# Feature: Payments

## Overview
Payment is taken at registration. When Stripe is **not** configured the platform
falls back to **e-transfer** — a pending payment a studio admin marks received —
so everything works without any credentials. When Stripe **is** configured the
default rail becomes the **credit card**. The studio admin can override any
student's method (card / e-transfer / comp). Single bookings are charged once;
weekly reservations and group classes are charged the full term upfront. A
numbered receipt is emailed automatically when a payment is marked paid.

> **Implemented:** the payment ledger, studio settings, method resolution
> (e-transfer default with no Stripe; card default when configured; per-student
> override), the e-transfer/comp flow with admin confirmation + receipts,
> integration into booking/enrolment (a registration's `payment_id` is linked;
> comp auto-confirms; e-transfer stays pending until confirmed), and the **live
> Stripe card charge** — a PaymentIntent created on `POST /payments/intent`,
> confirmed in the browser with Stripe.js Payment Elements, and finalised by the
> `POST /payments/webhook` handler (signature-verified) on
> `payment_intent.succeeded`. Uses the `stripe/stripe-php` SDK.

## Stripe Configuration
Stripe credentials live in WordPress options, managed on the **Studio Settings**
page (`manage_billing`, studio admin only):

| Option                       | Notes                                  |
|------------------------------|----------------------------------------|
| `us_stripe_publishable_key`  | Stripe publishable key                 |
| `us_stripe_secret_key`       | Stripe secret key                      |
| `us_stripe_webhook_secret`   | Webhook signing secret (`whsec_…`)     |
| `us_stripe_mode`             | `test` or `live`                       |
| `us_currency`                | Default ISO 4217 currency, e.g. `CAD`  |
| `us_etransfer_email`         | Studio-default e-transfer destination  |
| `us_hst_rate`                | Default HST/tax percentage, e.g. `13`  |

## HST / Tax

A studio-default **HST rate** (percentage) is configured on **Studio Settings**
(`us_hst_rate`, `manage_billing`). At booking the rate is **frozen onto the
payment** (`us_payments.tax_rate`) and the tax is computed against the pre-tax
subtotal (`tax_amount = round(amount × rate / 100, 2)`). The billed total is
`amount + tax_amount` (`Payment::total()`). Comped registrations are never taxed
(rate and amount are 0).

The rate is overridable **per booking** on **My Lessons** (instructor) while the
payment is still unpaid; saving recomputes `tax_amount` from the current
subtotal (`PaymentRepository::updateTax`). Receipts break out subtotal, HST, and
total when tax applies.

## Per-Student Billing Method
Each student's billing method is stored in user meta `us_payment_method`, set by the
studio admin (`Students → student detail → Billing method`). When unset, the studio
default applies — `card` if Stripe is configured, otherwise `etransfer`
(`BillingMethodResolver`):

| Method     | Behaviour                                                              |
|------------|-----------------------------------------------------------------------|
| `card`     | Charged immediately via Stripe; payment `paid` on success             |
| `etransfer`| Payment row created `pending`; admin marks it `paid` when funds arrive |
| `comp`     | No charge; registration is confirmed immediately, no payment row required |

## E-transfer Destination Email
Where students send e-transfers is resolved and **frozen onto the payment** at
booking time (`us_payments.etransfer_email`), so each record keeps the destination
the student was given. Resolution at creation:

1. **Offering override** — `us_offerings.etransfer_email`, set by the instructor on the offering.
2. **Studio default** — the `us_etransfer_email` option (Studio Settings, `manage_billing`).

After booking, the destination on a payment can be corrected per booking:
- **My Lessons** — the instructor edits the e-transfer email for a pending lesson payment.
- **Payments queue** — when marking an e-transfer received, the studio admin can update the email it was actually sent to before confirming.

## Data Model — `{prefix}us_payments`

| Column                     | Type             | Notes                                                  |
|----------------------------|------------------|--------------------------------------------------------|
| `id`                       | BIGINT UNSIGNED  | Primary key                                            |
| `student_id`               | BIGINT UNSIGNED  | WordPress user ID                                     |
| `instructor_id`            | BIGINT UNSIGNED  | WordPress user ID (denormalised for reporting)        |
| `registration_type`        | VARCHAR(20)      | `lesson` or `enrollment`                              |
| `registration_id`          | BIGINT UNSIGNED  | FK → `us_lessons.id` or `us_group_enrollments.id`     |
| `amount`                   | DECIMAL(10,2)    | Charged amount in dollars (matches the offering price) |
| `currency`                 | VARCHAR(3)       | ISO 4217, e.g. `CAD`                                  |
| `method`                   | VARCHAR(20)      | `card` / `etransfer` / `comp`                         |
| `status`                   | VARCHAR(20)      | `pending` / `paid` / `failed` / `refunded`            |
| `tax_rate`                 | DECIMAL(5,2)     | HST rate % frozen at booking; editable until paid     |
| `tax_amount`               | DECIMAL(10,2)    | Computed tax in dollars (`amount × tax_rate / 100`)   |
| `etransfer_email`          | VARCHAR(191)     | Frozen e-transfer destination; editable until confirmed |
| `stripe_payment_intent_id` | VARCHAR(255)     | Stripe PaymentIntent id; NULL for e-transfer / comp   |
| `receipt_number`           | VARCHAR(50)      | Sequential receipt id; set when `paid`                |
| `receipt_sent_at`          | DATETIME         | When the receipt email was sent; NULL until sent      |
| `created_at`               | DATETIME         | Insertion time                                        |
| `paid_at`                  | DATETIME         | When marked `paid`; NULL otherwise                    |

## Payment Flow
1. During registration the front-end calls `POST /payments/intent`, which creates a Stripe PaymentIntent for a `card` student and returns the client secret. (`etransfer` returns a `pending` payment; `comp` returns none.)
2. The browser confirms the card payment with Stripe.
3. Stripe calls `POST /payments/webhook`; on `payment_intent.succeeded` the payment is marked `paid`, `paid_at` is stamped, and the linked lesson/enrolment is `confirmed`.
4. On transition to `paid`, `ReceiptMailer` assigns a `receipt_number`, emails the student a receipt, and stamps `receipt_sent_at`.
5. For an e-transfer, the studio admin later calls `PATCH /payments/{id}` to mark it `paid`, which triggers the same confirmation + receipt.

## REST API
| Method  | Endpoint                                    | Permission                  |
|---------|---------------------------------------------|-----------------------------|
| `POST`  | `/wp-json/us-scheduler/v1/payments/intent`  | `book_lesson`               |
| `POST`  | `/wp-json/us-scheduler/v1/payments/webhook` | Public (Stripe signature verified) |
| `PATCH` | `/wp-json/us-scheduler/v1/payments/{id}`    | `manage_billing`            |

See `payment-reporting.md` for the monthly report and CSV export endpoints.

## Implementation
- Repository: `Unsupervised\Schedular\Payment\PaymentRepository`
- Model: `Unsupervised\Schedular\Payment\Payment`
- Stripe gateway: `Unsupervised\Schedular\Payment\StripeGateway`
- Receipts: `Unsupervised\Schedular\Payment\ReceiptMailer`
- Settings page: `Unsupervised\Schedular\Payment\StudioSettings`
- REST endpoint: `Unsupervised\Schedular\Payment\PaymentEndpoint`

## Tests
- `tests/Unit/Payment/PaymentRepositoryTest.php`
- `tests/Unit/Payment/PaymentTest.php`
- `tests/Unit/Payment/StripeGatewayTest.php`
- `tests/Unit/Payment/ReceiptMailerTest.php`