fix: do not confuse renaming and joining a room

src/main/java/org/synyx/matrix/bot/internal/MatrixEventNotifier.java

@@ -20,6 +20,7 @@
 import org.synyx.matrix.bot.domain.MatrixTextMessage;
 import org.synyx.matrix.bot.domain.MatrixUserId;
 import org.synyx.matrix.bot.internal.api.dto.ClientEventDto;
+import org.synyx.matrix.bot.internal.api.dto.MembershipStateDto;
 import org.synyx.matrix.bot.internal.api.dto.StrippedStateEventDto;
 import org.synyx.matrix.bot.internal.api.dto.SyncResponseDto;
 import org.synyx.matrix.bot.internal.api.dto.event.MemberEventContentDto;
@@ -184,15 +185,29 @@ private void notifyAboutMemberEvent(MatrixState state, MatrixRoom room, ClientEv
       throw new RuntimeException(e);
     }
 
+    final var maybePreviousContent = getPreviousContent(event, MemberEventContentDto.class);
+
+    // > If not present, the user's previous membership must be assumed as leave.
+    final var previousMembership =
+        maybePreviousContent
+            .flatMap(
+                memberEventContentDto -> Optional.ofNullable(memberEventContentDto.membership()))
+            .filter(membershipStateDto -> membershipStateDto != MembershipStateDto.UNKNOWN)
+            .orElse(MembershipStateDto.LEAVE);
+
     final var sender = MatrixUserId.from(event.sender()).orElseThrow(IllegalStateException::new);
 
     try {
-      if (content.membership() == MemberEventContentDto.MembershipState.LEAVE
-          || content.membership() == MemberEventContentDto.MembershipState.BAN) {
-        consumer.onUserLeaveRoom(state, room, sender);
-      } else if (content.membership() == MemberEventContentDto.MembershipState.JOIN
+      if (content.membership() == MembershipStateDto.LEAVE
+          || content.membership() == MembershipStateDto.BAN) {
+        if (previousMembership == MembershipStateDto.JOIN) {
+          consumer.onUserLeaveRoom(state, room, sender);
+        }
+      } else if (content.membership() == MembershipStateDto.JOIN
           && !sender.equals(state.getOwnUserId())) {
-        consumer.onUserJoinRoom(state, room, sender);
+        if (previousMembership == MembershipStateDto.LEAVE) {
+          consumer.onUserJoinRoom(state, room, sender);
+        }
       }
     } catch (Exception e) {
       LOG.error("Uncaught exception when consuming member event", e);
@@ -213,7 +228,7 @@ private void notifyAboutInviteEvent(
       throw new RuntimeException(e);
     }
 
-    if (messageEventContent.membership() != MemberEventContentDto.MembershipState.INVITE) {
+    if (messageEventContent.membership() != MembershipStateDto.INVITE) {
       return;
     }
 
@@ -235,4 +250,22 @@ private void notifyAboutInviteEvent(
       LOG.error("Uncaught exception when consuming room invite", e);
     }
   }
+
+  private <T> Optional<T> getPreviousContent(ClientEventDto event, Class<T> clazz) {
+
+    final var maybeJson =
+        Optional.ofNullable(event)
+            .flatMap(clientEventDto -> Optional.ofNullable(clientEventDto.unsigned()))
+            .flatMap(unsignedDataDto -> Optional.ofNullable(unsignedDataDto.prevContent()));
+
+    if (maybeJson.isEmpty()) {
+      return Optional.empty();
+    }
+
+    try {
+      return Optional.ofNullable(objectMapper.treeToValue(maybeJson.get(), clazz));
+    } catch (JsonProcessingException e) {
+      throw new RuntimeException(e);
+    }
+  }
 }

