added implementation

7 files changed, 258 insertions, 4 deletions

diff --git a/src/main/java/eu/ortlepp/notificationsender/NotificationHandler.java b/src/main/java/eu/ortlepp/notificationsender/NotificationHandler.java
index 43e1aa9..17b4a46 100644
--- a/src/main/java/eu/ortlepp/notificationsender/NotificationHandler.java
+++ b/src/main/java/eu/ortlepp/notificationsender/NotificationHandler.java
@@ -1,12 +1,97 @@
 package eu.ortlepp.notificationsender;
 
 import com.amazonaws.services.lambda.runtime.Context;
+import com.amazonaws.services.lambda.runtime.LambdaLogger;
 import com.amazonaws.services.lambda.runtime.RequestHandler;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import eu.ortlepp.notificationsender.model.Notifications;
+import eu.ortlepp.notificationsender.model.Response;
+import eu.ortlepp.notificationsender.model.Status;
+import eu.ortlepp.notificationsender.service.NotificationSender;
+import eu.ortlepp.notificationsender.service.SnsNotificationSender;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
 
-public class NotificationHandler implements RequestHandler<String, String> {
+/**
+ * AWS Lambda implementation.
+ */
+public class NotificationHandler implements RequestHandler<Map<String, Object>, Response> {
 
-  public String handleRequest(String event, Context context) {
-    return event.toLowerCase();
+  private LambdaLogger logger;
+
+  private NotificationSender sender;
+
+
+  /**
+   * Standard constructor for AWS runtime. Uses default NotificationSender implementation.
+   */
+  public NotificationHandler() {
+    this.sender = null;
+  }
+
+
+  /**
+   * Constructor with custom NotificationSender implementation. Mainly for testing purposes.
+   *
+   * @param sender A custom NotificationSender
+   */
+  public NotificationHandler(final NotificationSender sender) {
+    this.sender = sender;
+  }
+
+
+  /**
+   * Constructor with custom NotificationSender and Context implementation.
+   * Mainly for testing purposes.
+   *
+   * @param sender A custom NotificationSender
+   * @param context A custom Context (to initialize the build-in logger)
+   */
+  public NotificationHandler(final NotificationSender sender, final Context context) {
+    this.sender = sender;
+    this.logger = context.getLogger();
+  }
+
+
+  /**
+   * The AWS Lambda handler; executes the Lambda functionality.
+   *
+   * @param event The incoming event which triggered the Lambda
+   * @param context The context of the Lambda execution
+   * @return The final status of the execution
+   */
+  public Response handleRequest(final Map<String, Object> event, final Context context) {
+    logger = context.getLogger();
+    if (sender == null) {
+      sender = new SnsNotificationSender(logger);
+    }
+
+    List<String> notifications = extractNotifications(event.get("body"));
+    if (!notifications.isEmpty() && sender.sendNotifications(notifications)) {
+      return new Response(Status.SUCCESS);
+    }
+    return new Response(Status.FAILED);
+  }
+
+
+  /**
+   * Extract the notifications from the input JSON.
+   *
+   * @param body The input JSON
+   * @return The extracted messages; empty list if an error occurred while parsing the JSON
+   */
+  protected List<String> extractNotifications(final Object body) {
+    try {
+      Notifications notifications =
+          new ObjectMapper().readValue(body.toString(), Notifications.class);
+      return Arrays.asList(notifications.messages());
+    } catch (JsonProcessingException ex) {
+      logger.log("parsing input JSON failed : " + ex.getMessage());
+      return new ArrayList<>();
+    }
   }
 
