Fix follower handling

src/main/java/org/operaton/fitpub/model/entity/Follow.java

@@ -31,13 +31,22 @@ public class Follow {
 
     /**
      * The local user who is following.
+     * NULL if this is a remote user following a local user.
      */
-    @Column(name = "follower_id", nullable = false)
+    @Column(name = "follower_id")
     private UUID followerId;
 
     /**
-     * The ActivityPub actor URI being followed (local or remote).
+     * The remote actor URI of the follower (for remote-to-local follows).
      * Example: https://mastodon.social/users/alice
+     * NULL if followerId is set (local follower).
+     */
+    @Column(name = "remote_actor_uri", length = 512)
+    private String remoteActorUri;
+
+    /**
+     * The ActivityPub actor URI being followed (local or remote).
+     * Example: https://example.com/users/bob
      */
     @Column(name = "following_actor_uri", nullable = false, length = 512)
     private String followingActorUri;

src/main/java/org/operaton/fitpub/service/FederationService.java

@@ -128,7 +128,14 @@ public class FederationService {
     @Transactional
     public void sendAcceptActivity(Follow follow, User localUser) {
         try {
-            RemoteActor remoteActor = fetchRemoteActor(follow.getFollowingActorUri());
+            // Get the remote actor who sent the follow request
+            String remoteActorUri = follow.getRemoteActorUri();
+            if (remoteActorUri == null) {
+                log.error("Cannot send Accept: Follow has no remote actor URI");
+                return;
+            }
+
+            RemoteActor remoteActor = fetchRemoteActor(remoteActorUri);
 
             String acceptId = baseUrl + "/activities/" + UUID.randomUUID();
             String actorUri = baseUrl + "/users/" + localUser.getUsername();

src/main/java/org/operaton/fitpub/service/InboxProcessor.java

@@ -95,6 +95,7 @@ public class InboxProcessor {
             // Note: We're storing it from the perspective of "who is following whom"
             Follow follow = Follow.builder()
                 .followerId(null) // Remote actor, so no local user ID
+                .remoteActorUri(actor) // The remote actor who is following
                 .followingActorUri(expectedObjectUri) // The local user being followed
                 .status(Follow.FollowStatus.ACCEPTED) // Auto-accept for now
                 .activityId(activityId)

src/main/resources/db/migration/V8__add_remote_actor_uri_to_follows.sql

@@ -0,0 +1,19 @@
+-- Migration V8: Add remote_actor_uri column to follows table
+
+-- Add the column
+ALTER TABLE follows ADD COLUMN remote_actor_uri VARCHAR(512);
+
+-- Add index for remote_actor_uri
+CREATE INDEX idx_follows_remote_actor_uri ON follows(remote_actor_uri) WHERE remote_actor_uri IS NOT NULL;
+
+-- Update the constraint to allow either follower_id OR remote_actor_uri
+ALTER TABLE follows ALTER COLUMN follower_id DROP NOT NULL;
+
+-- Add check constraint to ensure either follower_id or remote_actor_uri is set (but not both)
+ALTER TABLE follows ADD CONSTRAINT chk_follows_actor CHECK (
+    (follower_id IS NOT NULL AND remote_actor_uri IS NULL) OR
+    (follower_id IS NULL AND remote_actor_uri IS NOT NULL)
+);
+
+-- Add comment for documentation
+COMMENT ON COLUMN follows.remote_actor_uri IS 'Remote ActivityPub actor URI for remote-to-local follows (null if local follower)';