import { escapeHtml } from "./format.js";

const listeners = new Set();
let rootElement = null;
let routeElement = null;
let current = null;
let routeTable = [];
let rendering = false;
let pendingRender = null;

export function parseLocation() {
  // 兼容旧的 #/home 链接：读取后由 startRouter 替换成干净的路径。
  if (window.location.hash.startsWith("#/")) {
    const raw = window.location.hash.slice(1);
    const [pathPart, queryPart = ""] = raw.split("?");
    return {
      path: pathPart.startsWith("/") ? pathPart : `/${pathPart}`,
      query: new URLSearchParams(queryPart),
      legacyHash: true,
    };
  }
  const path = window.location.pathname === "/" ? "/home" : window.location.pathname;
  return { path, query: new URLSearchParams(window.location.search), legacyHash: false };
}

function setUrl(path, query, { replace = false } = {}) {
  const params = new URLSearchParams();
  if (query) {
    for (const [key, value] of Object.entries(query)) {
      if (value === null || value === undefined || value === "") continue;
      params.set(key, String(value));
    }
  }
  const text = params.toString();
  const url = `${path}${text ? `?${text}` : ""}`;
  if (replace) window.history.replaceState({ path }, "", url);
  else window.history.pushState({ path }, "", url);
}

export function navigate(path, query) {
  setUrl(path, query);
  render({ scrollTop: true });
}

export function replaceQuery(changes) {
  const { path, query } = parseLocation();
  for (const [key, value] of Object.entries(changes)) {
    if (value === null || value === undefined || value === "") query.delete(key);
    else query.set(key, String(value));
  }
  const flat = Object.fromEntries(query.entries());
  setUrl(path, flat, { replace: true });
  render({ preserveScroll: true });
}

export function onRoute(listener) {
  listeners.add(listener);
}

export function startRouter({ root, outlet, routes }) {
  rootElement = root;
  routeElement = outlet;
  routeTable = routes;
  if ("scrollRestoration" in window.history) {
    window.history.scrollRestoration = "manual";
  }
  window.addEventListener("popstate", () => render({ scrollTop: false }));
  document.addEventListener("click", handleClick);
  const initial = parseLocation();
  if (initial.legacyHash) {
    setUrl(initial.path, Object.fromEntries(initial.query.entries()), { replace: true });
  } else if (window.location.pathname === "/") {
    setUrl("/home", null, { replace: true });
  }
  render({ scrollTop: true });
}

function handleClick(event) {
  if (event.defaultPrevented || event.button !== 0) return;
  if (event.metaKey || event.ctrlKey || event.shiftKey || event.altKey) return;
  const anchor = event.target.closest("a[href]");
  if (!anchor || anchor.target || anchor.hasAttribute("download")) return;
  const url = new URL(anchor.href, window.location.origin);
  if (url.origin !== window.location.origin) return;
  if (
    url.pathname.startsWith("/api/") ||
    url.pathname.startsWith("/static/") ||
    url.pathname === "/login" ||
    url.pathname === "/logout"
  ) {
    return;
  }
  event.preventDefault();
  navigate(url.pathname, Object.fromEntries(url.searchParams.entries()));
}

export function currentRoute() {
  return current;
}

function matchRoute(path, routes) {
  for (const route of routes) {
    const match = route.pattern.exec(path);
    if (match) return { route, match };
  }
  return null;
}

async function render(options = {}) {
  if (rendering) {
    pendingRender = options;
    return;
  }
  rendering = true;
  const { scrollTop = false, preserveScroll = false } = options;
  const previousScroll = window.scrollY;
  const { path, query } = parseLocation();
  const matched = matchRoute(path, routeTable);
  if (!matched) {
    routeElement.innerHTML = `
      <section class="page">
        <div class="empty-state"><strong>页面不存在</strong>
        <p>${escapeHtml(path)}</p><a class="button" href="/home">回到首页</a></div>
      </section>`;
    finishRender();
    return;
  }
  current = { path, query, route: matched.route };
  for (const listener of listeners) {
    try {
      listener(current);
    } catch {
      // 导航状态更新不应阻断页面渲染
    }
  }
  if (scrollTop && !preserveScroll) {
    window.scrollTo({ top: 0, behavior: "auto" });
  }
  routeElement.innerHTML = `<div class="page-loading"><div class="skeleton skeleton-title"></div>
    <div class="skeleton skeleton-card"></div><div class="skeleton skeleton-card"></div></div>`;
  try {
    await matched.route.view(routeElement, {
      params: matched.match.slice(1),
      query,
      path,
    });
  } catch (error) {
    routeElement.innerHTML = `
      <section class="page">
        <div class="empty-state error-state">
          <strong>加载失败</strong>
          <p>${escapeHtml(error.message || "未知错误")}</p>
          <button class="button" id="retry-button" type="button">重试</button>
        </div>
      </section>`;
    routeElement.querySelector("#retry-button")?.addEventListener("click", () => render({ scrollTop: true }));
  }
  if (preserveScroll) {
    window.scrollTo({ top: previousScroll, behavior: "auto" });
  }
  rootElement?.classList.remove("is-loading");
  finishRender();
}

function finishRender() {
  rendering = false;
  if (pendingRender) {
    const next = pendingRender;
    pendingRender = null;
    render(next);
  }
}