/**
 * 任务轮询配置（Task 86 扩展）。
 *
 * 把隐藏页面轮询间隔、前台恢复与退避策略统一收敛为可编程配置：
 * - getTaskPollIntervalMs / getTaskProgressCacheTtlMs：按 document.visibilityState
 *   自适应切换可见/隐藏间隔与缓存 TTL（历史行为不变）；
 * - getTaskPollBackoffMs(attempt)：指数退避（base × 2^attempt，封顶 max），
 *   供轮询失败/in-flight 重试使用，重试次数不再硬编码；
 * - getTaskForegroundRefreshEnabled / getTaskForegroundRefreshDelayMs：控制
 *   页面切回前台时是否立即拉取一轮及其延迟；
 * - configureTaskPolling / resetTaskPollingConfig：运行时配置与恢复默认。
 *
 * 纯 TS 模块：配置校验失败时抛错且保持原值（零状态变更），document 缺失
 * （Node/SSR）时按可见间隔降级；所有 getter 在任意配置下都有确定返回值。
 */
export const TASK_POLL_VISIBLE_INTERVAL_MS = 10000;
export const TASK_POLL_HIDDEN_INTERVAL_MS = 60000;
export const TASK_PROGRESS_VISIBLE_CACHE_MILLIS = 5000;
export const TASK_PROGRESS_HIDDEN_CACHE_MILLIS = 30000;
export const TASK_POLL_BACKOFF_BASE_MS = 500;
export const TASK_POLL_BACKOFF_MAX_MS = 10000;
export const TASK_POLL_BACKOFF_FACTOR = 2;
export const TASK_PROGRESS_TIMEOUT_MS = 10000;

export interface TaskPollingConfig {
  /** 退避基数（毫秒），必须为正数 */
  backoffBaseMs?: number;
  /** 退避上限（毫秒），必须为正数 */
  backoffMaxMs?: number;
  /** 退避指数因子，<1 时钳制为 1 */
  backoffFactor?: number;
  /** 页面切回前台时是否立即拉取一轮，默认 true */
  foregroundRefreshEnabled?: boolean;
  /** 前台恢复延迟（毫秒），默认 0 */
  foregroundRefreshDelayMs?: number;
  /** 进度类请求超时（毫秒），默认 10s，必须为正数 */
  progressTimeoutMs?: number;
}

const DEFAULTS: Required<TaskPollingConfig> = {
  backoffBaseMs: TASK_POLL_BACKOFF_BASE_MS,
  backoffMaxMs: TASK_POLL_BACKOFF_MAX_MS,
  backoffFactor: TASK_POLL_BACKOFF_FACTOR,
  foregroundRefreshEnabled: true,
  foregroundRefreshDelayMs: 0,
  progressTimeoutMs: TASK_PROGRESS_TIMEOUT_MS,
};

let config: Required<TaskPollingConfig> = { ...DEFAULTS };

function isVisible() {
  return typeof document === "undefined" || document.visibilityState === "visible";
}

export function getTaskPollIntervalMs() {
  if (!isVisible()) {
    return TASK_POLL_HIDDEN_INTERVAL_MS;
  }
  return TASK_POLL_VISIBLE_INTERVAL_MS;
}

export function getTaskProgressCacheTtlMs() {
  if (typeof document !== "undefined" && document.hidden) {
    return TASK_PROGRESS_HIDDEN_CACHE_MILLIS;
  }
  return TASK_PROGRESS_VISIBLE_CACHE_MILLIS;
}

/** 第 attempt 次退避延迟：base × factor^attempt，封顶 max；attempt 省略/非法时按首次（0）处理 */
export function getTaskPollBackoffMs(attempt?: number) {
  const safe = Number.isFinite(attempt) && (attempt as number) > 0 ? Math.floor(attempt as number) : 0;
  const factor = getTaskPollBackoffFactor();
  const scaled = config.backoffBaseMs * Math.pow(factor, safe);
  return scaled > config.backoffMaxMs ? config.backoffMaxMs : scaled;
}

export function getTaskPollBackoffMaxMs() {
  return config.backoffMaxMs;
}

/** 退避指数因子，<1 时钳制为 1 */
export function getTaskPollBackoffFactor() {
  return config.backoffFactor < 1 ? 1 : config.backoffFactor;
}

export function getTaskForegroundRefreshEnabled() {
  return config.foregroundRefreshEnabled;
}

export function getTaskForegroundRefreshDelayMs() {
  return config.foregroundRefreshDelayMs;
}

export function getTaskProgressTimeoutMs() {
  return config.progressTimeoutMs;
}

export function configureTaskPolling(partial: TaskPollingConfig) {
  const next = { ...config, ...partial };
  if (!(next.backoffBaseMs > 0)) {
    throw new Error("退避基数必须为正数: " + next.backoffBaseMs);
  }
  if (!(next.backoffMaxMs > 0)) {
    throw new Error("退避上限必须为正数: " + next.backoffMaxMs);
  }
  if (!(next.foregroundRefreshDelayMs >= 0)) {
    throw new Error("恢复延迟不能为负数: " + next.foregroundRefreshDelayMs);
  }
  if (!(next.progressTimeoutMs > 0)) {
    throw new Error("progressTimeoutMs 必须为正数: " + next.progressTimeoutMs);
  }
  config = next;
}

export function resetTaskPollingConfig() {
  config = { ...DEFAULTS };
}