import { useSyncExternalStore } from "react";

/**
 * 当前主输入是触屏还是鼠标,写在 <html data-input="touch|mouse"> 上,CSS 用 `touch:` 变体读它,
 * React 用 useTouchInput() 读它。
 *
 * 只看 (pointer: coarse) 不够:车机、触屏电视盒、一体机这类设备常跑桌面 Linux / 桌面版 Chromium,
 * 报告的是精细指针和可悬停(按 PC 处理),实际只有触屏,悬停展开、音量簇、点按呼出控制条就全错了。
 * 通用判断分三层,前一层认不出时后一层兜底:
 *
 * 1. 系统 / 浏览器报告:粗指针,或有触点却没有能悬停的指针 → 触屏。UA 只作提示(已知车机直接从触屏起步)。
 * 2. 实际输入:
 *    - 手指 / 笔按下(pointerType touch / pen)→ 触屏;
 *    - 触屏被系统模拟成鼠标时(Linux 车机常见),按下前没有移动轨迹、光标「瞬移」到按下位置;
 *      连续两次瞬移按下 → 触屏;
 *    - 真鼠标连续移动一段 → 回到鼠标(带触屏的笔记本、平板接鼠标)。
 * 3. 手动:地址带 ?input=touch|mouse|auto,记在 localStorage,优先于自动判断。只作排障口子,界面上不给用户选。
 *
 * 迁自 uhd_web app/lib/input-modality.ts(2026-10-08)。
 */
export type InputMode = "touch" | "mouse";
export type InputPreference = "auto" | InputMode;

const STORAGE_KEY = "umt-input-override";
// 已知跑桌面浏览器内核的车机 / 车载系统 UA 片段(只作初始提示,不锁定)
const TOUCH_UA_HINTS =
  /\b(Tesla|QtCarBrowser|Automotive|AAOS|MBUX|Rivian|Lucid|Polestar|NIO|XPENG|LiAuto|HarmonyOS.*Car)\b/i;
// 真鼠标点击前的移动是连续的小步。瞬移判定:按下点离上一次移动位置超过这个距离,
// 或按下前紧挨着的那次移动本身就是一次大跳(触屏模拟的鼠标会先把光标跳到按下点再按下)。
// 原地不动再点不算:电脑用户手放着连点两下不能被误判成触屏
const TELEPORT_PX = 24;
const JUMP_BEFORE_DOWN_MS = 120;
const TELEPORTS_TO_TOUCH = 2;
// 连续这么多次小步移动才算真鼠标回来了(模拟鼠标在按下前通常只有 0~1 次移动)
const STEADY_MOVES_TO_MOUSE = 6;

let auto: InputMode = "mouse";
let pref: InputPreference = "auto";
let started = false;
const listeners = new Set<() => void>();

function effective(): InputMode {
  return pref === "auto" ? auto : pref;
}

function publish() {
  document.documentElement.dataset.input = effective();
  for (const fn of listeners) fn();
}

function setAuto(next: InputMode) {
  if (next === auto) return;
  const before = effective();
  auto = next;
  if (effective() !== before) publish();
}

function mq(q: string) {
  return window.matchMedia?.(q).matches ?? false;
}

function detect(): InputMode {
  if (mq("(pointer: coarse)")) return "touch";
  if (navigator.maxTouchPoints > 0 && !mq("(any-hover: hover)")) return "touch";
  if (TOUCH_UA_HINTS.test(navigator.userAgent)) return "touch";
  return "mouse";
}

function readPreference(): InputPreference {
  try {
    const fromUrl = new URLSearchParams(window.location.search).get("input");
    if (fromUrl === "auto" || fromUrl === "touch" || fromUrl === "mouse") {
      localStorage.setItem(STORAGE_KEY, fromUrl);
      return fromUrl;
    }
    const saved = localStorage.getItem(STORAGE_KEY);
    if (saved === "touch" || saved === "mouse") return saved;
  } catch {
    // 隐私模式等拿不到存储时按自动处理
  }
  return "auto";
}

/** 在客户端入口调用一次;重复调用无副作用 */
export function initInputModality() {
  if (started || typeof window === "undefined") return;
  started = true;
  pref = readPreference();
  auto = detect();
  document.documentElement.dataset.input = effective();

  let lastMove: { x: number; y: number; t: number; jumped: boolean } | null = null;
  let teleports = 0;
  let steadyMoves = 0;

  window.addEventListener(
    "pointerdown",
    (event) => {
      if (event.pointerType === "touch" || event.pointerType === "pen") {
        teleports = 0;
        steadyMoves = 0;
        setAuto("touch");
        return;
      }
      if (event.pointerType !== "mouse") return;
      const jumped =
        !lastMove ||
        Math.hypot(event.clientX - lastMove.x, event.clientY - lastMove.y) > TELEPORT_PX ||
        (lastMove.jumped && event.timeStamp - lastMove.t < JUMP_BEFORE_DOWN_MS);
      steadyMoves = 0;
      if (jumped) {
        teleports += 1;
        if (teleports >= TELEPORTS_TO_TOUCH) setAuto("touch");
      } else {
        teleports = 0;
      }
    },
    { capture: true, passive: true },
  );

  window.addEventListener(
    "pointermove",
    (event) => {
      if (event.pointerType !== "mouse") return;
      const prev = lastMove;
      const step = prev ? Math.hypot(event.clientX - prev.x, event.clientY - prev.y) : Infinity;
      lastMove = { x: event.clientX, y: event.clientY, t: event.timeStamp, jumped: step > TELEPORT_PX };
      // 按住拖动(滑动进度条、触屏拖拽被模拟成鼠标)不算「真鼠标回来了」
      if (event.buttons !== 0 || !prev) return;
      if (step > 0 && step <= TELEPORT_PX && event.timeStamp - prev.t < 200) {
        steadyMoves += 1;
        if (steadyMoves >= STEADY_MOVES_TO_MOUSE) {
          teleports = 0;
          setAuto("mouse");
        }
      } else {
        steadyMoves = 0;
      }
    },
    { capture: true, passive: true },
  );

  window.matchMedia?.("(pointer: coarse)").addEventListener("change", () => setAuto(detect()));
}

export function getInputMode(): InputMode {
  return effective();
}

/**
 * 这次指针事件按触屏还是鼠标处理。手指 / 笔一律算触屏;鼠标类型的事件在全站判定为触屏模式时
 * 也算触屏 —— 车机等把触屏报告成鼠标的设备,播放器手势、进度条、点按显隐靠它才能生效。
 */
export function pointerKind(event: { pointerType: string }): InputMode {
  if (event.pointerType === "touch" || event.pointerType === "pen") return "touch";
  return effective();
}

function subscribe(fn: () => void) {
  listeners.add(fn);
  return () => listeners.delete(fn);
}

/** 主输入是否为触屏。SSR 阶段返回 false,水合后按实际校正 */
export function useTouchInput(): boolean {
  return useSyncExternalStore(
    subscribe,
    () => effective() === "touch",
    () => false,
  );
}