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This article explores how Clean Architecture can be applied when integrating the CometChat SDK into a Flutter application. Instead of allowing UI components or SDK-specific logic to dominate the codebase, we will separate domain logic, data handling, and presentation layers into clear boundaries. This approach helps teams maintain long-term flexibility, improve code readability, and reduce the risk of technical debt as chat features evolve from MVP prototypes into production-ready systems.
By the end of this guide, readers will understand how to design a modular chat architecture that supports real-time messaging while remaining testable, maintainable, and scalable ⚙️. The concepts discussed are especially useful for Flutter developers, software architects, and engineering leads who want to build scalable in-app communication systems using CometChat - whether starting with the UI Kit or building fully customized chat experiences with the SDK.
Why Clean Architecture for In-App Chat?
Modern chat systems look simple on the surface, but behind every message sent lies a complex chain of real-time events, state updates, and synchronization challenges. When developers integrate chat features directly into UI layers or tightly couple them with SDK calls, the codebase can quickly become fragile and difficult to evolve. This is where Clean Architecture becomes a strategic decision rather than just a structural preference.
🔧 Technical Challenges of Chat Applications
- Real-time event handling: Managing live message streams, typing indicators, delivery receipts, and presence updates requires consistent event orchestration.
- Data consistency: Ordering messages correctly, preventing duplication, and supporting offline queues demand clear domain rules.
- Feature growth: Adding reactions, attachments, moderation tools, or calls can introduce architectural complexity if boundaries are unclear.
⚙️ Non-Functional Concerns Developers Often Face
- Testability: Chat logic mixed with UI widgets makes unit testing difficult.
- Observability: Without clear layers, tracking failures or performance issues becomes harder.
- Maintainability: Rapid feature changes can introduce technical debt when responsibilities overlap.
- Team scaling: Larger teams need predictable structure to collaborate efficiently.
🚀 Mapping Chat Problems to Clean Architecture Benefits
- Dependency rule ensures that business rules remain independent from SDK implementations or UI frameworks.
- Easier migration path when switching between CometChat UI Kit and custom SDK-based implementations.
- Reduced ripple effect when introducing new features or replacing infrastructure components.
Separating domain entities and use-cases allows chat behavior to evolve without forcing major rewrites in presentation or data layers. As CometChat offers both a rapid UI Kit and a flexible SDK for Flutter, developers gain freedom to start fast while still planning a scalable architecture foundation. This balance between speed and structure is especially valuable for teams moving from MVP experimentation toward long-term production systems.
Overview of the CometChat Flutter Stack
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🧩 Key Components in the CometChat Flutter Ecosystem
- Flutter SDK (Dart APIs)
- Provides the core real-time capabilities such as messaging, presence tracking, event listeners, and user or group management. The SDK acts as the communication bridge between your Flutter application and CometChat cloud infrastructure, making it ideal for developers who want full control over business logic and UI behavior.
- UI Kit (Prebuilt Widgets)
- A collection of ready-to-use chat components designed to accelerate development. Developers can quickly integrate messaging screens, conversation lists, and user interfaces while still allowing customization through theming and configuration. This layer is useful for rapid MVP development without sacrificing scalability.
- UI Kit Builder and Sample Apps
- CometChat also provides design assets, builder tools, and reference implementations through platforms like Figma and GitHub. These resources help teams visualize layouts, understand integration patterns, and reduce the learning curve when implementing advanced features.
⚙️ Core Capabilities Supported by the Stack
- One-to-one messaging and real-time conversation updates.
- Group chat features including roles and participation management.
- Media attachments such as images, files, and rich message types.
- Voice and video calling support through integrated calling modules.
Together, these components form a flexible ecosystem where teams can start with rapid UI integration and gradually move toward fully customized implementations using the SDK. From an architectural perspective, understanding where each tool fits allows developers to isolate infrastructure concerns while keeping domain logic clean and independent.
Design Goals and Constraints for the Reference Architecture
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Before defining layers or writing implementation details, it is important to clarify the design goals and practical constraints that shape a clean chat architecture. Real-time systems evolve quickly, so having clearly defined targets helps teams avoid over-engineering while still building a scalable foundation.
🎯 Design Goals
- Independence of business rules from SDK and UI
- Domain logic should remain isolated from CometChat-specific implementations so that features like messaging rules, conversation states, or moderation logic can evolve without rewriting presentation layers.
- Easy to test (unit and integration)
- A layered structure allows developers to test use-cases independently from network dependencies. This is especially important for chat flows that involve retries, message ordering, or state transitions.
