stylus/background/storage.js

/* global LZString */
/* global usercss, openEditor */

'use strict';

const RX_NAMESPACE = new RegExp([/[\s\r\n]*/,
  /(@namespace[\s\r\n]+(?:[^\s\r\n]+[\s\r\n]+)?url\(http:\/\/.*?\);)/,
  /[\s\r\n]*/].map(rx => rx.source).join(''), 'g');
const RX_CSS_COMMENTS = /\/\*[\s\S]*?\*\//g;
// eslint-disable-next-line no-var
var SLOPPY_REGEXP_PREFIX = '\0';

// CSS transition bug workaround: since we insert styles asynchronously,
// the browsers, especially Firefox, may apply all transitions on page load
const CSS_TRANSITION_SUPPRESSOR = '* { transition: none !important; }';
const RX_CSS_TRANSITION_DETECTOR = /([\s\n;/{]|-webkit-|-moz-)transition[\s\n]*:[\s\n]*(?!none)/;

// Note, only 'var'-declared variables are visible from another extension page
// eslint-disable-next-line no-var
var cachedStyles = {
  list: null,            // array of all styles
  byId: new Map(),       // all styles indexed by id
  filters: new Map(),    // filterStyles() parameters mapped to the returned results, 10k max
  regexps: new Map(),    // compiled style regexps
  urlDomains: new Map(), // getDomain() results for 100 last checked urls
  needTransitionPatch: new Map(), // FF bug workaround
  mutex: {
    inProgress: false,   // while getStyles() is reading IndexedDB all subsequent calls
    onDone: [],          // to getStyles() are queued and resolved when the first one finishes
  },
};

// eslint-disable-next-line no-var
var chromeLocal = {
  get(options) {
    return new Promise(resolve => {
      chrome.storage.local.get(options, data => resolve(data));
    });
  },
  set(data) {
    return new Promise(resolve => {
      chrome.storage.local.set(data, () => resolve(data));
    });
  },
  remove(keyOrKeys) {
    return new Promise(resolve => {
      chrome.storage.local.remove(keyOrKeys, resolve);
    });
  },
  getValue(key) {
    return chromeLocal.get(key).then(data => data[key]);
  },
  setValue(key, value) {
    return chromeLocal.set({[key]: value});
  },
};

// eslint-disable-next-line no-var
var chromeSync = {
  get(options) {
    return new Promise(resolve => {
      chrome.storage.sync.get(options, resolve);
    });
  },
  set(data) {
    return new Promise(resolve => {
      chrome.storage.sync.set(data, () => resolve(data));
    });
  },
  getLZValue(key) {
    return chromeSync.getLZValues([key]).then(data => data[key]);
  },
  getLZValues(keys) {
    return chromeSync.get(keys).then((data = {}) => {
      for (const key of keys) {
        const value = data[key];
        data[key] = value && tryJSONparse(LZString.decompressFromUTF16(value));
      }
      return data;
    });
  },
  setLZValue(key, value) {
    return chromeSync.set({[key]: LZString.compressToUTF16(JSON.stringify(value))});
  }
};

// eslint-disable-next-line no-var
var dbExec = dbExecIndexedDB;
dbExec.initialized = false;

// we use chrome.storage.local fallback if IndexedDB doesn't save data,
// which, once detected on the first run, is remembered in chrome.storage.local
// for reliablility and in localStorage for fast synchronous access
// (FF may block localStorage depending on its privacy options)
do {
  const done = () => {
    getStyles().then(() => {
      dbExec.initialized = true;
      window.dispatchEvent(new Event('storageReady'));
    });
  };
  const fallback = () => {
    dbExec = dbExecChromeStorage;
    chromeLocal.set({dbInChromeStorage: true});
    localStorage.dbInChromeStorage = 'true';
    ignoreChromeError();
    done();
  };
  const fallbackSet = localStorage.dbInChromeStorage;
  if (fallbackSet === 'true' || !tryCatch(() => indexedDB)) {
    fallback();
    break;
  } else if (fallbackSet === 'false') {
    done();
    break;
  }
  chromeLocal.get('dbInChromeStorage')
    .then(data =>
      data && data.dbInChromeStorage && Promise.reject())
    .then(() => dbExecIndexedDB('getAllKeys', IDBKeyRange.lowerBound(1), 1))
    .then(({target}) => (
      (target.result || [])[0] ?
        Promise.reject('ok') :
        dbExecIndexedDB('put', {id: -1})))
    .then(() =>
      dbExecIndexedDB('get', -1))
    .then(({target}) => (
      (target.result || {}).id === -1 ?
        dbExecIndexedDB('delete', -1) :
        Promise.reject()))
    .then(() =>
      Promise.reject('ok'))
    .catch(result => {
      if (result === 'ok') {
        chromeLocal.set({dbInChromeStorage: false});
        localStorage.dbInChromeStorage = 'false';
        done();
      } else {
        fallback();
      }
    });
} while (0);


