/**
 * @license
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
(function() {
  'use strict';

  const CHANGE_ID_ERROR = {
    MISMATCH: 'mismatch',
    MISSING: 'missing',
  };
  const CHANGE_ID_REGEX_PATTERN = /^Change-Id\:\s(I[0-9a-f]{8,40})/gm;

  const MIN_LINES_FOR_COMMIT_COLLAPSE = 30;
  const DEFAULT_NUM_FILES_SHOWN = 200;

  const REVIEWERS_REGEX = /^(R|CC)=/gm;
  const MIN_CHECK_INTERVAL_SECS = 0;

  // These are the same as the breakpoint set in CSS. Make sure both are changed
  // together.
  const BREAKPOINT_RELATED_SMALL = '50em';
  const BREAKPOINT_RELATED_MED = '75em';

  // In the event that the related changes medium width calculation is too close
  // to zero, provide some height.
  const MINIMUM_RELATED_MAX_HEIGHT = 100;

  const SMALL_RELATED_HEIGHT = 400;

  const REPLY_REFIT_DEBOUNCE_INTERVAL_MS = 500;

  const TRAILING_WHITESPACE_REGEX = /[ \t]+$/gm;

  const MSG_PREFIX = '#message-';

  const ReloadToastMessage = {
    NEWER_REVISION: 'A newer patch set has been uploaded',
    RESTORED: 'This change has been restored',
    ABANDONED: 'This change has been abandoned',
    MERGED: 'This change has been merged',
    NEW_MESSAGE: 'There are new messages on this change',
  };

  const DiffViewMode = {
    SIDE_BY_SIDE: 'SIDE_BY_SIDE',
    UNIFIED: 'UNIFIED_DIFF',
  };

  const CHANGE_DATA_TIMING_LABEL = 'ChangeDataLoaded';
  const CHANGE_RELOAD_TIMING_LABEL = 'ChangeReloaded';
  const SEND_REPLY_TIMING_LABEL = 'SendReply';

  /**
   * @appliesMixin Gerrit.FireMixin
   * @appliesMixin Gerrit.KeyboardShortcutMixin
   * @appliesMixin Gerrit.PatchSetMixin
   * @appliesMixin Gerrit.RESTClientMixin
   * @extends Polymer.Element
   */
  class GrChangeView extends Polymer.mixinBehaviors( [
    Gerrit.FireBehavior,
    Gerrit.KeyboardShortcutBehavior,
    Gerrit.PatchSetBehavior,
    Gerrit.RESTClientBehavior,
  ], Polymer.GestureEventListeners(
      Polymer.LegacyElementMixin(
          Polymer.Element))) {
    static get is() { return 'gr-change-view'; }
    /**
     * Fired when the title of the page should change.
     *
     * @event title-change
     */

    /**
     * Fired if an error occurs when fetching the change data.
     *
     * @event page-error
     */

    /**
     * Fired if being logged in is required.
     *
     * @event show-auth-required
     */

