export interface ApiErrorBody {
  error: {
    code: string;
    message: string;
    details?: Record<string, unknown>;
  };
}

export class ApiError extends Error {
  readonly code: string;
  readonly status: number;
  readonly details?: Record<string, unknown>;

  constructor(status: number, code: string, message: string, details?: Record<string, unknown>) {
    super(message);
    this.name = 'ApiError';
    this.status = status;
    this.code = code;
    if (details !== undefined) {
      this.details = details;
    }
  }
}

const API_PREFIX = '/api/v1';

export function isApiErrorPayload(value: unknown): value is ApiErrorBody['error'] {
  if (typeof value !== 'object' || value === null) {
    return false;
  }
  const candidate = value as { code?: unknown; message?: unknown };
  return typeof candidate.code === 'string' && typeof candidate.message === 'string';
}

export function apiErrorCode(error: unknown): string | null {
  if (error === null || typeof error !== 'object') {
    return null;
  }
  const payload = (error as { apiError?: unknown }).apiError;
  return isApiErrorPayload(payload) ? payload.code : null;
}

/**
 * Дополнительное поле конверта ошибки (например, `retry_after_ms` у 429).
 *
 * Сервер кладёт детали рядом с `code`/`message`, а не во вложенный `details`,
 * поэтому ищем значение в исходном конверте; `details` остаётся запасным
 * вариантом для ошибок, собранных вручную.
 */
export function apiErrorField(error: unknown, key: string): unknown {
  if (error === null || typeof error !== 'object') {
    return undefined;
  }
  const record = error as { apiError?: unknown; details?: unknown };
  if (isApiErrorPayload(record.apiError)) {
    const value = (record.apiError as unknown as Record<string, unknown>)[key];
    if (value !== undefined) {
      return value;
    }
  }
  const details = record.details;
  if (typeof details === 'object' && details !== null) {
    return (details as Record<string, unknown>)[key];
  }
  return undefined;
}

export interface RequestOptions {
  method?: 'GET' | 'POST' | 'PATCH' | 'PUT' | 'DELETE';
  body?: unknown;
  /** Тело multipart (загрузка файлов): заменяет JSON-тело. */
  form?: FormData;
  signal?: AbortSignal;
  headers?: Record<string, string>;
}

export function parsePayload(text: string, contentType: string | null): unknown {
  if (text.length === 0) {
    return null;
  }
  if (contentType !== null && !contentType.includes('application/json')) {
    return null;
  }
  try {
    return JSON.parse(text) as unknown;
  } catch {
    return null;
  }
}

export async function request<T>(path: string, options: RequestOptions = {}): Promise<T> {
  // Multipart отдаёт браузер: Content-Type с boundary выставляет он сам.
  const isForm = options.form !== undefined;
  const init: RequestInit = {
    method: options.method ?? 'GET',
    credentials: 'same-origin',
    headers: {
      Accept: 'application/json',
      ...(options.body === undefined || isForm ? {} : { 'Content-Type': 'application/json' }),
      ...options.headers,
    },
  };
  if (isForm) {
    init.body = options.form ?? null;
  } else if (options.body !== undefined) {
    init.body = JSON.stringify(options.body);
  }
  if (options.signal !== undefined) {
    init.signal = options.signal;
  }

  const response = await fetch(`${API_PREFIX}${path}`, init);
  const text = await response.text();
  const payload = parsePayload(text, response.headers.get('Content-Type'));

  if (!response.ok) {
    const envelope =
      typeof payload === 'object' && payload !== null
        ? (payload as { error?: unknown }).error
        : undefined;
    if (isApiErrorPayload(envelope)) {
      const error = new ApiError(
        response.status,
        envelope.code,
        envelope.message,
        envelope.details,
      );
      Object.defineProperty(error, 'apiError', {
        value: envelope,
        enumerable: false,
        writable: false,
      });
      throw error;
    }
    throw new ApiError(response.status, 'internal.error', 'unexpected response');
  }
  return payload as T;
}