# Vereinfacht API Integration

This document describes the current integration with the Vereinfacht (verein.visuel.dev) accounting API for syncing members as finance contacts.

## Overview

- **Purpose:** Create and update external finance contacts in Vereinfacht when members are created or updated; support bulk sync for members without a contact ID.
- **Configuration:** ENV or Settings: `VEREINFACHT_API_URL`, `VEREINFACHT_API_KEY`, `VEREINFACHT_CLUB_ID`, optional `VEREINFACHT_APP_URL` for contact view links.
- **Modules:** `Mv.Vereinfacht` (business logic), `Mv.Vereinfacht.Client` (HTTP client), `Mv.Vereinfacht.Changes.SyncContact` (Ash after_transaction change).

## API Usage

### Finding an existing contact by email

The API supports filtered list requests. Use a single GET instead of paginating:

- **Endpoint:** `GET /api/v1/finance-contacts?filter[isExternal]=true&filter[email]=<email>`
- **Client:** `Mv.Vereinfacht.Client.find_contact_by_email/1` builds this URL (with encoded email) and returns `{:ok, contact_id}` if the first match exists, `{:error, :not_found}` otherwise.
- No member fields are required in the app solely for this lookup.

### Creating a contact

When creating an external finance contact, the API only requires:

- **Attributes:** `contactType` (e.g. `"person"`), `isExternal: true`
- **Relationship:** `club` (club ID from config)

Additional attributes (firstName, lastName, email, address, zipCode, city, country) are optional and are sent when present on the member so the contact is filled in. The app does **not** enforce extra required member fields for Vereinfacht; only Settings-based required fields and email apply.

- **Client:** `Mv.Vereinfacht.Client.create_contact/1` builds the JSON:API body from the member; `Mv.Constants.vereinfacht_required_member_fields/0` is an empty list.

### Updating a contact

- **Endpoint:** `PATCH /api/v1/finance-contacts/:id`
- **Client:** `Mv.Vereinfacht.Client.update_contact/2` sends current member attributes. The API may still validate presence/format of fields on update.

## Flow

1. **Member create/update:** `SyncContact` runs after the transaction. If the member has no `vereinfacht_contact_id`, the client tries `find_contact_by_email(email)`; if found, it updates that contact and stores the ID on the member; otherwise it creates a contact and stores the new ID. If the member already has a contact ID, the client updates the contact.
2. **Bulk sync:** “Sync all members without Vereinfacht contact” calls `Vereinfacht.sync_members_without_contact/0`, which loads members with nil/blank `vereinfacht_contact_id` and runs the same create/update flow per member.

## References

- **Config:** `Mv.Config` (`vereinfacht_api_url`, `vereinfacht_api_key`, `vereinfacht_club_id`, `vereinfacht_app_url`, `vereinfacht_configured?/0`).
- **Constants:** `Mv.Constants.vereinfacht_required_member_fields/0` (empty), `vereinfacht_required_field?/1` (legacy; currently unused in UI or validation).
- **Tests:** `test/mv/vereinfacht/`, `test/mv/config_vereinfacht_test.exs`; see `test/mv/vereinfacht/vereinfacht_test_README.md` for scope.
- **Roadmap:** Payment/transaction import and deeper integration are tracked in `docs/feature-roadmap.md` and `docs/membership-fee-architecture.md`.