TF-3697 Open specific thread detail email

lib/features/thread_detail/domain/state/get_emails_by_ids_state.dart

@@ -2,7 +2,14 @@ import 'package:core/presentation/state/failure.dart';
 import 'package:core/presentation/state/success.dart';
 import 'package:model/email/presentation_email.dart';
 
-class GettingEmailsByIds extends LoadingState {}
+class GettingEmailsByIds extends LoadingState {
+  GettingEmailsByIds({this.loadingIndex});
+
+  final int? loadingIndex;
+
+  @override
+  List<Object?> get props => [loadingIndex];
+}
 
 class GetEmailsByIdsSuccess extends UIState {
   GetEmailsByIdsSuccess(this.presentationEmails);

lib/features/thread_detail/domain/usecases/get_emails_by_ids_interactor.dart

@@ -22,6 +22,7 @@ class GetEmailsByIdsInteractor {
     AccountId accountId,
     List<EmailId> emailIds, {
     Properties? properties,
+    int? loadMoreIndex,
   }) async* {
     try {
       if (emailIds.length > 1 && (
@@ -31,7 +32,7 @@ class GetEmailsByIdsInteractor {
         throw ThreadDetailOverloadException();
       }
 
-      yield Right(GettingEmailsByIds());
+      yield Right(GettingEmailsByIds(loadingIndex: loadMoreIndex));
       final result = await _threadDetailRepository.getEmailsByIds(
         session,
         accountId,

lib/features/thread_detail/presentation/extension/get_thread_details_email_views.dart

@@ -1,4 +1,3 @@
-import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:model/email/email_action_type.dart';
 import 'package:model/extensions/presentation_email_extension.dart';
@@ -8,6 +7,8 @@ import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/load_more_thread_detail_emails.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/thread_detail_on_email_action_click.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/thread_detail_open_email_address_detail_action.dart';
+import 'package:tmail_ui_user/features/thread_detail/domain/state/get_emails_by_ids_state.dart';
+import 'package:tmail_ui_user/features/thread_detail/presentation/extension/thread_detail_load_more_segments.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/toggle_thread_detail_collape_expand.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_controller.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/widgets/thread_detail_collapsed_email.dart';
@@ -16,35 +17,29 @@ import 'package:tmail_ui_user/main/routes/route_navigation.dart';
 
 extension GetThreadDetailEmailViews on ThreadDetailController {
   List<Widget> getThreadDetailEmailViews() {
-    int? firstEmailNotLoadedIndex;
+    final loadMoreSegments = Map<LoadMoreIndex, LoadMoreCount>.from(this.loadMoreSegments);
-    if (emailsToLoadMoreCount > 0) {
-      final firstNotLoadedEmailId = emailIdsPresentation.entries.firstWhereOrNull(
-        (entry) => entry.value == null
-      )?.key;
-      if (firstNotLoadedEmailId == null) {
-        firstEmailNotLoadedIndex = -1;
-      } else {
-        firstEmailNotLoadedIndex = emailIdsPresentation
-          .keys
-          .toList()
-          .indexOf(firstNotLoadedEmailId);
-      }
-    }
 
     return emailIdsPresentation.entries.map((entry) {
       final emailId = entry.key;
       final presentationEmail = entry.value;
       final indexOfEmailId = emailIdsPresentation.keys.toList().indexOf(emailId);
       if (presentationEmail == null) {
-        if (indexOfEmailId != firstEmailNotLoadedIndex) {
+        if (loadMoreSegments[indexOfEmailId] == null) {
           return const SizedBox.shrink();
         }
 
         return ThreadDetailLoadMoreCircle(
-          count: emailsToLoadMoreCount,
+          count: loadMoreSegments[indexOfEmailId]!,
-          onTap: loadMoreThreadDetailEmails,
+          onTap: () => loadMoreThreadDetailEmails(
+            loadMoreIndex: indexOfEmailId,
+            loadMoreCount: loadMoreSegments[indexOfEmailId]!,
+          ),
           imagePaths: imagePaths,
-          isLoading: loadingThreadDetail,
+          isLoading: viewState.value.fold(
+            (failure) => false,
+            (success) => success is GettingEmailsByIds &&
+              success.loadingIndex == indexOfEmailId,
+          ),
         );
       }
 

lib/features/thread_detail/presentation/extension/handle_get_emails_by_ids_success.dart

@@ -13,6 +13,7 @@ extension HandleGetEmailsByIdsSuccess on ThreadDetailController {
       return;
     }
 
