/* 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";

// This is loaded into chrome windows with the subscript loader. Wrap in
// a block to prevent accidentally leaking globals onto `window`.
{
  const lazy = {};
  ChromeUtils.defineESModuleGetters(lazy, {
    TabMetrics: "moz-src:///browser/components/tabbrowser/TabMetrics.sys.mjs",
  });

  class MozTabbrowserTab extends MozElements.MozTab {
    static markup = `
      <stack class="tab-stack" flex="1">
        <vbox class="tab-background">
          <hbox class="tab-context-line"/>
          <hbox class="tab-loading-burst" flex="1"/>
          <hbox class="tab-group-line"/>
        </vbox>
        <hbox class="tab-content" align="center">
          <stack class="tab-icon-stack">
            <hbox class="tab-throbber"/>
            <hbox class="tab-icon-pending"/>
            <html:img class="tab-icon-image" role="presentation" decoding="sync" />
            <image class="tab-sharing-icon-overlay" role="presentation"/>
            <image class="tab-icon-overlay" role="presentation"/>
            <image class="tab-note-icon-overlay" role="presentation"/>
          </stack>
          <html:moz-button type="icon ghost" size="small" class="tab-audio-button" tabindex="-1"></html:moz-button>
          <vbox class="tab-label-container"
                align="start"
                pack="center"
                flex="1">
            <label class="tab-text tab-label" role="presentation"/>
          </vbox>
          <image class="tab-note-icon" role="presentation"/>
          <image class="tab-close-button close-icon" role="button" data-l10n-id="tabbrowser-close-tabs-button" data-l10n-args='{"tabCount": 1}' keyNav="false"/>
        </hbox>
      </stack>
      `;

    constructor() {
      super();

      this.addEventListener("mouseover", this);
      this.addEventListener("mouseout", this);
      this.addEventListener("dragstart", this, true);
      this.addEventListener("dragstart", this);
      this.addEventListener("mousedown", this);
      this.addEventListener("mouseup", this);
      this.addEventListener("click", this);
      this.addEventListener("dblclick", this, true);
      this.addEventListener("animationstart", this);
      this.addEventListener("animationend", this);
      this.addEventListener("focus", this);
      this.addEventListener("AriaFocus", this);

      this._hover = false;
      this._selectedOnFirstMouseDown = false;
      this._noteIconHover = false;

      /**
       * Describes how the tab ended up in this mute state. May be any of:
       *
       * - undefined: The tabs mute state has never changed.
       * - null: The mute state was last changed through the UI.
       * - Any string: The ID was changed through an extension API. The string
       * must be the ID of the extension which changed it.
       */
      this.muteReason = undefined;

      this.closing = false;
    }

    static get inheritedAttributes() {
      return {
        ".tab-background":
          "selected=visuallyselected,fadein,multiselected,dragover-groupTarget",
        ".tab-group-line": "selected=visuallyselected,multiselected",
        ".tab-loading-burst": "pinned,bursting,notselectedsinceload",
        ".tab-content":
          "pinned,selected=visuallyselected,multiselected,titlechanged,attention",
        ".tab-icon-stack":
          "sharing,pictureinpicture,crashed,busy,soundplaying,soundplaying-scheduledremoval,pinned,muted,blocked,selected=visuallyselected,activemedia-blocked",
        ".tab-throbber":
          "fadein,pinned,busy,progress,selected=visuallyselected",
        ".tab-icon-pending":
          "fadein,pinned,busy,progress,selected=visuallyselected,pendingicon",
        ".tab-icon-image":
          "src=image,requestcontextid,fadein,pinned,selected=visuallyselected,busy,crashed,sharing,pictureinpicture,pending,discarded",
        ".tab-sharing-icon-overlay": "sharing,selected=visuallyselected,pinned",
        ".tab-icon-overlay":
          "sharing,pictureinpicture,crashed,busy,soundplaying,soundplaying-scheduledremoval,pinned,muted,blocked,selected=visuallyselected,activemedia-blocked",
        ".tab-audio-button":
          "crashed,soundplaying,soundplaying-scheduledremoval,pinned,muted,activemedia-blocked",
        ".tab-label-container":
          "pinned,selected=visuallyselected,labeldirection",
        ".tab-label":
          "text=label,accesskey,fadein,pinned,selected=visuallyselected,attention",
        ".tab-close-button": "fadein,pinned,selected=visuallyselected",
      };
    }

