Date(); // Default to today
+  private selectedDate: Date = new Date(Temporal.Now.instant().epochMilliseconds); // Default to today
 
   constructor() {
     this.container = document.getElementById('timeline-container') as HTMLElement;
@@ -1323,15 +1323,16 @@ function saveTimezoneCache(): void {
  * Initialize timezone data by processing all browser timezones for June and December
  * This expensive operation should only be done once on page load
  */
-function initializeTimezoneData(year: number = new Date().getFullYear()): ProcessedTimezoneData {
+function initializeTimezoneData(year: number = Temporal.Now.plainDateISO().year): ProcessedTimezoneData {
   const userTimezone = Temporal.Now.timeZoneId();
 
   // Get all supported timezones (comprehensive list)
   const allTimezones = Intl.supportedValuesOf('timeZone');
 
-  // Create dates for June 1st and December 31st to capture DST variations
-  const juneDate = new Date(year, 5, 1); // June 1st
-  const decemberDate = new Date(year, 11, 31); // December 31st
+  // Create neutral dates for June 1st and December 31st to capture DST variations
+  // Using UTC to avoid local timezone interpretation issues
+  const juneDate = new Date(Date.UTC(year, 5, 1)); // June 1st in UTC
+  const decemberDate = new Date(Date.UTC(year, 11, 31)); // December 31st in UTC
 
   console.log(`Processing ${allTimezones.length} timezones for June and December variants...`);
 
@@ -1464,7 +1465,7 @@ function getTimezoneSetForDate(date: Date, processedData: ProcessedTimezoneData)
  * @returns Array of timezone objects ordered from user's timezone around the globe
  */
 export function getAllTimezonesOrdered(date?: Date): TimeZone[] {
-  const now = date || new Date();
+  const now = date || new Date(Temporal.Now.instant().epochMilliseconds);
   const currentYear = now.getFullYear();
 
   // Load cache from localStorage on first call
@@ -1496,12 +1497,13 @@ export function getAllTimezonesOrdered(date?: Date): TimeZone[] {
  * Get timezone variations for a given IANA identifier using fixed dates
  * Returns both summer (June 1st) and winter (December 31st) variations
  */
-function getTimezoneVariations(iana: string, year: number = new Date().getFullYear()): TimeZone[] {
+function getTimezoneVariations(iana: string, year: number = Temporal.Now.plainDateISO().year): TimeZone[] {
   const variations: TimeZone[] = [];
 
   // Use June 1st for summer time and December 31st for winter time
-  const summerDate = new Date(year, 5, 1); // June 1st
-  const winterDate = new Date(year, 11, 31); // December 31st
+  // Create neutral UTC dates and let Intl.DateTimeFormat handle timezone conversion
+  const summerDate = new Date(Date.UTC(year, 5, 1)); // June 1st in UTC
+  const winterDate = new Date(Date.UTC(year, 11, 31)); // December 31st in UTC
 
   for (const date of [summerDate, winterDate]) {
     const formatter = new Intl.DateTimeFormat('en', {
@@ -1574,7 +1576,7 @@ function extractRegion(iana: string): string {
  * Get grouped timezones with DST/Standard variations, prioritized by selected date
  */
 export function getGroupedTimezones(selectedDate?: Date): GroupedTimezone[] {
-  const date = selectedDate || new Date();
+  const date = selectedDate || new Date(Temporal.Now.instant().epochMilliseconds);
   const allTimezones = Intl.supportedValuesOf('timeZone');
   const locationGroups = new Map<string, GroupedTimezone>();
 
@@ -1809,7 +1811,7 @@ export class TimezoneModal {
   private selectedDate: Date; // Date to use for timezone calculations
 
   constructor(onTimezoneSelected?: (timezone: TimeZone, isOffCycle?: boolean) => void, selectedDate?: Date) {
-    this.selectedDate = selectedDate || new Date();
+    this.selectedDate = selectedDate || new Date(Temporal.Now.instant().epochMilliseconds);
     this.modal = document.getElementById('timezone-modal') as HTMLElement;
     this.overlay = document.getElementById('timezone-modal-overlay') as HTMLElement;
     this.input = document.getElementById('timezone-input') as HTMLInputElement;
@@ -2226,11 +2228,8 @@ export class TimezoneModal {
     if (plusBtn && group.alternate) {
       plusBtn.addEventListener('click', e => {
         e.stopPropagation();
-        // Select the alternate timezone directly and mark as off-cycle
-        if (this.onTimezoneSelectedCallback && group.alternate) {
-          this.onTimezoneSelectedCallback(group.alternate, true); // Mark alternate as off-cycle
-        }
-        this.close();
+        // Expand to show both timezone options instead of directly adding alternate
+        this.showTimezoneOptions(group);
       });
     }
 