+    final selectedEmailId = mailboxDashBoardController.selectedEmail.value?.id;
     final isLoadMore = emailIdsPresentation.values.whereNotNull().isNotEmpty;
     final currentScrollPosition = scrollController?.position.pixels;
     final maxScrollExtent = scrollController?.position.maxScrollExtent;
@@ -23,12 +24,12 @@ extension HandleGetEmailsByIdsSuccess on ThreadDetailController {
     
     for (var presentationEmail in success.presentationEmails) {
       if (presentationEmail.id == null) continue;
-      if (presentationEmail.id == emailIdsPresentation.keys.last) {
+      if (presentationEmail.id == selectedEmailId) {
         EmailBindings(currentEmailId: presentationEmail.id).dependencies();
         currentExpandedEmailId.value = presentationEmail.id;
       }
       emailIdsPresentation[presentationEmail.id!] = presentationEmail.copyWith(
-        emailInThreadStatus: presentationEmail.id == emailIdsPresentation.keys.last
+        emailInThreadStatus: presentationEmail.id == selectedEmailId
           ? EmailInThreadStatus.expanded
           : EmailInThreadStatus.collapsed,
       );

lib/features/thread_detail/presentation/extension/initialize_thread_detail_emails.dart

@@ -7,9 +7,9 @@ import 'package:tmail_ui_user/features/thread_detail/presentation/utils/thread_d
 
 extension InitializeThreadDetailEmails on ThreadDetailController {
   void initializeThreadDetailEmails() {
-    final emailIdToLoadContent = emailIdsPresentation.keys.last;
+    final emailIdsToLoadMetaData = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
-    final emailIdsToLoadMetaData = ThreadDetailPresentationUtils.getEmailIdsToLoad(
+      emailIdsPresentation.keys.toList(),
-      Map.from(emailIdsPresentation)..remove(emailIdToLoadContent),
+      selectedEmailId: mailboxDashBoardController.selectedEmail.value?.id,
     );
 
     if (accountId == null || session == null) {
@@ -21,7 +21,7 @@ extension InitializeThreadDetailEmails on ThreadDetailController {
     consumeState(getEmailsByIdsInteractor.execute(
       session!,
       accountId!,
-      [...emailIdsToLoadMetaData, emailIdToLoadContent],
+      emailIdsToLoadMetaData,
       properties: EmailUtils.getPropertiesForEmailGetMethod(
         session!,
         accountId!,

lib/features/thread_detail/presentation/extension/load_more_thread_detail_emails.dart

@@ -1,3 +1,5 @@
+import 'dart:math';
+
 import 'package:dartz/dartz.dart';
 import 'package:tmail_ui_user/features/email/presentation/utils/email_utils.dart';
 import 'package:tmail_ui_user/features/home/data/exceptions/session_exceptions.dart';
@@ -6,7 +8,10 @@ import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_
 import 'package:tmail_ui_user/features/thread_detail/presentation/utils/thread_detail_presentation_utils.dart';
 
 extension LoadMoreThreadDetailEmails on ThreadDetailController {
-  void loadMoreThreadDetailEmails() {
+  void loadMoreThreadDetailEmails({
+    required int loadMoreIndex,
+    required int loadMoreCount,
+  }) {
     if (accountId == null || session == null) {
       consumeState(Stream.value(Left(GetEmailsByIdsFailure(
         exception: NotFoundSessionException(),
@@ -14,8 +19,21 @@ extension LoadMoreThreadDetailEmails on ThreadDetailController {
       return;
     }
 
-    final emailIdsToLoadMetaData = ThreadDetailPresentationUtils
+    final currentExpandedEmailIndex = currentExpandedEmailId.value == null
-      .getEmailIdsToLoad(emailIdsPresentation);
+      ? -1
+      : emailIdsPresentation.keys.toList().indexOf(currentExpandedEmailId.value!);
+    final loadMoreEmailIds = emailIdsPresentation.keys.toList().sublist(
+      loadMoreIndex,
+      min(
+        loadMoreIndex + loadMoreCount,
+        emailIdsPresentation.length,
+      ),
+    );
+
+    final emailIdsToLoadMetaData = ThreadDetailPresentationUtils.getLoadMoreEmailIds(
+      loadMoreEmailIds,
+      loadEmailsAfterSelectedEmail: loadMoreIndex > currentExpandedEmailIndex,
+    );
     if (emailIdsToLoadMetaData.isEmpty) {
       return;
     }
@@ -27,6 +45,7 @@ extension LoadMoreThreadDetailEmails on ThreadDetailController {
         session!,
         accountId!,
       ).union(additionalProperties),
+      loadMoreIndex: loadMoreIndex,
     ));
   }
 }

lib/features/thread_detail/presentation/extension/thread_detail_load_more_segments.dart

