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/* -*- js-indent-level: 2; indent-tabs-mode: nil -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

var EXPORTED_SYMBOLS = [
  "BrowserUsageTelemetry",
  "getUniqueDomainsVisitedInPast24Hours",
  "URICountListener",
  "URLBAR_SELECTED_RESULT_TYPES",
  "URLBAR_SELECTED_RESULT_METHODS",
  "MINIMUM_TAB_COUNT_INTERVAL_MS",
];

const { XPCOMUtils } = ChromeUtils.import(
  "resource://gre/modules/XPCOMUtils.jsm"
);

XPCOMUtils.defineLazyModuleGetters(this, {
  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
  SearchTelemetry: "resource:///modules/SearchTelemetry.jsm",
  Services: "resource://gre/modules/Services.jsm",
  setTimeout: "resource://gre/modules/Timer.jsm",
});

// This pref is in seconds!
XPCOMUtils.defineLazyPreferenceGetter(
  this,
  "gRecentVisitedOriginsExpiry",
  "browser.engagement.recent_visited_origins.expiry"
);

// The upper bound for the count of the visited unique domain names.
const MAX_UNIQUE_VISITED_DOMAINS = 100;

// Observed topic names.
const TAB_RESTORING_TOPIC = "SSTabRestoring";
const TELEMETRY_SUBSESSIONSPLIT_TOPIC =
  "internal-telemetry-after-subsession-split";
const DOMWINDOW_OPENED_TOPIC = "domwindowopened";
const AUTOCOMPLETE_ENTER_TEXT_TOPIC = "autocomplete-did-enter-text";

// Probe names.
const MAX_TAB_COUNT_SCALAR_NAME = "browser.engagement.max_concurrent_tab_count";
const MAX_WINDOW_COUNT_SCALAR_NAME =
  "browser.engagement.max_concurrent_window_count";
const TAB_OPEN_EVENT_COUNT_SCALAR_NAME =
  "browser.engagement.tab_open_event_count";
const MAX_TAB_PINNED_COUNT_SCALAR_NAME =
  "browser.engagement.max_concurrent_tab_pinned_count";
const TAB_PINNED_EVENT_COUNT_SCALAR_NAME =
  "browser.engagement.tab_pinned_event_count";
const WINDOW_OPEN_EVENT_COUNT_SCALAR_NAME =
  "browser.engagement.window_open_event_count";
const UNIQUE_DOMAINS_COUNT_SCALAR_NAME =
  "browser.engagement.unique_domains_count";
const TOTAL_URI_COUNT_SCALAR_NAME = "browser.engagement.total_uri_count";
const UNFILTERED_URI_COUNT_SCALAR_NAME =
  "browser.engagement.unfiltered_uri_count";

// A list of known search origins.
const KNOWN_SEARCH_SOURCES = [
  "abouthome",
  "contextmenu",
  "newtab",
  "searchbar",
  "urlbar",
  "webextension",
];

const KNOWN_ONEOFF_SOURCES = [
  "oneoff-urlbar",
  "oneoff-searchbar",
  "unknown", // Edge case: this is the searchbar (see bug 1195733 comment 7).
];

/**
 * The buckets used for logging telemetry to the FX_URLBAR_SELECTED_RESULT_TYPE
 * histogram.
 */
const URLBAR_SELECTED_RESULT_TYPES = {
  autofill: 0,
  bookmark: 1,
  history: 2,
  keyword: 3,
  searchengine: 4,
  searchsuggestion: 5,
  switchtab: 6,
  tag: 7,
  visiturl: 8,
  remotetab: 9,
  extension: 10,
  "preloaded-top-site": 11,
  tip: 12,
};