    static get properties() {
      return {
      /**
       * URL params passed from the router.
       */
        params: {
          type: Object,
          observer: '_paramsChanged',
        },
        /** @type {?} */
        viewState: {
          type: Object,
          notify: true,
          value() { return {}; },
          observer: '_viewStateChanged',
        },
        backPage: String,
        hasParent: Boolean,
        keyEventTarget: {
          type: Object,
          value() { return document.body; },
        },
        disableEdit: {
          type: Boolean,
          value: false,
        },
        disableDiffPrefs: {
          type: Boolean,
          value: false,
        },
        _diffPrefsDisabled: {
          type: Boolean,
          computed: '_computeDiffPrefsDisabled(disableDiffPrefs, _loggedIn)',
        },
        _commentThreads: Array,
        /** @type {?} */
        _serverConfig: {
          type: Object,
          observer: '_startUpdateCheckTimer',
        },
        _diffPrefs: Object,
        _numFilesShown: {
          type: Number,
          value: DEFAULT_NUM_FILES_SHOWN,
          observer: '_numFilesShownChanged',
        },
        _account: {
          type: Object,
          value: {},
        },
        _prefs: Object,
        /** @type {?} */
        _changeComments: Object,
        _canStartReview: {
          type: Boolean,
          computed: '_computeCanStartReview(_change)',
        },
        _comments: Object,
        /** @type {?} */
        _change: {
          type: Object,
          observer: '_changeChanged',
        },
        _revisionInfo: {
          type: Object,
          computed: '_getRevisionInfo(_change)',
        },
        /** @type {?} */
        _commitInfo: Object,
        _currentRevision: {
          type: Object,
          computed: '_computeCurrentRevision(_change.current_revision, ' +
            '_change.revisions)',
        },
        _files: Object,
        _changeNum: String,
        _diffDrafts: {
          type: Object,
          value() { return {}; },
        },
        _editingCommitMessage: {
          type: Boolean,
          value: false,
        },
        _hideEditCommitMessage: {
          type: Boolean,
          computed: '_computeHideEditCommitMessage(_loggedIn, ' +
            '_editingCommitMessage, _change, _editMode)',
        },
        _diffAgainst: String,
        /** @type {?string} */
        _latestCommitMessage: {
          type: String,
          value: '',
        },
        _lineHeight: Number,
        _changeIdCommitMessageError: {
          type: String,
          computed:
          '_computeChangeIdCommitMessageError(_latestCommitMessage, _change)',
        },
        /** @type {?} */
        _patchRange: {
          type: Object,
        },
        _filesExpanded: String,
        _basePatchNum: String,
        _selectedRevision: Object,
        _currentRevisionActions: Object,
        _allPatchSets: {
          type: Array,
          computed: 'computeAllPatchSets(_change, _change.revisions.*)',
        },
        _loggedIn: {
          type: Boolean,
          value: false,
        },
        _loading: Boolean,
        /** @type {?} */
        _projectConfig: Object,
        _rebaseOnCurrent: Boolean,
        _replyButtonLabel: {
          type: String,
          value: 'Reply',
          computed: '_computeReplyButtonLabel(_diffDrafts.*, _canStartReview)',
        },
        _selectedPatchSet: String,
        _shownFileCount: Number,
        _initialLoadComplete: {
          type: Boolean,
          value: false,
        },
        _replyDisabled: {
          type: Boolean,
          value: true,
          computed: '_computeReplyDisabled(_serverConfig)',
        },
        _changeStatus: {
          type: String,
          computed: 'changeStatusString(_change)',
        },
        _changeStatuses: {
          type: String,
          computed:
          '_computeChangeStatusChips(_change, _mergeable, _submitEnabled)',
        },
        _commitCollapsed: {
          type: Boolean,
          value: true,
        },
        _relatedChangesCollapsed: {
          type: Boolean,
          value: true,
        },
        /** @type {?number} */
        _updateCheckTimerHandle: Number,
        _editMode: {
          type: Boolean,
          computed: '_computeEditMode(_patchRange.*, params.*)',
        },
        _showRelatedToggle: {
          type: Boolean,
          value: false,
          observer: '_updateToggleContainerClass',
        },
        _parentIsCurrent: Boolean,
        _submitEnabled: {
          type: Boolean,
          computed: '_isSubmitEnabled(_currentRevisionActions)',
        },

        /** @type {?} */
        _mergeable: {
          type: Boolean,
          value: undefined,
        },
        _showMessagesView: {
          type: Boolean,
          value: true,
        },
        _showFileTabContent: {
          type: Boolean,
          value: true,
        },
        /** @type {Array<string>} */
        _dynamicTabHeaderEndpoints: {
          type: Array,
        },
        _showPrimaryTabs: {
          type: Boolean,
          computed: '_computeShowPrimaryTabs(_dynamicTabHeaderEndpoints)',
        },
        /** @type {Array<string>} */
        _dynamicTabContentEndpoints: {
          type: Array,
        },
        _selectedFilesTabPluginEndpoint: {
          type: String,
        },
      };
    }

    static get observers() {
      return [
        '_labelsChanged(_change.labels.*)',
        '_paramsAndChangeChanged(params, _change)',
        '_patchNumChanged(_patchRange.patchNum)',
      ];
    }

