import { useEffect, useRef, useState } from 'react';

import type { InstanceContext } from '../app-shell.js';

export type OverviewFieldValue = string | number | boolean | null;
export type OverviewSection = Readonly<Record<string, OverviewFieldValue>>;

export interface OverviewSnapshot {
  readonly observedAt?: string;
  readonly device: OverviewSection;
  readonly sim: OverviewSection;
  readonly network: OverviewSection;
  readonly stats: OverviewSection;
  readonly cpu: OverviewSection;
  readonly connectivity: OverviewSection;
}

export interface OverviewDataSource {
  /** Implementations are injected by the application owner; this component has no production endpoint. */
  load(instanceId: string, signal: AbortSignal): Promise<OverviewSnapshot>;
}

export interface OverviewSystemPageProps {
  readonly instance: InstanceContext;
  readonly dataSource?: OverviewDataSource;
  /** Change this value when an external owner has requested a refresh. */
  readonly refreshSignal?: unknown;
}

type ReadState =
  | { kind: 'idle' }
  | { kind: 'loading'; snapshot?: OverviewSnapshot }
  | { kind: 'ready'; snapshot: OverviewSnapshot }
  | { kind: 'error'; message: string; snapshot?: OverviewSnapshot };

const SECTIONS = [
  ['device', '设备'],
  ['sim', 'SIM'],
  ['network', '网络'],
  ['stats', '统计'],
  ['cpu', 'CPU'],
  ['connectivity', '连接状态'],
] as const;

const FIELD_LABELS: Readonly<Record<string, string>> = {
  Model: '型号',
  Uptime: '运行时间',
  Slots: '卡槽数',
  Active: '活跃数',
  Operator: '运营商',
  Registration: '注册状态',
  'Messages today': '今日消息数',
  Calls: '通话数',
  Usage: '使用率',
  Temperature: '温度',
  State: '状态',
  Latency: '延迟',
};

const ENUM_LABELS: Readonly<Record<string, string>> = {
  connected: '已连接',
  disconnected: '未连接',
  connecting: '正在连接',
  registered: '已注册',
  unregistered: '未注册',
  searching: '正在搜索',
  roaming: '漫游中',
  online: '在线',
  offline: '离线',
  unknown: '未知',
};

function displayFieldLabel(key: string): string {
  return FIELD_LABELS[key] ?? key;
}

function displayFieldValue(value: OverviewFieldValue): string {
  if (value == null) return '不可用';
  if (typeof value === 'boolean') return value ? '是' : '否';
  if (typeof value === 'string') return ENUM_LABELS[value.toLocaleLowerCase()] ?? value;
  return String(value);
}

function StructuredSection({ label, values }: { label: string; values: OverviewSection }) {
  const entries = Object.entries(values);
  return (
    <section className="overview-card" aria-label={label}>
      <h2>{label}</h2>
      {entries.length ? (
        <dl>
          {entries.map(([key, value]) => (
            <div key={key}>
              <dt>{displayFieldLabel(key)}</dt>
              <dd>{displayFieldValue(value)}</dd>
            </div>
          ))}
        </dl>
      ) : (
        <p>未提供{label}数据。</p>
      )}
    </section>
  );
}

export function OverviewSystemPage({
  instance,
  dataSource,
  refreshSignal,
}: OverviewSystemPageProps) {
  const requestOwner = useRef(0);
  const [retry, setRetry] = useState(0);
  const [state, setState] = useState<ReadState>({ kind: 'idle' });

  useEffect(() => {
    const request = ++requestOwner.current;
    const controller = new AbortController();

    if (instance.authentication === 'auth-required') {
      setState({ kind: 'idle' });
      return () => controller.abort();
    }
    if (!dataSource) {
      setState({ kind: 'idle' });
      return () => controller.abort();
    }

    setState((current) => ({
      kind: 'loading',
      ...(current.kind === 'ready' || current.kind === 'error'
        ? current.snapshot
          ? { snapshot: current.snapshot }
          : {}
        : {}),
    }));
    void dataSource.load(instance.id, controller.signal).then(
      (snapshot) => {
        if (request === requestOwner.current && !controller.signal.aborted)
          setState({ kind: 'ready', snapshot });
      },
      (reason: unknown) => {
        void reason;
        if (request === requestOwner.current && !controller.signal.aborted)
          setState((current) => ({
            kind: 'error',
            message: '无法加载概览数据。',
            ...(current.kind === 'loading' && current.snapshot
              ? { snapshot: current.snapshot }
              : {}),
          }));
      },
    );
    return () => controller.abort();
  }, [dataSource, instance.authentication, instance.id, refreshSignal, retry]);

  if (instance.authentication === 'auth-required')
    return (
      <div className="state-panel state-error" role="alert">
        需要先完成认证，才能读取概览数据。
      </div>
    );

  if (!dataSource)
    return (
      <div className="state-panel" role="status" aria-label="概览不可用">
        没有可用的安全概览只读数据源。此控制台不会臆造或调用未签订契约的生产端点。
      </div>
    );

  const retainedSnapshot =
    state.kind === 'loading' || state.kind === 'error' ? state.snapshot : undefined;

  if ((state.kind === 'loading' || state.kind === 'idle') && !retainedSnapshot)
    return (
      <p role="status" aria-label="概览加载状态">
        正在加载概览…
      </p>
    );

  if (state.kind === 'error' && !state.snapshot)
    return (
      <div className="state-panel state-error" role="alert">
        <p>无法加载概览： {state.message}</p>
        <button type="button" onClick={() => setRetry((value) => value + 1)}>
          重试加载概览
        </button>
      </div>
    );

  const snapshot = state.kind === 'ready' ? state.snapshot : retainedSnapshot;
  if (!snapshot) return null;

  return (
    <div className="overview-system">
      {state.kind === 'loading' ? <p role="status">正在刷新概览…</p> : null}
      {state.kind === 'error' ? (
        <div className="state-panel state-error" role="alert">
          <p>刷新失败，正在显示上次已知的概览数据。</p>
          <button type="button" onClick={() => setRetry((value) => value + 1)}>
            重试加载概览
          </button>
        </div>
      ) : null}
      {instance.freshness !== 'fresh' ? (
        <p className="state-panel" role="status" aria-label="概览数据新鲜度">
          概览数据可能已过期；使用这些值前请先核实数据新鲜度。
        </p>
      ) : null}
      {snapshot.observedAt ? <p>观测时间：{snapshot.observedAt}</p> : null}
      <div className="overview-grid">
        {SECTIONS.map(([key, label]) => (
          <StructuredSection key={key} label={label} values={snapshot[key]} />
        ))}
      </div>
      <section className="state-panel" aria-label="系统操作">
        <h2>系统操作</h2>
        <p>重启不可用，因为后端尚未实现 R3 重启操作，因此不提供任何操作。</p>
      </section>
    </div>
  );
}