From fbee0cb995962656fb2d28f9f7305d5d2d17924a Mon Sep 17 00:00:00 2001
From: Oliver Browne <oliverbrowne627@gmail.com>
Date: Wed, 23 Oct 2024 11:43:32 +0300
Subject: [PATCH 1/3] fix: alias has user and previous swapped

---
 index.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index f8938c7..4ca18d2 100644
--- a/index.js
+++ b/index.js
@@ -174,8 +174,8 @@ async function onAlias(event, settings) {
             ...event,
             event: '$create_alias',
             properties: {
-                alias: event.previousId,
-                distinct_id: event.userId,
+                alias: event.userId,
+                distinct_id: event.previousId,
             },
         },
         settings

From 0854bcc52fac7a4144a82e8749db0e0a9b1fe14f Mon Sep 17 00:00:00 2001
From: Oliver Browne <oliverbrowne627@gmail.com>
Date: Wed, 23 Oct 2024 11:46:57 +0300
Subject: [PATCH 2/3] Update test.js

---
 test.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test.js b/test.js
index 102dfc4..66efc9e 100644
--- a/test.js
+++ b/test.js
@@ -270,8 +270,8 @@ describe('Segment Integration', () => {
                     segment_ip: '8.8.8.8',
                     segment_userAgent:
                         'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36',
-                    alias: '39239-239239-239239-23923',
-                    distinct_id: '507f191e81',
+                    alias: '507f191e81',
+                    distinct_id: '39239-239239-239239-23923',
                     $lib: 'Segment',
                 },
             })

From d205ddc61017c1c3cc4bbacf56aa308396b5b4a1 Mon Sep 17 00:00:00 2001
From: Oliver Browne <oliver@posthog.com>
Date: Wed, 23 Oct 2024 12:00:10 +0300
Subject: [PATCH 3/3] fix

---
 index.js | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 4ca18d2..6e438cd 100644
--- a/index.js
+++ b/index.js
@@ -68,6 +68,16 @@ async function onTrack(event, settings) {
         event.properties['$groups'] = { segment_group: event.context.groupId }
     }
 
+    // In alias cases, we set the distinct id explicitly and it has to be what's expected. In all other
+    // cases, we use the userId if it exists, otherwise the anonymousId.
+    let distinct_id = null;
+
+    if (event.event === '$create_alias') {
+        distinct_id = event.properties.distinct_id;
+    } else {
+        distinct_id = event.userId || event.anonymousId;
+    }
+
     const res = await fetch(endpoint, {
         body: JSON.stringify({
             uuid,
@@ -77,7 +87,7 @@ async function onTrack(event, settings) {
             properties: {
                 ...parseContext(event.context),
                 ...event.properties,
-                distinct_id: event.userId || event.anonymousId,
+                distinct_id: distinct_id,
                 $lib: 'Segment',
             },
         }),