    keyboardShortcuts() {
      return {
        [this.Shortcut.SEND_REPLY]: null, // DOC_ONLY binding
        [this.Shortcut.EMOJI_DROPDOWN]: null, // DOC_ONLY binding
        [this.Shortcut.REFRESH_CHANGE]: '_handleRefreshChange',
        [this.Shortcut.OPEN_REPLY_DIALOG]: '_handleOpenReplyDialog',
        [this.Shortcut.OPEN_DOWNLOAD_DIALOG]:
            '_handleOpenDownloadDialogShortcut',
        [this.Shortcut.TOGGLE_DIFF_MODE]: '_handleToggleDiffMode',
        [this.Shortcut.TOGGLE_CHANGE_STAR]: '_handleToggleChangeStar',
        [this.Shortcut.UP_TO_DASHBOARD]: '_handleUpToDashboard',
        [this.Shortcut.EXPAND_ALL_MESSAGES]: '_handleExpandAllMessages',
        [this.Shortcut.COLLAPSE_ALL_MESSAGES]: '_handleCollapseAllMessages',
        [this.Shortcut.OPEN_DIFF_PREFS]: '_handleOpenDiffPrefsShortcut',
        [this.Shortcut.EDIT_TOPIC]: '_handleEditTopic',
      };
    }

    /** @override */
    created() {
      super.created();

      this.addEventListener('topic-changed',
          () => this._handleTopicChanged());

      this.addEventListener(
          // When an overlay is opened in a mobile viewport, the overlay has a full
          // screen view. When it has a full screen view, we do not want the
          // background to be scrollable. This will eliminate background scroll by
          // hiding most of the contents on the screen upon opening, and showing
          // again upon closing.
          'fullscreen-overlay-opened',
          () => this._handleHideBackgroundContent());

      this.addEventListener('fullscreen-overlay-closed',
          () => this._handleShowBackgroundContent());

      this.addEventListener('diff-comments-modified',
          () => this._handleReloadCommentThreads());
    }

    /** @override */
    attached() {
      super.attached();
      this._getServerConfig().then(config => {
        this._serverConfig = config;
      });

      this._getLoggedIn().then(loggedIn => {
        this._loggedIn = loggedIn;
        if (loggedIn) {
          this.$.restAPI.getAccount().then(acct => {
            this._account = acct;
          });
        }
        this._setDiffViewMode();
      });

      Gerrit.awaitPluginsLoaded()
          .then(() => {
            this._dynamicTabHeaderEndpoints =
            Gerrit._endpoints.getDynamicEndpoints('change-view-tab-header');
            this._dynamicTabContentEndpoints =
            Gerrit._endpoints.getDynamicEndpoints('change-view-tab-content');
            if (this._dynamicTabContentEndpoints.length !==
            this._dynamicTabHeaderEndpoints.length) {
              console.warn('Different number of tab headers and tab content.');
            }
          })
          .then(() => this._setPrimaryTab());

      this.addEventListener('comment-save', this._handleCommentSave.bind(this));
      this.addEventListener('comment-refresh', this._reloadDrafts.bind(this));
      this.addEventListener('comment-discard',
          this._handleCommentDiscard.bind(this));
      this.addEventListener('editable-content-save',
          this._handleCommitMessageSave.bind(this));
      this.addEventListener('editable-content-cancel',
          this._handleCommitMessageCancel.bind(this));
      this.addEventListener('open-fix-preview',
          this._onOpenFixPreview.bind(this));
      this.addEventListener('close-fix-preview',
          this._onCloseFixPreview.bind(this));
      this.listen(window, 'scroll', '_handleScroll');
      this.listen(document, 'visibilitychange', '_handleVisibilityChange');
    }

    /** @override */
    detached() {
      super.detached();
      this.unlisten(window, 'scroll', '_handleScroll');
      this.unlisten(document, 'visibilitychange', '_handleVisibilityChange');

      if (this._updateCheckTimerHandle) {
        this._cancelUpdateCheckTimer();
      }
    }

    get messagesList() {
      return this.$$('gr-messages-list');
    }

    get threadList() {
      return this.$$('gr-thread-list');
    }

    /**
     * @param {boolean=} opt_reset
     */
    _setDiffViewMode(opt_reset) {
      if (!opt_reset && this.viewState.diffViewMode) { return; }

      return this._getPreferences()
          .then( prefs => {
            if (!this.viewState.diffMode) {
              this.set('viewState.diffMode', prefs.default_diff_view);
            }
          })
          .then(() => {
            if (!this.viewState.diffMode) {
              this.set('viewState.diffMode', 'SIDE_BY_SIDE');
            }
          });
    }