    #lastGroup;
    connectedCallback() {
      this.#updateOnTabGrouped();
      this.#updateOnTabSplit();
      this.#lastGroup = this.group;

      this.initialize();
    }

    disconnectedCallback() {
      this.#updateOnTabUngrouped();
      this.#updateOnTabUnsplit();
    }

    initialize() {
      if (this._initialized) {
        return;
      }

      this.textContent = "";
      this.appendChild(this.constructor.fragment);
      this.initializeAttributeInheritance();
      this.setAttribute("context", "tabContextMenu");
      this._initialized = true;

      if (!("_lastAccessed" in this)) {
        this.updateLastAccessed();
      }

      let labelContainer = this.querySelector(".tab-label-container");
      labelContainer.addEventListener("overflow", this);
      labelContainer.addEventListener("underflow", this);

      // Tabs in the tab strip default to being at the top level (level 1)
      // Tabs in tab groups are one level down (level 2); this tab will
      // update its value when it moves in and out of tab groups.
      this.setAttribute("aria-level", 1);
    }

    #elementIndex;
    get elementIndex() {
      if (!this.visible) {
        throw new Error("Tab is not visible, so does not have an elementIndex");
      }
      // Make sure the index is up to date.
      this.container.dragAndDropElements;
      return this.#elementIndex;
    }

    set elementIndex(index) {
      this.#elementIndex = index;
    }

    #owner;
    get owner() {
      let owner = this.#owner?.deref();
      if (owner && !owner.closing) {
        return owner;
      }
      return null;
    }

    set owner(owner) {
      this.#owner = owner ? new WeakRef(owner) : null;
    }

    get container() {
      return gBrowser.tabContainer;
    }

    set attention(val) {
      if (val == this.hasAttribute("attention")) {
        return;
      }

      this.toggleAttribute("attention", val);
      gBrowser._tabAttrModified(this, ["attention"]);
    }

    set _visuallySelected(val) {
      if (val == this.hasAttribute("visuallyselected")) {
        return;
      }

      this.toggleAttribute("visuallyselected", val);
      gBrowser._tabAttrModified(this, ["visuallyselected"]);
    }

    set _selected(val) {
      // in e10s we want to only pseudo-select a tab before its rendering is done, so that
      // the rest of the system knows that the tab is selected, but we don't want to update its
      // visual status to selected until after we receive confirmation that its content has painted.
      if (val) {
        this.setAttribute("selected", "true");
      } else {
        this.removeAttribute("selected");
      }

      // If we're non-e10s we need to update the visual selection at the same
      // time, otherwise AsyncTabSwitcher will take care of this.
      if (!gMultiProcessBrowser) {
        this._visuallySelected = val;
      }
    }

    get pinned() {
      return this.hasAttribute("pinned");
    }

    get isOpen() {
      return (
        this.isConnected && !this.closing && this != FirefoxViewHandler.tab
      );
    }

    get visible() {
      return (
        this.isOpen &&
        !this.hidden &&
        (!this.group || this.group.isTabVisibleInGroup(this))
      );
    }

    get hidden() {
      // This getter makes `hidden` read-only
      return super.hidden;
    }

    get muted() {
      return this.hasAttribute("muted");
    }

    get multiselected() {
      return this.hasAttribute("multiselected");
    }

    get userContextId() {
      return this.hasAttribute("usercontextid")
        ? parseInt(this.getAttribute("usercontextid"))
        : 0;
    }