/**
 * This maps the categories used by the FX_URLBAR_SELECTED_RESULT_METHOD and
 * FX_SEARCHBAR_SELECTED_RESULT_METHOD histograms to their indexes in the
 * `labels` array.  This only needs to be used by tests that need to map from
 * category names to indexes in histogram snapshots.  Actual app code can use
 * these category names directly when they add to a histogram.
 */
const URLBAR_SELECTED_RESULT_METHODS = {
  enter: 0,
  enterSelection: 1,
  click: 2,
  arrowEnterSelection: 3,
  tabEnterSelection: 4,
  rightClickEnter: 5,
};

const MINIMUM_TAB_COUNT_INTERVAL_MS = 5 * 60 * 1000; // 5 minutes, in ms

function getOpenTabsAndWinsCounts() {
  let tabCount = 0;
  let winCount = 0;

  for (let win of Services.wm.getEnumerator("navigator:browser")) {
    winCount++;
    tabCount += win.gBrowser.tabs.length;
  }

  return { tabCount, winCount };
}

function getTabCount() {
  return getOpenTabsAndWinsCounts().tabCount;
}

function getPinnedTabsCount() {
  let pinnedTabs = 0;

  for (let win of Services.wm.getEnumerator("navigator:browser")) {
    pinnedTabs += [...win.ownerGlobal.gBrowser.tabs].filter(t => t.pinned)
      .length;
  }

  return pinnedTabs;
}

function getSearchEngineId(engine) {
  if (engine) {
    if (engine.identifier) {
      return engine.identifier;
    }
    if (engine.name) {
      return "other-" + engine.name;
    }
  }
  return "other";
}

function shouldRecordSearchCount(tabbrowser) {
  return (
    !PrivateBrowsingUtils.isWindowPrivate(tabbrowser.ownerGlobal) ||
    !Services.prefs.getBoolPref("browser.engagement.search_counts.pbm", false)
  );
}

let URICountListener = {
  // A set containing the visited domains, see bug 1271310.
  _domainSet: new Set(),
  // A set containing the visited origins during the last 24 hours (similar to domains, but not quite the same)
  _domain24hrSet: new Set(),
  // A map to keep track of the URIs loaded from the restored tabs.
  _restoredURIsMap: new WeakMap(),

  isHttpURI(uri) {
    // Only consider http(s) schemas.
    return uri.schemeIs("http") || uri.schemeIs("https");
  },

  addRestoredURI(browser, uri) {
    if (!this.isHttpURI(uri)) {
      return;
    }

    this._restoredURIsMap.set(browser, uri.spec);
  },

  onLocationChange(browser, webProgress, request, uri, flags) {
    // By default, assume we no longer need to track this tab.
    SearchTelemetry.stopTrackingBrowser(browser);

    // Don't count this URI if it's an error page.
    if (flags & Ci.nsIWebProgressListener.LOCATION_CHANGE_ERROR_PAGE) {
      return;
    }

    // We only care about top level loads.
    if (!webProgress.isTopLevel) {
      return;
    }

    // The SessionStore sets the URI of a tab first, firing onLocationChange the
    // first time, then manages content loading using its scheduler. Once content
    // loads, we will hit onLocationChange again.
    // We can catch the first case by checking for null requests: be advised that
    // this can also happen when navigating page fragments, so account for it.
    if (
      !request &&
      !(flags & Ci.nsIWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT)
    ) {
      return;
    }

    // Don't include URI and domain counts when in private mode.
    let shouldCountURI =
      !PrivateBrowsingUtils.isWindowPrivate(browser.ownerGlobal) ||
      Services.prefs.getBoolPref(
        "browser.engagement.total_uri_count.pbm",
        false
      );

    // Track URI loads, even if they're not http(s).
    let uriSpec = null;
    try {
      uriSpec = uri.spec;
    } catch (e) {
      // If we have troubles parsing the spec, still count this as
      // an unfiltered URI.
      if (shouldCountURI) {
        Services.telemetry.scalarAdd(UNFILTERED_URI_COUNT_SCALAR_NAME, 1);
      }
      return;
    }

    // Don't count about:blank and similar pages, as they would artificially
    // inflate the counts.
    if (browser.ownerGlobal.gInitialPages.includes(uriSpec)) {
      return;
    }

    // If the URI we're loading is in the _restoredURIsMap, then it comes from a
    // restored tab. If so, let's skip it and remove it from the map as we want to
    // count page refreshes.
    if (this._restoredURIsMap.get(browser) === uriSpec) {
      this._restoredURIsMap.delete(browser);
      return;
    }