function dbExecIndexedDB(method, ...args) {
  return new Promise((resolve, reject) => {
    Object.assign(indexedDB.open('stylish', 2), {
      onsuccess(event) {
        const database = event.target.result;
        if (!method) {
          resolve(database);
        } else {
          const transaction = database.transaction(['styles'], 'readwrite');
          const store = transaction.objectStore('styles');
          Object.assign(store[method](...args), {
            onsuccess: event => resolve(event, store, transaction, database),
            onerror: reject,
          });
        }
      },
      onerror(event) {
        console.warn(event.target.error || event.target.errorCode);
        reject(event);
      },
      onupgradeneeded(event) {
        if (event.oldVersion === 0) {
          event.target.result.createObjectStore('styles', {
            keyPath: 'id',
            autoIncrement: true,
          });
        }
      },
    });
  });
}


function dbExecChromeStorage(method, data) {
  const STYLE_KEY_PREFIX = 'style-';
  switch (method) {
    case 'get':
      return chromeLocal.getValue(STYLE_KEY_PREFIX + data)
        .then(result => ({target: {result}}));

    case 'put':
      if (!data.id) {
        return getStyles().then(() => {
          data.id = 1;
          for (const style of cachedStyles.list) {
            data.id = Math.max(data.id, style.id + 1);
          }
          return dbExecChromeStorage('put', data);
        });
      }
      return chromeLocal.setValue(STYLE_KEY_PREFIX + data.id, data)
        .then(() => (chrome.runtime.lastError ? Promise.reject() : data.id));

    case 'delete':
      return chromeLocal.remove(STYLE_KEY_PREFIX + data);

    case 'getAll':
      return chromeLocal.get(null).then(storage => {
        const styles = [];
        for (const key in storage) {
          if (key.startsWith(STYLE_KEY_PREFIX) &&
              Number(key.substr(STYLE_KEY_PREFIX.length))) {
            styles.push(storage[key]);
          }
        }
        return {target: {result: styles}};
      });
  }
  return Promise.reject();
}


function getStyles(options) {
  if (cachedStyles.list) {
    return Promise.resolve(filterStyles(options));
  }
  if (cachedStyles.mutex.inProgress) {
    return new Promise(resolve => {
      cachedStyles.mutex.onDone.push({options, resolve});
    });
  }
  cachedStyles.mutex.inProgress = true;

  return dbExec('getAll').then(event => {
    cachedStyles.list = event.target.result || [];
    cachedStyles.byId.clear();
    for (const style of cachedStyles.list) {
      cachedStyles.byId.set(style.id, style);
    }

    cachedStyles.mutex.inProgress = false;
    for (const {options, resolve} of cachedStyles.mutex.onDone) {
      resolve(filterStyles(options));
    }
    cachedStyles.mutex.onDone = [];
    return filterStyles(options);
  });
}


function filterStyles({
  enabled = null,
  url = null,
  id = null,
  matchUrl = null,
  asHash = null,
  strictRegexp = true, // used by the popup to detect bad regexps
} = {}) {
  enabled = enabled === null || typeof enabled === 'boolean' ? enabled :
    typeof enabled === 'string' ? enabled === 'true' : null;
  id = id === null ? null : Number(id);

  if (
    enabled === null &&
    url === null &&
    id === null &&
    matchUrl === null &&
    asHash !== true
  ) {
    return cachedStyles.list;
  }

  if (matchUrl && !URLS.supported(matchUrl)) {
    return asHash ? {} : [];
  }

  const blankHash = asHash && {
    disableAll: prefs.get('disableAll'),
    exposeIframes: prefs.get('exposeIframes'),
  };

