Crypto-Exchange

The Crypto-Exchange web application sample obtains the top 100 crypto currencies from https://coinmarketcap.com/api and converts their values to USD, EUR, BRL, GBP, and AUD (rates obtained from https://exchangeratesapi.io/).

Task Scheduler

TaskScheduler is in charge of scheduling two tasks:

• UpdateRates: Get rates from https://exchangeratesapi.io/
• UpdateListings: Get listing from https://coinmarketcap.com/api

Because these free APIs have a monthly request limit, we must compute the number of times we can fetch the data (in days, hours, and minutes). The app schedules tasks based on the times.

sequenceDiagram
    TaskSchedulerOptions->>CalculateRateLimit: Read MonthlyRequestLimit
    CalculateRateLimit->>TaskScheduler: Convert MonthlyRequestLimit to the times
    TaskScheduler->>ScheduleJobs: Schedule UpdateRates, UpdateListings recurring jobs based on API request limit

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UpdateRates task

sequenceDiagram
    participant TaskScheduler
    participant UpdateRates
    participant Notify
    participant CqsCommandBus
    participant RateRepository    
    TaskScheduler->>UpdateRates: Run the job
    UpdateRates->>CqsQueryBus: Send FetchRatesQuery
    CqsQueryBus->>CqsQueryHandler: Handle the FetchRatesQuery
    CqsQueryHandler->>RateService: GetRates 
    RateService->>RestQueryBus: Send GetRates request query    
    RestQueryBus->>+api.apilayer.com: Get /exchangerates_data/latest
    alt OK
    api.apilayer.com-->>RestQueryBus: RatesResponse    
    RestQueryBus-->>RateService: RatesResponse
    RateService-->>CqsQueryHandler: RatesResponse
    CqsQueryHandler-->>UpdateRates: RatesResponse
    UpdateRates-->>CqsCommandBus: Send UpdateRatesCommand
    CqsCommandBus-->>RateRepository: Upsert RatesResponse
    CqsCommandBus-->>UpdateRates: Upserted
    UpdateRates-->>Notify: Notify all of clients
    else ERROR
    api.apilayer.com-->>-RestQueryBus: Exception
    RestQueryBus-->>RestQueryBus: Catch Exception, Fill the exception in the ExternalCommandResult
    RestQueryBus-->>RateService: RatesResponse with Exception
    RateService-->>RateService: Throw Exception
    end

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UpdateListings task

The sequence is same as UpdateRates

Streaming price changes

App uses SignalR to send the updates to the clients. SignalR first attempts to establish a WebSocket connection if possible.

sequenceDiagram
    participant WebBrowser
    participant WebServer(Notify)
    WebBrowser->>WebServer(Notify): Subscribe 
    WebServer(Notify)->SignalR: Send the updates to clients
    SignalR->WebBrowser: Updates 

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Architcture

The app adheres to Clean Architecture.

Explanation:

• Core.Abstraction: The innermost layer is free of dependencies.

• Domain: Implements the entity interface using Core.Abstraction.

• Application: Domain is used for entities (input) and Integration is used for DTOs (output).

• Integration: Makes use of Core to implement IMediatR commands and queries, as well as DTOs.

• Core: Implements technologies using Core.Abstraction and registers IMediatR commands and queries using Core.Infrastructure:

  • IMediatR: For the CQS pattern (at the class or component level).

  • Newtonsoft: To serialize

  • RestSharp: For rest requests

  • FluentValidation: This is used for DTO validations.

• Core.Infrastructure: Contains an assembly helper that allows us to register all classes using a single interface to IoC.

• Application.TaskScheduler: This layer uses Core.Abstraction and Integration to schedule a task. It also uses 'HangFire' as the technology.

• Data.InMemory: For entity access, uses Core.Abstraction and Domain.

• Application.ExchangeRatesApi: Application and Integration are used. It contains the ExchangeRatesApiService, which is in charge of retrieving rates from api.apilayer.com.

• Application.CoinMarketCap: Application and Integration are used. It includes the CoinMarketCapService component, which is in charge of retrieving listings from https://pro-api.coinmarketcap.com.

• Web:

  • Application.TaskScheduler: For job registration.

  • Data.InMemory: This method is used to register InMemory repositories.

  • Application.ExchangeRatesApi: To register the ExchangeRatesApiService class.

  • Application.CoinMarketCap: To register CoinMarketCapService

  • Integration: Using DTOs for the end-points.