    get soundPlaying() {
      return this.hasAttribute("soundplaying");
    }

    get pictureinpicture() {
      return this.hasAttribute("pictureinpicture");
    }

    get activeMediaBlocked() {
      return this.hasAttribute("activemedia-blocked");
    }

    get undiscardable() {
      return this.hasAttribute("undiscardable");
    }

    set undiscardable(val) {
      if (val == this.hasAttribute("undiscardable")) {
        return;
      }

      this.toggleAttribute("undiscardable", val);
      gBrowser._tabAttrModified(this, ["undiscardable"]);
    }

    get animationsEnabled() {
      return this.style.transition == "";
    }

    set animationsEnabled(val) {
      this.style.transition = val ? "" : "none";
    }

    get isEmpty() {
      // Determines if a tab is "empty", usually used in the context of determining
      // if it's ok to close the tab.
      if (this.hasAttribute("busy")) {
        return false;
      }

      if (this.hasAttribute("customizemode")) {
        return false;
      }

      let browser = this.linkedBrowser;
      if (!isBlankPageURL(browser.currentURI.spec)) {
        return false;
      }

      if (!BrowserUIUtils.checkEmptyPageOrigin(browser)) {
        return false;
      }

      if (browser.canGoForward || browser.canGoBack) {
        return false;
      }

      return true;
    }

    get lastAccessed() {
      return this._lastAccessed == Infinity ? Date.now() : this._lastAccessed;
    }

    /**
     * Returns a timestamp which attempts to represent the last time the user saw this tab.
     * If the tab has not been active in this session, any lastAccessed is used. We
     * differentiate between selected and explicitly visible; a selected tab in a hidden
     * window is last seen when that window and tab were last visible.
     * We use the application start time as a fallback value when no other suitable value
     * is available.
     */
    get lastSeenActive() {
      const isForegroundWindow =
        this.documentGlobal ==
        BrowserWindowTracker.getTopWindow({ allowPopups: true });
      // the timestamp for the selected tab in the active window is always now
      if (isForegroundWindow && this.selected) {
        return Date.now();
      }
      if (this._lastSeenActive) {
        return this._lastSeenActive;
      }

      if (
        !this._lastAccessed ||
        this._lastAccessed >= this.container.startupTime
      ) {
        // When the tab was created this session but hasn't been seen by the user,
        // default to the application start time.
        return this.container.startupTime;
      }
      // The tab was restored from a previous session but never seen.
      // Use the lastAccessed as the best proxy for when the user might have seen it.
      return this._lastAccessed;
    }

    get _overPlayingIcon() {
      return this.overlayIcon?.matches(":hover");
    }

    get _overAudioButton() {
      return this.audioButton?.matches(":hover");
    }

    get overlayIcon() {
      return this.querySelector(".tab-icon-overlay");
    }

    get audioButton() {
      return this.querySelector(".tab-audio-button");
    }

    get throbber() {
      return this.querySelector(".tab-throbber");
    }

    get iconImage() {
      return this.querySelector(".tab-icon-image");
    }

    get sharingIcon() {
      return this.querySelector(".tab-sharing-icon-overlay");
    }

    get textLabel() {
      return this.querySelector(".tab-label");
    }

    get closeButton() {
      return this.querySelector(".tab-close-button");
    }

    get noteIcon() {
      return this.querySelector(".tab-note-icon");
    }

    get noteIconOverlay() {
      return this.querySelector(".tab-note-icon-overlay");
    }

    get group() {
      return this.closest("tab-group");
    }

    get splitview() {
      if (this.parentElement?.tagName == "tab-split-view-wrapper") {
        return this.parentElement;
      }
      return null;
    }

    /**
     * @returns {boolean}
     */
    get hasTabNote() {
      return this.hasAttribute("tab-note");
    }