@@ -2293,13 +2292,30 @@ export class TimezoneModal {
       ? `${timezone.cityName} (${timezone.abbreviation})`
       : `${timezone.cityName} (${timezone.abbreviation} ${offsetStr})`;
 
+    // Check if this timezone has an alternate available (for DST support in search results)
+    const matchingGroup = this.groupedTimezonesLookup.get(timezone.iana);
+    const hasAlternate = matchingGroup && matchingGroup.alternate;
+
     item.innerHTML = `
       <div class="wheel-timezone-name">
         ${displayText}
+        ${hasAlternate ? '<span class="timezone-plus-btn" title="Select alternate timezone">+</span>' : ''}
       </div>
       <div class="wheel-timezone-display">${timezone.displayName}</div>
     `;
 
+    // Handle plus button clicks (for search results)
+    if (hasAlternate) {
+      const plusBtn = item.querySelector('.timezone-plus-btn');
+      if (plusBtn && matchingGroup && matchingGroup.alternate) {
+        plusBtn.addEventListener('click', e => {
+          e.stopPropagation();
+          // Expand to show both timezone options instead of directly adding alternate
+          this.showTimezoneOptions(matchingGroup);
+        });
+      }
+    }
+
     // Click handler
     item.addEventListener('click', () => {
       if (!isCenter) {
@@ -2369,6 +2385,86 @@ export class TimezoneModal {
     document.body.style.overflow = '';
   }
 
+  /**
+   * Show expanded view with both timezone options for selection
+   */
+  private showTimezoneOptions(group: GroupedTimezone): void {
+    // Clear wheel and show both timezone options
+    this.wheel.innerHTML = '';
+
+    const optionsContainer = document.createElement('div');
+    optionsContainer.className = 'timezone-options-container';
+    optionsContainer.innerHTML = `
+      <div class="timezone-options-header">
+        <h3>Select ${group.location} Timezone</h3>
+        <div class="timezone-options-subtitle">Choose your preferred time offset</div>
+      </div>
+      <div class="timezone-options-list">
+      </div>
+      <div class="timezone-options-actions">
+        <button type="button" class="timezone-option-back">← Back to Search</button>
+      </div>
+    `;
+
+    const optionsList = optionsContainer.querySelector('.timezone-options-list') as HTMLElement;
+
+    // Add current timezone option
+    const currentOption = document.createElement('div');
+    currentOption.className = 'timezone-option current-option';
+    currentOption.innerHTML = `
+      <div class="timezone-option-header">
+        <div class="timezone-option-name">${group.current.cityName} (${group.current.abbreviation})</div>
+        <div class="timezone-option-badge">Current</div>
+      </div>
+      <div class="timezone-option-details">
+        <div class="timezone-option-offset">${formatOffset(group.current.offset)}</div>
+        <div class="timezone-option-display">${group.current.displayName}</div>
+      </div>
+    `;
+
+    currentOption.addEventListener('click', () => {
+      if (this.onTimezoneSelectedCallback) {
+        this.onTimezoneSelectedCallback(group.current);
+      }
+      this.close();
+    });
+
+    optionsList.appendChild(currentOption);
+
+    // Add alternate timezone option if available
+    if (group.alternate) {
+      const alternateOption = document.createElement('div');
+      alternateOption.className = 'timezone-option alternate-option';
+      alternateOption.innerHTML = `
+        <div class="timezone-option-header">
+          <div class="timezone-option-name">${group.alternate.cityName} (${group.alternate.abbreviation})</div>
+          <div class="timezone-option-badge">Alternate</div>
+        </div>
+        <div class="timezone-option-details">
+          <div class="timezone-option-offset">${formatOffset(group.alternate.offset)}</div>
+          <div class="timezone-option-display">${group.alternate.displayName}</div>
+        </div>
+      `;
+
+      alternateOption.addEventListener('click', () => {
+        if (this.onTimezoneSelectedCallback && group.alternate) {
+          this.onTimezoneSelectedCallback(group.alternate, true); // Mark alternate as off-cycle
+        }
+        this.close();
+      });
+
+      optionsList.appendChild(alternateOption);
+    }
+
+    // Back button functionality
+    const backButton = optionsContainer.querySelector('.timezone-option-back') as HTMLElement;
+    backButton.addEventListener('click', () => {
+      this.renderWheel();
+    });
+
+    this.wheel.appendChild(optionsContainer);
+  }
+
   /**
    * Show custom timezone creation option when offset query has no matches
    */
@@ -2606,7 +2702,7 @@ export class DateTimeModal {
 
     // Set current datetime as default if no value is set
     if (!this.input.value) {
-      const now = new Date();
+      const now = new Date(Temporal.Now.instant().epochMilliseconds);
       // Format to datetime-local format (YYYY-MM-DDTHH:MM)
       const year = now.getFullYear();
       const month = String(now.getMonth() + 1).padStart(2, '0');