- Clear boundaries for real-time event handling
- Real-time events such as incoming messages, typing indicators, or presence updates should pass through a controlled domain layer rather than being handled directly inside UI widgets.
- Smooth migration path from UI Kit to custom SDK-based UI
- CometChat provides both UI Kit components and a flexible SDK, which means architecture should allow teams to start quickly and gradually move toward deeper customization without large refactors.
⚙️ Practical Constraints to Consider
- Support both one-to-one and group chat
- The architecture must handle private conversations as well as group-based interactions, including membership roles and real-time updates.
- Offline caching and synchronization
- Since real-time apps must handle intermittent connectivity, a local data layer is necessary to queue messages and reconcile state once connectivity returns.
- Compatibility with common Flutter state managers
- The structure should work smoothly with patterns such as Bloc, Riverpod, or Provider so teams can choose tools that match their development workflow.
Defining these goals and constraints early ensures that architectural decisions remain intentional rather than reactive. Instead of tightly coupling UI logic with SDK calls, developers can build a modular system that scales from MVP experimentation into long-term production environments.
Proposed Clean Architecture for In-App Chat (High-Level)
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Designing a scalable in-app chat system requires a clear separation of responsibilities across layers. Using an Onion or Hexagonal Architecture approach helps ensure that domain logic stays independent from frameworks, UI decisions, or external SDK implementations. In the context of CometChat and Flutter, this layered design makes it easier to manage real-time complexity while keeping the codebase flexible and testable.
🧱 Layer Breakdown (Onion Style)
1) Domain Layer (Entities and Use Cases)
- Core Entities: Message, Conversation, User, Attachment, Reaction, and Role or Permission models that represent business concepts independent from any SDK.
- Use Case Interfaces: SendMessage, FetchConversations, MarkAsRead, SyncOffline, and JoinGroup define how the application behaves without exposing infrastructure details.
- Key Principle: Pure Dart models and interfaces with no external dependencies, allowing easier testing and long-term maintainability.
2) Data Layer (Repositories and Data Sources)
- Repository Interfaces act as contracts defined in the domain layer, while implementations communicate with external services.
- Remote Data Source wraps CometChat SDK calls behind abstractions so that SDK-specific logic does not leak into higher layers.
- Local Data Source can use SQLite, Hive, or sembast to store cached conversations, enabling offline-first chat experiences.
3) Infrastructure Layer - SDK Adapter
- Adapter Implementations delegate repository operations to CometChat SDK methods and map incoming DTOs into domain entities.
- Event Adapter translates real-time SDK streams such as onMessageReceived, typing indicators, or presence updates into domain-level events that the application can react to safely.
- This layer acts as the boundary where external dependencies live, protecting the rest of the system from vendor lock-in.
4) Presentation Layer
- UI Components can be built using CometChat UI Kit widgets or fully custom Flutter widgets depending on the level of customization required.
- State Management using Bloc, Cubit, or Riverpod exposes reactive streams derived from domain use cases rather than directly from SDK calls.
🔄 Understanding the Dependency Flow
In Clean Architecture, dependencies always point inward. The presentation layer interacts with domain use cases, the domain communicates with repository contracts, and only the infrastructure layer knows about the CometChat SDK. This flow ensures that replacing UI frameworks or adjusting backend integrations does not break core business logic.
Detailed Responsibilities and Interfaces per Layer (Deep Dive)
After defining the high-level architecture, the next step is understanding how responsibilities are distributed across layers. A well-defined contract between domain logic, repositories, and infrastructure adapters ensures that real-time chat features remain scalable and maintainable without tightly coupling business rules to SDK implementations.
🧠 Domain Layer Responsibilities
- Entities Definition
- Define core models such as Message, Conversation, and User with clear fields, validation rules, and invariants. These entities should remain independent from CometChat SDK structures.
- Use Case Signatures
- Use cases expose clear interfaces such as SendMessage or FetchConversations, typically returning reactive types like Stream, Result, or Either to represent asynchronous real-time operations.
- Business Rules Enforcement
- Handle message ordering, read-receipt updates, retry strategies, and backoff mechanisms inside the domain layer instead of the UI.
📦 Repository Contracts
- Core Methods
- Stream subscribeMessages(conversationId)
- Future sendMessage(Message message)
- Future<List> fetchConversations(int page)
- Error Modeling Strategy
- Use typed exceptions or sealed result objects to differentiate between network errors, SDK failures, and domain-level validation issues. This separation allows consistent error handling across presentation layers.