    _onOpenFixPreview(e) {
      this.$.applyFixDialog.open(e);
    }

    _onCloseFixPreview(e) {
      this._reload();
    }

    _handleToggleDiffMode(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      if (this.viewState.diffMode === DiffViewMode.SIDE_BY_SIDE) {
        this.$.fileListHeader.setDiffViewMode(DiffViewMode.UNIFIED);
      } else {
        this.$.fileListHeader.setDiffViewMode(DiffViewMode.SIDE_BY_SIDE);
      }
    }

    _handleCommentTabChange() {
      this._showMessagesView = this.$.commentTabs.selected === 0;
    }

    _handleFileTabChange(e) {
      const selectedIndex = this.shadowRoot
          .querySelector('#primaryTabs').selected;
      this._showFileTabContent = selectedIndex === 0;
      // Initial tab is the static files list.
      const newSelectedTab =
          this._dynamicTabContentEndpoints[selectedIndex - 1];
      if (newSelectedTab !== this._selectedFilesTabPluginEndpoint) {
        this._selectedFilesTabPluginEndpoint = newSelectedTab;

        const tabName = this._selectedFilesTabPluginEndpoint || 'files';
        const source = e && e.type ? e.type : '';
        this.$.reporting.reportInteraction('tab-changed',
            `tabname: ${tabName}, source: ${source}`);
      }
    }

    _handleShowTab(e) {
      const idx = this._dynamicTabContentEndpoints.indexOf(e.detail.tab);
      if (idx === -1) {
        console.warn(e.detail.tab + ' tab not found');
        return;
      }
      this.shadowRoot.querySelector('#primaryTabs').selected = idx + 1;
      this.shadowRoot.querySelector('#primaryTabs').scrollIntoView();
      this.$.reporting.reportInteraction('show-tab', e.detail.tab);
    }

    _handleEditCommitMessage(e) {
      this._editingCommitMessage = true;
      this.$.commitMessageEditor.focusTextarea();
    }

    _handleCommitMessageSave(e) {
      // Trim trailing whitespace from each line.
      const message = e.detail.content.replace(TRAILING_WHITESPACE_REGEX, '');

      this.$.jsAPI.handleCommitMessage(this._change, message);

      this.$.commitMessageEditor.disabled = true;
      this.$.restAPI.putChangeCommitMessage(
          this._changeNum, message).then(resp => {
        this.$.commitMessageEditor.disabled = false;
        if (!resp.ok) { return; }

        this._latestCommitMessage = this._prepareCommitMsgForLinkify(
            message);
        this._editingCommitMessage = false;
        this._reloadWindow();
      })
          .catch(err => {
            this.$.commitMessageEditor.disabled = false;
          });
    }

    _reloadWindow() {
      window.location.reload();
    }

    _handleCommitMessageCancel(e) {
      this._editingCommitMessage = false;
    }

    _computeChangeStatusChips(change, mergeable, submitEnabled) {
      // Polymer 2: check for undefined
      if ([
        change,
        mergeable,
      ].some(arg => arg === undefined)) {
        // To keep consistent with Polymer 1, we are returning undefined
        // if not all dependencies are defined
        return undefined;
      }

      // Show no chips until mergeability is loaded.
      if (mergeable === null) {
        return [];
      }

      const options = {
        includeDerived: true,
        mergeable: !!mergeable,
        submitEnabled: !!submitEnabled,
      };
      return this.changeStatuses(change, options);
    }

    _computeHideEditCommitMessage(loggedIn, editing, change, editMode) {
      if (!loggedIn || editing ||
          (change && change.status === this.ChangeStatus.MERGED) ||
          editMode) {
        return true;
      }

      return false;
    }

    _handleReloadCommentThreads() {
      // Get any new drafts that have been saved in the diff view and show
      // in the comment thread view.
      this._reloadDrafts().then(() => {
        this._commentThreads = this._changeComments.getAllThreadsForChange()
            .map(c => Object.assign({}, c));
        Polymer.dom.flush();
      });
    }

