import { calendarById, type CalendarSlug } from "@/lib/calendars";
import { API_BASE_URL } from "@/lib/env";
import { parseApiEvents } from "@/lib/events";
import type { AdminUser, ApiEvent, CalendarEvent, EventPayload } from "@/lib/types";

/**
 * Every call to the API, made from the browser straight to the API's origin.
 *
 * `credentials: "include"` is mandatory, not a detail: the API is a different
 * origin, so without it the browser leaves the session cookie behind and every
 * call is anonymous. That fails as a plain 401, which reads like an expired
 * login rather than a missing option.
 *
 * Callers must tell 401 from 403 (see `ApiError.status`): 401 means nobody is
 * signed in and is the only status worth a trip to the login page; redirecting
 * on 403 loops, because signing in succeeds and lands straight back on the
 * refusal.
 */

export class ApiError extends Error {
  status: number;
  body: unknown;
  constructor(status: number, body: { message?: string } & Record<string, unknown>, message?: string) {
    super(message ?? body?.message ?? `API request failed with ${status}`);
    this.status = status;
    this.body = body;
  }
}

const request = async <T>(path: string, init?: RequestInit): Promise<T> => {
  let res: Response;
  try {
    res = await fetch(`${API_BASE_URL}${path}`, {
      ...init,
      credentials: "include",
      headers: { "Content-Type": "application/json", ...init?.headers },
    });
  } catch {
    // Network failure or a CORS refusal - the browser hides which. Status 0
    // keeps it apart from anything the API itself answered.
    throw new ApiError(0, {}, "Keine Verbindung zum Server.");
  }
  if (res.status === 204) {
    return undefined as T;
  }
  const data = await res.json().catch(() => ({}));
  if (!res.ok) {
    throw new ApiError(res.status, data);
  }
  return data as T;
};

const eventsPath = "/calendar/events";

export const api = {
  /** Who is signed in, across all four apps. */
  me: (): Promise<AdminUser> => request<AdminUser>("/admin/me"),

  /**
   * One calendar's events, as the admin view: all statuses, deleted ones
   * already dropped by the parser. A signed-in editor gets drafts; the same
   * URL without a session returns only published events (or 403 for the
   * internal calendars).
   */
  getEvents: async (slug: CalendarSlug): Promise<CalendarEvent[]> =>
    parseApiEvents(await request<ApiEvent[]>(`${eventsPath}/${slug}/json`)),

  createEvent: async (payload: EventPayload): Promise<number> => {
    const res = await request<{ eventId?: number }>(eventsPath, { method: "POST", body: JSON.stringify(payload) });
    if (typeof res?.eventId !== "number") {
      throw new ApiError(200, res ?? {}, "Der Server hat keine Termin-ID zurückgegeben.");
    }
    return res.eventId;
  },

  /**
   * The API answers 200 even when nothing was written, with
   * `{message: "0 rows were updated"}` - so that body is a failure here.
   */
  updateEvent: async (eventId: number, payload: EventPayload): Promise<void> => {
    const res = await request<{ message?: string }>(`${eventsPath}/${eventId}`, {
      method: "PUT",
      body: JSON.stringify(payload),
    });
    if (res?.message === "0 rows were updated") {
      throw new ApiError(200, res, "Der Termin wurde nicht gespeichert.");
    }
  },

  /** Moves the event to `payload.calendarId`. Only the calendar changes server-side. */
  moveEvent: async (eventId: number, payload: EventPayload): Promise<void> => {
    if (!calendarById(payload.calendarId)) {
      throw new Error(`Unknown calendar ${payload.calendarId}`);
    }
    await request(`${eventsPath}/move/${eventId}`, { method: "PUT", body: JSON.stringify(payload) });
  },

  /**
   * Ready-made iCal URLs per calendar, with the shared password in place where
   * one is needed. Calendars whose password isn't configured are missing.
   */
  getSubscriptions: (): Promise<{ calendar: CalendarSlug; icalUrl: string }[]> =>
    request(`${eventsPath}/subscriptions`),

  /** A soft delete: the API appends a version with status DELETED. */
  deleteEvent: async (eventId: number): Promise<void> => {
    await request(`${eventsPath}/${eventId}`, { method: "DELETE" });
  },
};