  // add \t after url to prevent collisions (not sure it can actually happen though)
  const cacheKey = ' ' + enabled + url + '\t' + id + matchUrl + '\t' + asHash + strictRegexp;
  const cached = cachedStyles.filters.get(cacheKey);
  if (cached) {
    cached.hits++;
    cached.lastHit = Date.now();
    return asHash
      ? Object.assign(blankHash, cached.styles)
      : cached.styles;
  }

  return filterStylesInternal({
    enabled,
    url,
    id,
    matchUrl,
    asHash,
    strictRegexp,
    blankHash,
    cacheKey,
  });
}


function filterStylesInternal({
  // js engines don't like big functions (V8 often deoptimized the original filterStyles)
  // it also makes sense to extract the less frequently executed code
  enabled,
  url,
  id,
  matchUrl,
  asHash,
  strictRegexp,
  blankHash,
  cacheKey,
}) {
  if (matchUrl && !cachedStyles.urlDomains.has(matchUrl)) {
    cachedStyles.urlDomains.set(matchUrl, getDomains(matchUrl));
    for (let i = cachedStyles.urlDomains.size - 100; i > 0; i--) {
      const firstKey = cachedStyles.urlDomains.keys().next().value;
      cachedStyles.urlDomains.delete(firstKey);
    }
  }

  const styles = id === null
    ? cachedStyles.list
    : [cachedStyles.byId.get(id)];
  if (!styles[0]) {
    // may happen when users [accidentally] reopen an old URL
    // of edit.html with a non-existent style id parameter
    return asHash ? blankHash : [];
  }
  const filtered = asHash ? {} : [];
  const needSections = asHash || matchUrl !== null;
  const matchUrlBase = matchUrl && matchUrl.includes('#') && matchUrl.split('#', 1)[0];

  let style;
  for (let i = 0; (style = styles[i]); i++) {
    if ((enabled === null || style.enabled === enabled)
    && (url === null || style.url === url)
    && (id === null || style.id === id)) {
      const sections = needSections &&
        getApplicableSections({
          style,
          matchUrl,
          strictRegexp,
          stopOnFirst: !asHash,
          skipUrlCheck: true,
          matchUrlBase,
        });
      if (asHash) {
        if (sections.length) {
          filtered[style.id] = sections;
        }
      } else if (matchUrl === null || sections.length) {
        filtered.push(style);
      }
    }
  }

  cachedStyles.filters.set(cacheKey, {
    styles: filtered,
    lastHit: Date.now(),
    hits: 1,
  });
  if (cachedStyles.filters.size > 10000) {
    cleanupCachedFilters();
  }

  // a shallow copy is needed because the cache doesn't store options like disableAll
  return asHash
    ? Object.assign(blankHash, filtered)
    : filtered;
}


// Parse the source and find the duplication
// {id: int, style: object, source: string, checkDup: boolean}
function filterUsercss(req) {
  return Promise.resolve().then(() => {
    let style;
    if (req.source) {
      style = usercss.buildMeta(req.source);
    } else {
      style = req.style;
    }
    if (!style.id && req.id) {
      style.id = req.id;
    }
    let pending;
    if (!style.sections || !style.sections.length) {
      pending = usercss.buildCode(style);
    } else {
      pending = Promise.resolve(style);
    }
    if (!style.id && req.checkDup) {
      return Promise.all([pending, findDupUsercss(style)])
        .then(([, dup]) => ({status: 'success', style, dup}));
    }
    return pending.then(() => ({status: 'success', style}));
  }).catch(err => ({status: 'error', error: String(err)}));
}

function saveUsercss(style) {
  // This function use `saveStyle`, however the response is different.
  return Promise.resolve()
    .then(() => {
      if (!style.name || !style.namespace) {
        return Object.assign(usercss.buildMeta(style.source), style);
      }
      return style;
    })
    .then(saveStyle)
    .then(result => ({
      status: 'success',
      style: result
    }))
    .catch(err => ({
      status: 'error',
      error: String(err)
    }));
}


function saveStyle(style) {
  let id = Number(style.id) || null;
  const reason = style.reason;
  const notify = style.notify !== false;
  delete style.method;
  delete style.reason;
  delete style.notify;
  if (!style.name) {
    delete style.name;
  }
  let existed;
  let codeIsUpdated;

  if (style.usercss) {
    return processUsercss(style).then(decide);
  }

  if (reason === 'update' || reason === 'update-digest') {
    return calcStyleDigest(style).then(digest => {
      style.originalDigest = digest;
      return decide();
    });
  }
  if (reason === 'import') {
    style.originalDigest = style.originalDigest || style.styleDigest; // TODO: remove in the future
    delete style.styleDigest; // TODO: remove in the future
    if (typeof style.originalDigest !== 'string' || style.originalDigest.length !== 40) {
      delete style.originalDigest;
    }
  }
  return decide();

