# Feature: Availability Management

## Overview
Instructors define same-day date/time windows during which they are available for private lessons. On save, a window is split into consecutive lesson-length slots (09:00–16:00 with 60-minute lessons becomes seven rows), each independently bookable by students. Windows may be generated as a weekly-recurring series.

## Data Model — `{prefix}us_availability`

| Column             | Type             | Notes                                                        |
|--------------------|------------------|-------------------------------------------------------------|
| `id`               | BIGINT UNSIGNED  | Primary key                                                 |
| `instructor_id`    | BIGINT UNSIGNED  | WordPress user ID                                           |
| `offering_id`      | BIGINT UNSIGNED  | Nullable FK → `us_offerings.id` (private-lesson type)       |
| `start_dt`         | DATETIME         | Slot start — stored as `Y-m-d H:i:s`                        |
| `end_dt`           | DATETIME         | Slot end — always `start_dt + duration_minutes`             |
| `duration_minutes` | SMALLINT         | Lesson length (e.g. 30, 60)                                 |
| `is_booked`        | TINYINT(1)       | 0 = available, 1 = booked                                  |
| `recurrence_group` | BIGINT UNSIGNED  | Nullable — weekly-recurring windows share one group id     |
| `created_at`       | DATETIME         | Insertion time                                             |

A slot's `duration_minutes` is matched against the offering a student picks: a
30-minute private offering can only be booked into a slot whose
`duration_minutes` accommodates it.

## Window Splitting
`AvailabilitySlot::splitByDuration()` chunks a submitted window into consecutive
`duration_minutes` slots; `AvailabilityRepository::createFromWindow()` persists
one row per chunk. A trailing remainder shorter than the lesson length is
dropped. Windows must start and end on the same day and fit at least one lesson
(REST responds `400 invalid_window` otherwise; the admin form is a no-op).
`AvailabilityRepository::splitOversizedWindows()` is a data migration (run by
`Installer` on activation or version change) that rewrites pre-split rows.

## Weekly-Recurring Windows
Instructors may generate a window weekly across a date range. Each lesson-length
chunk becomes its own weekly series: occurrences of the same time-of-day share
one `recurrence_group` id, so a recurring set can be added or removed together
while individual occurrences are still booked independently.

## Admin Interface
Instructors access **My Availability** in wp-admin (`?page=us-availability`).
- Add availability: provide a same-day start/end window, lesson length, and (optionally) a linked private-lesson offering
- Add a weekly series: tick weekly repeat and choose the number of weeks
- Delete a slot: only allowed if `is_booked = 0`
- Bulk delete: the list view has a checkbox per unbooked slot (with a select-all header checkbox) and a **Delete selected** button (`usc_action=bulk_delete`, `slot_ids[]`); each id is ownership-checked, and booked slots are refused at the repository level
- Current slots can be shown as a **weekly calendar** (the default, navigated with `usc_week=Y-m-d`) or a **list** (`usc_view=list`); the grid honours the site's `start_of_week` option via `Availability\WeekCalendar`

## Public Calendar
The front-end booking shortcode renders open slots from `GET /availability`
either as an agenda-style list grouped by day or as a **weekly calendar** with
previous/next-week navigation (toggle rendered by `assets/js/booking.js`; the
site's `start_of_week` option is passed through the `usScheduler` JS config).
Both views can be narrowed to the slots bookable as chosen private-lesson types
with the **Show Only** lesson-type filter — see `lesson-booking.md`.

## REST API
| Method   | Endpoint                                      | Permission                         |
|----------|-----------------------------------------------|------------------------------------|
| `GET`    | `/wp-json/us-scheduler/v1/availability`       | `book_lesson`                      |
| `POST`   | `/wp-json/us-scheduler/v1/availability`       | `manage_availability`              |
| `DELETE` | `/wp-json/us-scheduler/v1/availability/{id}`  | `manage_availability` + slot owner |

`GET` supports query params: `instructor_id`, `offering_id`, `duration_minutes`, `from` (datetime), `to` (datetime).
Slots whose start has already passed are never returned.

`POST` validates `start_dt`/`end_dt` (admin form and REST alike) via
`AvailabilitySlot::normalizeDateTime()`: the canonical `Y-m-d H:i[:s]` and HTML
`datetime-local` (`Y-m-d\TH:i[:s]`) forms are normalised to `Y-m-d H:i:s`;
anything else — or an end not after the start — is rejected (REST responds
`400 invalid_datetime`; the admin form is a no-op). A valid window is stored as
lesson-length slots and `201` returns `{ "ids": [...] }` for every row created.

Times are displayed in 12-hour AM/PM form in the booking calendar and wp-admin
lists.

## Implementation
- Repository: `Unsupervised\Schedular\Availability\AvailabilityRepository`
- Model: `Unsupervised\Schedular\Availability\AvailabilitySlot`
- Week bucketing: `Unsupervised\Schedular\Availability\WeekCalendar`
- Admin controller: `Unsupervised\Schedular\Availability\AvailabilityController`
- REST endpoint: `Unsupervised\Schedular\Availability\AvailabilityEndpoint`

## Tests
- `tests/Unit/Availability/AvailabilityControllerTest.php`
- `tests/Unit/Availability/AvailabilityRepositoryTest.php`
- `tests/Unit/Availability/AvailabilitySlotTest.php`
- `tests/Unit/Availability/AvailabilityEndpointTest.php`
- `tests/Unit/Availability/WeekCalendarTest.php`