import { Result, ok, err, assertNever } from '@shared/kernel/fp';
import { Postcode, parsePostcode } from '@registratie/domain/value-objects/postcode';
import { Email, parseEmail } from '@registratie/domain/value-objects/email';
import {
  UploadState,
  UploadMsg,
  DeliveryChannel,
  initialUpload,
  reduceUpload,
  requiredCategoriesSatisfied,
  deliveryRefs,
} from '@shared/upload/upload.machine';

/**
 * A FIXED 3-step registration wizard. The steps never change in number (always
 * `STEPS`): (1) adres + correspondentievoorkeur, (2) beroep o.b.v. diploma,
 * (3) controle & indienen. Follow-up questions appear *inline within a step*
 * (e.g. choosing 'email' reveals the e-mail field). "Is this field required
 * right now" is a pure function (`validateStep`), so it is trivial to test and
 * impossible to get out of sync with the data. Invariants live here, not in the
 * UI: the wizard reaches `Indienen` only when a complete `ValidRegistratie` parses.
 */

export type StepId = 'adres' | 'beroep' | 'controle';

/** The fixed step list. Number of steps never changes; questions reveal inline. */
export const STEPS: StepId[] = ['adres', 'beroep', 'controle'];

/** Where a piece of data came from — recorded on the aggregate (PRD §5). */
export type AdresHerkomst = 'brp' | 'handmatig';
export type DiplomaHerkomst = 'duo' | 'handmatig';
export type Correspondentie = 'email' | 'post';

/** One record carried across every step (and persisted). All optional: the user
    fills it in gradually. Adres fields are kept flat so one `SetField` message
    serves them all (mirrors the intake machine). */
export interface Draft {
  straat?: string;
  postcode?: string;
  woonplaats?: string;
  adresHerkomst?: AdresHerkomst;
  correspondentie?: Correspondentie;
  email?: string;
  diplomaId?: string;
  diplomaHerkomst?: DiplomaHerkomst;
  beroep?: string; // DERIVED from the chosen DUO diploma (or declared for a manual one)
  vraagIds?: string[]; // ids of the policy questions that apply to the chosen diploma
  antwoorden: Record<string, string>; // geldigheidsantwoorden, keyed by question id
}

/** What we have after the controle step parses — guaranteed valid/typed. */
export interface ValidRegistratie {
  adres: { straat: string; postcode: Postcode; woonplaats: string };
  adresHerkomst: AdresHerkomst;
  correspondentie: Correspondentie;
  email?: Email; // only when correspondentie === 'email'
  diplomaId: string;
  diplomaHerkomst: DiplomaHerkomst;
  beroep: string;
  antwoorden: Record<string, string>;
  documents: Array<{ categoryId: string; channel: DeliveryChannel; documentId?: string }>;
}

/** Text fields settable via SetField. */
export type DraftField = 'straat' | 'postcode' | 'woonplaats' | 'email';

/** Per-field error map. `antwoorden` holds per-policy-question errors, keyed by
    question id (a step can show several questions). */
export interface Errors {
  straat?: string;
  postcode?: string;
  woonplaats?: string;
  email?: string;
  correspondentie?: string;
  diploma?: string;
  documenten?: string;
  antwoorden?: Record<string, string>;
}

export type RegistratieState =
  | { tag: 'Invullen'; draft: Draft; cursor: number; errors: Errors; upload: UploadState }
  | { tag: 'Indienen'; data: ValidRegistratie }
  | { tag: 'Ingediend'; data: ValidRegistratie; referentie: string }
  | { tag: 'Mislukt'; data: ValidRegistratie; error: string };

const emptyDraft: Draft = { antwoorden: {} };
export const initial: RegistratieState = { tag: 'Invullen', draft: emptyDraft, cursor: 0, errors: {}, upload: initialUpload };

/** Which step the cursor currently points at (clamped to the fixed list). */
export function currentStep(s: Extract<RegistratieState, { tag: 'Invullen' }>): StepId {
  return STEPS[Math.min(s.cursor, STEPS.length - 1)];
}

/** Has the user meaningfully started, so it's worth persisting as a Concept? Excludes
    the automatic BRP address prefill on step 0 — a bare page visit creates nothing.
    ponytail: an address typed at step 0 without any of these signals is not yet
    persisted (created once they advance/choose); accepted regression vs. sessionStorage. */
export function hasProgress(s: Extract<RegistratieState, { tag: 'Invullen' }>): boolean {
  const d = s.draft;
  return (
    s.cursor > 0 ||
    !!d.correspondentie ||
    !!d.email ||
    !!d.diplomaId ||
    !!d.beroep ||
    deliveryRefs(s.upload).some((r) => r.channel === 'digital' && !!r.documentId)
  );
}