@@ -0,0 +1,33 @@
+import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_controller.dart';
+
+typedef LoadMoreIndex = int;
+typedef LoadMoreCount = int;
+typedef LoadMoreSegments = Map<LoadMoreIndex, LoadMoreCount>;
+
+extension ThreadDetailLoadMoreSegments on ThreadDetailController {
+  LoadMoreSegments get loadMoreSegments {
+    final loadMoreInfo = <LoadMoreIndex, LoadMoreCount>{};
+    int currentIndex = 0;
+    final emailIds = emailIdsPresentation.values.toList();
+
+    while (currentIndex < emailIdsPresentation.length) {
+      if (emailIds[currentIndex] == null) {
+        // Found start of a null segment
+        int segmentIndex = currentIndex;
+        int segmentCount = 0;
+        
+        // Count consecutive nulls
+        while (currentIndex < emailIdsPresentation.length &&
+              emailIds[currentIndex] == null) {
+          segmentCount++;
+          currentIndex++;
+        }
+        
+        loadMoreInfo[segmentIndex] = segmentCount;
+      } else {
+        currentIndex++;
+      }
+    }
+    return loadMoreInfo;
+  }
+}

lib/features/thread_detail/presentation/thread_detail_controller.dart

@@ -90,15 +90,6 @@ class ThreadDetailController extends BaseController {
     PresentationMailbox.roleSent,
   );
   String? get ownEmailAddress => session?.getOwnEmailAddress();
-  int get emailsToLoadMoreCount => emailIdsPresentation
-    .values
-    .where((email) => email == null)
-    .length;
-  bool get loadingThreadDetail => viewState.value.fold(
-    (failure) => false,
-    (success) => success is GettingThreadById
-      || success is GettingEmailsByIds,
-  );
   bool get isSearchRunning {
     final isWebSearchRunning = mailboxDashBoardController
       .searchController

lib/features/thread_detail/presentation/utils/thread_detail_presentation_utils.dart

@@ -2,7 +2,6 @@ import 'dart:math';
 
 import 'package:flutter/material.dart';
 import 'package:jmap_dart_client/jmap/mail/email/email.dart';
-import 'package:model/email/presentation_email.dart';
 
 class ThreadDetailPresentationUtils {
   const ThreadDetailPresentationUtils._();
@@ -11,29 +10,48 @@ class ThreadDetailPresentationUtils {
   static const _defaultLoadSize = 20;
 
   @visibleForTesting
-  static get initialLoadSize => _initialLoadSize;
+  static int get defaultLoadSize => _defaultLoadSize;
-  @visibleForTesting
-  static get defaultLoadSize => _defaultLoadSize;
 
-  static List<EmailId> getEmailIdsToLoad(
+  static List<EmailId> getFirstLoadEmailIds(
-    Map<EmailId, PresentationEmail?> emailIdsPresentation,
+    List<EmailId> emailIds, {
-  ) {
+    EmailId? selectedEmailId,
-    final validEmailIdsToLoad = emailIdsPresentation.entries
+  }) {
-      .where((entry) => entry.value == null)
+    // Default first, second and last email
-      .map((entry) => entry.key)
+    if (emailIds.length <= 3) return emailIds;
-      .toList();
 
-    if (validEmailIdsToLoad.length == emailIdsPresentation.length) {
+    if (selectedEmailId == null ||
-      // No email loaded yet
+        !emailIds.contains(selectedEmailId) ||
-      return validEmailIdsToLoad.sublist(
+        selectedEmailId == emailIds.first ||
-        0,
+        selectedEmailId == emailIds.last ||
-        min(validEmailIdsToLoad.length, _initialLoadSize),
+        selectedEmailId == emailIds.elementAt(1)) {
-      );
+
+      return [
+        ...emailIds.sublist(
+          0,
+          min(emailIds.length, _initialLoadSize),
+        ),
+        emailIds.last,
+      ];
     }
 
-    return validEmailIdsToLoad.sublist(
+    return [
-      validEmailIdsToLoad.length - min(validEmailIdsToLoad.length, _defaultLoadSize),
+      emailIds.first,
-      validEmailIdsToLoad.length,
+      selectedEmailId,
+      emailIds.last,
+    ];
+  }
+
+  static getLoadMoreEmailIds(
+    List<EmailId> emailIds, {
+    bool loadEmailsAfterSelectedEmail = false,
+  }) {
+    if (loadEmailsAfterSelectedEmail) {
+      return emailIds.sublist(0, min(emailIds.length, _defaultLoadSize));
+    }
+
+    return emailIds.sublist(
+      emailIds.length - min(_defaultLoadSize, emailIds.length),
+      emailIds.length,
     );
   }
 }

test/features/thread_detail/presentation/extension/initialize_thread_detail_emails_test.dart

