/**
 * The typed API client (openapi-fetch over the generated `schema.d.ts`). Same origin as the SPA (`/me`, `/sync`, …).
 * Every call carries the headers of SPEC §14.3.1: `X-Kvitt-Protocol: 1`, `X-Kvitt-App-Version`,
 * `X-Kvitt-App-Version-Name`, `Accept-Language`, and `Authorization: Bearer <token>` while signed in. A 401 signs the
 * session out (`unauthorized` or `device_revoked`), which sends the router to /app/login.
 */
import createClient, { type Client } from 'openapi-fetch';
import { BUILD } from '../app/buildInfo';
import type { Language } from '../i18n/language';
import type { paths } from './schema';
import type { SessionStore } from './session';
import type { ErrorBody, ErrorCode } from './types';

/** The protocol version this client speaks (SPEC §14.4). */
export const PROTOCOL_VERSION = '1';

/** The operations' header parameters are set by the middleware below, so callers never pass them. */
type WithoutHeaderParams<Operation> = Operation extends { parameters: infer Params }
  ? Omit<Operation, 'parameters'> & { parameters: Omit<Params, 'header'> & { header?: never } }
  : Operation;
export type ApiPaths = {
  [Path in keyof paths]: { [Method in keyof paths[Path]]: WithoutHeaderParams<paths[Path][Method]> };
};
export type Api = Client<ApiPaths>;

export interface ApiOptions {
  /** The origin the SPA is served from; the API lives at its root (OpenAPI `servers`). */
  baseUrl: string;
  session: SessionStore;
  language: () => Language;
  fetch?: (request: Request) => Promise<Response>;
}

/** An API failure: an error body of SPEC §14.3.2, or `network` when the server could not be reached. */
export class ApiError extends Error {
  constructor(
    readonly status: number,
    readonly code: ErrorCode | 'network' | 'unexpected',
    readonly field: string | null,
    message: string,
    readonly retryAfterSeconds: number | null = null,
  ) {
    super(message);
    this.name = 'ApiError';
  }
}

function isErrorBody(value: unknown): value is ErrorBody {
  return typeof value === 'object' && value !== null && typeof (value as { code?: unknown }).code === 'string';
}

async function errorCodeOf(response: Response): Promise<string | null> {
  try {
    const body: unknown = await response.clone().json();
    return isErrorBody(body) ? body.code : null;
  } catch (error) {
    if (error instanceof SyntaxError || error instanceof TypeError) return null;
    throw error;
  }
}

export function createApi(options: ApiOptions): Api {
  const client = createClient<ApiPaths>({ baseUrl: options.baseUrl, fetch: options.fetch });
  client.use({
    onRequest({ request }) {
      request.headers.set('X-Kvitt-Protocol', PROTOCOL_VERSION);
      request.headers.set('X-Kvitt-App-Version', String(BUILD.versionCode));
      request.headers.set('X-Kvitt-App-Version-Name', BUILD.versionName);
      request.headers.set('Accept-Language', options.language());
      const session = options.session.get();
      if (session !== null) request.headers.set('Authorization', `Bearer ${session.token}`);
      return request;
    },
    async onResponse({ request, response }) {
      if (response.status === 401 && request.headers.has('Authorization')) {
        const code = await errorCodeOf(response);
        options.session.signOut(code === 'device_revoked' ? 'device_revoked' : 'unauthorized');
      }
      return response;
    },
  });
  return client;
}

interface Outcome<D> {
  data?: D;
  error?: unknown;
  response: Response;
}

async function settle<D>(pending: Promise<Outcome<D>>): Promise<Outcome<D>> {
  try {
    return await pending;
  } catch (cause) {
    if (cause instanceof DOMException && cause.name === 'AbortError') throw cause;
    throw new ApiError(0, 'network', null, cause instanceof Error ? cause.message : 'network error');
  }
}

function failure(outcome: Outcome<unknown>): ApiError {
  const { response, error } = outcome;
  const retryAfter = response.headers.get('Retry-After');
  const retryAfterSeconds = retryAfter === null ? null : Number(retryAfter);
  if (isErrorBody(error)) {
    return new ApiError(response.status, error.code, error.field, error.message, retryAfterSeconds);
  }
  return new ApiError(response.status, 'unexpected', null, `HTTP ${response.status}`, retryAfterSeconds);
}

/** The response body of a successful call; throws ApiError otherwise. */
export async function unwrap<D>(pending: Promise<Outcome<D>>): Promise<D> {
  const outcome = await settle(pending);
  if (!outcome.response.ok) throw failure(outcome);
  if (outcome.data === undefined) throw new ApiError(outcome.response.status, 'unexpected', null, 'empty body');
  return outcome.data;
}

/** For calls answered with 204 No Content; throws ApiError on failure. */
export async function unwrapEmpty(pending: Promise<Outcome<unknown>>): Promise<void> {
  const outcome = await settle(pending);
  if (!outcome.response.ok) throw failure(outcome);
}