    _handleReloadDiffComments(e) {
      // Keeps the file list counts updated.
      this._reloadDrafts().then(() => {
        // Get any new drafts that have been saved in the thread view and show
        // in the diff view.
        this.$.fileList.reloadCommentsForThreadWithRootId(e.detail.rootId,
            e.detail.path);
        Polymer.dom.flush();
      });
    }

    _computeTotalCommentCounts(unresolvedCount, changeComments) {
      if (!changeComments) return undefined;
      const draftCount = changeComments.computeDraftCount();
      const unresolvedString = GrCountStringFormatter.computeString(
          unresolvedCount, 'unresolved');
      const draftString = GrCountStringFormatter.computePluralString(
          draftCount, 'draft');

      return unresolvedString +
          // Add a comma and space if both unresolved and draft comments exist.
          (unresolvedString && draftString ? ', ' : '') +
          draftString;
    }

    _handleCommentSave(e) {
      const draft = e.detail.comment;
      if (!draft.__draft) { return; }

      draft.patch_set = draft.patch_set || this._patchRange.patchNum;

      // The use of path-based notification helpers (set, push) can’t be used
      // because the paths could contain dots in them. A new object must be
      // created to satisfy Polymer’s dirty checking.
      // https://github.com/Polymer/polymer/issues/3127
      const diffDrafts = Object.assign({}, this._diffDrafts);
      if (!diffDrafts[draft.path]) {
        diffDrafts[draft.path] = [draft];
        this._diffDrafts = diffDrafts;
        return;
      }
      for (let i = 0; i < this._diffDrafts[draft.path].length; i++) {
        if (this._diffDrafts[draft.path][i].id === draft.id) {
          diffDrafts[draft.path][i] = draft;
          this._diffDrafts = diffDrafts;
          return;
        }
      }
      diffDrafts[draft.path].push(draft);
      diffDrafts[draft.path].sort((c1, c2) =>
        // No line number means that it’s a file comment. Sort it above the
        // others.
        (c1.line || -1) - (c2.line || -1)
      );
      this._diffDrafts = diffDrafts;
    }

    _handleCommentDiscard(e) {
      const draft = e.detail.comment;
      if (!draft.__draft) { return; }

      if (!this._diffDrafts[draft.path]) {
        return;
      }
      let index = -1;
      for (let i = 0; i < this._diffDrafts[draft.path].length; i++) {
        if (this._diffDrafts[draft.path][i].id === draft.id) {
          index = i;
          break;
        }
      }
      if (index === -1) {
        // It may be a draft that hasn’t been added to _diffDrafts since it was
        // never saved.
        return;
      }

      draft.patch_set = draft.patch_set || this._patchRange.patchNum;

      // The use of path-based notification helpers (set, push) can’t be used
      // because the paths could contain dots in them. A new object must be
      // created to satisfy Polymer’s dirty checking.
      // https://github.com/Polymer/polymer/issues/3127
      const diffDrafts = Object.assign({}, this._diffDrafts);
      diffDrafts[draft.path].splice(index, 1);
      if (diffDrafts[draft.path].length === 0) {
        delete diffDrafts[draft.path];
      }
      this._diffDrafts = diffDrafts;
    }

    _handleReplyTap(e) {
      e.preventDefault();
      this._openReplyDialog(this.$.replyDialog.FocusTarget.ANY);
    }

    _handleOpenDiffPrefs() {
      this.$.fileList.openDiffPrefs();
    }

    _handleOpenIncludedInDialog() {
      this.$.includedInDialog.loadData().then(() => {
        Polymer.dom.flush();
        this.$.includedInOverlay.refit();
      });
      this.$.includedInOverlay.open();
    }

    _handleIncludedInDialogClose(e) {
      this.$.includedInOverlay.close();
    }

    _handleOpenDownloadDialog() {
      this.$.downloadOverlay.open().then(() => {
        this.$.downloadOverlay
            .setFocusStops(this.$.downloadDialog.getFocusStops());
        this.$.downloadDialog.focus();
      });
    }

    _handleDownloadDialogClose(e) {
      this.$.downloadOverlay.close();
    }

    _handleOpenUploadHelpDialog(e) {
      this.$.uploadHelpOverlay.open();
    }

    _handleCloseUploadHelpDialog(e) {
      this.$.uploadHelpOverlay.close();
    }

    _handleMessageReply(e) {
      const msg = e.detail.message.message;
      const quoteStr = msg.split('\n').map(
          line => '> ' + line)
          .join('\n') + '\n\n';
      this.$.replyDialog.quote = quoteStr;
      this._openReplyDialog(this.$.replyDialog.FocusTarget.BODY);
    }