@@ -6,6 +6,7 @@ import 'package:jmap_dart_client/jmap/core/properties/properties.dart';
 import 'package:jmap_dart_client/jmap/mail/email/email.dart';
 import 'package:mockito/annotations.dart';
 import 'package:mockito/mockito.dart';
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart';
 import 'package:tmail_ui_user/features/thread_detail/domain/usecases/get_emails_by_ids_interactor.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/initialize_thread_detail_emails.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_controller.dart';
@@ -16,15 +17,18 @@ import 'initialize_thread_detail_emails_test.mocks.dart';
 @GenerateNiceMocks([
   MockSpec<GetEmailsByIdsInteractor>(),
   MockSpec<ThreadDetailController>(),
+  MockSpec<MailboxDashBoardController>(),
 ])
 void main() {
   group('InitializeThreadDetailEmails', () {
     late MockGetEmailsByIdsInteractor getEmailsByIdsInteractor;
     late MockThreadDetailController threadDetailController;
+    late MockMailboxDashBoardController mailboxDashboardController;
 
     setUp(() {
       getEmailsByIdsInteractor = MockGetEmailsByIdsInteractor();
       threadDetailController = MockThreadDetailController();
+      mailboxDashboardController = MockMailboxDashBoardController();
     });
 
     test('initializeThreadDetailEmails should call getEmailsByIdsInteractor with 3 elements', () async {
@@ -52,6 +56,8 @@ void main() {
       final session = SessionFixtures.aliceSession;
       when(threadDetailController.accountId).thenReturn(accountId);
       when(threadDetailController.session).thenReturn(session);
+      when(threadDetailController.mailboxDashBoardController).thenReturn(mailboxDashboardController);
+      when(mailboxDashboardController.selectedEmail).thenReturn(Rxn());
 
       // Act
       threadDetailController.initializeThreadDetailEmails();

test/features/thread_detail/presentation/extension/load_more_thread_detail_emails_test.dart

@@ -7,9 +7,11 @@ import 'package:mockito/annotations.dart';
 import 'package:mockito/mockito.dart';
 import 'package:model/email/presentation_email.dart';
 import 'package:tmail_ui_user/features/email/presentation/utils/email_utils.dart';
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart';
 import 'package:tmail_ui_user/features/thread_detail/domain/usecases/get_emails_by_ids_interactor.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/extension/load_more_thread_detail_emails.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_controller.dart';
+import 'package:tmail_ui_user/features/thread_detail/presentation/utils/thread_detail_presentation_utils.dart';
 
 import '../../../../fixtures/account_fixtures.dart';
 import '../../../../fixtures/session_fixtures.dart';
@@ -18,55 +20,66 @@ import 'load_more_thread_detail_emails_test.mocks.dart';
 @GenerateNiceMocks([
   MockSpec<ThreadDetailController>(),
   MockSpec<GetEmailsByIdsInteractor>(),
+  MockSpec<MailboxDashBoardController>(),
 ])
 void main() {
   late MockThreadDetailController controller;
   late MockGetEmailsByIdsInteractor getEmailsByIdsInteractor;
+  late MockMailboxDashBoardController mailboxDashBoardController;
 
   setUp(() {
     controller = MockThreadDetailController();
     getEmailsByIdsInteractor = MockGetEmailsByIdsInteractor();
+    mailboxDashBoardController = MockMailboxDashBoardController();
   });
 
   test('Only call getEmailsByIdsInteractor.execute on emails where presentation email is null, max 20 emails', () async {
     // Arrange
     when(controller.emailIdsPresentation).thenReturn({
-      for (int i = 0; i < 40; i++)
+      for (int i = 0; i < 40; i++) EmailId(Id('$i')): null,
-        EmailId(Id('$i')): null,
-      EmailId(Id('40')): PresentationEmail(),
     }.obs);
+    when(controller.currentExpandedEmailId).thenReturn(Rxn());
     when(controller.session).thenReturn(SessionFixtures.aliceSession);
     when(controller.accountId).thenReturn(AccountFixtures.aliceAccountId);
     when(controller.getEmailsByIdsInteractor).thenReturn(getEmailsByIdsInteractor);
     when(controller.additionalProperties).thenReturn(Properties.empty());
+    when(controller.mailboxDashBoardController).thenReturn(mailboxDashBoardController);
+    when(mailboxDashBoardController.selectedEmail).thenReturn(Rxn());
 
     // Act
-    controller.loadMoreThreadDetailEmails();
+    controller.loadMoreThreadDetailEmails(
+      loadMoreIndex: 0,
+      loadMoreCount: controller.emailIdsPresentation.length,
+    );
 
