// ==UserScript==
// @name         LINUX DO Auto Nested View
// @name:zh-CN   LINUX DO 自动嵌套视图
// @namespace    https://github.com/kai-wei-kfuse/linux-do-auto-nested-view
// @version      1.5.1
// @description  Automatically redirect linux.do topic pages and topic links to nested view.
// @description:zh-CN 自动将 linux.do 主题页和主题链接切换到嵌套视图。
// @author       kai-wei-kfuse
// @license      MIT
// @match        https://linux.do/*
// @homepageURL  https://github.com/kai-wei-kfuse/linux-do-auto-nested-view
// @supportURL   https://github.com/kai-wei-kfuse/linux-do-auto-nested-view/issues
// @run-at       document-start
// @grant        GM_registerMenuCommand
// @grant        GM_unregisterMenuCommand
// @grant        GM_getValue
// @grant        GM_setValue
// @grant        unsafeWindow
// ==/UserScript==

(function () {
  "use strict";

  const ENABLED_STORAGE_KEY = "linuxdo-auto-nested-view-enabled";
  const pageWindow =
    typeof unsafeWindow === "undefined" ? window : unsafeWindow;

  let lastHandledUrl = "";
  let observer = null;
  let menuCommandId = null;
  let autoConvertEnabled = loadAutoConvertEnabled();
  const rewrittenLinks = new WeakSet();

  function loadAutoConvertEnabled() {
    try {
      return GM_getValue(ENABLED_STORAGE_KEY, true) !== false;
    } catch {
      return true;
    }
  }

  function saveAutoConvertEnabled(enabled) {
    autoConvertEnabled = enabled;

    try {
      GM_setValue(ENABLED_STORAGE_KEY, enabled);
    } catch {
      // Ignore storage failures so the script still works with its default state.
    }
  }

  function registerToggleMenu() {
    if (typeof GM_registerMenuCommand !== "function") {
      return;
    }

    if (
      menuCommandId !== null &&
      typeof GM_unregisterMenuCommand === "function"
    ) {
      GM_unregisterMenuCommand(menuCommandId);
    }

    const status = autoConvertEnabled ? "开启" : "关闭";
    menuCommandId = GM_registerMenuCommand(
      `自动转换嵌套视图：${status}`,
      () => {
        saveAutoConvertEnabled(!autoConvertEnabled);
        registerToggleMenu();
        applyAutoConvertState();

        if (!autoConvertEnabled) {
          pageWindow.location.reload();
        }
      }
    );
  }

  function stopObserver() {
    if (!observer) {
      return;
    }

    observer.disconnect();
    observer = null;
  }

  function applyAutoConvertState() {
    lastHandledUrl = "";

    if (!autoConvertEnabled) {
      stopObserver();
      return;
    }

    startObserver();
    rewriteTopicLinks();
    redirectToNested();
  }

  function extractTopicId(pathname) {
    const nestedMatch = pathname.match(/^\/n\/topic\/(\d+)(?:\/.*)?$/);
    if (nestedMatch) {
      return nestedMatch[1];
    }

    const topicMatch = pathname.match(/^\/t\/[^/]+\/(\d+)(?:\/.*)?$/);
    if (topicMatch) {
      return topicMatch[1];
    }

    return null;
  }

  function isTopicPage(pathname) {
    return pathname.startsWith("/t/") && Boolean(extractTopicId(pathname));
  }

  function isNestedPage(pathname) {
    return pathname.startsWith("/n/topic/") && Boolean(extractTopicId(pathname));
  }

  function toNestedUrl(urlLike) {
    const url = new URL(urlLike, pageWindow.location.origin);
    const topicId = extractTopicId(url.pathname);
    if (!topicId) {
      return null;
    }

    url.pathname = `/n/topic/${topicId}`;
    return url.toString();
  }

  function rewriteTopicLinks(root = document) {
    if (!autoConvertEnabled) {
      return;
    }

    const links = root.querySelectorAll('a[href]');
    for (const link of links) {
      const nestedUrl = toNestedUrl(link.href);
      if (!nestedUrl) {
        continue;
      }

      if (link.href === nestedUrl && rewrittenLinks.has(link)) {
        continue;
      }

      link.href = nestedUrl;
      rewrittenLinks.add(link);
    }
  }

  function rewriteLinkElement(link) {
    if (!autoConvertEnabled) {
      return;
    }