🔌 SDK Adapter (CometChatAdapter)
- Primary Responsibilities
- Initialize the CometChat SDK during app startup.
- Map SDK events into domain-level streams.
- Handle token refresh and authentication lifecycle.
- Manage reconnection logic for real-time stability.
- Example Event Mapping
- Convert CometChat.onMessageReceived callbacks into a domain Message stream that presentation layers can subscribe to without depending on SDK-specific APIs.
🔄 Local Cache and Synchronization Strategy
- Conflict Resolution Rules
- Implement strategies such as server-wins or last-write-wins depending on product requirements. Advanced systems may adopt vector-clock strategies for collaborative environments.
- Offline Queue Management
- Queue outgoing messages locally when connectivity drops, then replay the queue once reconnection occurs to maintain a seamless user experience.
By defining detailed responsibilities at each layer, developers can keep CometChat-specific logic isolated while allowing the domain layer to evolve independently. This separation is critical when scaling chat features such as attachments, moderation workflows, or multi-device synchronization.
State Management and Event Flow in Flutter Presentation
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A well-structured presentation layer plays a critical role in maintaining Clean Architecture boundaries. Instead of allowing UI components to directly consume SDK events, state management should act as a controlled gateway between domain use cases and visual widgets. This approach ensures predictable updates, easier debugging, and a more maintainable real-time chat experience.
🧩 Recommended State Management Patterns
- Bloc or Cubit
- Provides a clear separation between events, states, and UI rendering. This pattern works well for chat applications where message streams, typing indicators, and presence updates must remain predictable and testable.
- Riverpod
- Offers simpler dependency injection and flexible provider composition. Riverpod is especially useful for modular applications that want reactive state without tightly coupling logic to widget trees.
⚡ Real-Time Event Handling Strategies
- Event Bus vs Direct Stream Subscription
- Event bus patterns allow centralized control over incoming SDK events but may introduce additional complexity.
- Direct stream subscriptions are simpler but require careful lifecycle management to avoid memory leaks or duplicated listeners.
- Throttling UI Updates
- Batch message updates or debounce rapid event streams to prevent excessive widget rebuilds, especially during high message throughput.
🧱 UI Kit Integration Strategies
- Wrap UI Kit Widgets with Presentation Controllers
- Even though CometChat UI Kit provides ready-made components, wrapping them inside Bloc or Riverpod controllers ensures that business logic continues to flow through domain use cases.
- Example Architecture Approach
- Compose a ChatPage where MessageBloc acts as the single source of truth. UI Kit widgets consume Bloc state streams instead of calling the CometChat SDK directly, preserving architectural boundaries.
Practical Integration Guide (Mapping to Code and File Structure)
Implementing Clean Architecture with CometChat in Flutter becomes easier when the project structure reflects clear boundaries between domain logic, infrastructure, and presentation. A feature-first folder layout helps teams scale chat features without mixing responsibilities across layers.
📁 Recommended Folder Layout
lib/
features/chat/
domain/
entities/
usecases/
repositories/
data/
models/
datasources/
repositories_impl/
presentation/
bloc/
pages/
widgets/
infra/
cometchat_adapter.dart
Structure Explanation:
- domain/
- Contains pure Dart entities, business rules, and repository contracts. No SDK imports should exist here.
- data/
- Holds implementation details such as DTO models, remote or local data sources, and repository implementations that bridge domain contracts with infrastructure.
- presentation/
- Includes Bloc or Riverpod logic, UI pages, and reusable widgets that render chat experiences based on domain state.
- infra/
- Dedicated layer for SDK-specific adapters such as
cometchat_adapter.dart, isolating external dependencies from the rest of the system.
🛠️ Step-by-Step Integration Checklist
- Add SDK dependency and initialize at app startup
- Register the CometChat SDK inside the application bootstrap layer to ensure authentication and event streams are ready before UI rendering begins.
- Create domain entities and repository interfaces
- Define Message, Conversation, and User entities along with abstract repository contracts that describe expected behaviors.
- Implement SDK adapter
- Map CometChat SDK callbacks into domain-friendly streams and handle initialization logic within the infrastructure layer.
- Implement repository with adapter and local cache
- Compose repository implementations that merge remote SDK data with local persistence for offline support.
- Connect use cases to Bloc or Riverpod providers
- Expose domain logic to the presentation layer through controlled state management instead of direct SDK access.
- Render UI using UI Kit widgets or custom Flutter UI
- Widgets should read state from controllers, ensuring architecture boundaries remain intact.