     // Assert
     verify(getEmailsByIdsInteractor.execute(
       SessionFixtures.aliceSession,
       AccountFixtures.aliceAccountId,
-      List.generate(20, (i) => EmailId(Id('${i + 20}'))),
+      List.generate(20, (i) => EmailId(Id('$i'))),
       properties: EmailUtils.getPropertiesForEmailGetMethod(
         SessionFixtures.aliceSession,
         AccountFixtures.aliceAccountId,
       ),
+      loadMoreIndex: 0,
     )).called(1);
   });
 
   test('No getEmailsByIdsInteractor.execute call if emailIdsToLoadMetaData is empty', () async {
     // Arrange
-    when(controller.emailIdsPresentation).thenReturn({
+    when(controller.emailIdsPresentation).thenReturn(<EmailId, PresentationEmail?>{}.obs);
-      EmailId(Id('1')): PresentationEmail(),
+    when(controller.currentExpandedEmailId).thenReturn(Rxn());
-      EmailId(Id('2')): PresentationEmail(),
-    }.obs);
     when(controller.session).thenReturn(SessionFixtures.aliceSession);
     when(controller.accountId).thenReturn(AccountFixtures.aliceAccountId);
     when(controller.getEmailsByIdsInteractor).thenReturn(getEmailsByIdsInteractor);
+    when(controller.mailboxDashBoardController).thenReturn(mailboxDashBoardController);
+    when(mailboxDashBoardController.selectedEmail).thenReturn(Rxn());
 
     // Act
-    controller.loadMoreThreadDetailEmails();
+    controller.loadMoreThreadDetailEmails(
+      loadMoreIndex: 0,
+      loadMoreCount: controller.emailIdsPresentation.length,
+    );
 
     // Assert
     verifyNever(getEmailsByIdsInteractor.execute(
@@ -81,17 +94,21 @@ void main() {
     // Arrange
     const limit = 15;
     when(controller.emailIdsPresentation).thenReturn({
-      for (int i = 0; i < limit; i++)
+      for (int i = 0; i < limit; i++) EmailId(Id('$i')): null,
-        EmailId(Id('$i')): null,
-      EmailId(Id('$limit')): PresentationEmail(),
     }.obs);
+    when(controller.currentExpandedEmailId).thenReturn(Rxn());
     when(controller.session).thenReturn(SessionFixtures.aliceSession);
     when(controller.accountId).thenReturn(AccountFixtures.aliceAccountId);
     when(controller.getEmailsByIdsInteractor).thenReturn(getEmailsByIdsInteractor);
     when(controller.additionalProperties).thenReturn(Properties.empty());
+    when(controller.mailboxDashBoardController).thenReturn(mailboxDashBoardController);
+    when(mailboxDashBoardController.selectedEmail).thenReturn(Rxn());
 
     // Act
-    controller.loadMoreThreadDetailEmails();
+    controller.loadMoreThreadDetailEmails(
+      loadMoreIndex: 0,
+      loadMoreCount: controller.emailIdsPresentation.length,
+    );
 