    /**
     * @param {boolean} val
     */
    set hasTabNote(val) {
      this.toggleAttribute("tab-note", val);
    }

    updateLastAccessed(aDate) {
      this._lastAccessed = this.selected ? Infinity : aDate || Date.now();
    }

    updateLastSeenActive() {
      this._lastSeenActive = Date.now();
    }

    updateLastUnloadedByTabUnloader() {
      this._lastUnloaded = Date.now();
      Glean.browserEngagement.tabUnloadCount.add(1);
    }

    recordTimeFromUnloadToReload() {
      if (!this._lastUnloaded) {
        return;
      }

      const diff_in_msec = Date.now() - this._lastUnloaded;
      Glean.browserEngagement.tabUnloadToReload.accumulateSingleSample(
        diff_in_msec / 1000
      );
      Glean.browserEngagement.tabReloadCount.add(1);
      delete this._lastUnloaded;
    }

    on_mouseover(event) {
      if (!this.visible) {
        return;
      }

      let tabToWarm = event.target.classList.contains("tab-close-button")
        ? gBrowser._findTabToBlurTo(this)
        : this;
      gBrowser.warmupTab(tabToWarm);

      if (this.hasTabNote) {
        const noteIcon = this.noteIcon;
        const noteIconOverlay = this.noteIconOverlay;
        const isOverNoteIcon =
          (noteIcon && noteIcon.contains(event.target)) ||
          (noteIconOverlay && noteIconOverlay.contains(event.target));

        if (isOverNoteIcon && !this._noteIconHover) {
          this._noteIconHover = true;
          this.dispatchEvent(
            new CustomEvent("TabNoteIconHoverStart", {
              bubbles: true,
              detail: {
                noteIconElement: noteIcon?.contains(event.target)
                  ? noteIcon
                  : noteIconOverlay,
              },
            })
          );
        }
      }

      // If the previous target wasn't part of this tab then this is a mouseenter event.
      if (!this.contains(event.relatedTarget)) {
        this._mouseenter();
      }
    }

    on_mouseout(event) {
      if (this._noteIconHover) {
        const noteIcon = this.noteIcon;
        const noteIconOverlay = this.noteIconOverlay;
        const stillOverNoteIcon =
          (noteIcon && noteIcon.contains(event.relatedTarget)) ||
          (noteIconOverlay && noteIconOverlay.contains(event.relatedTarget));

        if (!stillOverNoteIcon) {
          this._noteIconHover = false;
          this.dispatchEvent(
            new CustomEvent("TabNoteIconHoverEnd", {
              bubbles: true,
              detail: { returningToTab: this.contains(event.relatedTarget) },
            })
          );
        }
      }

      // If the new target is not part of this tab then this is a mouseleave event.
      if (!this.contains(event.relatedTarget)) {
        this._mouseleave();
      }
    }

    on_dragstart(event) {
      // We use "failed" drag end events that weren't cancelled by the user
      // to detach tabs. Ensure that we do not show the drag image returning
      // to its point of origin when this happens, as it makes the drag
      // finishing feel very slow.
      event.dataTransfer.mozShowFailAnimation = false;
      if (event.eventPhase == Event.CAPTURING_PHASE) {
        this.style.MozUserFocus = "";
      } else if (
        event.target.classList?.contains("tab-close-button") ||
        gSharedTabWarning.willShowSharedTabWarning(this)
      ) {
        event.stopPropagation();
      }
    }

    on_mousedown(event) {
      let eventMaySelectTab = true;
      let tabContainer = this.container;

      if (
        tabContainer._closeTabByDblclick &&
        event.button == 0 &&
        event.detail == 1
      ) {
        this._selectedOnFirstMouseDown = this.selected;
      }

      if (this.selected) {
        this.style.MozUserFocus = "ignore";
      } else if (
        event.target.classList.contains("tab-close-button") ||
        event.target.classList.contains("tab-icon-overlay") ||
        event.target.classList.contains("tab-audio-button")
      ) {
        eventMaySelectTab = false;
      }

