Design Patterns Implementation¶

DocuSnap-Frontend implements several design patterns to improve code quality, maintainability, and extensibility. This page analyzes how these patterns are applied throughout the application.

MVVM Pattern Implementation¶

The application fully adopts the MVVM (Model-View-ViewModel) architecture pattern, implementing these core concepts:

1. Data Binding¶

Implemented through StateFlow and collectAsState
UI automatically responds to data changes
Example:

// In ViewModel
private val _documents = MutableStateFlow<List<Document>>(emptyList())
val documents: StateFlow<List<Document>> = _documents.asStateFlow()

// In UI
val documents by viewModel.documents.collectAsState()

2. State Management¶

ViewModels encapsulate and manage UI state
Immutable state objects improve predictability
Example:

data class ImageProcessingUiState(
    val isLoading: Boolean = false,
    val originalImageUris: List<String> = emptyList(),
    val currentImageIndex: Int = 0,
    val editingBitmap: Bitmap? = null,
    // Other state properties
)

3. Command Pattern¶

User actions are executed through ViewModel methods
Operation results are reflected in UI through state updates
Example:

// Command execution in ViewModel
fun deleteDocument(id: String) {
    viewModelScope.launch {
        repository.deleteDocument(id)
        loadDocuments() // Refresh list
    }
}

MVVM Implementation Quality Assessment¶

Strengths: Clear separation of concerns, good state management
Areas for Improvement: Some ViewModels could be further divided to reduce complexity

Repository Pattern Application¶

The Repository pattern is well-implemented in the application:

1. Data Abstraction¶

Repositories abstract data source details
Provide unified data access interfaces
Example:

class DocumentRepository(private val deviceDBService: DeviceDBService) {
    suspend fun getAllDocuments(): List<Document> {
        return deviceDBService.getDocumentGallery().mapNotNull { json ->
            // Mapping logic
        }
    }
}

2. Data Transformation¶

Converts between entities and models
Handles data format and structure changes
Example:

suspend fun getDocument(id: String): Document? {
    val json = deviceDBService.getDocument(id) ?: return null
    return try {
        Document(
            id = json.getString("id"),
            name = json.getString("name"),
            // Other property mapping
        )
    } catch (e: Exception) {
        null
    }
}

3. Caching Strategy¶

Implements local caching to improve performance
Handles online/offline states
Example:

suspend fun getDocumentWithCache(id: String): Document? {
    // Check cache first
    cachedDocuments[id]?.let { return it }

    // If not in cache, load from database
    val document = getDocument(id)

    // Update cache
    document?.let { cachedDocuments[id] = it }

    return document
}

Repository Pattern Quality Assessment¶

Strengths: Good data source abstraction, clear responsibility division
Areas for Improvement: Could enhance caching strategy, optimize data synchronization mechanisms

Observer Pattern (Flow)¶

The application uses Kotlin Flow to implement the Observer pattern:

1. Data Streams¶

StateFlow manages UI state
Flow retrieves data from database
Example:

@Query("SELECT * FROM documents ORDER BY last_used DESC")
fun getAllDocuments(): Flow<List<DocumentEntity>>

2. Automatic Updates¶

UI automatically updates through collectAsState
Data changes propagate to all observers
Example:

@Composable
fun DocumentScreen(viewModel: DocumentViewModel) {
    val documents by viewModel.documents.collectAsState()

    LazyColumn {
        items(documents) { document ->
            DocumentItem(document)
        }
    }
}

3. Operator Chains¶

Flow operators process data transformations
Implement complex data processing workflows
Example:

repository.searchDocuments(query)
    .map { documents -> documents.sortedByDescending { it.lastUsed } }
    .filter { documents -> documents.isNotEmpty() }
    .catch { emit(emptyList()) }
    .collect { documents ->
        _searchResults.value = documents
    }

Flow Implementation Quality Assessment¶

Strengths: Concise reactive programming model, reduced boilerplate code
Areas for Improvement: Could better handle backpressure and error propagation

Factory Pattern and Strategy Pattern¶

The application implements several other design patterns:

1. Factory Pattern¶

ViewModelFactory creates ViewModel instances
Supports dependency injection and testing
Example:

class DocumentViewModelFactory(
    private val repository: DocumentRepository
) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(DocumentViewModel::class.java)) {
            @Suppress("UNCHECKED_CAST")
            return DocumentViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

2. Strategy Pattern¶

Encapsulates different algorithms in image processing
Supports dynamic algorithm switching and configuration
Example:

// Strategy selection through higher-order functions
fun applyFilter(filterName: String, filter: suspend (Bitmap) -> Bitmap) {
    // Implementation
}

// Strategy usage
applyBinarizationFilter() {
    applyFilter("Black & White") { bitmap ->
        imageProcService.applyThresholdFilter(bitmap, 4)
    }
}

3. Command Pattern¶

Operations are encapsulated as independent commands
Supports operation history and undo functionality
Example:

sealed class ImageProcessingCommand {
    data class ApplyFilter(val filterType: String, val parameters: Map<String, Any>) : ImageProcessingCommand()
    data class Crop(val rect: Rect) : ImageProcessingCommand()
    data class Rotate(val degrees: Float) : ImageProcessingCommand()
    object Reset : ImageProcessingCommand()
}

4. Adapter Pattern¶

Adapts REST API through Retrofit interface
Converts HTTP requests to local method calls
Example:

interface BackendApiInterface {
    @POST("process")
    suspend fun process(@Body requestBody: String): JSONObject

    @POST("status")
    suspend fun checkStatus(@Body requestBody: String): JSONObject
}

5. Decorator Pattern¶

Enhances objects with additional functionality
Used in security and logging aspects
Example:

// Encryption decorator for API communication
private suspend fun process(
    type: String,
    payload: Any
): ProcessingResult {
    // Original data preparation
    val innerJson = JSONObject().apply {
        // Setup payload
    }

    // Decoration with encryption
    val aesKey = cryptoUtil.generateAesKey()
    val encryptedContent = cryptoUtil.aesEncrypt(innerJson.toString().toByteArray(), aesKey)
    val sha256 = cryptoUtil.computeSHA256(encryptedContent)
    val encryptedAesKey = cryptoUtil.rsaEncrypt(aesKey, cryptoUtil.getPublicKey(settingsManager.getPublicKeyPem()))

    // Continue with decorated data
}

Design Pattern Quality Assessment¶

The application's use of design patterns demonstrates a good understanding of software design principles:

Strengths: Enhances code flexibility and extensibility, follows established patterns
Areas for Improvement: Could apply patterns more consistently across the codebase

Overall, DocuSnap-Frontend effectively leverages design patterns to create a maintainable, flexible, and robust application architecture.