     // Assert
     verify(getEmailsByIdsInteractor.execute(
@@ -102,6 +119,96 @@ void main() {
         SessionFixtures.aliceSession,
         AccountFixtures.aliceAccountId,
       ),
+      loadMoreIndex: 0,
+    )).called(1);
+  });
+
+
+  test(
+    'should call getEmailsByIdsInteractor.execute '
+    'with ThreadDetailPresentationUtils.defaultLoadSize (20) top to bottom '
+    'when loadMoreIndex is larger than index of currentExpandedEmailId',
+  () {
+    // arrange
+    final loadMoreEmails = {
+      for (int i = 31; i < 60; i++) EmailId(Id('$i')): null
+    };
+    const loadMoreIndex = 32;
+    when(controller.emailIdsPresentation).thenReturn({
+      for (int i = 0; i < 30; i++) EmailId(Id('$i')): null,
+      EmailId(Id('30')): PresentationEmail(),
+      ...loadMoreEmails,
+    }.obs);
+    when(controller.currentExpandedEmailId).thenReturn(Rxn(EmailId(Id('30'))));
+    when(controller.session).thenReturn(SessionFixtures.aliceSession);
+    when(controller.accountId).thenReturn(AccountFixtures.aliceAccountId);
+    when(controller.getEmailsByIdsInteractor).thenReturn(getEmailsByIdsInteractor);
+    when(controller.mailboxDashBoardController).thenReturn(mailboxDashBoardController);
+    when(mailboxDashBoardController.selectedEmail).thenReturn(Rxn());
+    
+    // act
+    controller.loadMoreThreadDetailEmails(
+      loadMoreIndex: loadMoreIndex,
+      loadMoreCount: loadMoreEmails.length,
+    );
+    
+    // assert
+    verify(getEmailsByIdsInteractor.execute(
+      SessionFixtures.aliceSession,
+      AccountFixtures.aliceAccountId,
+      List.generate(
+        ThreadDetailPresentationUtils.defaultLoadSize,
+        (i) => EmailId(Id('${i + loadMoreIndex}')),
+      ),
+      properties: EmailUtils.getPropertiesForEmailGetMethod(
+        SessionFixtures.aliceSession,
+        AccountFixtures.aliceAccountId,
+      ),
+      loadMoreIndex: loadMoreIndex,
+    )).called(1);
+  });
+
+  test(
+    'should call getEmailsByIdsInteractor.execute '
+    'with ThreadDetailPresentationUtils.defaultLoadSize (20) bottom to top '
+    'when loadMoreIndex is larger than index of currentExpandedEmailId',
+  () {
+    // arrange
+    final loadMoreEmails = {
+      for (int i = 0; i < 30; i++) EmailId(Id('$i')): null
+    };
+    const loadMoreIndex = 0;
+    when(controller.emailIdsPresentation).thenReturn({
+      ...loadMoreEmails,
+      EmailId(Id('30')): PresentationEmail(),
+      for (int i = 31; i < 60; i++) EmailId(Id('$i')): null,
+    }.obs);
+    when(controller.currentExpandedEmailId).thenReturn(Rxn(EmailId(Id('30'))));
+    when(controller.session).thenReturn(SessionFixtures.aliceSession);
+    when(controller.accountId).thenReturn(AccountFixtures.aliceAccountId);
+    when(controller.getEmailsByIdsInteractor).thenReturn(getEmailsByIdsInteractor);
+    when(controller.mailboxDashBoardController).thenReturn(mailboxDashBoardController);
+    when(mailboxDashBoardController.selectedEmail).thenReturn(Rxn());
+    
+    // act
+    controller.loadMoreThreadDetailEmails(
+      loadMoreIndex: loadMoreIndex,
+      loadMoreCount: loadMoreEmails.length,
+    );
+    
+    // assert
+    verify(getEmailsByIdsInteractor.execute(
+      SessionFixtures.aliceSession,
+      AccountFixtures.aliceAccountId,
+      List.generate(
+        ThreadDetailPresentationUtils.defaultLoadSize,
+        (i) => EmailId(Id('${loadMoreEmails.length - i - 1}')),
+      ).reversed.toList(),
+      properties: EmailUtils.getPropertiesForEmailGetMethod(
+        SessionFixtures.aliceSession,
+        AccountFixtures.aliceAccountId,
+      ),
+      loadMoreIndex: loadMoreIndex,
     )).called(1);
   });
 }

test/features/thread_detail/presentation/extension/thread_detail_load_more_segments_test.dart

@@ -0,0 +1,76 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:get/get.dart';
+import 'package:jmap_dart_client/jmap/core/id.dart';
+import 'package:jmap_dart_client/jmap/mail/email/email.dart';
+import 'package:mockito/annotations.dart';
+import 'package:mockito/mockito.dart';
+import 'package:model/email/presentation_email.dart';
+import 'package:tmail_ui_user/features/thread_detail/presentation/extension/thread_detail_load_more_segments.dart';
+import 'package:tmail_ui_user/features/thread_detail/presentation/thread_detail_controller.dart';
+
+import 'thread_detail_load_more_segments_test.mocks.dart';
+
+@GenerateNiceMocks([MockSpec<ThreadDetailController>()])
+void main() {
+  late MockThreadDetailController controller;
+
+  setUp(() {
+    controller = MockThreadDetailController();
+  });
+
+  group('ThreadDetailLoadMoreSegments', () {
+    test(
+      'should return empty map when emailIdsPresentation is empty',
+    () {
+      // arrange
+      when(controller.emailIdsPresentation).thenReturn(<EmailId, PresentationEmail?>{}.obs);
+      
+      // act
+      final result = controller.loadMoreSegments;
+
+      // assert
+      expect(result, {});
+    });
+
+    test(
+      'should return correct load more segments when there are null values in emailIdsPresentation',
+    () {
+      // arrange
+      when(controller.emailIdsPresentation).thenReturn({
+        EmailId(Id('1')): PresentationEmail(),
+        EmailId(Id('2')): null,
+        EmailId(Id('3')): null,
+        EmailId(Id('4')): PresentationEmail(),
+        EmailId(Id('5')): null,
+      }.obs);
+      
+      // act
+      final result = controller.loadMoreSegments;
+      
+      // assert
+      expect(result, {
+        1: 2,
+        4: 1,
+      });
+    });
+
+    test(
+      'should return correct load more segments when there are no null values in emailIdsPresentation',
+    () {
+      // arrange
+      when(controller.emailIdsPresentation).thenReturn({
+        EmailId(Id('1')): PresentationEmail(),
+        EmailId(Id('2')): PresentationEmail(),
+        EmailId(Id('3')): PresentationEmail(),
+        EmailId(Id('4')): PresentationEmail(),
+        EmailId(Id('5')): PresentationEmail(),
+      }.obs);
+      
+      // act
+      final result = controller.loadMoreSegments;
+      
+      // assert
+      expect(result, {});
+    });
+  });
+}