    // The URI wasn't from a restored tab. Count it among the unfiltered URIs.
    // If this is an http(s) URI, this also gets counted by the "total_uri_count"
    // probe.
    if (shouldCountURI) {
      Services.telemetry.scalarAdd(UNFILTERED_URI_COUNT_SCALAR_NAME, 1);
    }

    if (!this.isHttpURI(uri)) {
      return;
    }

    if (
      shouldRecordSearchCount(browser.getTabBrowser()) &&
      !(flags & Ci.nsIWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT)
    ) {
      SearchTelemetry.updateTrackingStatus(browser, uriSpec);
    }

    if (!shouldCountURI) {
      return;
    }

    // Update the URI counts.
    Services.telemetry.scalarAdd(TOTAL_URI_COUNT_SCALAR_NAME, 1);

    // Update tab count
    BrowserUsageTelemetry._recordTabCount();

    // Unique domains should be aggregated by (eTLD + 1): x.test.com and y.test.com
    // are counted once as test.com.
    let baseDomain;
    try {
      // Even if only considering http(s) URIs, |getBaseDomain| could still throw
      // due to the URI containing invalid characters or the domain actually being
      // an ipv4 or ipv6 address.
      baseDomain = Services.eTLD.getBaseDomain(uri);
    } catch (e) {
      return;
    }

    // We only want to count the unique domains up to MAX_UNIQUE_VISITED_DOMAINS.
    if (this._domainSet.size < MAX_UNIQUE_VISITED_DOMAINS) {
      this._domainSet.add(baseDomain);
      Services.telemetry.scalarSet(
        UNIQUE_DOMAINS_COUNT_SCALAR_NAME,
        this._domainSet.size
      );
    }

    this._domain24hrSet.add(baseDomain);
    if (gRecentVisitedOriginsExpiry) {
      setTimeout(() => {
        this._domain24hrSet.delete(baseDomain);
      }, gRecentVisitedOriginsExpiry * 1000);
    }
  },

  /**
   * Reset the counts. This should be called when breaking a session in Telemetry.
   */
  reset() {
    this._domainSet.clear();
  },

  /**
   * Returns the number of unique domains visited in this session during the
   * last 24 hours.
   */
  get uniqueDomainsVisitedInPast24Hours() {
    return this._domain24hrSet.size;
  },

  /**
   * Resets the number of unique domains visited in this session.
   */
  resetUniqueDomainsVisitedInPast24Hours() {
    this._domain24hrSet.clear();
  },

  QueryInterface: ChromeUtils.generateQI([
    Ci.nsIWebProgressListener,
    Ci.nsISupportsWeakReference,
  ]),
};

let urlbarListener = {
  // This is needed for recordUrlbarSelectedResultMethod().
  selectedIndex: -1,

  init() {
    Services.obs.addObserver(this, AUTOCOMPLETE_ENTER_TEXT_TOPIC, true);
  },

  uninit() {
    Services.obs.removeObserver(this, AUTOCOMPLETE_ENTER_TEXT_TOPIC);
  },

  observe(subject, topic, data) {
    switch (topic) {
      case AUTOCOMPLETE_ENTER_TEXT_TOPIC:
        this._handleURLBarTelemetry(
          subject.QueryInterface(Ci.nsIAutoCompleteInput)
        );
        break;
    }
  },

  /**
   * Used to log telemetry when the user enters text in the urlbar.
   *
   * @param {nsIAutoCompleteInput} input  The autocomplete element where the
   *                                      text was entered.
   */
  _handleURLBarTelemetry(input) {
    if (!input || input.id != "urlbar") {
      return;
    }
    if (input.inPrivateContext || input.popup.selectedIndex < 0) {
      this.selectedIndex = -1;
      return;
    }

    // Except for the history popup, the urlbar always has a selection.  The
    // first result at index 0 is the "heuristic" result that indicates what
    // will happen when you press the Enter key.  Treat it as no selection.
    this.selectedIndex =
      input.popup.selectedIndex > 0 || !input.popup._isFirstResultHeuristic
        ? input.popup.selectedIndex
        : -1;

    let controller = input.popup.view.QueryInterface(
      Ci.nsIAutoCompleteController
    );
    let idx = input.popup.selectedIndex;
    let value = controller.getValueAt(idx);
    let action = input._parseActionUrl(value);
    let actionType;
    if (action) {
      actionType =
        action.type == "searchengine" && action.params.searchSuggestion
          ? "searchsuggestion"
          : action.type;
    }
    if (!actionType) {
      let styles = new Set(controller.getStyleAt(idx).split(/\s+/));
      let style = ["preloaded-top-site", "autofill", "tag", "bookmark"].find(
        s => styles.has(s)
      );
      actionType = style || "history";
    }