  function processUsercss(style) {
    return findDupUsercss(style).then(dup => {
      if (!dup) {
        return;
      }
      if (!id) {
        id = dup.id;
      }
      if (reason === 'config') {
        return;
      }
      // preserve style.vars during update
      usercss.assignVars(style, dup);
    })
    .then(() => usercss.buildCode(style));
  }

  function decide() {
    if (id !== null) {
      // Update or create
      style.id = id;
      return dbExec('get', id).then((event, store) => {
        const oldStyle = event.target.result;
        existed = Boolean(oldStyle);
        if (reason === 'update-digest' && oldStyle.originalDigest === style.originalDigest) {
          return style;
        }
        codeIsUpdated = !existed || 'sections' in style && !styleSectionsEqual(style, oldStyle);
        style = Object.assign({}, oldStyle, style);
        return write(style, store);
      });
    } else {
      // Create
      delete style.id;
      style = Object.assign({
        // Set optional things if they're undefined
        enabled: true,
        updateUrl: null,
        md5Url: null,
        url: null,
        originalMd5: null,
      }, style);
      return write(style);
    }
  }

  function write(style, store) {
    style.sections = normalizeStyleSections(style);
    if (store) {
      return new Promise(resolve => {
        store.put(style).onsuccess = event => resolve(done(event));
      });
    } else {
      return dbExec('put', style).then(done);
    }
  }

  function done(event) {
    if (reason === 'update-digest') {
      return style;
    }
    style.id = style.id || event.target.result;
    invalidateCache(existed ? {updated: style} : {added: style});
    if (notify) {
      notifyAllTabs({
        method: existed ? 'styleUpdated' : 'styleAdded',
        style, codeIsUpdated, reason,
      });
    }
    if (style.usercss && !existed && reason === 'install') {
      // open the editor for usercss with the first install?
      openEditor(style.id);
    }
    return style;
  }
}


function deleteStyle({id, notify = true}) {
  id = Number(id);
  return dbExec('delete', id).then(() => {
    invalidateCache({deletedId: id});
    if (notify) {
      notifyAllTabs({method: 'styleDeleted', id});
    }
    return id;
  });
}

function findDupUsercss(style) {
  if (style.id) {
    return getStyles({id: style.id}).then(s => s[0]);
  }
  return getStyles().then(styles =>
    styles.find(
      s => s.name === style.name && s.namespace === style.namespace
    )
  );
}


function getApplicableSections({
  style,
  matchUrl,
  strictRegexp = true,
  // filterStylesInternal() sets the following to avoid recalc on each style:
  stopOnFirst,
  skipUrlCheck,
  matchUrlBase = matchUrl.includes('#') && matchUrl.split('#', 1)[0],
  // as per spec the fragment portion is ignored in @-moz-document:
  // https://www.w3.org/TR/2012/WD-css3-conditional-20120911/#url-of-doc
  // but the spec is outdated and doesn't account for SPA sites
  // so we only respect it in case of url("http://exact.url/without/hash")
}) {
  if (!skipUrlCheck && !URLS.supported(matchUrl)) {
    return [];
  }
  const sections = [];
  for (const section of style.sections) {
    const {urls, domains, urlPrefixes, regexps, code} = section;
    const isGlobal = !urls.length && !urlPrefixes.length && !domains.length && !regexps.length;
    const isMatching = !isGlobal && (
      urls.length
        && (urls.includes(matchUrl) || matchUrlBase && urls.includes(matchUrlBase))
      || urlPrefixes.length
        && arraySomeIsPrefix(urlPrefixes, matchUrl)
      || domains.length
        && arraySomeIn(cachedStyles.urlDomains.get(matchUrl) || getDomains(matchUrl), domains)
      || regexps.length
        && arraySomeMatches(regexps, matchUrl, strictRegexp));
    if (isGlobal && !styleCodeEmpty(code) || isMatching) {
      sections.push(section);
      if (stopOnFirst) {
        break;
      }
    }
  }
  return sections;

  function arraySomeIsPrefix(array, string) {
    for (const prefix of array) {
      if (string.startsWith(prefix)) {
        return true;
      }
    }
    return false;
  }

  function arraySomeIn(array, haystack) {
    for (const el of array) {
      if (haystack.indexOf(el) >= 0) {
        return true;
      }
    }
    return false;
  }