Handling Real-Time Concerns: Presence, Delivery, Ordering, Typing, and Read Receipts
Real-time messaging introduces multiple synchronization challenges that must be handled carefully inside the architecture. Instead of placing this logic directly in UI components, a domain-driven approach ensures that presence updates, delivery acknowledgements, and message ordering remain consistent across devices and sessions.
🟢 Presence and Typing Indicators
- Subscribe to presence events through the SDK adapter
- Real-time presence and typing updates should flow from the CometChat SDK into domain streams via the adapter layer.
- Maintain a lightweight presence store in the domain layer
- Store only essential status information such as online, offline, or typing state to avoid unnecessary UI complexity while keeping business logic centralized.
📬 Delivery and Read Receipts
- Model acknowledgements at the domain level
- Delivery and read states should be handled as part of domain entities so that UI components only react to state changes rather than implementing logic themselves.
- Update local storage and emit events after acknowledgement
- Once a message is delivered or read, update the local cache and notify presentation layers through streams or state controllers.
⏱️ Message Ordering Strategy
- Use server timestamps with client fallback
- Server-generated timestamps help maintain consistent ordering across devices, while client-side timestamps act as a temporary fallback during offline scenarios.
- Maintain stable sort identifiers or sequence numbers
- This prevents UI glitches when messages arrive out of order due to network latency.
♻️ Idempotency and Deduplication
- Client-generated message IDs
- Assign unique identifiers before sending messages so retries do not create duplicates.
- Server-side validation
- Combine client IDs with backend checks to ensure the same message is not processed multiple times during reconnection or retry flows.
Testing Strategy (Unit, Integration, and End-to-End)
Testing plays a crucial role in ensuring that a real-time chat architecture remains reliable as features grow. Because Clean Architecture separates responsibilities across layers, teams can validate business logic without relying directly on SDK behavior or UI rendering. A structured testing approach also helps detect issues early, especially when dealing with asynchronous message flows and reconnection scenarios.
🧪 Unit Testing Approach
Unit tests should focus on validating domain entities and use cases in isolation. By keeping the domain layer free from external dependencies, developers can verify message ordering rules, retry strategies, and read-receipt logic using pure Dart tests. This ensures that core chat behavior remains stable even when SDK implementations evolve.
🔌 Adapter and Repository Testing
When testing the infrastructure layer, the CometChat SDK should be abstracted behind interfaces so that adapters can be replaced with mocks or fakes. Instead of relying on live SDK calls, developers can simulate message events and validate whether repository implementations correctly map incoming data into domain entities. Integration testing at this level ensures that data transformations and event mapping remain consistent.
🎨 UI and Widget Testing
Presentation tests should validate how widgets react to state changes rather than testing SDK logic directly. Using fake Bloc or Riverpod providers allows teams to confirm that message lists, typing indicators, and delivery states render correctly under different scenarios without requiring real network connections.
⚡ Load and Reliability Testing
Beyond functional testing, real-time chat systems benefit from stress simulations that replicate high event throughput or unstable network conditions. Simulating rapid message streams, reconnections, and delayed acknowledgements helps uncover race conditions and performance bottlenecks before deployment.
Security, Moderation, and Privacy Considerations
Security and privacy are essential aspects of any real-time communication system, especially when handling personal conversations and user-generated content. When integrating CometChat within a Clean Architecture setup, security concerns should be handled at clearly defined boundaries so that authentication logic, moderation workflows, and data policies remain consistent across the application lifecycle.
🔐 Authentication and Token Management
Authentication should be treated as an infrastructure concern while still exposing controlled access through domain use cases. Token lifecycle management includes generating tokens securely, refreshing them when sessions expire, and storing credentials using secure storage solutions provided by the platform. A well-designed adapter layer helps ensure that token refresh logic does not leak into presentation components, reducing the risk of accidental exposure or inconsistent authentication flows.
🛡️ Moderation Strategies
Modern chat applications often require both server-side and client-side moderation approaches. Server-side moderation hooks can automatically filter harmful content or enforce role-based permissions, while client-level safeguards such as profanity filtering or reporting workflows provide an additional layer of protection. By routing moderation events through domain use cases, teams can maintain consistent behavior regardless of whether UI Kit components or custom widgets are used.
📁 Data Retention and Privacy Compliance
Handling user data responsibly involves defining clear retention policies and ensuring sensitive information is protected. Local message caches may need encryption depending on product requirements, and applications should provide mechanisms for message deletion, export, or account-related data requests. Structuring these policies inside repository and infrastructure layers helps align privacy practices with scalable architectural patterns.
