Custom WP Booking Calendar Plugin

I need a fully-fledged WordPress booking calendar built from scratch for my brand. Once installed, the plugin has to sync seamlessly with Google Calendar, Outlook Calendar and Apple Calendar, keeping availability and confirmations perfectly aligned in both directions.

Core functionality I expect at launch
• Customers can pick time slots I define in the backend, with the option for me to create one-off or recurring availability patterns.
• Reminder notifications (email and, if you can, push/ICS alerts) fire automatically at configurable intervals.
• Recurring bookings are handled elegantly, obeying exceptions or blackout dates I set.
• Slot lengths, buffers and daily limits stay fully customizable from an intuitive settings panel.

Interface & UX
The front-end widget should feel clean and modern, matching contemporary WordPress themes without heavy styling. In the admin area, a streamlined React/Vue-like feel is welcome, but stick to WordPress guidelines so updates remain painless.

Technical notes
– Please code it as a standard installable .zip plugin (no child-theme hacks).
– Use WordPress hooks/APIs only; no hard-coded paths.
– Calendar sync may rely on the official Google, Microsoft and Apple calendars’ APIs/OAuth flows. Store tokens securely.
– I will need shortcodes and/or a Gutenberg block for easy placement.
– Hand over documented source, basic user guide and a changelog so I can maintain future versions.

Acceptance criteria
1. Install, activate, connect calendars, set slots in under 10 minutes.
2. Create a booking on the site → appears instantly in all three external calendars.
3. Cancel on an external calendar → removes the booking on the site.
4. Notifications trigger at the chosen interval.
5. Core PHP/JS passes WP_DEBUG with no errors or deprecated notices.

If you have past SaaS or plugin examples that show similar calendar sync, that will help me decide quickly.
Cancellations will be handled by instructors individually