[docs] Add documentation for new SMS API

Author: andrewnicols

docs/apis/subsystems/sms/index.md

@@ -0,0 +1,124 @@
+---
+title: SMS API
+---
+
+<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.
+
+## Sending an SMS
+
+Messages can be sent using the `send()` method of the SMS Manager class, which should be fetched using Dependency Injection, for example:
+
+```php title="Sending a message"
+$message = \core\di::get(\core_sms\manager::class)
+    ->send(
+        recipientnumber: '+61987654321',
+        content: 'This is the content of the message',
+        component: 'mod_example',
+        messagetype: 'demonstrationmessage',
+        recipientuserid: $user->id,
+        issensitive: false,
+        async: false,
+    );
+```
+
+:::info Message lengths
+
+A single SMS sent by the API may consist of up to 480 UTF-8 characters. It is up to the message _gateway_ plugin to determine how this message is sent to the recipient.
+
+Any message longer than the maximum length will be immediately rejected.
+
+:::
+
+### Sending messages containing sensitive information
+
+When sending a message containing something like a 2FA login token, you should make use of the `issensitive` flag.
+
+Passing this flag prevents the SMS subsystem from storing the content of the message in the message log.
+
+The `send()` method return an instance of `\core_sms\message` which can be used to check on the message status.
+
+## Fetching messages
+
+Every sent message is stored in the database for subsequent reporting, and to check statuses.
+
+Messages can be fetched from the database by calling the `\core_sms\manager::get_message()` and `\core_sms\manager::get_messages()` methods and supplying a filter.
+
+```php title="Fetching messages"
+$message = \core\di::get(\core_sms\manager::class)
+    ->get_message(['id' => $id]);
+
+$messages = \core\di::get(\core_sms\manager::class)
+    ->get_messages(['recipientuserid' => $userid]);
+```
+
+:::note Sensitive content
+
+If the message was sent with the `issensitive` flag the message body will not be stored.
+
+:::
+
+## Checking the status of a message
+
+Once a message is sent, a status is recorded against it. This can be used to determine whether the message was sent successfully.
+
+:::info
+
+The level of status information available will depend on individual message gateways and recipient regions. In some regions delivery status may be available, but not in others.
+
+:::
+
+Message status can be checked using the `\core_sms\message::$status` property.
+
+Statuses are represented by a PHP Enum object with each status having a translatable description, and methods to determine whether the message was sent, is failed, or still in-progress.
+
+```php title="Checking the status of a message"
+$message = \core\di::get(\core_sms\manager::class)
+    ->get_message(['id' => $id]);
+
+// Check if the message is failed.
+$message->is_failed();
+
+// Check if the message is still in transit.
+$message->is_in_progress();
+
+// Check if the message is sent.
+$message->is_sent();
+
+// Get the description of the state.
+$message->description();
+```
+
+```mermaid
+graph TD
+
+    classDef failed fill:#f00,color:white,font-weight:bold,stroke:yellow
+    classDef inprogress fill:orange
+    classDef success fill:green,color:white,font-weight:bold
+
+    unknown["UNKNOWN"]
+    MOS["MESSAGE_OVER_SIZE"]:::failed
+    GNA["GATEWAY_NOT_AVAILABLE"]:::failed
+    GQ["GATEWAY_QUEUED"]:::inprogress
+    GS["GATEWAY_SENT"]:::success
+    GF["GATEWAY_FAILED"]:::failed
+    GR["GATEWAY_REJECTED"]:::failed
+    MLC{Message length check}
+    GWSEL{Gateway selection}
+
+    direction TB
+    start[/Start/] --> |Initial state| unknown
+    unknown --> |Initial message checks| MLC
+    MLC --> |Message over length| MOS
+    MLC --> |Message within limits| GWSEL
+
+    GWSEL --> |No gateway available to send this message| GNA
+    GWSEL --> |Message passed to Gateway| Gateway
+
+    subgraph Gateway
+        GQ --> |The gateway rejected the message| GR
+        GQ --> |Sent to recipient by Gateway| GS
+        GQ --> |Gateway failed to send the message| GF
+    end
+```

docs/devupdate.md

@@ -47,6 +47,10 @@ Please note that the same limitations regarding access to the Database, Session,
 
 :::
 
+### SMS API
+
+A new SMS API was introduced. See the [SMS API documentation](./apis/subsystems/sms/index.md) for more information.
+
 ## Course
 
 ### Reset course page