src/main/java/org/synyx/matrix/bot/internal/MatrixStateSynchronizer.java

@@ -12,6 +12,7 @@
 import org.synyx.matrix.bot.domain.MatrixUser;
 import org.synyx.matrix.bot.domain.MatrixUserId;
 import org.synyx.matrix.bot.internal.api.dto.ClientEventDto;
+import org.synyx.matrix.bot.internal.api.dto.MembershipStateDto;
 import org.synyx.matrix.bot.internal.api.dto.StrippedStateEventDto;
 import org.synyx.matrix.bot.internal.api.dto.SyncResponseDto;
 import org.synyx.matrix.bot.internal.api.dto.event.CanonicalAliasEventContentDto;
@@ -156,13 +157,13 @@ private void handleCanonicalAliasEvent(MatrixRoom room, CanonicalAliasEventConte
   private void handleMemberEvent(
       MatrixRoom room, MatrixUserId sender, MemberEventContentDto content) {
 
-    if (content.membership() == MemberEventContentDto.MembershipState.JOIN) {
+    if (content.membership() == MembershipStateDto.JOIN) {
       final var user = getOrCreateUserInRoom(room, sender);
       if (content.displayName() != null) {
         user.setDisplayName(content.displayName());
       }
-    } else if (content.membership() == MemberEventContentDto.MembershipState.LEAVE
-        || content.membership() == MemberEventContentDto.MembershipState.BAN) {
+    } else if (content.membership() == MembershipStateDto.LEAVE
+        || content.membership() == MembershipStateDto.BAN) {
       room.getRoomUsers().removeIf(user -> user.getId().equals(sender));
     }
   }

src/main/java/org/synyx/matrix/bot/internal/api/dto/ClientEventDto.java

@@ -9,4 +9,5 @@ public record ClientEventDto(
     @JsonProperty("origin_server_ts") long originServerTs,
     String sender,
     @JsonProperty("state_key") String stateKey,
-    String type) {}
+    String type,
+    UnsignedDataDto unsigned) {}

src/main/java/org/synyx/matrix/bot/internal/api/dto/MembershipStateDto.java

@@ -0,0 +1,20 @@
+package org.synyx.matrix.bot.internal.api.dto;
+
+import com.fasterxml.jackson.annotation.JsonEnumDefaultValue;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public enum MembershipStateDto {
+  @JsonEnumDefaultValue
+  UNKNOWN,
+
+  @JsonProperty("invite")
+  INVITE,
+  @JsonProperty("join")
+  JOIN,
+  @JsonProperty("leave")
+  LEAVE,
+  @JsonProperty("ban")
+  BAN,
+  @JsonProperty("knock")
+  KNOCK
+}

src/main/java/org/synyx/matrix/bot/internal/api/dto/UnsignedDataDto.java

@@ -0,0 +1,10 @@
+package org.synyx.matrix.bot.internal.api.dto;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.JsonNode;
+
+public record UnsignedDataDto(
+    long age,
+    MembershipStateDto membership,
+    @JsonProperty("prev_content") JsonNode prevContent,
+    @JsonProperty("transaction_id") String transactionId) {}

src/main/java/org/synyx/matrix/bot/internal/api/dto/event/MemberEventContentDto.java

@@ -1,26 +1,10 @@
 package org.synyx.matrix.bot.internal.api.dto.event;
 
-import com.fasterxml.jackson.annotation.JsonEnumDefaultValue;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import org.synyx.matrix.bot.internal.api.dto.MembershipStateDto;
 
 public record MemberEventContentDto(
-    @JsonProperty("displayname") String displayName, MembershipState membership) {
+    @JsonProperty("displayname") String displayName, MembershipStateDto membership) {
 
   public static final String TYPE = "m.room.member";
-
-  public enum MembershipState {
-    @JsonEnumDefaultValue
-    UNKNOWN,
-
-    @JsonProperty("invite")
-    INVITE,
-    @JsonProperty("join")
-    JOIN,
-    @JsonProperty("leave")
-    LEAVE,
-    @JsonProperty("ban")
-    BAN,
-    @JsonProperty("knock")
-    KNOCK
-  }
 }