    if (!link || !link.href) {
      return;
    }

    const nestedUrl = toNestedUrl(link.href);
    if (!nestedUrl || link.href === nestedUrl) {
      return;
    }

    link.href = nestedUrl;
    rewrittenLinks.add(link);
  }

  function findAnchorFromEventTarget(target) {
    if (!(target instanceof Element)) {
      return null;
    }

    return target.closest("a[href]");
  }

  function isNotificationArea(target) {
    if (!(target instanceof Element)) {
      return false;
    }

    return Boolean(
      target.closest(
        [
          "#quick-access-notifications",
          ".user-notifications-list",
          ".notifications-list",
          ".notification-history",
          ".menu-panel.notifications",
          ".quick-access-panel",
          ".notification",
          "[data-notification-id]",
        ].join(",")
      )
    );
  }

  function forceNotificationNavigation(event) {
    if (!autoConvertEnabled) {
      return;
    }

    if (!isNotificationArea(event.target)) {
      return;
    }

    const link = findAnchorFromEventTarget(event.target);
    if (!link) {
      return;
    }

    const nestedUrl = toNestedUrl(link.href);
    if (!nestedUrl) {
      return;
    }

    event.preventDefault();
    event.stopPropagation();
    event.stopImmediatePropagation?.();
    pageWindow.location.assign(nestedUrl);
  }

  function interceptNavigationEvent(event) {
    if (!autoConvertEnabled) {
      return;
    }

    const link = findAnchorFromEventTarget(event.target);
    if (!link) {
      return;
    }

    rewriteLinkElement(link);
  }

  function redirectToNested() {
    if (!autoConvertEnabled) {
      lastHandledUrl = "";
      return;
    }

    const { pathname, href } = pageWindow.location;

    if (href === lastHandledUrl) {
      return;
    }

    if (isNestedPage(pathname)) {
      const normalizedNestedUrl = toNestedUrl(href);
      if (normalizedNestedUrl && normalizedNestedUrl !== href) {
        lastHandledUrl = href;
        pageWindow.location.replace(normalizedNestedUrl);
        return;
      }

      lastHandledUrl = href;
      return;
    }

    if (!isTopicPage(pathname)) {
      lastHandledUrl = href;
      return;
    }

    const link = document.querySelector("a.nested-view-link");
    if (link && link.href) {
      lastHandledUrl = href;
      pageWindow.location.href = link.href;
      return;
    }

    const nestedUrl = toNestedUrl(href);
    if (nestedUrl && nestedUrl !== href) {
      lastHandledUrl = href;
      pageWindow.location.href = nestedUrl;
    }
  }

  function startObserver() {
    if (!autoConvertEnabled) {
      stopObserver();
      return;
    }

    if (observer) {
      observer.disconnect();
    }

    observer = new MutationObserver((mutations) => {
      for (const mutation of mutations) {
        for (const node of mutation.addedNodes) {
          if (node.nodeType !== Node.ELEMENT_NODE) {
            continue;
          }

          if (node.matches?.("a[href]")) {
            rewriteTopicLinks(node.parentElement ?? document);
            continue;
          }

          rewriteTopicLinks(node);
        }
      }

      redirectToNested();
    });

    observer.observe(document.documentElement, {
      childList: true,
      subtree: true,
    });
  }

  function hookHistoryMethod(methodName) {
    const original = pageWindow.history[methodName];
    pageWindow.history[methodName] = function (...args) {
      if (autoConvertEnabled && args.length >= 3 && args[2] != null) {
        const nestedUrl = toNestedUrl(args[2]);
        if (nestedUrl) {
          args[2] = nestedUrl;
        }
      }

      const result = original.apply(this, args);
      if (autoConvertEnabled) {
        setTimeout(redirectToNested, 0);
      }
      return result;
    };
  }

  registerToggleMenu();
  hookHistoryMethod("pushState");
  hookHistoryMethod("replaceState");
  window.addEventListener("popstate", () => setTimeout(redirectToNested, 0));
  window.addEventListener("DOMContentLoaded", () => {
    rewriteTopicLinks();
    redirectToNested();
  });
  window.addEventListener("click", forceNotificationNavigation, true);
  window.addEventListener("pointerdown", interceptNavigationEvent, true);
  window.addEventListener("mousedown", interceptNavigationEvent, true);
  window.addEventListener("click", interceptNavigationEvent, true);
  window.addEventListener("auxclick", interceptNavigationEvent, true);

  applyAutoConvertState();
})();