maraphon-app/plans/initial-implementation/phase-4-application-and-workers.md

Phase 4: Application Layer + Background Workers

Status: ⬜ Not Started Parent plan: PLAN.md Domain: backend Depends on: Phase 1 (Domain), Phase 2 (Storage), Phase 3 (Scraping)

Objective

Wire scraping + storage together via use-case orchestrators in the Application layer and background services that execute pollers on configurable intervals.

Tasks

• Implement use cases in Marathon.Application/UseCases/:
  • PullUpcomingEventsUseCase(IOddsScraper, IEventRepository, ISnapshotRepository)
    • ExecuteAsync(CancellationToken) → fetch upcoming events, persist new ones, capture initial pre-match snapshots for each
  • PullLiveOddsUseCase(IOddsScraper, IEventRepository, ISnapshotRepository)
    • ExecuteAsync(CancellationToken) → for each currently-live event, fetch a fresh snapshot, persist it
  • PullResultsUseCase(IOddsScraper, IEventRepository, IResultRepository)
    • ExecuteAsync(DateRange range, IReadOnlyList<EventId>? selection, CancellationToken) → fetch results for completed events (all or selected)
  • ExportToExcelUseCase(IExcelExporter, IEventRepository)
    • ExecuteAsync(DateRange, ExportKind, CancellationToken)
• Implement background services in Marathon.Infrastructure/Workers/:
  • UpcomingEventsPoller : BackgroundService — runs PullUpcomingEventsUseCase on a configurable cron-like schedule (default: every 6 hours)
  • LiveOddsPoller : BackgroundService — runs PullLiveOddsUseCase every Scraping:PollingIntervalSeconds seconds
  • Both honor CancellationToken, log via ILogger<T>, and skip cycles gracefully on errors (don't crash the host)
• Add WorkerOptions POCO bound to Workers:* config:

  public sealed class WorkerOptions {
    public string UpcomingScheduleCron { get; init; } = "0 0 */6 * * *"; // every 6h
    public bool LivePollerEnabled { get; init; } = true;
    public bool UpcomingPollerEnabled { get; init; } = true;
  }
  

  Use Cronos package or simple TimeSpan for upcoming schedule.
• Add DI extension AddMarathonApplication(IServiceCollection, IConfiguration) in Marathon.Application/DependencyInjection.cs:
  • Registers all use cases
• Update Marathon.Infrastructure/DependencyInjection.cs to also register BackgroundServices under services.AddHostedService<T>().
• Tests in Marathon.Application.Tests:
  • Mock IOddsScraper + repos with NSubstitute
  • Test: PullUpcomingEventsUseCase persists new events, skips duplicates
  • Test: PullLiveOddsUseCase writes a snapshot per live event
  • Test: PullResultsUseCase respects selection filter (when null, fetches all)
  • Test: ExportToExcelUseCase invokes IExcelExporter.ExportAsync with correct date range
• Tests in Marathon.Infrastructure.Tests/Workers/:
  • Test: LiveOddsPoller invokes use case at configured interval (use FakeTimeProvider)
  • Test: poller continues after a use-case exception (logs, doesn't propagate)

Files to Modify/Create

• src/Marathon.Application/UseCases/*.cs
• src/Marathon.Application/DependencyInjection.cs
• src/Marathon.Infrastructure/Workers/UpcomingEventsPoller.cs
• src/Marathon.Infrastructure/Workers/LiveOddsPoller.cs
• src/Marathon.Infrastructure/Configuration/WorkerOptions.cs
• tests/Marathon.Application.Tests/UseCases/**
• tests/Marathon.Infrastructure.Tests/Workers/**

Acceptance Criteria

• Compiles (Big Bang).
• Use cases depend only on Application abstractions (no Infrastructure refs).
• Workers honor cancellation and don't crash on transient errors.
• All variable timing/enabling is configurable.

Notes

• Use IHostedService from Microsoft.Extensions.Hosting — works in WPF host via Host.CreateApplicationBuilder() pattern (Phase 5 will expose this).
• For the cron-style upcoming poller, prefer the Cronos package (small, mature) over hand-rolled scheduling.
• Big Bang: compile-only smoke check.

Review Checklist

• Use cases have no Infrastructure dependencies
• Both pollers configurable (interval, enable/disable)
• Cancellation propagated correctly
• Errors logged, not propagated out of ExecuteAsync

Handoff to Next Phase