test/features/thread_detail/presentation/utils/thread_detail_presentation_utils_test.dart

@@ -1,68 +1,326 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:jmap_dart_client/jmap/core/id.dart';
 import 'package:jmap_dart_client/jmap/mail/email/email.dart';
-import 'package:model/email/presentation_email.dart';
 import 'package:tmail_ui_user/features/thread_detail/presentation/utils/thread_detail_presentation_utils.dart';
 
 void main() {
   group('ThreadDetailPresentationUtils', () {
     group('getEmailIdsToLoad', () {
-      test('loads first time with length equal or more than initial load size', () {
+      test(
-        final emailIdsPresentation = {
+        'should return empty list '
-          EmailId(Id('1')): null,
+        'when emailIds is empty',
-          EmailId(Id('2')): null,
+      () {
-          EmailId(Id('3')): null,
+        // arrange
-          EmailId(Id('4')): null,
+        final emailIds = <EmailId>[];
-          EmailId(Id('5')): null,
+        
-        };
+        // act
-
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
-        final result = ThreadDetailPresentationUtils.getEmailIdsToLoad(emailIdsPresentation);
+          emailIds,
-
+        );
-        expect(result.length, equals(ThreadDetailPresentationUtils.initialLoadSize));
+        
-        expect(result, equals([EmailId(Id('1')), EmailId(Id('2'))]));
+        // assert
+        expect(result, isEmpty);
       });
 
-      test('loads first time with length smaller than initial load size', () {
+      test(
-        final emailIdsPresentation = {
+        'should return all email ids in emailIds '
-          EmailId(Id('1')): null,
+        'when isFirstLoad is true '
-          EmailId(Id('2')): null,
+        'and emailIds contains equal to or less than 3 email ids',
-        };
+      () {
-
+        // arrange
-        final result = ThreadDetailPresentationUtils.getEmailIdsToLoad(emailIdsPresentation);
+        final emailIds = [
-
+          EmailId(Id('1')),
-        expect(result.length, equals(emailIdsPresentation.length));
+          EmailId(Id('2')),
-        expect(result, equals([EmailId(Id('1')), EmailId(Id('2'))]));
+          EmailId(Id('3')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+        );
+        
+        // assert
+        expect(result, equals(emailIds));
       });
 
-      test('loads with length equal or more than default load size', () {
+      test(
-        final emailIdsPresentation = {
+        'should return first two emails and last email '
-          EmailId(Id('1')): PresentationEmail(),
+        'when isFirstLoad is true '
-          EmailId(Id('2')): null,
+        'and emailIds contains more than 3 email ids '
-          EmailId(Id('3')): null,
+        'and selectedEmailId is not null ',
-          EmailId(Id('4')): null,
+      () {
-          EmailId(Id('5')): null,
+        // arrange
-          EmailId(Id('6')): null,
+        final emailIds = [
-          EmailId(Id('7')): null,
+          EmailId(Id('1')),
-        };
+          EmailId(Id('2')),
-
+          EmailId(Id('3')),
-        final result = ThreadDetailPresentationUtils.getEmailIdsToLoad(emailIdsPresentation);
+          EmailId(Id('4')),
-
+          EmailId(Id('5')),
-        expect(result.length, equals(6));
+        ];
-        expect(result, equals([EmailId(Id('2')), EmailId(Id('3')), EmailId(Id('4')), EmailId(Id('5')), EmailId(Id('6')), EmailId(Id('7'))]));
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([EmailId(Id('1')), EmailId(Id('2')), EmailId(Id('5'))]),
+        );
       });
 
-      test('loads with length smaller than default load size', () {
+      test(
-        final emailIdsPresentation = {
+        'should return first two emails and last email '
-          EmailId(Id('1')): PresentationEmail(),
+        'when isFirstLoad is true '
-          EmailId(Id('2')): null,
+        'and emailIds contains more than 3 email ids '
-          EmailId(Id('3')): null,
+        'and selectedEmailId is not inside emailIds',
-        };
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+          selectedEmailId: EmailId(Id('6')),
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([EmailId(Id('1')), EmailId(Id('2')), EmailId(Id('5'))]),
+        );
+      });
 
