From 50b47b707ccc4f0d7ed3887f08f0a88a39686f29 Mon Sep 17 00:00:00 2001
From: Sascha Szott <szott@gmx.de>
Date: Tue, 14 Nov 2023 20:36:52 +0100
Subject: [PATCH] subscription email: do not send email if nothing has changed
 (#8981)

* improved subscriptions email template

* do not send emails without content

* fixed coding style violations

* removed unnecessary isEmpty check as suggested by reviewer

* moved null check on indexableObjects in generateBodyMail

* fixed unhandled IOException

* fixed typo in bodyCommunities

* do not use != to compare strings

* fixed improper handling of empty list
---
 .../subscriptions/ContentGenerator.java       | 34 +++++++++++--------
 dspace/config/emails/subscriptions_content    | 16 +++++----
 2 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/dspace-api/src/main/java/org/dspace/subscriptions/ContentGenerator.java b/dspace-api/src/main/java/org/dspace/subscriptions/ContentGenerator.java
index a913f2504a5..c3035614343 100644
--- a/dspace-api/src/main/java/org/dspace/subscriptions/ContentGenerator.java
+++ b/dspace-api/src/main/java/org/dspace/subscriptions/ContentGenerator.java
@@ -56,8 +56,16 @@ public void notifyForSubscriptions(Context context, EPerson ePerson,
                 Locale supportedLocale = I18nUtil.getEPersonLocale(ePerson);
                 Email email = Email.getEmail(I18nUtil.getEmailFilename(supportedLocale, "subscriptions_content"));
                 email.addRecipient(ePerson.getEmail());
-                email.addArgument(generateBodyMail(context, indexableComm));
-                email.addArgument(generateBodyMail(context, indexableColl));
+
+                String bodyCommunities = generateBodyMail(context, indexableComm);
+                String bodyCollections = generateBodyMail(context, indexableColl);
+                if (bodyCommunities.equals(EMPTY) && bodyCollections.equals(EMPTY)) {
+                    log.debug("subscription(s) of eperson {} do(es) not match any new items: nothing to send" +
+                            " - exit silently", ePerson::getID);
+                    return;
+                }
+                email.addArgument(bodyCommunities);
+                email.addArgument(bodyCollections);
                 email.send();
             }
         } catch (Exception e) {
@@ -67,21 +75,19 @@ public void notifyForSubscriptions(Context context, EPerson ePerson,
     }
 
     private String generateBodyMail(Context context, List<IndexableObject> indexableObjects) {
+        if (indexableObjects == null || indexableObjects.isEmpty()) {
+            return EMPTY;
+        }
         try {
             ByteArrayOutputStream out = new ByteArrayOutputStream();
             out.write("\n".getBytes(UTF_8));
-            if (indexableObjects.size() > 0) {
-                for (IndexableObject indexableObject : indexableObjects) {
-                    out.write("\n".getBytes(UTF_8));
-                    Item item = (Item) indexableObject.getIndexedObject();
-                    String entityType = itemService.getEntityTypeLabel(item);
-                    Optional.ofNullable(entityType2Disseminator.get(entityType))
-                            .orElseGet(() -> entityType2Disseminator.get("Item"))
-                            .disseminate(context, item, out);
-                }
-                return out.toString();
-            } else {
-                out.write("No items".getBytes(UTF_8));
+            for (IndexableObject indexableObject : indexableObjects) {
+                out.write("\n".getBytes(UTF_8));
+                Item item = (Item) indexableObject.getIndexedObject();
+                String entityType = itemService.getEntityTypeLabel(item);
+                Optional.ofNullable(entityType2Disseminator.get(entityType))
+                        .orElseGet(() -> entityType2Disseminator.get("Item"))
+                        .disseminate(context, item, out);
             }
             return out.toString();
         } catch (Exception e) {
diff --git a/dspace/config/emails/subscriptions_content b/dspace/config/emails/subscriptions_content
index a330c595371..9b8c91e559d 100644
--- a/dspace/config/emails/subscriptions_content
+++ b/dspace/config/emails/subscriptions_content
@@ -2,15 +2,17 @@
 ##
 ## Parameters: {0} Collections updates
 ##             {1} Communities updates
-#set($subject = "${config.get('dspace.name')} Subscription")
-
+#set($subject = "${config.get('dspace.name')} Subscriptions")
 This email is sent from ${config.get('dspace.name')} based on the chosen subscription preferences.
 
-Communities
------------
+#if( not( "$params[0]" == "" ))
+Community Subscriptions:
+------------------------
 List of changed items : ${params[0]}
 
-Collections
------------
+#end
+#if( not( "$params[1]" == "" ))
+Collection Subscriptions:
+-------------------------
 List of changed items : ${params[1]}
-
+#end