      if (event.button == 1) {
        gBrowser.warmupTab(gBrowser._findTabToBlurTo(this));
      }

      if (event.button == 0) {
        let shiftKey = event.shiftKey;
        let accelKey = event.getModifierState("Accel");
        if (shiftKey) {
          eventMaySelectTab = false;
          const lastSelectedTab = gBrowser.lastMultiSelectedTab;
          if (!accelKey) {
            gBrowser.selectedTab = lastSelectedTab;

            // Make sure selection is cleared when tab-switch doesn't happen.
            gBrowser.clearMultiSelectedTabs();
          }
          gBrowser.addRangeToMultiSelectedTabs(lastSelectedTab, this);
        } else if (accelKey) {
          // Ctrl (Cmd for mac) key is pressed
          eventMaySelectTab = false;
          if (this.multiselected) {
            gBrowser.removeFromMultiSelectedTabs(this);
          } else if (this != gBrowser.selectedTab) {
            gBrowser.addToMultiSelectedTabs(this);
            gBrowser.lastMultiSelectedTab = this;
          }
        } else if (
          event.altKey &&
          Services.prefs.getBoolPref("browser.tabs.splitView.enabled", false)
        ) {
          eventMaySelectTab = false;
        } else if (!this.selected && this.multiselected) {
          gBrowser.lockClearMultiSelectionOnce();
        }
      }

      if (gSharedTabWarning.willShowSharedTabWarning(this)) {
        eventMaySelectTab = false;
      }

      if (eventMaySelectTab) {
        super.on_mousedown(event);
      }
    }

    on_mouseup() {
      // Make sure that clear-selection is released.
      // Otherwise selection using Shift key may be broken.
      gBrowser.unlockClearMultiSelection();

      this.style.MozUserFocus = "";
    }

    on_click(event) {
      if (event.button != 0) {
        return;
      }

      if (event.altKey) {
        if (
          !event.target.classList.contains("tab-close-button") &&
          !event.target.classList.contains("tab-icon-overlay") &&
          !event.target.classList.contains("tab-audio-button") &&
          !this.selected &&
          !gBrowser.selectedTab.hidden &&
          Services.prefs.getBoolPref("browser.tabs.splitView.enabled", false) &&
          !this.splitview &&
          !gBrowser.selectedTab.splitview &&
          !this.pinned &&
          !gBrowser.selectedTab.pinned
        ) {
          gBrowser.addTabSplitView([gBrowser.selectedTab, this], {
            insertBefore: gBrowser.selectedTab,
            trigger: "alt_click",
          });
        }
        return;
      }

      if (event.getModifierState("Accel") || event.shiftKey) {
        return;
      }

      if (
        gBrowser.multiSelectedTabsCount > 0 &&
        !event.target.classList.contains("tab-close-button") &&
        !event.target.classList.contains("tab-icon-overlay") &&
        !event.target.classList.contains("tab-audio-button")
      ) {
        // Tabs were previously multi-selected and user clicks on a tab
        // without holding Ctrl/Cmd Key
        gBrowser.clearMultiSelectedTabs();
      }

      if (
        event.target.classList.contains("tab-icon-overlay") ||
        event.target.classList.contains("tab-audio-button")
      ) {
        if (this.activeMediaBlocked) {
          if (this.multiselected) {
            gBrowser.resumeDelayedMediaOnMultiSelectedTabs(this);
          } else {
            this.resumeDelayedMedia();
          }
        } else if (this.soundPlaying || this.muted) {
          if (this.multiselected) {
            gBrowser.toggleMuteAudioOnMultiSelectedTabs(this);
          } else {
            this.toggleMuteAudio();
          }
        }
        return;
      }