    _handleHideBackgroundContent() {
      this.$.mainContent.classList.add('overlayOpen');
    }

    _handleShowBackgroundContent() {
      this.$.mainContent.classList.remove('overlayOpen');
    }

    _handleReplySent(e) {
      this.$.replyOverlay.close();
      this._reload().then(() => {
        this.$.reporting.timeEnd(SEND_REPLY_TIMING_LABEL);
      });
    }

    _handleReplyCancel(e) {
      this.$.replyOverlay.close();
    }

    _handleReplyAutogrow(e) {
      // If the textarea resizes, we need to re-fit the overlay.
      this.debounce('reply-overlay-refit', () => {
        this.$.replyOverlay.refit();
      }, REPLY_REFIT_DEBOUNCE_INTERVAL_MS);
    }

    _handleShowReplyDialog(e) {
      let target = this.$.replyDialog.FocusTarget.REVIEWERS;
      if (e.detail.value && e.detail.value.ccsOnly) {
        target = this.$.replyDialog.FocusTarget.CCS;
      }
      this._openReplyDialog(target);
    }

    _handleScroll() {
      this.debounce('scroll', () => {
        this.viewState.scrollTop = document.body.scrollTop;
      }, 150);
    }

    _setShownFiles(e) {
      this._shownFileCount = e.detail.length;
    }

    _expandAllDiffs() {
      this.$.fileList.expandAllDiffs();
    }

    _collapseAllDiffs() {
      this.$.fileList.collapseAllDiffs();
    }

    _paramsChanged(value) {
      // Change the content of the comment tabs back to messages list, but
      // do not yet change the tab itself. The animation of tab switching will
      // get messed up if changed here, because it requires the tabs to be on
      // the streen, and they are hidden shortly after this. The tab switching
      // animation will happen in post render tasks.
      this._showMessagesView = true;

      if (value.view !== Gerrit.Nav.View.CHANGE) {
        this._initialLoadComplete = false;
        return;
      }

      if (value.changeNum && value.project) {
        this.$.restAPI.setInProjectLookup(value.changeNum, value.project);
      }

      const patchChanged = this._patchRange &&
          (value.patchNum !== undefined && value.basePatchNum !== undefined) &&
          (this._patchRange.patchNum !== value.patchNum ||
          this._patchRange.basePatchNum !== value.basePatchNum);

      if (this._changeNum !== value.changeNum) {
        this._initialLoadComplete = false;
      }

      const patchRange = {
        patchNum: value.patchNum,
        basePatchNum: value.basePatchNum || 'PARENT',
      };

      this.$.fileList.collapseAllDiffs();
      this._patchRange = patchRange;

      // If the change has already been loaded and the parameter change is only
      // in the patch range, then don't do a full reload.
      if (this._initialLoadComplete && patchChanged) {
        if (patchRange.patchNum == null) {
          patchRange.patchNum = this.computeLatestPatchNum(this._allPatchSets);
        }
        this._reloadPatchNumDependentResources().then(() => {
          this._sendShowChangeEvent();
        });
        return;
      }

      this._changeNum = value.changeNum;
      this.$.relatedChanges.clear();

      this._reload(true).then(() => {
        this._performPostLoadTasks();
      });
    }

    _sendShowChangeEvent() {
      this.$.jsAPI.handleEvent(this.$.jsAPI.EventType.SHOW_CHANGE, {
        change: this._change,
        patchNum: this._patchRange.patchNum,
        info: {mergeable: this._mergeable},
      });
    }

    _setPrimaryTab() {
      // Selected has to be set after the paper-tabs are visible because
      // the selected underline depends on calculations made by the browser.
      this.$.commentTabs.selected = 0;
      const primaryTabs = this.shadowRoot.querySelector('#primaryTabs');
      if (primaryTabs) primaryTabs.selected = 0;
    }

