# Add to Calendar Button

## Objective

Let people put an event straight into whichever calendar they already use.

A control beside every date-bearing event that hands the event off to the user's calendar of choice.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Find every place the app already shows a date and time a person would want to keep: a confirmed booking, a webinar, a trial expiry, a deadline. Put the control there rather than inventing a new events page.
2. Offer a handoff for the common hosted calendars and a downloadable calendar file for everything else, and let the download be the fallback rather than a separate hidden option.
3. Build the event payload on the server from the same record the confirmation email uses, so the title, location, and description never disagree between the two.
4. If the app already creates events directly through Google Calendar Event Creation or Microsoft Outlook Calendar Events, treat this as the unauthenticated path for people who have not connected an account, and reuse the same event-building code rather than writing a second version of it.
5. Do not paste the raw event fields into a link and hope for the best. Escape line breaks, commas, and semicolons in the title, location, and notes, because an unescaped one silently truncates or corrupts the event on arrival.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Line breaks, commas, and semicolons inside the title, location, or notes must be escaped for the destination format. Unescaped, they end the field early and the user gets an event whose description stops mid-sentence.
- An all-day event is encoded as a date range whose end is the day after the last day. Getting this wrong shifts the event by one day, and the user finds out by arriving on the wrong date.
- Give each event a stable identifier derived from the record, not from the moment of generation. Without it, a user who adds the event twice, or adds it after a time change, ends up with two conflicting entries instead of one updated one.
- When a handoff link fails or the destination is blocked by the user's network, fall back to the downloadable file with an explanation rather than leaving a dead button.
- Cap the description length before the destination provider truncates it. Put the essential detail and a link back to the app in the first line, so anything trimmed is trimmed from the end.
- Timed events must carry an explicit time zone, not a floating local time. A floating time moves when the user travels.
- A cancelled or rescheduled booking should not keep offering the old time. Regenerate from the current record every time the control is rendered.
- The control needs a text label, not only an icon, and must be reachable and operable from the keyboard.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Every event surface in the app offers an add-to-calendar control.
- [ ] Titles, locations, and notes containing punctuation and line breaks arrive intact in the calendar.
- [ ] All-day events land on the correct day, and timed events carry an explicit time zone.
- [ ] Adding the same event twice updates the existing entry rather than creating a duplicate.
- [ ] A failed handoff falls back to a downloadable calendar file with a visible explanation.
- [ ] The event payload is generated from the same server-side source as the confirmation email.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.