      if (event.target.classList.contains("tab-close-button")) {
        if (this.multiselected) {
          gBrowser.removeMultiSelectedTabs(
            lazy.TabMetrics.userTriggeredContext(
              lazy.TabMetrics.METRIC_SOURCE.TAB_STRIP
            )
          );
        } else {
          gBrowser.removeTab(this, {
            animate: true,
            triggeringEvent: event,
            ...lazy.TabMetrics.userTriggeredContext(
              lazy.TabMetrics.METRIC_SOURCE.TAB_STRIP
            ),
          });
        }
        // This enables double-click protection for the tab container
        // (see tabbrowser-tabs 'click' handler).
        gBrowser.tabContainer._blockDblClick = true;
      }
    }

    on_dblclick(event) {
      if (event.button != 0) {
        return;
      }

      // for the one-close-button case
      if (event.target.classList.contains("tab-close-button")) {
        event.stopPropagation();
      }

      let tabContainer = this.container;
      if (
        tabContainer._closeTabByDblclick &&
        this._selectedOnFirstMouseDown &&
        this.selected &&
        !event.target.classList.contains("tab-icon-overlay")
      ) {
        gBrowser.removeTab(this, {
          animate: true,
          triggeringEvent: event,
        });
      }
    }

    on_animationstart(event) {
      if (!event.animationName.startsWith("tab-throbber-animation")) {
        return;
      }
      // The animation is on a pseudo-element so we need to use `subtree: true`
      // to get our hands on it.
      for (let animation of event.target.getAnimations({ subtree: true })) {
        if (animation.animationName === event.animationName) {
          // Ensure all tab throbber animations are synchronized by sharing an
          // start time.
          animation.startTime = 0;
        }
      }
    }

    on_animationend(event) {
      if (event.target.classList.contains("tab-loading-burst")) {
        this.removeAttribute("bursting");
      }
    }

    _mouseenter() {
      this._hover = true;

      if (this.selected) {
        this.container._handleTabSelect();
      } else if (this.linkedPanel) {
        this.linkedBrowser.unselectedTabHover(true);
      }

      // Prepare connection to host beforehand.
      SessionStore.speculativeConnectOnTabHover(this);

      this.dispatchEvent(new CustomEvent("TabHoverStart", { bubbles: true }));
    }

    _mouseleave() {
      if (!this._hover) {
        return;
      }
      this._hover = false;
      if (this.linkedPanel && !this.selected) {
        this.linkedBrowser.unselectedTabHover(false);
      }
      this.dispatchEvent(new CustomEvent("TabHoverEnd", { bubbles: true }));
    }

    resumeDelayedMedia() {
      if (this.activeMediaBlocked) {
        this.removeAttribute("activemedia-blocked");
        this.linkedBrowser.resumeMedia();
        gBrowser._tabAttrModified(this, ["activemedia-blocked"]);
      }
    }

    toggleMuteAudio(aMuteReason) {
      let browser = this.linkedBrowser;
      if (browser.audioMuted) {
        if (this.linkedPanel) {
          // "Lazy Browser" should not invoke its unmute method
          browser.unmute();
        }
        this.removeAttribute("muted");
      } else {
        if (this.linkedPanel) {
          // "Lazy Browser" should not invoke its mute method
          browser.mute();
        }
        this.toggleAttribute("muted", true);
      }
      this.muteReason = aMuteReason || null;

      gBrowser._tabAttrModified(this, ["muted"]);
    }

    setUserContextId(aUserContextId) {
      if (aUserContextId) {
        if (this.linkedBrowser) {
          this.linkedBrowser.setAttribute("usercontextid", aUserContextId);
        }
        this.setAttribute("usercontextid", aUserContextId);
      } else {
        if (this.linkedBrowser) {
          this.linkedBrowser.removeAttribute("usercontextid");
        }
        this.removeAttribute("usercontextid");
      }