  function arraySomeMatches(array, matchUrl, strictRegexp) {
    for (const regexp of array) {
      for (let pass = 1; pass <= (strictRegexp ? 1 : 2); pass++) {
        const cacheKey = pass === 1 ? regexp : SLOPPY_REGEXP_PREFIX + regexp;
        let rx = cachedStyles.regexps.get(cacheKey);
        if (rx === false) {
          // invalid regexp
          break;
        }
        if (!rx) {
          const anchored = pass === 1 ? '^(?:' + regexp + ')$' : '^' + regexp + '$';
          rx = tryRegExp(anchored);
          cachedStyles.regexps.set(cacheKey, rx || false);
          if (!rx) {
            // invalid regexp
            break;
          }
        }
        if (rx.test(matchUrl)) {
          return true;
        }
      }
    }
    return false;
  }
}


function styleCodeEmpty(code) {
  // Collect the global section if it's not empty, not comment-only, not namespace-only.
  const cmtOpen = code && code.indexOf('/*');
  if (cmtOpen >= 0) {
    const cmtCloseLast = code.lastIndexOf('*/');
    if (cmtCloseLast < 0) {
      code = code.substr(0, cmtOpen);
    } else {
      code = code.substr(0, cmtOpen) +
        code.substring(cmtOpen, cmtCloseLast + 2).replace(RX_CSS_COMMENTS, '') +
        code.substr(cmtCloseLast + 2);
    }
  }
  return !code
    || !code.trim()
    || code.includes('@namespace') && !code.replace(RX_NAMESPACE, '').trim();
}


function styleSectionsEqual({sections: a}, {sections: b}) {
  if (!a || !b) {
    return undefined;
  }
  if (a.length !== b.length) {
    return false;
  }
  const checkedInB = [];
  return a.every(sectionA => b.some(sectionB => {
    if (!checkedInB.includes(sectionB) && propertiesEqual(sectionA, sectionB)) {
      checkedInB.push(sectionB);
      return true;
    }
  }));

  function propertiesEqual(secA, secB) {
    for (const name of ['urlPrefixes', 'urls', 'domains', 'regexps']) {
      if (!equalOrEmpty(secA[name], secB[name], 'every', arrayMirrors)) {
        return false;
      }
    }
    return equalOrEmpty(secA.code, secB.code, 'substr', (a, b) => a === b);
  }

  function equalOrEmpty(a, b, telltale, comparator) {
    const typeA = a && typeof a[telltale] === 'function';
    const typeB = b && typeof b[telltale] === 'function';
    return (
      (a === null || a === undefined || (typeA && !a.length)) &&
      (b === null || b === undefined || (typeB && !b.length))
    ) || typeA && typeB && a.length === b.length && comparator(a, b);
  }

  function arrayMirrors(array1, array2) {
    for (const el of array1) {
      if (array2.indexOf(el) < 0) {
        return false;
      }
    }
    for (const el of array2) {
      if (array1.indexOf(el) < 0) {
        return false;
      }
    }
    return true;
  }
}


function invalidateCache({added, updated, deletedId} = {}) {
  if (!cachedStyles.list) {
    return;
  }
  const id = added ? added.id : updated ? updated.id : deletedId;
  const cached = cachedStyles.byId.get(id);
  if (updated) {
    if (cached) {
      Object.assign(cached, updated);
      cachedStyles.filters.clear();
      cachedStyles.needTransitionPatch.delete(id);
      return;
    } else {
      added = updated;
    }
  }
  if (added) {
    if (!cached) {
      cachedStyles.list.push(added);
      cachedStyles.byId.set(added.id, added);
      cachedStyles.filters.clear();
      cachedStyles.needTransitionPatch.delete(id);
    }
    return;
  }
  if (deletedId !== undefined) {
    if (cached) {
      const cachedIndex = cachedStyles.list.indexOf(cached);
      cachedStyles.list.splice(cachedIndex, 1);
      cachedStyles.byId.delete(deletedId);
      cachedStyles.filters.clear();
      cachedStyles.needTransitionPatch.delete(id);
      return;
    }
  }
  cachedStyles.list = null;
  cachedStyles.filters.clear();
  cachedStyles.needTransitionPatch.clear(id);
}


