Add a built-in way to send notifications

Create a provider pattern for sending notifications (T383992).
There is no base notifications handler in core; they can only
be provided by extensions.

A handler in the Echo extension, compatible with the existing
Echo notifications system, will be implemented in T383993.

Co-Authored-By: Piotr Miazga <pmiazga@wikimedia.org>
Bug: T383992
Change-Id: I16b309935c3d29c3cde4459b5e36abce063a8534

1 files changed, 40 insertions, 0 deletions

diff --git a/includes/Notification/RecipientSet.php b/includes/Notification/RecipientSet.php
new file mode 100644
index 000000000000..b8f2895fd5e9
--- /dev/null
+++ b/includes/Notification/RecipientSet.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace MediaWiki\Notification;
+
+use ArrayIterator;
+use IteratorAggregate;
+use MediaWiki\User\UserIdentity;
+use Wikimedia\Assert\Assert;
+
+/**
+ * @since 1.44
+ * @unstable
+ */
+class RecipientSet implements IteratorAggregate {
+
+	/**
+	 * @var UserIdentity[]
+	 */
+	private array $recipients;
+
+	/**
+	 * @param UserIdentity|UserIdentity[] $recipients
+	 */
+	public function __construct( $recipients ) {
+		if ( !is_array( $recipients ) ) {
+			$recipients = [ $recipients ];
+		}
+		Assert::parameterElementType( UserIdentity::class, $recipients, '$recipients' );
+		$this->recipients = $recipients;
+	}
+
+	/** @return UserIdentity[] */
+	public function getRecipients(): array {
+		return $this->recipients;
+	}
+
+	public function getIterator(): ArrayIterator {
+		return new ArrayIterator( $this->recipients );
+	}
+}