Rework and unify the system messages.

// FREEBIE

src/Contacts/Threads/TSContactThread.m

@@ -20,6 +20,8 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)initWithContactId:(NSString *)contactId {
     NSString *uniqueIdentifier = [[self class] threadIdFromContactId:contactId];
 
+    OWSAssert(contactId.length > 0);
+
     self = [super initWithUniqueId:uniqueIdentifier];
 
     return self;
@@ -29,7 +31,8 @@ NS_ASSUME_NONNULL_BEGIN
                                    transaction:(YapDatabaseReadWriteTransaction *)transaction
                                          relay:(nullable NSString *)relay
 {
-    OWSAssert(contactId);
+    OWSAssert(contactId.length > 0);
+
     SignalRecipient *recipient =
         [SignalRecipient recipientWithTextSecureIdentifier:contactId withTransaction:transaction];
 
@@ -55,6 +58,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (instancetype)getOrCreateThreadWithContactId:(NSString *)contactId
                                    transaction:(YapDatabaseReadWriteTransaction *)transaction {
+    OWSAssert(contactId.length > 0);
+
     TSContactThread *thread =
         [self fetchObjectWithUniqueID:[self threadIdFromContactId:contactId] transaction:transaction];
 
@@ -68,6 +73,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (instancetype)getOrCreateThreadWithContactId:(NSString *)contactId
 {
+    OWSAssert(contactId.length > 0);
+
     __block TSContactThread *thread;
     [[self dbConnection] readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
         thread = [self getOrCreateThreadWithContactId:contactId transaction:transaction];

src/Contacts/Threads/TSGroupThread.m

@@ -18,6 +18,13 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)initWithGroupModel:(TSGroupModel *)groupModel
 {
+    OWSAssert(groupModel);
+    OWSAssert(groupModel.groupId.length > 0);
+    OWSAssert(groupModel.groupMemberIds.count > 0);
+    for (NSString *recipientId in groupModel.groupMemberIds) {
+        OWSAssert(recipientId.length > 0);
+    }
+
     NSString *uniqueIdentifier = [[self class] threadIdFromGroupId:groupModel.groupId];
     self = [super initWithUniqueId:uniqueIdentifier];
     if (!self) {
@@ -31,6 +38,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)initWithGroupIdData:(NSData *)groupId
 {
+    OWSAssert(groupId.length > 0);
+
     TSGroupModel *groupModel = [[TSGroupModel alloc] initWithTitle:nil memberIds:nil image:nil groupId:groupId];
 
     self = [self initWithGroupModel:groupModel];
@@ -43,11 +52,16 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (instancetype)threadWithGroupModel:(TSGroupModel *)groupModel transaction:(YapDatabaseReadTransaction *)transaction
 {
+    OWSAssert(groupModel);
+    OWSAssert(groupModel.groupId.length > 0);
+
     return [self fetchObjectWithUniqueID:[self threadIdFromGroupId:groupModel.groupId] transaction:transaction];
 }
 
 + (instancetype)getOrCreateThreadWithGroupIdData:(NSData *)groupId
 {
+    OWSAssert(groupId.length > 0);
+
     TSGroupThread *thread = [self fetchObjectWithUniqueID:[self threadIdFromGroupId:groupId]];
     if (!thread) {
         thread = [[self alloc] initWithGroupIdData:groupId];
@@ -58,6 +72,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (instancetype)getOrCreateThreadWithGroupModel:(TSGroupModel *)groupModel
                                     transaction:(YapDatabaseReadWriteTransaction *)transaction {
+    OWSAssert(groupModel);
+    OWSAssert(groupModel.groupId.length > 0);
+
     TSGroupThread *thread =
         [self fetchObjectWithUniqueID:[self threadIdFromGroupId:groupModel.groupId] transaction:transaction];
 
@@ -70,6 +87,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (instancetype)getOrCreateThreadWithGroupModel:(TSGroupModel *)groupModel
 {
+    OWSAssert(groupModel);
+    OWSAssert(groupModel.groupId.length > 0);
+
     __block TSGroupThread *thread;
     [[self dbConnection] readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
         thread = [self getOrCreateThreadWithGroupModel:groupModel transaction:transaction];
@@ -79,11 +99,15 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (NSString *)threadIdFromGroupId:(NSData *)groupId
 {
+    OWSAssert(groupId.length > 0);
+
     return [TSGroupThreadPrefix stringByAppendingString:[groupId base64EncodedString]];
 }
 
 + (NSData *)groupIdFromThreadId:(NSString *)threadId
 {
+    OWSAssert(threadId.length > 0);
+
     return [NSData dataFromBase64String:[threadId substringWithRange:NSMakeRange(1, threadId.length - 1)]];
 }
 

src/Messages/Interactions/TSErrorMessage.h

@@ -16,7 +16,7 @@ typedef NS_ENUM(int32_t, TSErrorMessageType) {
     TSErrorMessageInvalidKeyException,
     TSErrorMessageMissingKeyId, // unused
     TSErrorMessageInvalidMessage,
-    TSErrorMessageDuplicateMessage,
+    TSErrorMessageDuplicateMessage, // unused
     TSErrorMessageInvalidVersion,
     TSErrorMessageNonBlockingIdentityChange,
     TSErrorMessageUnknownContactBlockOffer,

src/Messages/Interactions/TSInfoMessage.h

@@ -12,6 +12,7 @@ NS_ASSUME_NONNULL_BEGIN
 typedef NS_ENUM(NSInteger, TSInfoMessageType) {
     TSInfoMessageTypeSessionDidEnd,
     TSInfoMessageUserNotRegistered,
+    // TSInfoMessageTypeUnsupportedMessage appears to be obsolete.
     TSInfoMessageTypeUnsupportedMessage,
     TSInfoMessageTypeGroupUpdate,
     TSInfoMessageTypeGroupQuit,