import type { ApiErrorBody, HealthResponse } from '@dorfteich/shared';

/**
 * Typed fetch helper for the REST api. Non-2xx responses reject with an
 * ApiError carrying the uniform body — callers translate `code` via the
 * errors namespace and map `details` onto form fields.
 */
export class ApiError extends Error {
  constructor(
    readonly status: number,
    readonly body: ApiErrorBody,
  ) {
    super(body.message);
  }
}

/**
 * Fired once any api call answers 503 `maintenance_mode` (an in-app backup
 * restore is running, issue #103) — App.tsx listens and swaps the UI for
 * the maintenance screen, whatever the user was doing.
 */
export const MAINTENANCE_EVENT = 'dorfteich:maintenance';

function noteMaintenance(status: number, body: ApiErrorBody | null): void {
  if (status === 503 && body?.code === 'maintenance_mode') {
    window.dispatchEvent(new CustomEvent(MAINTENANCE_EVENT));
  }
}

async function requestJson<T>(method: string, path: string, body?: unknown): Promise<T> {
  let response: Response;
  try {
    response = await fetch(`/api/v1${path}`, {
      method,
      headers: {
        Accept: 'application/json',
        ...(body !== undefined ? { 'Content-Type': 'application/json' } : {}),
      },
      body: body !== undefined ? JSON.stringify(body) : undefined,
    });
  } catch {
    throw new ApiError(0, { code: 'network', message: 'network error' });
  }
  if (!response.ok) {
    const parsed = (await response.json().catch(() => null)) as ApiErrorBody | null;
    noteMaintenance(response.status, parsed);
    throw new ApiError(
      response.status,
      parsed ?? { code: `http_${response.status}`, message: response.statusText },
    );
  }
  // 201/204 responses may carry no body at all.
  const text = await response.text();
  return (text ? JSON.parse(text) : undefined) as T;
}

export const apiGet = <T>(path: string): Promise<T> => requestJson<T>('GET', path);
export const apiPost = <T>(path: string, body?: unknown): Promise<T> =>
  requestJson<T>('POST', path, body);
export const apiPut = <T>(path: string, body?: unknown): Promise<T> =>
  requestJson<T>('PUT', path, body);
export const apiPatch = <T>(path: string, body?: unknown): Promise<T> =>
  requestJson<T>('PATCH', path, body);
export const apiDelete = <T>(path: string): Promise<T> => requestJson<T>('DELETE', path);

/** Multipart upload (issue #27/#28) — a FormData body, unlike every other
 * endpoint here, so it can't share `requestJson`'s JSON serialization; the
 * error handling is kept identical. */
export async function apiUploadFile<T>(
  path: string,
  file: File,
  fields: Record<string, string> = {},
): Promise<T> {
  const form = new FormData();
  form.append('file', file);
  for (const [name, value] of Object.entries(fields)) form.append(name, value);
  let response: Response;
  try {
    response = await fetch(`/api/v1${path}`, { method: 'POST', body: form });
  } catch {
    throw new ApiError(0, { code: 'network', message: 'network error' });
  }
  if (!response.ok) {
    const parsed = (await response.json().catch(() => null)) as ApiErrorBody | null;
    throw new ApiError(
      response.status,
      parsed ?? { code: `http_${response.status}`, message: response.statusText },
    );
  }
  return response.json() as Promise<T>;
}

/** Multipart upload of a whole form (issue #304's font upload: several files
 * plus metadata in one request). `apiUploadFile` above covers the single-file
 * case; this one takes the `FormData` the caller assembled. */
export async function apiPostForm<T>(path: string, form: FormData): Promise<T> {
  let response: Response;
  try {
    response = await fetch(`/api/v1${path}`, { method: 'POST', body: form });
  } catch {
    throw new ApiError(0, { code: 'network', message: 'network error' });
  }
  if (!response.ok) {
    const parsed = (await response.json().catch(() => null)) as ApiErrorBody | null;
    throw new ApiError(
      response.status,
      parsed ?? { code: `http_${response.status}`, message: response.statusText },
    );
  }
  const text = await response.text();
  return (text ? JSON.parse(text) : undefined) as T;
}

export function fetchHealth(): Promise<HealthResponse> {
  return apiGet<HealthResponse>('/healthz');
}

/** Plain-text response (issue #30's Markdown export) — every other endpoint
 * here returns JSON, so this can't share `requestJson`'s `JSON.parse`. */
export async function apiGetText(path: string): Promise<string> {
  let response: Response;
  try {
    response = await fetch(`/api/v1${path}`);
  } catch {
    throw new ApiError(0, { code: 'network', message: 'network error' });
  }
  if (!response.ok) {
    const parsed = (await response.json().catch(() => null)) as ApiErrorBody | null;
    throw new ApiError(
      response.status,
      parsed ?? { code: `http_${response.status}`, message: response.statusText },
    );
  }
  return response.text();
}