-        final result = ThreadDetailPresentationUtils.getEmailIdsToLoad(emailIdsPresentation);
+      test(
+        'should return first two emails and last email '
+        'when isFirstLoad is true '
+        'and emailIds contains more than 3 email ids '
+        'and selectedEmailId is first element of emailIds',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+          selectedEmailId: emailIds.first,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([EmailId(Id('1')), EmailId(Id('2')), EmailId(Id('5'))]),
+        );
+      });
 
-        expect(result.length, equals(emailIdsPresentation.length - 1));
+      test(
-        expect(result, equals([EmailId(Id('2')), EmailId(Id('3'))]));
+        'should return first two emails and last email '
+        'when isFirstLoad is true '
+        'and emailIds contains more than 3 email ids '
+        'and selectedEmailId is last element of emailIds',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+          selectedEmailId: emailIds.last,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([EmailId(Id('1')), EmailId(Id('2')), EmailId(Id('5'))]),
+        );
+      });
+
+      test(
+        'should return first two emails and last email '
+        'when isFirstLoad is true '
+        'and emailIds contains more than 3 email ids '
+        'and selectedEmailId is second element of emailIds',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+          selectedEmailId: emailIds.elementAt(1),
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([EmailId(Id('1')), EmailId(Id('2')), EmailId(Id('5'))]),
+        );
+      });
+
+      test(
+        'should return first, last and selected email '
+        'when emailIds contains more than 3 email ids '
+        'and isFirstLoad is true '
+        'and selectedEmailId is inside emailIds '
+        'and selectedEmailId is not first, last or second element of emailIds',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        final selectedEmail = EmailId(Id('3'));
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getFirstLoadEmailIds(
+          emailIds,
+          selectedEmailId: selectedEmail,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals([emailIds.first, selectedEmail, emailIds.last]),
+        );
+      });
+
+      test(
+        'should return all emails '
+        'when emailIds contains more than 3 email ids '
+        'and isFirstLoad is false '
+        'and loadEmailsAfterSelectedEmail is true '
+        'and emailsIds.length is less than defaultLoadSize',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getLoadMoreEmailIds(
+          emailIds,
+          loadEmailsAfterSelectedEmail: true,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals(emailIds),
+        );
+      });
+
+      test(
+        'should return first defaultLoadSize (20) emails '
+        'when emailIds contains more than 3 email ids '
+        'and isFirstLoad is false '
+        'and loadEmailsAfterSelectedEmail is true '
+        'and emailsIds.length is more than defaultLoadSize',
+      () {
+        // arrange
+        final emailIds = List.generate(30, (i) => EmailId(Id('$i')));
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getLoadMoreEmailIds(
+          emailIds,
+          loadEmailsAfterSelectedEmail: true,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals(emailIds.sublist(
+            0,
+            ThreadDetailPresentationUtils.defaultLoadSize,
+          )),
+        );
+      });
+      
+      test(
+        'should return all emails '
+        'when emailIds contains more than 3 email ids '
+        'and isFirstLoad is false '
+        'and loadEmailsAfterSelectedEmail is false '
+        'and emailsIds.length is less than defaultLoadSize',
+      () {
+        // arrange
+        final emailIds = [
+          EmailId(Id('1')),
+          EmailId(Id('2')),
+          EmailId(Id('3')),
+          EmailId(Id('4')),
+          EmailId(Id('5')),
+        ];
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getLoadMoreEmailIds(
+          emailIds,
+          loadEmailsAfterSelectedEmail: false,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals(emailIds),
+        );
+      });
+
+      test(
+        'should return last defaultLoadSize (20) emails '
+        'when emailIds contains more than 3 email ids '
+        'and isFirstLoad is false '
+        'and loadEmailsAfterSelectedEmail is false '
+        'and emailsIds.length is more than defaultLoadSize',
+      () {
+        // arrange
+        final emailIds = List.generate(30, (i) => EmailId(Id('$i')));
+        
+        // act
+        final result = ThreadDetailPresentationUtils.getLoadMoreEmailIds(
+          emailIds,
+          loadEmailsAfterSelectedEmail: false,
+        );
+        
+        // assert
+        expect(
+          result,
+          equals(emailIds.sublist(
+            emailIds.length - ThreadDetailPresentationUtils.defaultLoadSize,
+            emailIds.length,
+          )),
+        );
       });
     });
   });
-}
+}