Add plugintype and API docs for SMS subsystem

Co-authored-by: David Woloszyn <[email protected]>

docs/apis/plugintypes/sms/index.md

@@ -0,0 +1,125 @@
+---
+title: SMS gateway
+tags:
+    - SMS
+    - Gateway
+    - Notification
+---
+
+<Since version="4.5" issueNumber="MDL-83406" />
+
+SMS gateway plugins allow you to create SMS gateway providers.
+Providers are an interface between [SMS API](/apis/subsystems/sms/index.md) and the external SMS provider (e.g. Amazon Web Services).
+This allows for the sending of SMS notifications to users from your Moodle instance.
+
+For example, you set up MFA (Multi-Factor Authentication) in Moodle and choose 'AWS' as your SMS gateway provider.
+This enables users to receive SMS notifications as part of the authentication process.
+
+## File structure
+
+SMS gateway plugins are located in the `/sms/gateway` directory. A plugin should not include any custom files outside its own
+plugin folder.
+
+Each plugin is in a separate subdirectory and consists of a number of mandatory files and any other files the developer is going to use. See the [common plugin files](/apis/commonfiles/index.mdx) documentation for other files which may be useful in your plugin.
+
+<details>
+  <summary>The directory layout for the `smsgateway` plugin.</summary>
+
+```console
+sms/gateway/example
+├── classes
+│   ├── gateway.php
+│   ├── hook_listener.php
+│   └── privacy
+│       └── provider.php
+├── lang
+│   └── en
+│       └── smsgateway_example.php
+├── settings.php
+└── version.php
+```
+
+</details>
+
+## Key files
+
+There are a number of key files within the SMS gateway plugin which will need to be configured for correct functionality.
+
+- gateway.php
+- hook_listener.php
+
+### gateway.php
+
+Each plugin must create a class called `gateway` which extends the `\core_sms\gateway` class.
+The SMS API will use the extended methods from this class.
+
+```php title="Implementing the base SMS gateway"
+
+class gateway extends \core_sms\gateway {
+
+    #[\Override]
+    public function send(
+        message $message,
+    ): message {
+        // Sample code to send an SMS message.
+        $config = (object)json_decode($awsconfig, true, 512, JSON_THROW_ON_ERROR);
+        $class = '\smsgateway_aws\local\service\\' . $config->gateway;
+        $recipientnumber = manager::format_number(
+            phonenumber: $message->recipientnumber,
+            countrycode: isset($config->countrycode) ?? null,
+        );
+        if (class_exists($class)) {
+            $status = call_user_func(
+                $class . '::send_sms_message',
+                $message->content,
+                $recipientnumber,
+                $config,
+            );
+        }
+        return $message->with(
+            status: $status,
+        );
+    }
+
+    #[\Override]
+    public function get_send_priority(message $message): int {
+        return 50;
+    }
+}
+
+```
+
+### hook_listener.php
+
+[Hooks](/apis/core/hooks/index.md) can be dispatched from the SMS API which the plugin can then listened to.
+It is necessary for plugins developers to assess these hooks and implement accordingly.
+
+#### after_sms_gateway_form_hook
+
+This hook will allow plugins to add required form fields to assist users in configuring their SMS gateway.
+
+```php title="Listener method for after_sms_gateway_form_hook"
+
+public static function set_form_definition_for_aws_sms_gateway(after_sms_gateway_form_hook $hook): void {
+    if ($hook->plugin !== 'smsgateway_example') {
+        return;
+    }
+
+    $gateways = [
+        'smsgateway_example' => get_string('list', 'smsgateway_example'),
+    ];
+    $mform->addElement(
+        'select',
+        'gateway',
+        get_string('gateway', 'smsgateway_example'),
+        $gateways,
+    );
+}
+
+```
+
+:::info
+
+For a real plugin example, see the [AWS SMS Gateway plugin](https://github.com/moodle/moodle/tree/main/sms/gateway/aws).
+
+:::

docs/apis/subsystems/sms/index.md

@@ -1,10 +1,24 @@
 ---
 title: SMS API
+tags:
+    - SMS
 ---
 
 <Since version="4.5" issueNumber="MDL-79808" />
 
-The SMS API lets you send SMS messages using configured gateways, fetch messages that were previously sent, and check on their status.
+The SMS API allows developers to implement SMS-related features into their plugins.
+The subsystem contains an SMS Manager class `\core_sms\manager` which facilitates the actions performed by the API.
+
+Some of the actions made possible are:
+
+- Sending messages
+- Fetching messages
+- Checking the status of a message
+- Getting SMS gateways.
+
+Currently, the design of the SMS API features the following plugin types:
+
+- [SMS gateway](/apis/plugintypes/sms/index.md)
 
 ## Sending an SMS
 
@@ -20,12 +34,13 @@ $message = \core\di::get(\core_sms\manager::class)
         recipientuserid: $user->id,
         issensitive: false,
         async: false,
+        gatewayid: 22,
     );
 ```
 
 :::info Message lengths
 
-A single SMS sent by the API may consist of up to 480 UTF-8 characters. It is up to the message _gateway_ plugin to determine how this message is sent to the recipient.
+A single SMS sent by the API may consist of up to 480 UTF-8 characters. It is up to the message _gateway plugin_ to determine how this message is sent to the recipient.
 
 Any message longer than the maximum length will be immediately rejected.
 
@@ -122,3 +137,47 @@ graph TD
         GQ --> |Gateway failed to send the message| GF
     end
 ```
+
+## Getting SMS gateways
+
+[SMS gateways](/apis/plugintypes/sms/index.md) are plugins that provide a way to interface with external SMS providers.
+Once a gateway is configured, any component implementing the SMS API can get a list of gateways.
+
+```php title="Getting the list of enabled gateways"
+$manager = \core\di::get(\core_sms\manager::class);
+$gatewayrecords = $manager->get_gateway_records();
+
+// It is also possible to filter the request.
+$gatewayrecords = $manager->get_gateway_records(['id' => $id]);
+
+// To get all the enabled gateway instances.
+$gatewayrecords = $manager->get_enabled_gateway_instances();
+```
+
+## Important hooks
+
+The SMS API dispatches some [hooks](/apis/core/hooks/index.md) which should be considered when implemented by a plugin/component.
+
+- before_gateway_deleted
+- before_gateway_disabled
+
+Before deleting or disabling an [SMS gateways](/apis/plugintypes/sms/index.md), these two hooks are dispatched from the SMS API.
+This allows components that are actively using that gateway to stop the action, or do necessary cleanup.
+Listening to these hooks is crucial to avoid data loss or accidental deletion when disabling an active gateway.
+
+```php title="Implement the hooks to check for usage before deletion or deactivation"
+
+public static function check_gateway_usage_in_example_plugin(
+    before_gateway_deleted|before_gateway_disabled $hook,
+): void {
+    try {
+        $smsgatewayid = (int)get_config('example_plugin', 'smsgateway');
+        if ($smsgatewayid && $smsgatewayid === (int)$hook->gateway->id) {
+            $hook->stop_propagation();
+        }
+    } catch (\dml_exception $exception) {
+        $hook->stop_propagation();
+    }
+}
+
+```