feat(notifications): Implement Notification & Event Delivery API

src/notifications/channels/channel.interface.ts

@@ -1,11 +1,35 @@
-import { Notification } from '../entities/notification.entity';
+import { EventType } from '../enums/event-type.enum';
+import { DeliveryChannel } from '../interfaces/notification.types';
+
+export interface RenderedNotificationPayload {
+  userId: string;
+  channel: DeliveryChannel;
+  rendered: {
+    title?: string;
+    subject?: string;
+    body: string;
+    html?: string;
+    markdown?: string;
+    actionUrl?: string;
+  };
+  eventType: EventType;
+  metadata: Record<string, any>;
+}
 
 export interface ChannelDeliveryResult {
   success: boolean;
   error?: string;
   deliveryTimestamp?: Date;
+  channelMessageId?: string; // Channel-specific message ID for tracking
 }
 
+/**
+ * NotificationChannel
+ * 
+ * Base interface for all notification delivery channels.
+ * Implementations handle the specifics of their delivery mechanism
+ * (email, push, webhook, etc.) while conforming to this contract.
+ */
 export interface NotificationChannel {
   /**
    * Unique identifier for the channel
@@ -19,11 +43,23 @@ export interface NotificationChannel {
 
   /**
    * Send a notification through this channel
+   * @param payload Rendered notification with user context and metadata
+   * @returns Delivery result with success status and optional error message
    */
-  send(notification: Notification): Promise<ChannelDeliveryResult>;
+  send(payload: RenderedNotificationPayload): Promise<ChannelDeliveryResult>;
 
   /**
    * Validate user configuration for this channel
+   * @returns { valid: boolean, errors: string[] }
    */
   validateConfig(userId: string): Promise<{ valid: boolean; errors: string[] }>;
+
+  /**
+   * Optional: Get channel-specific metrics
+   */
+  getMetrics?(): Promise<{
+    successCount: number;
+    failureCount: number;
+    averageDeliveryTimeMs: number;
+  }>;
 }