    _performPostLoadTasks() {
      this._maybeShowReplyDialog();
      this._maybeShowRevertDialog();

      this._sendShowChangeEvent();

      this._setPrimaryTab();

      this.async(() => {
        if (this.viewState.scrollTop) {
          document.documentElement.scrollTop =
              document.body.scrollTop = this.viewState.scrollTop;
        } else {
          this._maybeScrollToMessage(window.location.hash);
        }
        this._initialLoadComplete = true;
      });
    }

    _paramsAndChangeChanged(value, change) {
      // Polymer 2: check for undefined
      if ([value, change].some(arg => arg === undefined)) {
        return;
      }

      // If the change number or patch range is different, then reset the
      // selected file index.
      const patchRangeState = this.viewState.patchRange;
      if (this.viewState.changeNum !== this._changeNum ||
          patchRangeState.basePatchNum !== this._patchRange.basePatchNum ||
          patchRangeState.patchNum !== this._patchRange.patchNum) {
        this._resetFileListViewState();
      }
    }

    _viewStateChanged(viewState) {
      this._numFilesShown = viewState.numFilesShown ?
        viewState.numFilesShown : DEFAULT_NUM_FILES_SHOWN;
    }

    _numFilesShownChanged(numFilesShown) {
      this.viewState.numFilesShown = numFilesShown;
    }

    _handleMessageAnchorTap(e) {
      const hash = MSG_PREFIX + e.detail.id;
      const url = Gerrit.Nav.getUrlForChange(this._change,
          this._patchRange.patchNum, this._patchRange.basePatchNum,
          this._editMode, hash);
      history.replaceState(null, '', url);
    }

    _maybeScrollToMessage(hash) {
      if (hash.startsWith(MSG_PREFIX)) {
        this.messagesList.scrollToMessage(hash.substr(MSG_PREFIX.length));
      }
    }

    _getLocationSearch() {
      // Not inlining to make it easier to test.
      return window.location.search;
    }

    _getUrlParameter(param) {
      const pageURL = this._getLocationSearch().substring(1);
      const vars = pageURL.split('&');
      for (let i = 0; i < vars.length; i++) {
        const name = vars[i].split('=');
        if (name[0] == param) {
          return name[0];
        }
      }
      return null;
    }

    _maybeShowRevertDialog() {
      Gerrit.awaitPluginsLoaded()
          .then(this._getLoggedIn.bind(this))
          .then(loggedIn => {
            if (!loggedIn || !this._change ||
                this._change.status !== this.ChangeStatus.MERGED) {
            // Do not display dialog if not logged-in or the change is not
            // merged.
              return;
            }
            if (this._getUrlParameter('revert')) {
              this.$.actions.showRevertDialog();
            }
          });
    }

    _maybeShowReplyDialog() {
      this._getLoggedIn().then(loggedIn => {
        if (!loggedIn) { return; }

        if (this.viewState.showReplyDialog) {
          this._openReplyDialog(this.$.replyDialog.FocusTarget.ANY);
          // TODO(kaspern@): Find a better signal for when to call center.
          this.async(() => { this.$.replyOverlay.center(); }, 100);
          this.async(() => { this.$.replyOverlay.center(); }, 1000);
          this.set('viewState.showReplyDialog', false);
        }
      });
    }

    _resetFileListViewState() {
      this.set('viewState.selectedFileIndex', 0);
      this.set('viewState.scrollTop', 0);
      if (!!this.viewState.changeNum &&
          this.viewState.changeNum !== this._changeNum) {
        // Reset the diff mode to null when navigating from one change to
        // another, so that the user's preference is restored.
        this._setDiffViewMode(true);
        this.set('_numFilesShown', DEFAULT_NUM_FILES_SHOWN);
      }
      this.set('viewState.changeNum', this._changeNum);
      this.set('viewState.patchRange', this._patchRange);
    }

    _changeChanged(change) {
      if (!change || !this._patchRange || !this._allPatchSets) { return; }

      // We get the parent first so we keep the original value for basePatchNum
      // and not the updated value.
      const parent = this._getBasePatchNum(change, this._patchRange);

      this.set('_patchRange.patchNum', this._patchRange.patchNum ||
              this.computeLatestPatchNum(this._allPatchSets));

      this.set('_patchRange.basePatchNum', parent);

      const title = change.subject + ' (' + change.change_id.substr(0, 9) + ')';
      this.fire('title-change', {title});
    }

