/**
 * Willkommensmail-Vorlage — API-Client (Administrator → Willkommensmail).
 * Konsumiert `/welcome-mail-template`. Muster `custom-modules-api.ts`:
 * `credentials: 'include'` fuer Cookie-Auth, `NEXT_PUBLIC_API_URL` als Basis.
 */

import type { WelcomeMailTexts } from '@tessera/shared';

const API_URL = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:3001';

/** Antwort von GET/PUT/DELETE /welcome-mail-template. */
export interface WelcomeMailTemplateState {
  /** `true` = eigene Vorlage gespeichert, `false` = Standardtexte. */
  custom: boolean;
  texts: WelcomeMailTexts;
  defaults: WelcomeMailTexts;
  updatedAt: string | null;
  updatedBy: string | null;
}

export interface WelcomeMailPreview {
  subject: string;
  html: string;
  text: string;
}

/** Fehler mit HTTP-Status und den Servermeldungen (400: je Feld eine). */
export class WelcomeMailTemplateRequestError extends Error {
  constructor(
    readonly status: number,
    readonly messages: string[],
  ) {
    super(messages.join(' ') || `HTTP ${status}`);
    this.name = 'WelcomeMailTemplateRequestError';
  }
}

async function readMessages(res: Response): Promise<string[]> {
  try {
    const body = (await res.json()) as { message?: unknown };
    if (Array.isArray(body.message)) return body.message.map(String);
    if (typeof body.message === 'string' && body.message) return [body.message];
  } catch {
    // kein JSON — Status allein
  }
  return [];
}

async function request<T>(path: string, init: RequestInit = {}): Promise<T> {
  const res = await fetch(`${API_URL}/welcome-mail-template${path}`, {
    credentials: 'include',
    ...init,
    headers: init.body ? { 'Content-Type': 'application/json' } : undefined,
  });
  if (!res.ok) throw new WelcomeMailTemplateRequestError(res.status, await readMessages(res));
  return (await res.json()) as T;
}

/** Nur die sechs Texte senden — nie weitere Felder aus dem Formularzustand. */
function textsOf(texts: WelcomeMailTexts): WelcomeMailTexts {
  return {
    subject: texts.subject,
    heading: texts.heading,
    intro: texts.intro,
    loginHintDirectory: texts.loginHintDirectory,
    loginHintLocal: texts.loginHintLocal,
    closing: texts.closing,
  };
}

export function fetchWelcomeMailTemplate(): Promise<WelcomeMailTemplateState> {
  return request('');
}

export function saveWelcomeMailTemplate(
  texts: WelcomeMailTexts,
): Promise<WelcomeMailTemplateState> {
  return request('', { method: 'PUT', body: JSON.stringify(textsOf(texts)) });
}

export function resetWelcomeMailTemplate(): Promise<WelcomeMailTemplateState> {
  return request('', { method: 'DELETE' });
}

export function previewWelcomeMail(
  texts: WelcomeMailTexts,
  account: 'directory' | 'local',
  signal?: AbortSignal,
): Promise<WelcomeMailPreview> {
  return request('/preview', {
    method: 'POST',
    body: JSON.stringify({ ...textsOf(texts), account }),
    signal,
  });
}

export function sendWelcomeMailTest(
  texts: WelcomeMailTexts,
): Promise<{ success: true; to: string }> {
  return request('/test', { method: 'POST', body: JSON.stringify(textsOf(texts)) });
}