function cleanupCachedFilters({force = false} = {}) {
  if (!force) {
    debounce(cleanupCachedFilters, 1000, {force: true});
    return;
  }
  const size = cachedStyles.filters.size;
  const oldestHit = cachedStyles.filters.values().next().value.lastHit;
  const now = Date.now();
  const timeSpan = now - oldestHit;
  const recencyWeight = 5 / size;
  const hitWeight = 1 / 4; // we make ~4 hits per URL
  const lastHitWeight = 10;
  // delete the oldest 10%
  [...cachedStyles.filters.entries()]
    .map(([id, v], index) => ({
      id,
      weight:
        index * recencyWeight +
        v.hits * hitWeight +
        (v.lastHit - oldestHit) / timeSpan * lastHitWeight,
    }))
    .sort((a, b) => a.weight - b.weight)
    .slice(0, size / 10 + 1)
    .forEach(({id}) => cachedStyles.filters.delete(id));
}


function getDomains(url) {
  let d = /.*?:\/*([^/:]+)|$/.exec(url)[1];
  if (!d || url.startsWith('file:')) {
    return [];
  }
  const domains = [d];
  while (d.indexOf('.') !== -1) {
    d = d.substring(d.indexOf('.') + 1);
    domains.push(d);
  }
  return domains;
}


function normalizeStyleSections({sections}) {
  // retain known properties in an arbitrarily predefined order
  return (sections || []).map(section => ({
    code: section.code || '',
    urls: section.urls || [],
    urlPrefixes: section.urlPrefixes || [],
    domains: section.domains || [],
    regexps: section.regexps || [],
  }));
}


function calcStyleDigest(style) {
  const jsonString = JSON.stringify(normalizeStyleSections(style));
  const text = new TextEncoder('utf-8').encode(jsonString);
  return crypto.subtle.digest('SHA-1', text).then(hex);

  function hex(buffer) {
    const parts = [];
    const PAD8 = '00000000';
    const view = new DataView(buffer);
    for (let i = 0; i < view.byteLength; i += 4) {
      parts.push((PAD8 + view.getUint32(i).toString(16)).slice(-8));
    }
    return parts.join('');
  }
}


function handleCssTransitionBug({tabId, frameId, url, styles}) {
  for (let id in styles) {
    id |= 0;
    if (!id) {
      continue;
    }
    let need = cachedStyles.needTransitionPatch.get(id);
    if (need === false) {
      continue;
    }
    if (need !== true) {
      need = styles[id].some(sectionContainsTransitions);
      cachedStyles.needTransitionPatch.set(id, need);
      if (!need) {
        continue;
      }
    }
    if (FIREFOX && !url.startsWith(URLS.ownOrigin)) {
      patchFirefox();
    } else {
      styles.needTransitionPatch = true;
    }
    break;
  }

  function patchFirefox() {
    browser.tabs.insertCSS(tabId, {
      frameId,
      code: CSS_TRANSITION_SUPPRESSOR,
      cssOrigin: 'user',
      runAt: 'document_start',
      matchAboutBlank: true,
    }).then(() => setTimeout(() => {
      browser.tabs.removeCSS(tabId, {
        frameId,
        code: CSS_TRANSITION_SUPPRESSOR,
        cssOrigin: 'user',
        matchAboutBlank: true,
      }).catch(ignoreChromeError);
    })).catch(ignoreChromeError);
  }

  function sectionContainsTransitions(section) {
    let code = section.code;
    const firstTransition = code.indexOf('transition');
    if (firstTransition < 0) {
      return false;
    }
    const firstCmt = code.indexOf('/*');
    // check the part before the first comment
    if (firstCmt < 0 || firstTransition < firstCmt) {
      if (quickCheckAround(code, firstTransition)) {
        return true;
      } else if (firstCmt < 0) {
        return false;
      }
    }
    // check the rest
    const lastCmt = code.lastIndexOf('*/');
    if (lastCmt < firstCmt) {
      // the comment is unclosed and we already checked the preceding part
      return false;
    }
    let mid = code.slice(firstCmt, lastCmt + 2);
    mid = mid.indexOf('*/') === mid.length - 2 ? '' : mid.replace(RX_CSS_COMMENTS, '');
    code = mid + code.slice(lastCmt + 2);
    return quickCheckAround(code) || RX_CSS_TRANSITION_DETECTOR.test(code);
  }

  function quickCheckAround(code, pos = code.indexOf('transition')) {
    return RX_CSS_TRANSITION_DETECTOR.test(code.substr(Math.max(0, pos - 10), 50));
  }
}