-}
\ No newline at end of file
+}
diff --git a/src/main/java/eu/ortlepp/notificationsender/model/Notifications.java b/src/main/java/eu/ortlepp/notificationsender/model/Notifications.java
new file mode 100644
index 0000000..65f7620
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/model/Notifications.java
@@ -0,0 +1,8 @@
+package eu.ortlepp.notificationsender.model;
+
+/**
+ * The expected input data of the Lambda.
+ *
+ * @param messages The messages / notifications
+ */
+public record Notifications(String[] messages) {}
diff --git a/src/main/java/eu/ortlepp/notificationsender/model/Response.java b/src/main/java/eu/ortlepp/notificationsender/model/Response.java
new file mode 100644
index 0000000..d931bed
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/model/Response.java
@@ -0,0 +1,8 @@
+package eu.ortlepp.notificationsender.model;
+
+/**
+ * The response of a Lambda execution.
+ *
+ * @param status The final execution status of the Lambda
+ */
+public record Response(Status status) {}
diff --git a/src/main/java/eu/ortlepp/notificationsender/model/Status.java b/src/main/java/eu/ortlepp/notificationsender/model/Status.java
new file mode 100644
index 0000000..caeb0cd
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/model/Status.java
@@ -0,0 +1,9 @@
+package eu.ortlepp.notificationsender.model;
+
+/**
+ * The status of a Lambda execution, shown in the response.
+ */
+public enum Status {
+  SUCCESS,
+  FAILED
+}
diff --git a/src/main/java/eu/ortlepp/notificationsender/service/NotificationSender.java b/src/main/java/eu/ortlepp/notificationsender/service/NotificationSender.java
new file mode 100644
index 0000000..8c39c72
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/service/NotificationSender.java
@@ -0,0 +1,41 @@
+package eu.ortlepp.notificationsender.service;
+
+import java.util.List;
+
+/**
+ * Interface for notification senders.
+ */
+public interface NotificationSender {
+
+  /**
+   * Send a list of notifications.
+   *
+   * @param notifications The notifications to send
+   * @return The result of the sending; true = successful, false = error occurred
+   */
+  boolean sendNotifications(final List<String> notifications);
+
+
+  /**
+   * Format notifications for sending.
+   * If only one notification is passed, it is returned as is.
+   * If multiple notifications are passed, a numbered list of notifications is returned.
+   *
+   * @param notifications The notifications to format
+   * @return The formatted notifications
+   */
+  default String formatNotifications(final List<String> notifications) {
+    if (notifications.size() == 1) {
+      return notifications.getFirst() + "\n\n";
+    }
+    StringBuilder builder = new StringBuilder();
+    for (int i = 0; i < notifications.size(); i++) {
+      builder.append(i + 1)
+              .append(". Notification:\n")
+              .append(notifications.get(i))
+              .append("\n\n");
+    }
+    return builder.toString();
+  }
+
+}
diff --git a/src/main/java/eu/ortlepp/notificationsender/service/SnsNotificationSender.java b/src/main/java/eu/ortlepp/notificationsender/service/SnsNotificationSender.java
new file mode 100644
index 0000000..958365a
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/service/SnsNotificationSender.java
@@ -0,0 +1,63 @@
+package eu.ortlepp.notificationsender.service;
+
+import com.amazonaws.services.lambda.runtime.LambdaLogger;
+import eu.ortlepp.notificationsender.util.Config;
+import java.util.List;
+import software.amazon.awssdk.http.HttpStatusCode;
+import software.amazon.awssdk.services.sns.SnsClient;
+import software.amazon.awssdk.services.sns.model.PublishRequest;
+import software.amazon.awssdk.services.sns.model.PublishResponse;
+import software.amazon.awssdk.services.sns.model.SnsException;
+
+/**
+ * A notification sender for Amazon SNS.
+ */
+public class SnsNotificationSender implements NotificationSender {
+
+  private final LambdaLogger logger;
+
+
+  /**
+   * Constructor to initialize the sender.
+   *
+   * @param logger The logger of the AWS Lambda
+   */
+  public SnsNotificationSender(final LambdaLogger logger) {
+    this.logger = logger;
+  }
+
+
+  /**
+   * Send a list of notifications to the configured SNS topic.
+   * All notifications are combined into a single message.
+   *
+   * @param notifications The notifications to send
+   * @return The result of the sending; true = successful, false = error occurred
+   */
+  @Override
+  public boolean sendNotifications(final List<String> notifications) {
+    String notification = formatNotifications(notifications);
+
+    try (SnsClient snsClient = SnsClient.builder().region(Config.REGION).build()) {
+      PublishRequest request =
+          PublishRequest.builder().message(notification).topicArn(Config.ARN).build();
+      PublishResponse result = snsClient.publish(request);
+      int resultStatusCode = result.sdkHttpResponse().statusCode();
+
+      if (resultStatusCode ==  HttpStatusCode.OK) {
+        logger.log("notification sent successfully");
+        return true;
+      }
+
+      logger.log("sending notification failed with status " + resultStatusCode);
+      logger.log("failed message was " + notification);
+      return false;
+
+    } catch (SnsException ex) {
+      logger.log("sending notification failed: " + ex.getMessage());
+      logger.log("failed message was " + notification);
+      return false;
+    }
+  }
+
+}
diff --git a/src/main/java/eu/ortlepp/notificationsender/util/Config.java b/src/main/java/eu/ortlepp/notificationsender/util/Config.java
new file mode 100644
index 0000000..139ea24
--- /dev/null
+++ b/src/main/java/eu/ortlepp/notificationsender/util/Config.java
@@ -0,0 +1,40 @@
+package eu.ortlepp.notificationsender.util;
+
+import software.amazon.awssdk.regions.Region;
+
+/**
+ * Required configuration values read from environment variables.
+ */
+public final class Config {
+
+  /**
+   * The region of the SNS topic. The Name of the environment variable is REGION.
+   * Value example: eu-central-1
+   */
+  public static final Region REGION;
+
+  /**
+   * The ARN of the SNS topic. The Name of the environment variable is ARN.
+   * Value example: arn:aws:sns:eu-central-1:123456789:Topic-Name
+   */
+  public static final String ARN;
+
+
+  static {
+    REGION = Region.of(getEnvVar("REGION"));
+    ARN = getEnvVar("ARN");
+  }
+
+
+  private static String getEnvVar(final String key) {
+    String value =  System.getenv(key);
+    if (value == null) {
+      throw new RuntimeException("environment variable not set: " + key);
+    }
+    return value;
+  }
+
+
+  private Config() {}
+
+}