    Services.telemetry
      .getHistogramById("FX_URLBAR_SELECTED_RESULT_INDEX")
      .add(idx);

    // You can add values but don't change any of the existing values.
    // Otherwise you'll break our data.
    if (actionType in URLBAR_SELECTED_RESULT_TYPES) {
      Services.telemetry
        .getHistogramById("FX_URLBAR_SELECTED_RESULT_TYPE")
        .add(URLBAR_SELECTED_RESULT_TYPES[actionType]);
      Services.telemetry
        .getKeyedHistogramById("FX_URLBAR_SELECTED_RESULT_INDEX_BY_TYPE")
        .add(actionType, idx);
    } else {
      Cu.reportError(
        "Unknown FX_URLBAR_SELECTED_RESULT_TYPE type: " + actionType
      );
    }
  },

  QueryInterface: ChromeUtils.generateQI([
    Ci.nsIObserver,
    Ci.nsISupportsWeakReference,
  ]),
};

let BrowserUsageTelemetry = {
  _inited: false,

  init() {
    this._lastRecordTabCount = 0;
    urlbarListener.init();
    this._setupAfterRestore();
    this._inited = true;
  },

  /**
   * Handle subsession splits in the parent process.
   */
  afterSubsessionSplit() {
    // Scalars just got cleared due to a subsession split. We need to set the maximum
    // concurrent tab and window counts so that they reflect the correct value for the
    // new subsession.
    const counts = getOpenTabsAndWinsCounts();
    Services.telemetry.scalarSetMaximum(
      MAX_TAB_COUNT_SCALAR_NAME,
      counts.tabCount
    );
    Services.telemetry.scalarSetMaximum(
      MAX_WINDOW_COUNT_SCALAR_NAME,
      counts.winCount
    );

    // Reset the URI counter.
    URICountListener.reset();
  },

  QueryInterface: ChromeUtils.generateQI([
    Ci.nsIObserver,
    Ci.nsISupportsWeakReference,
  ]),

  uninit() {
    if (!this._inited) {
      return;
    }
    Services.obs.removeObserver(this, DOMWINDOW_OPENED_TOPIC);
    Services.obs.removeObserver(this, TELEMETRY_SUBSESSIONSPLIT_TOPIC);
    urlbarListener.uninit();
  },

  observe(subject, topic, data) {
    switch (topic) {
      case DOMWINDOW_OPENED_TOPIC:
        this._onWindowOpen(subject);
        break;
      case TELEMETRY_SUBSESSIONSPLIT_TOPIC:
        this.afterSubsessionSplit();
        break;
    }
  },

  handleEvent(event) {
    switch (event.type) {
      case "TabOpen":
        this._onTabOpen();
        break;
      case "TabPinned":
        this._onTabPinned();
        break;
      case "unload":
        this._unregisterWindow(event.target);
        break;
      case TAB_RESTORING_TOPIC:
        // We're restoring a new tab from a previous or crashed session.
        // We don't want to track the URIs from these tabs, so let
        // |URICountListener| know about them.
        let browser = event.target.linkedBrowser;
        URICountListener.addRestoredURI(browser, browser.currentURI);
        break;
    }
  },

  /**
   * The main entry point for recording search related Telemetry. This includes
   * search counts and engagement measurements.
   *
   * Telemetry records only search counts per engine and action origin, but
   * nothing pertaining to the search contents themselves.
   *
   * @param {tabbrowser} tabbrowser
   *        The tabbrowser where the search was loaded.
   * @param {nsISearchEngine} engine
   *        The engine handling the search.
   * @param {String} source
   *        Where the search originated from. See KNOWN_SEARCH_SOURCES for allowed
   *        values.
   * @param {Object} [details] Options object.
   * @param {Boolean} [details.isOneOff=false]
   *        true if this event was generated by a one-off search.
   * @param {Boolean} [details.isSuggestion=false]
   *        true if this event was generated by a suggested search.
   * @param {String} [details.alias=null]
   *        The search engine alias used in the search, if any.
   * @param {Object} [details.type=null]
   *        The object describing the event that triggered the search.
   * @throws if source is not in the known sources list.
   */
  recordSearch(tabbrowser, engine, source, details = {}) {
    if (!shouldRecordSearchCount(tabbrowser)) {
      return;
    }

