Digital Wallet Service

A robust, event-sourced digital wallet service built with .NET Core, implementing Domain-Driven Design (DDD) and CQRS patterns.

Architecture Overview

The service is built using a clean, layered architecture following DDD principles:

Domain Layer

• Core business logic and rules
• Rich domain models with encapsulated behavior
• Domain events for state changes
• Value objects for immutable concepts
• Aggregates for transactional consistency

Application Layer

• Orchestrates use cases
• Implements CQRS pattern with commands and queries
• Handles domain events
• Manages transactions and business workflows

Infrastructure Layer

• Event sourcing implementation using EventStore
• Read model persistence using Entity Framework Core
• Repository implementations
• External service integrations

API Layer

• RESTful API endpoints
• Command and query handling
• Input validation
• Error handling

Key Features

Wallet Management

• Create and manage digital wallets
• Support for multiple currencies
• Balance tracking and updates
• Transaction history

Transaction Processing

• Funds transfers between wallets
• Top-up operations
• Withdrawals
• Payment processing
• Automatic transaction reconciliation

Account Management

• Multi-wallet accounts
• KYC level management
• Account status tracking
• Transaction limits

Risk Management

• Transaction monitoring
• Risk level assessment
• Account freezing capabilities
• Transaction limits enforcement

Settlement & Reconciliation

• Batch settlement processing
• Merchant settlement management
• Transaction reconciliation
• Dispute handling

Promotions & Rewards

• Cashback rules
• Referral bonuses
• Auto top-up rules
• Promotional campaigns

Design Patterns

Event Sourcing

• State reconstruction from events
• Complete audit trail
• Event store implementation
• Snapshot support for performance

CQRS

• Separate command and query models
• Optimized read and write operations
• Event-driven updates
• Read model projections

Domain-Driven Design

• Bounded contexts
• Rich domain models
• Aggregates
• Value objects
• Domain events

Repository Pattern

• Aggregate persistence
• Read model queries
• Event store integration
• Snapshot management

Technical Implementation

Event Store

• Event persistence
• Stream management
• Snapshot storage
• Optimistic concurrency

Read Models

• Denormalized views
• Query optimization
• Real-time updates
• Cached projections

API Design

• RESTful endpoints
• Resource-based routing
• Proper HTTP method usage
• Comprehensive documentation

Getting Started

1. Prerequisites:

   • .NET Core SDK
   • EventStore DB
   • SQL Server (for read models)

2. Configuration:

   {
     "EventStore": {
       "ConnectionString": "esdb://localhost:2113?tls=false"
     }
   }

3. Run the service:

   dotnet restore
   dotnet build
   dotnet run --project src/WalletService.API/WalletService.API.csproj

Testing

The service includes:

• Unit tests for domain logic
• Integration tests for repositories
• API tests for endpoints
• Event sourcing tests

Performance Considerations

• Snapshot creation for large event streams
• Read model optimization
• Caching strategies
• Batch processing for settlements

Security

• Transaction authorization
• KYC level enforcement
• Risk monitoring
• Account freezing capabilities

Monitoring

• Transaction monitoring
• Balance tracking
• Risk assessment
• System health checks

Error Handling

• Domain exceptions
• Business rule violations
• Concurrency conflicts
• Infrastructure failures

Future Enhancements

• Additional currency support
• Enhanced fraud detection
• Mobile wallet integration
• Blockchain integration
• Real-time reporting