Migration Notes: UI Kit to Custom SDK UI (Practical Path)
Migrating from prebuilt UI components to a fully customized chat experience is a common evolution in real-time Flutter applications. Many teams begin with the CometChat UI Kit to accelerate MVP development, then gradually transition toward SDK-driven interfaces as product requirements grow more complex. This migration should be approached as a controlled architectural progression rather than a complete rewrite.
🔄 When Does Migration Make Sense?
Migration usually becomes relevant when teams require deeper UI customization, performance optimization, or advanced business rules that extend beyond the capabilities of ready-made components. For example, products that introduce custom moderation workflows, unique message rendering logic, or specialized interaction patterns often benefit from moving toward SDK-level control while still preserving architectural boundaries defined earlier.
🧭 A Practical Migration Path
- Start by wrapping existing UI Kit components inside presentation controllers such as Bloc or Riverpod. This intermediate step helps isolate SDK usage while keeping the UI stable.
- Introduce repository and adapter layers so that data access flows through consistent interfaces. At this stage, teams can begin swapping internal implementations without affecting presentation logic.
- Replace UI Kit widgets incrementally with custom Flutter widgets that read from domain state instead of directly invoking SDK calls. Gradual replacement reduces risk and allows rollback if needed.
This phased approach allows teams to maintain delivery speed while steadily improving architectural control. Because CometChat provides UI Kit builders and sample implementations, developers can reference existing patterns while transitioning toward more flexible SDK-based solutions.
Observability, Monitoring, and Production Considerations
As real-time chat systems move from development into production environments, observability becomes essential for maintaining reliability and performance. A well-structured Clean Architecture makes it easier to introduce monitoring layers without polluting business logic, allowing teams to track system health while preserving clear boundaries between domain rules and infrastructure concerns.
📊 Logging Strategy
A balanced logging approach should differentiate between SDK-level logs and domain-level logs. SDK logs help diagnose connection issues, authentication failures, or real-time event interruptions, while domain logs provide insight into business events such as message state transitions or moderation actions. Introducing correlation identifiers for messages allows developers to trace a single message lifecycle across adapters, repositories, and presentation layers without exposing sensitive data.
📈 Key Metrics to Monitor
Production-ready chat systems benefit from consistent performance tracking. Important indicators include message latency, delivery success rates, failed send attempts, and reconnection frequency. Monitoring these metrics helps teams quickly identify degraded performance during high traffic or unstable network conditions.
🚨 Alerting and Production Safeguards
Alerting mechanisms should focus on meaningful signals rather than noisy events. Sudden spikes in failed message delivery, authentication errors, or unexpected reconnection loops can indicate deeper infrastructure problems. Integrating alert thresholds with monitoring dashboards allows teams to react proactively before user experience is affected.
Example Appendices (Code Snippets, Diagrams, and Checklist)
To complement the architectural concepts discussed throughout this guide, the following appendices provide practical references that help bridge theory with real-world implementation. These examples are intentionally simplified so developers can adapt them into their own projects without introducing unnecessary complexity.
📎 Appendix A - Minimal Adapter Pseudocode
This appendix illustrates a lightweight CometChat adapter structure that focuses on initialization, event subscription, and data mapping. The goal is to demonstrate how SDK-specific callbacks can be transformed into domain-friendly streams while preserving Clean Architecture boundaries.
🔁 Appendix B - Example Use Case: SendMessage Flow
A simplified SendMessage flow highlights how presentation layers trigger domain use cases, which then communicate with repositories and adapters. This sequence helps developers visualize how dependencies move inward while real-time responses propagate outward to the UI.
🧪 Appendix C - Test Stubs and SDK Mocking
Testing examples include mock adapters, fake repositories, and simple test stubs that simulate message streams without requiring a live SDK connection. These patterns support faster iteration and safer refactoring when chat features evolve.
Together, these appendices reinforce the idea that building a scalable in-app chat system is not only about selecting the right SDK but also about structuring responsibilities clearly across layers. By combining CometChat’s real-time capabilities with a thoughtful Clean Architecture approach, teams can create chat experiences that remain flexible, testable, and production-ready.
In conclusion, adopting a layered design encourages long-term maintainability while reducing the risk of tightly coupled code. Developers gain the freedom to evolve UI strategies, refine business logic, and adapt infrastructure without large-scale rewrites. As applications grow from MVP experiments into mature platforms, this balance between architectural discipline and development speed becomes a key factor in delivering reliable real-time communication features.
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