atomic-design-poc/src/app/registratie/domain/change-request.machine.ts

import { Result, assertNever } from '@shared/kernel/fp';
import { Postcode, parsePostcode } from '@registratie/domain/value-objects/postcode';

/** What the user is typing (raw, possibly invalid). */
export interface Draft {
  straat: string;
  postcode: string;
  woonplaats: string;
}

/** After parsing — postcode is the branded type, so downstream can't get a raw one. */
export interface Valid {
  straat: string;
  postcode: Postcode;
  woonplaats: string;
}

export type Errors = Partial<Record<keyof Draft, string>>;

/**
 * The change-request (adreswijziging) form as one tagged union — the SAME idiom
 * as the wizards, just single-step. `draft`/`errors` exist only while Editing;
 * Submitting/Submitted/Failed carry the parsed `Valid`. Illegal states (submitting
 * an invalid draft, a success screen with errors) are unrepresentable.
 */
export type State =
  | { tag: 'Editing'; draft: Draft; errors: Errors }
  | { tag: 'Submitting'; data: Valid }
  | { tag: 'Submitted'; data: Valid; referentie: string }
  | { tag: 'Failed'; data: Valid; error: string };

export const initial: State = {
  tag: 'Editing',
  draft: { straat: '', postcode: '', woonplaats: '' },
  errors: {},
};

/** Parse via the value objects; on success hand back a Valid, else per-field errors. */
function validate(draft: Draft): Result<Errors, Valid> {
  const straat = draft.straat.trim();
  const postcode = parsePostcode(draft.postcode);
  const errors: Errors = {};
  if (!straat) errors.straat = $localize`:@@validation.straat:Vul straat en huisnummer in.`;
  if (!postcode.ok) errors.postcode = postcode.error;
  if (straat && postcode.ok) {
    return { ok: true, value: { straat, postcode: postcode.value, woonplaats: draft.woonplaats.trim() } };
  }
  return { ok: false, error: errors };
}

export type Msg =
  | { tag: 'SetField'; key: keyof Draft; value: string }
  | { tag: 'Submit' }
  | { tag: 'Retry' }
  | { tag: 'SubmitConfirmed'; referentie: string }
  | { tag: 'SubmitFailed'; error: string }
  | { tag: 'Reset' }
  | { tag: 'Seed'; state: State }; // mount a specific state (stories/tests)

export function reduce(s: State, m: Msg): State {
  switch (m.tag) {
    case 'SetField':
      return s.tag === 'Editing' ? { ...s, draft: { ...s.draft, [m.key]: m.value } } : s;
    case 'Submit': {
      if (s.tag !== 'Editing') return s;
      const r = validate(s.draft);
      return r.ok ? { tag: 'Submitting', data: r.value } : { ...s, errors: r.error };
    }
    case 'Retry':
      return s.tag === 'Failed' ? { tag: 'Submitting', data: s.data } : s;
    case 'SubmitConfirmed':
      return s.tag === 'Submitting' ? { tag: 'Submitted', data: s.data, referentie: m.referentie } : s;
    case 'SubmitFailed':
      return s.tag === 'Submitting' ? { tag: 'Failed', data: s.data, error: m.error } : s;
    case 'Reset':
      return initial;
    case 'Seed':
      return m.state;
    default:
      return assertNever(m);
  }
}