    const countIdPrefix = getSearchEngineId(engine) + ".";
    const countIdSource = countIdPrefix + source;
    let histogram = Services.telemetry.getKeyedHistogramById("SEARCH_COUNTS");

    if (details.isOneOff) {
      if (!KNOWN_ONEOFF_SOURCES.includes(source)) {
        // Silently drop the error if this bogus call
        // came from 'urlbar' or 'searchbar'. They're
        // calling |recordSearch| twice from two different
        // code paths because they want to record the search
        // in SEARCH_COUNTS.
        if (["urlbar", "searchbar"].includes(source)) {
          histogram.add(countIdSource);
          return;
        }
        throw new Error("Unknown source for one-off search: " + source);
      }
    } else {
      if (!KNOWN_SEARCH_SOURCES.includes(source)) {
        throw new Error("Unknown source for search: " + source);
      }
      if (
        details.alias &&
        engine.wrappedJSObject._internalAliases.includes(details.alias)
      ) {
        // This search uses an internal @search keyword.  Record the source as
        // "alias", not "urlbar".
        histogram.add(countIdPrefix + "alias");
      } else {
        histogram.add(countIdSource);
      }
    }

    // Dispatch the search signal to other handlers.
    this._handleSearchAction(engine, source, details);
  },

  _recordSearch(engine, source, action = null) {
    let scalarKey = action ? "search_" + action : "search";
    Services.telemetry.keyedScalarAdd(
      "browser.engagement.navigation." + source,
      scalarKey,
      1
    );
    Services.telemetry.recordEvent("navigation", "search", source, action, {
      engine: getSearchEngineId(engine),
    });
  },

  _handleSearchAction(engine, source, details) {
    switch (source) {
      case "urlbar":
      case "oneoff-urlbar":
      case "searchbar":
      case "oneoff-searchbar":
      case "unknown": // Edge case: this is the searchbar (see bug 1195733 comment 7).
        this._handleSearchAndUrlbar(engine, source, details);
        break;
      case "abouthome":
        this._recordSearch(engine, "about_home", "enter");
        break;
      case "newtab":
        this._recordSearch(engine, "about_newtab", "enter");
        break;
      case "contextmenu":
      case "webextension":
        this._recordSearch(engine, source);
        break;
    }
  },

  /**
   * This function handles the "urlbar", "urlbar-oneoff", "searchbar" and
   * "searchbar-oneoff" sources.
   */
  _handleSearchAndUrlbar(engine, source, details) {
    // We want "urlbar" and "urlbar-oneoff" (and similar cases) to go in the same
    // scalar, but in a different key.

    // When using one-offs in the searchbar we get an "unknown" source. See bug
    // 1195733 comment 7 for the context. Fix-up the label here.
    const sourceName =
      source === "unknown" ? "searchbar" : source.replace("oneoff-", "");

    const isOneOff = !!details.isOneOff;
    if (isOneOff) {
      // We will receive a signal from the "urlbar"/"searchbar" even when the
      // search came from "oneoff-urlbar". That's because both signals
      // are propagated from search.xml. Skip it if that's the case.
      // Moreover, we skip the "unknown" source that comes from the searchbar
      // when performing searches from the default search engine. See bug 1195733
      // comment 7 for context.
      if (["urlbar", "searchbar", "unknown"].includes(source)) {
        return;
      }

      // If that's a legit one-off search signal, record it using the relative key.
      this._recordSearch(engine, sourceName, "oneoff");
      return;
    }

    // The search was not a one-off. It was a search with the default search engine.
    if (details.isSuggestion) {
      // It came from a suggested search, so count it as such.
      this._recordSearch(engine, sourceName, "suggestion");
      return;
    } else if (details.alias) {
      // This one came from a search that used an alias.
      this._recordSearch(engine, sourceName, "alias");
      return;
    }

