budget/.plans/10-project-split.md

Plan: Core / Infrastructure / API Project Split

Goal

Split the single Budget.Api project into three projects matching the stwaddle stack pattern:

• Budget.Core — entities, DTOs, enums. No ASP.NET or EF dependencies.
• Budget.Infrastructure — DbContext, EF configs, migrations, domain services.
• Budget.Api — controllers, middleware, Program.cs, DI wiring.

Current state

Everything lives in src/Budget.Api/:

Models/         Budget, Income, Outgo, BudgetShare, KnownUser, enums
DTOs/           BudgetDtos, IncomeDtos, OutgoDtos, ShareDtos, SummaryDtos
Data/           AppDbContext, Migrations/
Services/       BudgetAuthorizationService, FrequencyCalculator,
                KnownUserMiddleware, ErrorHandlingMiddleware, ClaimsPrincipalExtensions
Controllers/    BudgetsController, IncomesController, OutgosController,
                SharesController, SummaryController
Program.cs

Target state

src/
  Budget.Core/
    Models/     Budget, Income, Outgo, BudgetShare, KnownUser, enums
    DTOs/       all DTO records and request types
    Services/   FrequencyCalculator (pure logic, no EF/ASP.NET)

  Budget.Infrastructure/
    Data/       AppDbContext, Migrations/
    Services/   BudgetAuthorizationService

  Budget.Api/
    Controllers/
    Services/   KnownUserMiddleware, ErrorHandlingMiddleware,
                ClaimsPrincipalExtensions
    Program.cs

References: Budget.Api → Budget.Infrastructure → Budget.Core

Steps

Phase 1 — Create projects and move files

1. dotnet new classlib -n Budget.Core -o src/Budget.Core --framework net10.0
2. dotnet new classlib -n Budget.Infrastructure -o src/Budget.Infrastructure --framework net10.0
3. Add both to the solution: dotnet sln add src/Budget.Core/Budget.Core.csproj src/Budget.Infrastructure/Budget.Infrastructure.csproj
4. Move Models/ and DTOs/ to Budget.Core; update namespaces from Budget.Api.* to Budget.Core.*.
5. Move FrequencyCalculator.cs to Budget.Core/Services/.
6. Move Data/ (AppDbContext + Migrations) to Budget.Infrastructure/Data/.
7. Move BudgetAuthorizationService.cs to Budget.Infrastructure/Services/.

Phase 2 — Wire up project references and NuGet packages

8. Add project reference: Budget.Infrastructure → Budget.Core.
9. Move EF Core + Npgsql NuGet packages from Budget.Api.csproj to Budget.Infrastructure.csproj. Keep only Microsoft.AspNetCore.Authentication.JwtBearer and health-check packages in Budget.Api.csproj.
10. Add project references to Budget.Api.csproj: both Budget.Core and Budget.Infrastructure.
11. Add Microsoft.EntityFrameworkCore.Design to Budget.Api.csproj (needed for dotnet ef CLI to find the startup project).

Phase 3 — Update namespaces and using statements

12. Global search-replace across all moved files: namespace Budget.Api → namespace Budget.Core or namespace Budget.Infrastructure as appropriate.
13. Update using directives in all controllers, middleware, and Program.cs to reference the new namespaces.

Phase 4 — Update Dockerfile and EF migrations command

14. Update Dockerfile Stage 2 to copy and restore all three projects before publishing Budget.Api.
15. Verify dotnet ef migrations add command still works with --project Budget.Infrastructure --startup-project Budget.Api.
16. Build and confirm zero errors.

Key decisions

• ClaimsPrincipalExtensions and the two middleware classes stay in Budget.Api — they have direct ASP.NET dependencies and are not reusable across projects.
• BudgetAuthorizationService goes in Budget.Infrastructure because it queries the DbContext.
• FrequencyCalculator goes in Budget.Core because it is pure arithmetic with no external dependencies.
• DTOs stay in Budget.Core (not Budget.Api) so Budget.Infrastructure can reference them if needed without creating a circular dependency.

Files affected

• Budget.sln
• New: src/Budget.Core/Budget.Core.csproj
• New: src/Budget.Infrastructure/Budget.Infrastructure.csproj
• src/Budget.Api/Budget.Api.csproj (trim NuGet packages, add project refs)
• All .cs files under src/Budget.Api/ (namespace updates)
• Dockerfile (Stage 2 COPY pattern)