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 # LanguageStudy
+
+# Project Overview
+- **Architecture**: Multi-module Architecture
+
+# Domain
+**LanguageStudy**: A language learning application.
+
+# Dependencies
+
+- **Kotlin**
+- **Compose**
+- **Hilt**
+- **Room**
+- **Coroutines**
+
+# Current Status
+Preparing for MVP version development.
+
+# Design System Development
+- Establishing a comprehensive design system:
+    - Define design tokens
+    - Define color tokens
+    - Build minimal essential components (typography, buttons, etc.)
+    - Create a separate sample app to verify design system functionality
+
+# Code Style & Conventions
+
+## Kotlin Conventions
+- **Trailing Comma**: Always use trailing commas in multi-line declarations
+- **If Statements**: Always use braces with line breaks (no single-line if)
+- **When Statements**: Use braces for all branches, prefer `if` for 2 conditions, no `else` for enums/sealed
+- **Lambda**: Always use line breaks, specify field types explicitly
+- **Invoke Operator**: Use `obj()` not `obj.invoke()` for operator functions and lambdas
+- **Enum Classes**: Use `SCREAMING_SNAKE_CASE` for enum entries
+- **Declaration Order**: override → public → internal → protected → private (variables → functions → extensions)
+- **Object/Companion**: Always declare at bottom of class/interface
+- **Named Arguments**: Optional for 1 arg, required for 2+ args (Kotlin code only)
+- **Comments**: Use KDoc style, link TODO comments to JIRA tickets. Do not leave comments like `//` inside functions.
+- **Class Formatting**: The first line of a class should be written without a blank line.
+
+## Compose Conventions
+- **Function Naming**: Unit-returning Composables start with uppercase, value-returning with lowercase
+- **Parameter Order**: Required → Modifier (first optional) → Optional → Composable slots/lambdas
+- **Modifier Default**: Always use `modifier: Modifier = Modifier` (not `Modifier.something()`)
+- **ViewModel Injection**: Pass ViewModels as parameters, not create inside Composables
+- **Preview Functions**: Mark internal composable previews as `internal` (not `public`)
+- **Event Parameters**: Use consistent naming for event handlers (`onX` pattern)
+
+# Architecture
+Following Android's official recommended app architecture with a layered approach:
+- **Presentation Layer** → **Domain Layer (Optional)** → **Data Layer**
+
+## Architectural Pattern
+- **UI Pattern**: MVVM (Model-View-ViewModel)
+    - Considering MVI as an alternative, but MVVM is likely to be adopted
+
+## Layer Responsibilities
+
+### Presentation Layer
+- **Pattern**: MVVM with Jetpack Compose
+- **Components**:
+    - ViewModels: Business logic and state management
+    - UI States: Immutable state representations
+    - Contracts: Events and side effects
+    - Composables: UI components
+- **Dependencies**: Domain API modules only (no direct data layer access)
+
+### Domain Layer (Optional)
+- **Pattern**: UseCase-based business logic
+- **When to use**:
+    - Complex repository logic that needs coordination
+    - Combining data from multiple repositories
+    - Reusable business logic across features
+- **Components**:
+    - UseCases: Single-responsibility business operations
+    - DomainModels: Business entities
+    - Domain Mappers: Data to domain transformations
+- **Dependencies**: Repository API modules only (no direct data source access)
+
+### Data/Repository Layer
+- **Pattern**: Repository pattern with API/IMPL separation
+- **Components**:
+    - Repository interfaces (API): Contract definitions
+    - Repository implementations (IMPL): Data access logic
+    - DataModels: Data transfer objects
+    - Data Mappers: Network/DB to data model transformations
+- **Dependencies**: DataSource API modules, domain contracts
+
+### DataSource/Network Layer
+- **Pattern**: DataSource pattern with Request/Response DTOs
+- **Components**:
+    - RemoteDataSource: Firebase API interactions
+    - LocalDataSource: Local storage operations
+    - Response DTOs: API response models
+    - Request DTOs: API request parameters
+- **Dependencies**: Network clients (Firebase SDK), local storage APIs
+
+