    // The search signal was generated by typing something and pressing enter.
    this._recordSearch(engine, sourceName, "enter");
  },

  /**
   * Records the method by which the user selected a urlbar result for the
   * legacy urlbar.
   *
   * @param {Event} event
   *        The event that triggered the selection.
   * @param {string} userSelectionBehavior
   *        How the user cycled through results before picking the current match.
   *        Could be one of "tab", "arrow" or "none".
   */
  recordLegacyUrlbarSelectedResultMethod(
    event,
    userSelectionBehavior = "none"
  ) {
    // The reason this method relies on urlbarListener instead of having the
    // caller pass in an index is that by the time the urlbar handles a
    // selection, the selection in its popup has been cleared, so it's not easy
    // to tell which popup index was selected.  Fortunately this file already
    // has urlbarListener, which gets notified of selections in the urlbar
    // before the popup selection is cleared, so just use that.

    this._recordUrlOrSearchbarSelectedResultMethod(
      event,
      urlbarListener.selectedIndex,
      "FX_URLBAR_SELECTED_RESULT_METHOD",
      userSelectionBehavior
    );
  },

  /**
   * Records the method by which the user selected a urlbar result for the
   * legacy urlbar.
   *
   * @param {Event} event
   *        The event that triggered the selection.
   * @param {number} index
   *        The index that the user chose in the popup, or -1 if there wasn't a
   *        selection.
   * @param {string} userSelectionBehavior
   *        How the user cycled through results before picking the current match.
   *        Could be one of "tab", "arrow" or "none".
   */
  recordUrlbarSelectedResultMethod(
    event,
    index,
    userSelectionBehavior = "none"
  ) {
    // The reason this method relies on urlbarListener instead of having the
    // caller pass in an index is that by the time the urlbar handles a
    // selection, the selection in its popup has been cleared, so it's not easy
    // to tell which popup index was selected.  Fortunately this file already
    // has urlbarListener, which gets notified of selections in the urlbar
    // before the popup selection is cleared, so just use that.

    this._recordUrlOrSearchbarSelectedResultMethod(
      event,
      index,
      "FX_URLBAR_SELECTED_RESULT_METHOD",
      userSelectionBehavior
    );
  },

  /**
   * Records the method by which the user selected a searchbar result.
   *
   * @param {Event} event
   *        The event that triggered the selection.
   * @param {number} highlightedIndex
   *        The index that the user chose in the popup, or -1 if there wasn't a
   *        selection.
   */
  recordSearchbarSelectedResultMethod(event, highlightedIndex) {
    this._recordUrlOrSearchbarSelectedResultMethod(
      event,
      highlightedIndex,
      "FX_SEARCHBAR_SELECTED_RESULT_METHOD",
      "none"
    );
  },

  _recordUrlOrSearchbarSelectedResultMethod(
    event,
    highlightedIndex,
    histogramID,
    userSelectionBehavior
  ) {
    let histogram = Services.telemetry.getHistogramById(histogramID);
    // command events are from the one-off context menu.  Treat them as clicks.
    // Note that we don't care about MouseEvent subclasses here, since
    // those are not clicks.
    let isClick =
      event &&
      (ChromeUtils.getClassName(event) == "MouseEvent" ||
        event.type == "command");
    let category;
    if (isClick) {
      category = "click";
    } else if (highlightedIndex >= 0) {
      switch (userSelectionBehavior) {
        case "tab":
          category = "tabEnterSelection";
          break;
        case "arrow":
          category = "arrowEnterSelection";
          break;
        case "rightClick":
          // Selected by right mouse button.
          category = "rightClickEnter";
          break;
        default:
          category = "enterSelection";
      }
    } else {
      category = "enter";
    }
    histogram.add(category);
  },

  /**
   * This gets called shortly after the SessionStore has finished restoring
   * windows and tabs. It counts the open tabs and adds listeners to all the
   * windows.
   */
  _setupAfterRestore() {
    // Make sure to catch new chrome windows and subsession splits.
    Services.obs.addObserver(this, DOMWINDOW_OPENED_TOPIC, true);
    Services.obs.addObserver(this, TELEMETRY_SUBSESSIONSPLIT_TOPIC, true);

