ng-signals-template/README.md

# ng-signals-template

A minimal Angular 22 starter: signals for state, `resource()` for async data, and a
`RemoteData` type that makes "loading but has an error," "success with no value," and
similar illegal combinations impossible to construct. One worked feature (`users/`) shows
the whole pattern end to end, including an action (click a user → see their details →
go back).

It's extracted from a larger reference app — the "POC" referenced throughout this
document — which shows the same ideas grown up to production scale (multi-context DDD,
enforced architecture boundaries, i18n, a real design system, generated API clients). This
template deliberately keeps only the part of that setup useful from day one, and documents
exactly where to reach for the rest as a project grows.

## Running it

```bash
npm start   # ng serve
npm test    # ng test (Vitest)
```

## What's here

- **`RemoteData<E, T>`** (`shared/application/remote-data.ts`) — a 4-variant union
  (`Loading | Empty | Failure | Success`) plus `fromResource()`, which projects Angular's
  own `resource()` into one. No store, no reducer — `resource()` already holds the async
  state; `RemoteData` just normalizes it for exhaustive rendering.
- **`<app-async>`** (`shared/ui/molecules/async.component.ts`) — a `@switch` over all 4
  states: a spinner while loading, an empty message, a failure message with a retry
  button, or your projected content on success. Reused by both fetches in `users/`.
- **`<app-page-shell>`** (`shared/ui/templates/page-shell.component.ts`) — a heading plus
  one content slot. That's it.
- **`users/`** — one feature context, laid out the same way a bigger one would be:
  `domain/` (pure types, no Angular import), `infrastructure/` (the only file allowed to
  call `fetch`), `application/` (composes infrastructure + `resource()` — this is also
  exactly where a real store would slot in later), `ui/` (organisms + the page). Clicking
  a user in the list sets one plain `signal` on the page, which swaps in a
  `UserDetailComponent` that does its own independent fetch.
- Path aliases `@shared/*` and `@users/*` (see `tsconfig.json`) instead of relative
  `../../` imports, one per context — add one per new context you create.
- Tests are BDD-style (`describe`/`it`, one `expect` per `it`) and black-box: they assert
  on rendered DOM and emitted events, never on a component's private fields, so a test
  never breaks just because an internal was refactored.

## What's deliberately not here (vs. the POC)

| Missing                                                       | Why                                                                                                   |
| ------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------- |
| Elm-style store (`createStore`/Model-Msg-reduce)              | Not needed until a page's state has more than a couple of interacting fields — see Growth path below. |
| i18n (`$localize` + translation file)                         | POC-specific requirement (a Dutch app shipping English too); irrelevant for a single-locale starter.  |
| CIBG Huisstijl theming / token bridge                         | The POC's specific design system; a starter has no house style to vendor yet.                         |
| `dependency-cruiser` boundary enforcement                     | Real value once you have 2+ contexts that must not import each other; overhead for one.               |
| `contracts/` layer + generated API client + `parse*` boundary | Only earns its keep once you're consuming a real backend's OpenAPI contract, not a public test API.   |
| Storybook + axe a11y gate                                     | Testing/documentation infrastructure that pays off at a much bigger component count.                  |
| CI pipeline                                                   | Nothing to gate yet with one context and no deploy target.                                            |

## Growth path — when you outgrow this

Each of these is a real, working pattern in the POC — copy it when you actually need it,
not before:

- **A page's state grows past 2-3 interacting fields, or needs undo/multi-step flow** →
  add an Elm-style store: `shared/application/store.ts` (`createStore`) +
  a `*.machine.ts` per feature (Model/Msg/pure `reduce`).
- **You have 2+ contexts that must not import each other** → add
  `dependency-cruiser` (`.dependency-cruiser.js`) to enforce the `domain → application →
infrastructure`/`ui` direction this template already follows by convention but doesn't
  check.
- **You're consuming a real backend's OpenAPI contract** → add a `contracts/` layer
  (wire DTOs) + a generated typed client + a hand-written `parse*` boundary in
  `infrastructure/` (see ADR-0001, `.claude/skills/bff-endpoint/SKILL.md` if you're
  working from the POC directly).
- **A second locale** → wrap user-facing copy in `$localize` with a stable custom id and
  add a translation `.xlf` file (see the POC's `CLAUDE.md` "User-facing copy" convention).
- **A real design system** → vendor your CSS, then bridge your own token names onto it the
  way ADR-0003 (`docs/reference/architecture/0003-cibg-huisstijl.md` in the POC) does —
  keep your token names stable, only their values change.
- **Testing/a11y at real component count** → add Storybook + the axe a11y addon so every
  component's states are visually verifiable and accessibility-checked, not just
  behavior-tested.

## Folder convention

Each business capability is a context under `src/app/<context>/`, split into
`domain/application/infrastructure/ui` — dependencies point inward
(`ui → application → domain`; only `application` reaches `infrastructure`). Inside a
context's `ui/`, components are organized by atomic-design layer (`atoms → molecules →
organisms → templates → pages`); `shared/` holds only cross-context building blocks. When
you add a second context, mirror `users/`'s shape.