# Architecture

## The files that ship

18 files. `ci/`, `tests/` and `docs/` are not among them — `ci/dist-files.sh`
decides, and a static check asserts that every PHP file the code loads is in
that list.

| file | what it is |
| --- | --- |
| `woocommerce-email-discount-manager.php` | header, constants, boot order, activation and deactivation |
| `includes/class-db.php` | the five tables, `dbDelta()` schema, and every query |
| `includes/class-helpers.php` | matching an email to an assignment |
| `includes/class-frontend.php` | cart totals and shipping filtering |
| `includes/class-admin.php` | the menu, the three tabs, the dashboard card |
| `includes/class-admin-groups.php` | the Groups tab |
| `includes/class-admin-emails.php` | the Emails tab |
| `includes/class-admin-shipping.php` | the Shipping tab |
| `includes/class-admin-audit.php` | the audit log viewer |
| `includes/class-audit-log.php` | writing and pruning the audit log |
| `includes/class-rate-limiter.php` | per-method REST rate limiting |
| `includes/class-rest-api.php` | the `wc-edm/v1` routes |
| `includes/class-updater.php` | the release-feed update check |
| `includes/shared-menu.php` | the family's shared parent menu — byte-identical in all eight plugins |
| `assets/css/admin.css`, `assets/js/admin.js`, `assets/icon.svg` | admin UI and the icon WordPress draws on the Updates screen |
| `README.txt` | the readme WordPress parses |

## Boot order

The order matters and two of the steps are deliberately before the WooCommerce
check.

1. **File load.** Constants are defined: `WC_EDM_VERSION`,
   `WC_EDM_PLUGIN_FILE`, `WC_EDM_PLUGIN_DIR`, `WC_EDM_PLUGIN_URL`.
2. **`plugins_loaded`** → `init()`.
3. **The updater loads first**, before the WooCommerce check. A shop with
   WooCommerce switched off for an afternoon must not quietly stop receiving
   fixes for this plugin.
4. **The shared menu title filter is added**, also before that check, and for a
   related reason: the shared parent menu is registered by whichever family
   plugin boots first, and its label must not depend on whether *this* plugin
   got past a gate.
5. **WooCommerce check.** Missing → an admin notice, and `init()` returns. The
   plugin is dormant, not broken.
6. Text domain, then `includes()`. A file that failed to load is collected and
   reported as a notice rather than fataling.
7. **`WC_EDM_DB` and `WC_EDM_Helpers` are required to continue.** Without
   either, `init()` returns and the notice stands — everything else builds on
   them.
8. `init` priority 5 → `WC_EDM_DB::maybe_upgrade()`, so a schema change lands
   after an update that skipped re-activation.
9. Admin, frontend, audit log and REST objects are constructed, each behind a
   `class_exists()` check.

The shared menu is registered under `WPMGR_MENU_SLUG` with a
`function_exists( 'wpmgr_ensure_menu' )` fallback, so a site where an older
sibling's copy of `shared-menu.php` loads first still gets a menu.

## Where data lives

### Tables

Five, all prefixed `wp_wc_edm_` (whatever the site's `$wpdb->prefix` is),
created by `dbDelta()` with foreign keys added afterwards:

- `wp_wc_edm_groups` — discount groups
- `wp_wc_edm_group_categories` — group → product category
- `wp_wc_edm_emails` — email patterns and their assignment
- `wp_wc_edm_shipping_rules` — group → shipping method, show or hide
- `wp_wc_edm_audit_log` — admin actions

### Options

- `wc_edm_db_version` — schema version, the only thing `maybe_upgrade()` reads

That is the complete list. This plugin stores no settings in options; the three
tabs write to the tables.

### Transients

- `wc_edm_release_feed` — the update feed response
- `wc_edm_card_counts` — the two numbers on the dashboard card, 5 minutes

### Scheduled events

One: `wc_edm_prune_audit_log`, daily, scheduled on `init` if not already
present and unscheduled on deactivation. It deletes audit rows older than the
retention window.

## Lifecycle

**Activate** (`register_activation_hook`) — refuses with an error if WooCommerce
is not active, then creates the tables.

**Deactivate** (`register_deactivation_hook`) — unschedules the prune event.
Tables, options and transients stay.

**Uninstall** — 🔴 **nothing happens.** There is no `uninstall.php` and no
`register_uninstall_hook`, so deleting the plugin in wp-admin removes the files
and leaves all five tables, both options and the transients in the database.
Deliberate: deleting a plugin by accident should not destroy a shop's discount
configuration. The cost is that a genuine clean removal is manual — drop the
five `wp_wc_edm_*` tables and delete `wc_edm_db_version` by hand.

## The customer-facing path

`woocommerce_cart_calculate_fees` (priority 20) adds the discount as a negative
fee. `woocommerce_before_calculate_totals` (priority 20) applies a coupon for
the Coupon assignment type. `woocommerce_package_rates` (priority 20, 2 args)
filters shipping.

The shipping filter's shape is the part worth reading in full, because a subtle
version of it shipped free delivery to strangers for several releases:

```php
$match = $this->get_current_match();

if ( $match && 'group' === $match->assignment_type && $match->group_id ) {
    $rates = $this->apply_group_shipping_rules( $rates, (int) $match->group_id );
} else {
    $rates = $this->remove_restricted_rates( $rates );
}
```

The `else` is the fix. A customer who matches nothing must still have the
reserved methods taken away; before 1.6.0 that branch did not exist, so the
restriction only applied to people who matched a group — i.e. to nobody who
mattered. `apply_group_shipping_rules()` also falls back to
`remove_restricted_rates()` when a group has no rules at all, for the same
reason.

## Not present

- No drop-in, no mu-plugin, nothing that runs before WordPress boots.
- Nothing hooks `the_content` or buffers output.
- No cron beyond the one prune event.
- No custom post types, no taxonomies, no user meta.
- No `WP_CLI` commands.