# 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)