/** Validate every question currently visible in ONE step. Errors keyed per field. */
function validateStep(step: StepId, d: Draft, upload: UploadState): Result<Errors, void> {
  const errors: Errors = {};
  switch (step) {
    case 'adres': {
      if (!d.straat || d.straat.trim() === '') errors.straat = $localize`:@@validation.straat2:Vul een straat en huisnummer in.`;
      const pc = parsePostcode(d.postcode ?? '');
      if (!pc.ok) errors.postcode = pc.error;
      if (!d.woonplaats || d.woonplaats.trim() === '') errors.woonplaats = $localize`:@@validation.woonplaats:Vul een woonplaats in.`;
      if (!d.correspondentie) errors.correspondentie = $localize`:@@validation.maakKeuze:Maak een keuze.`;
      // E-mail is only required when 'email' is the chosen channel.
      if (d.correspondentie === 'email') {
        const e = parseEmail(d.email ?? '');
        if (!e.ok) errors.email = e.error;
      }
      break;
    }
    case 'beroep': {
      // A diploma must be chosen (or declared manually); its beroep is then known.
      if (!d.diplomaId || !d.beroep) {
        errors.diploma = $localize`:@@validation.diploma:Kies het diploma waarmee u zich wilt registreren, of voer het handmatig in.`;
        break;
      }
      // Every policy question the chosen diploma raised must be answered. Which
      // questions apply is server-decided (carried in `vraagIds`); we only check
      // they're answered.
      const open: Record<string, string> = {};
      for (const id of d.vraagIds ?? []) {
        if (!(d.antwoorden[id] ?? '').trim()) open[id] = $localize`:@@validation.beantwoordVraag:Beantwoord deze vraag.`;
      }
      if (Object.keys(open).length > 0) errors.antwoorden = open;
      // Required documents for this wizard attach to the beroep step (inline upload).
      if (!requiredCategoriesSatisfied(upload)) {
        errors.documenten = $localize`:@@validation.documenten:Lever de verplichte documenten aan (upload of kies "per post nasturen").`;
      }
      break;
    }
    case 'controle':
      break; // controle shows a summary; no own fields
    default:
      return assertNever(step);
  }
  return Object.keys(errors).length > 0 ? err(errors) : ok(undefined);
}

/** Parse the whole wizard into a ValidRegistratie (called on submit). */
function validateAll(d: Draft, upload: UploadState): Result<Errors, ValidRegistratie> {
  const errors: Errors = {};
  for (const step of STEPS) {
    const r = validateStep(step, d, upload);
    if (!r.ok) Object.assign(errors, r.error);
  }
  if (Object.keys(errors).length > 0) return err(errors);

  const pc = parsePostcode(d.postcode ?? '');
  // validateStep guaranteed these parse, but keep the compiler happy.
  if (!pc.ok || !d.diplomaId || !d.beroep || !d.correspondentie) return err(errors);
  const email = d.correspondentie === 'email' ? parseEmail(d.email ?? '') : undefined;
  // Keep only the answers to the questions that actually applied.
  const vraagIds = d.vraagIds ?? [];
  const antwoorden = Object.fromEntries(vraagIds.map((id) => [id, d.antwoorden[id] ?? '']));

  return ok({
    adres: { straat: d.straat!, postcode: pc.value, woonplaats: d.woonplaats! },
    adresHerkomst: d.adresHerkomst ?? 'handmatig',
    correspondentie: d.correspondentie,
    email: email?.ok ? email.value : undefined,
    diplomaId: d.diplomaId,
    diplomaHerkomst: d.diplomaHerkomst ?? 'handmatig',
    beroep: d.beroep,
    antwoorden,
    documents: deliveryRefs(upload),
  });
}

export function setField(s: RegistratieState, key: DraftField, value: string): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  const draft: Draft = { ...s.draft, [key]: value };
  // Editing an address field means the user owns it now — not the BRP copy.
  if (key === 'straat' || key === 'postcode' || key === 'woonplaats') draft.adresHerkomst = 'handmatig';
  return { ...s, draft };
}

export function setCorrespondentie(s: RegistratieState, value: Correspondentie): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, correspondentie: value } };
}

/** Prefill the address from a BRP lookup and flag its origin (PRD §7). */
export function prefillAdres(s: RegistratieState, straat: string, postcode: string, woonplaats: string): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, straat, postcode, woonplaats, adresHerkomst: 'brp' } };
}

/** Pick a DUO diploma; the beroep is derived from it and the applicable policy
    questions (`vraagIds`) come with it (both server-computed, passed in). */
export function kiesDiploma(s: RegistratieState, diplomaId: string, beroep: string, vraagIds: string[]): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, diplomaId, beroep, vraagIds, diplomaHerkomst: 'duo' }, errors: {} };
}