    // Attach the tabopen handlers to the existing Windows.
    for (let win of Services.wm.getEnumerator("navigator:browser")) {
      this._registerWindow(win);
    }

    // Get the initial tab and windows max counts.
    const counts = getOpenTabsAndWinsCounts();
    Services.telemetry.scalarSetMaximum(
      MAX_TAB_COUNT_SCALAR_NAME,
      counts.tabCount
    );
    Services.telemetry.scalarSetMaximum(
      MAX_WINDOW_COUNT_SCALAR_NAME,
      counts.winCount
    );
  },

  /**
   * Adds listeners to a single chrome window.
   */
  _registerWindow(win) {
    win.addEventListener("unload", this);
    win.addEventListener("TabOpen", this, true);
    win.addEventListener("TabPinned", this, true);

    win.gBrowser.tabContainer.addEventListener(TAB_RESTORING_TOPIC, this);
    win.gBrowser.addTabsProgressListener(URICountListener);
  },

  /**
   * Removes listeners from a single chrome window.
   */
  _unregisterWindow(win) {
    win.removeEventListener("unload", this);
    win.removeEventListener("TabOpen", this, true);
    win.removeEventListener("TabPinned", this, true);

    win.defaultView.gBrowser.tabContainer.removeEventListener(
      TAB_RESTORING_TOPIC,
      this
    );
    win.defaultView.gBrowser.removeTabsProgressListener(URICountListener);
  },

  /**
   * Updates the tab counts.
   * @param {Number} [newTabCount=0] The count of the opened tabs across all windows. This
   *        is computed manually if not provided.
   */
  _onTabOpen(tabCount = 0) {
    // Use the provided tab count if available. Otherwise, go on and compute it.
    tabCount = tabCount || getOpenTabsAndWinsCounts().tabCount;
    // Update the "tab opened" count and its maximum.
    Services.telemetry.scalarAdd(TAB_OPEN_EVENT_COUNT_SCALAR_NAME, 1);
    Services.telemetry.scalarSetMaximum(MAX_TAB_COUNT_SCALAR_NAME, tabCount);

    this._recordTabCount(tabCount);
  },

  _onTabPinned(target) {
    const pinnedTabs = getPinnedTabsCount();

    // Update the "tab pinned" count and its maximum.
    Services.telemetry.scalarAdd(TAB_PINNED_EVENT_COUNT_SCALAR_NAME, 1);
    Services.telemetry.scalarSetMaximum(
      MAX_TAB_PINNED_COUNT_SCALAR_NAME,
      pinnedTabs
    );
  },

  /**
   * Tracks the window count and registers the listeners for the tab count.
   * @param{Object} win The window object.
   */
  _onWindowOpen(win) {
    // Make sure to have a |nsIDOMWindow|.
    if (!(win instanceof Ci.nsIDOMWindow)) {
      return;
    }

    let onLoad = () => {
      win.removeEventListener("load", onLoad);

      // Ignore non browser windows.
      if (
        win.document.documentElement.getAttribute("windowtype") !=
        "navigator:browser"
      ) {
        return;
      }

      this._registerWindow(win);
      // Track the window open event and check the maximum.
      const counts = getOpenTabsAndWinsCounts();
      Services.telemetry.scalarAdd(WINDOW_OPEN_EVENT_COUNT_SCALAR_NAME, 1);
      Services.telemetry.scalarSetMaximum(
        MAX_WINDOW_COUNT_SCALAR_NAME,
        counts.winCount
      );

      // We won't receive the "TabOpen" event for the first tab within a new window.
      // Account for that.
      this._onTabOpen(counts.tabCount);
    };
    win.addEventListener("load", onLoad);
  },

  _recordTabCount(tabCount) {
    let currentTime = Date.now();
    if (
      currentTime >
      this._lastRecordTabCount + MINIMUM_TAB_COUNT_INTERVAL_MS
    ) {
      if (tabCount === undefined) {
        tabCount = getTabCount();
      }
      Services.telemetry.getHistogramById("TAB_COUNT").add(tabCount);
      this._lastRecordTabCount = currentTime;
    }
  },
};

// Used by nsIBrowserUsage
function getUniqueDomainsVisitedInPast24Hours() {
  return URICountListener.uniqueDomainsVisitedInPast24Hours;
}