      ContextualIdentityService.setTabStyle(this);
    }

    updateA11yDescription() {
      let prevDescTab = gBrowser.tabContainer.querySelector(
        "tab[aria-describedby]"
      );
      if (prevDescTab) {
        // We can only have a description for the focused tab.
        prevDescTab.removeAttribute("aria-describedby");
      }
      let desc = document.getElementById("tabbrowser-tab-a11y-desc");
      desc.textContent = gBrowser.getTabTooltip(this, false);
      this.setAttribute("aria-describedby", "tabbrowser-tab-a11y-desc");
    }

    on_focus() {
      this.updateA11yDescription();
    }

    on_AriaFocus() {
      this.updateA11yDescription();
    }

    on_overflow(event) {
      event.currentTarget.toggleAttribute("textoverflow", true);
    }

    on_underflow(event) {
      event.currentTarget.removeAttribute("textoverflow");
    }

    #updateOnTabGrouped() {
      if (this.group && this.#lastGroup != this.group) {
        // Trigger TabGrouped on the tab group, not the tab itself. This is a
        // bit unorthodox, but fixes bug1964152 where tab group events are not
        // fired correctly when tabs change windows (because the tab is
        // detached from the DOM at time of the event).
        this.group.dispatchEvent(
          new CustomEvent("TabGrouped", {
            bubbles: true,
            detail: this,
          })
        );
        this.setAttribute("aria-level", 2);
      }
    }

    #updateOnTabUngrouped() {
      if (this.#lastGroup && this.#lastGroup != this.group) {
        // Trigger TabUngrouped on the tab group, not the tab itself. This is a
        // bit unorthodox, but fixes bug1964152 where tab group events are not
        // fired correctly when tabs change windows (because the tab is
        // detached from the DOM at time of the event).
        this.#lastGroup.dispatchEvent(
          new CustomEvent("TabUngrouped", {
            bubbles: true,
            detail: this,
          })
        );
        // Tab could have moved to be ungrouped (level 1)
        // or to a different group (level 2).
        this.setAttribute("aria-level", this.group ? 2 : 1);
        // `posinset` and `setsize` only need to be set explicitly
        // on grouped tabs so that a11y tools can tell users that a
        // given tab is "2 of 7" in the group, for example.
        this.removeAttribute("aria-posinset");
        this.removeAttribute("aria-setsize");
      }
    }

    #updateOnTabSplit() {
      if (this.splitview) {
        this.setAttribute("aria-level", 2);
      }
    }

    #updateOnTabUnsplit() {
      if (!this.splitview) {
        this.setAttribute("aria-level", 1);
        // `posinset` and `setsize` only need to be set explicitly
        // on split view tabs so that a11y tools can tell users that a
        // given tab is "1 of 2" in the split view, for example.
        this.removeAttribute("aria-posinset");
        this.removeAttribute("aria-setsize");
        this.removeAttribute("aria-label");
      }
    }

    /**
     * Set `aria-label` for this tab to indicate that it's in a Split View,
     * along with its position within the Split View.
     *
     * @param {number} index
     *   The index of this tab in the Split View.
     */
    updateSplitViewAriaLabel(index) {
      let l10nId = "";
      switch (index) {
        case 0:
          l10nId = window.RTL_UI
            ? "tabbrowser-tab-label-tab-split-view-right"
            : "tabbrowser-tab-label-tab-split-view-left";
          break;
        case 1:
          l10nId = window.RTL_UI
            ? "tabbrowser-tab-label-tab-split-view-left"
            : "tabbrowser-tab-label-tab-split-view-right";
          break;
      }
      if (l10nId) {
        const ariaLabel = gBrowser.tabLocalization.formatValueSync(l10nId, {
          label: this.getAttribute("label"),
        });
        this.setAttribute("aria-label", ariaLabel);
      }
    }
  }

  customElements.define("tabbrowser-tab", MozTabbrowserTab, {
    extends: "tab",
  });
}