/** Switch to manual diploma entry: the diploma isn't in DUO, so the MAXIMAL
    policy-question set applies and the entry is flagged handmatig/unverified. The
    beroep is declared separately (declareerBeroep). */
export function kiesHandmatig(s: RegistratieState, vraagIds: string[]): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, diplomaId: 'handmatig', beroep: undefined, vraagIds, diplomaHerkomst: 'handmatig' }, errors: {} };
}

/** Declare the beroep for a manually-entered diploma (chosen from a fixed list). */
export function declareerBeroep(s: RegistratieState, beroep: string): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, beroep } };
}

export function setAntwoord(s: RegistratieState, vraagId: string, value: string): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, draft: { ...s.draft, antwoorden: { ...s.draft.antwoorden, [vraagId]: value } } };
}

export function next(s: RegistratieState): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  const r = validateStep(currentStep(s), s.draft, s.upload);
  if (!r.ok) return { ...s, errors: r.error };
  return { ...s, cursor: Math.min(s.cursor + 1, STEPS.length - 1), errors: {} };
}

export function back(s: RegistratieState): RegistratieState {
  if (s.tag !== 'Invullen' || s.cursor === 0) return s;
  return { ...s, cursor: s.cursor - 1, errors: {} };
}

/** Jump back to an earlier step to correct data (controle → step N). Forward
    jumps are not allowed (would skip validation). Preserves the draft. */
export function gaNaarStap(s: RegistratieState, cursor: number): RegistratieState {
  if (s.tag !== 'Invullen' || cursor < 0 || cursor >= s.cursor) return s;
  return { ...s, cursor, errors: {} };
}

export function submit(s: RegistratieState): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  const r = validateAll(s.draft, s.upload);
  return r.ok ? { tag: 'Indienen', data: r.value } : { ...s, errors: r.error };
}

/** Route an upload sub-message through the pure upload reducer (Invullen only). */
export function upload(s: RegistratieState, msg: UploadMsg): RegistratieState {
  if (s.tag !== 'Invullen') return s;
  return { ...s, upload: reduceUpload(s.upload, msg) };
}

export function resolve(s: RegistratieState, r: Result<string, string>): RegistratieState {
  if (s.tag !== 'Indienen') return s;
  return r.ok ? { tag: 'Ingediend', data: s.data, referentie: r.value } : { tag: 'Mislukt', data: s.data, error: r.error };
}

export type RegistratieMsg =
  | { tag: 'SetField'; key: DraftField; value: string }
  | { tag: 'SetCorrespondentie'; value: Correspondentie }
  | { tag: 'PrefillAdres'; straat: string; postcode: string; woonplaats: string }
  | { tag: 'KiesDiploma'; diplomaId: string; beroep: string; vraagIds: string[] }
  | { tag: 'KiesHandmatig'; vraagIds: string[] }
  | { tag: 'DeclareerBeroep'; beroep: string }
  | { tag: 'SetAntwoord'; vraagId: string; value: string }
  | { tag: 'Next' }
  | { tag: 'Back' }
  | { tag: 'GaNaarStap'; cursor: number }
  | { tag: 'Submit' }
  | { tag: 'Retry' }
  | { tag: 'SubmitConfirmed'; referentie: string }
  | { tag: 'SubmitFailed'; error: string }
  | { tag: 'Upload'; msg: UploadMsg }
  | { tag: 'Seed'; state: RegistratieState };

export function reduce(s: RegistratieState, m: RegistratieMsg): RegistratieState {
  switch (m.tag) {
    case 'SetField':
      return setField(s, m.key, m.value);
    case 'SetCorrespondentie':
      return setCorrespondentie(s, m.value);
    case 'PrefillAdres':
      return prefillAdres(s, m.straat, m.postcode, m.woonplaats);
    case 'KiesDiploma':
      return kiesDiploma(s, m.diplomaId, m.beroep, m.vraagIds);
    case 'KiesHandmatig':
      return kiesHandmatig(s, m.vraagIds);
    case 'DeclareerBeroep':
      return declareerBeroep(s, m.beroep);
    case 'SetAntwoord':
      return setAntwoord(s, m.vraagId, m.value);
    case 'Next':
      return next(s);
    case 'Back':
      return back(s);
    case 'GaNaarStap':
      return gaNaarStap(s, m.cursor);
    case 'Submit':
      return submit(s);
    case 'Retry':
      return s.tag === 'Mislukt' ? { tag: 'Indienen', data: s.data } : s;
    case 'SubmitConfirmed':
      return s.tag === 'Indienen' ? { tag: 'Ingediend', data: s.data, referentie: m.referentie } : s;
    case 'SubmitFailed':
      return s.tag === 'Indienen' ? { tag: 'Mislukt', data: s.data, error: m.error } : s;
    case 'Upload':
      return upload(s, m.msg);
    case 'Seed':
      return m.state;
    default:
      return assertNever(m);
  }
}