    /**
     * Gets base patch number, if it is a parent try and decide from
     * preference whether to default to `auto merge`, `Parent 1` or `PARENT`.
     *
     * @param {Object} change
     * @param {Object} patchRange
     * @return {number|string}
     */
    _getBasePatchNum(change, patchRange) {
      if (patchRange.basePatchNum &&
          patchRange.basePatchNum !== 'PARENT') {
        return patchRange.basePatchNum;
      }

      const revisionInfo = this._getRevisionInfo(change);
      if (!revisionInfo) return 'PARENT';

      const parentCounts = revisionInfo.getParentCountMap();
      // check that there is at least 2 parents otherwise fall back to 1,
      // which means there is only one parent.
      const parentCount = parentCounts.hasOwnProperty(1) ?
        parentCounts[1] : 1;

      const preferFirst = this._prefs &&
          this._prefs.default_base_for_merges === 'FIRST_PARENT';

      if (parentCount > 1 && preferFirst && !patchRange.patchNum) {
        return -1;
      }

      return 'PARENT';
    }

    _computeShowPrimaryTabs(dynamicTabHeaderEndpoints) {
      return dynamicTabHeaderEndpoints && dynamicTabHeaderEndpoints.length > 0;
    }

    _computeChangeUrl(change) {
      return Gerrit.Nav.getUrlForChange(change);
    }

    _computeShowCommitInfo(changeStatus, current_revision) {
      return changeStatus === 'Merged' && current_revision;
    }

    _computeMergedCommitInfo(current_revision, revisions) {
      const rev = revisions[current_revision];
      if (!rev || !rev.commit) { return {}; }
      // CommitInfo.commit is optional. Set commit in all cases to avoid error
      // in <gr-commit-info>. @see Issue 5337
      if (!rev.commit.commit) { rev.commit.commit = current_revision; }
      return rev.commit;
    }

    _computeChangeIdClass(displayChangeId) {
      return displayChangeId === CHANGE_ID_ERROR.MISMATCH ? 'warning' : '';
    }

    _computeTitleAttributeWarning(displayChangeId) {
      if (displayChangeId === CHANGE_ID_ERROR.MISMATCH) {
        return 'Change-Id mismatch';
      } else if (displayChangeId === CHANGE_ID_ERROR.MISSING) {
        return 'No Change-Id in commit message';
      }
    }

    _computeChangeIdCommitMessageError(commitMessage, change) {
      // Polymer 2: check for undefined
      if ([commitMessage, change].some(arg => arg === undefined)) {
        return undefined;
      }

      if (!commitMessage) { return CHANGE_ID_ERROR.MISSING; }

      // Find the last match in the commit message:
      let changeId;
      let changeIdArr;

      while (changeIdArr = CHANGE_ID_REGEX_PATTERN.exec(commitMessage)) {
        changeId = changeIdArr[1];
      }

      if (changeId) {
        // A change-id is detected in the commit message.

        if (changeId === change.change_id) {
          // The change-id found matches the real change-id.
          return null;
        }
        // The change-id found does not match the change-id.
        return CHANGE_ID_ERROR.MISMATCH;
      }
      // There is no change-id in the commit message.
      return CHANGE_ID_ERROR.MISSING;
    }

    _computeLabelNames(labels) {
      return Object.keys(labels).sort();
    }

    _computeLabelValues(labelName, labels) {
      const result = [];
      const t = labels[labelName];
      if (!t) { return result; }
      const approvals = t.all || [];
      for (const label of approvals) {
        if (label.value && label.value != labels[labelName].default_value) {
          let labelClassName;
          let labelValPrefix = '';
          if (label.value > 0) {
            labelValPrefix = '+';
            labelClassName = 'approved';
          } else if (label.value < 0) {
            labelClassName = 'notApproved';
          }
          result.push({
            value: labelValPrefix + label.value,
            className: labelClassName,
            account: label,
          });
        }
      }
      return result;
    }

    _computeReplyButtonLabel(changeRecord, canStartReview) {
      // Polymer 2: check for undefined
      if ([changeRecord, canStartReview].some(arg => arg === undefined)) {
        return 'Reply';
      }

      if (canStartReview) {
        return 'Start review';
      }

      const drafts = (changeRecord && changeRecord.base) || {};
      const draftCount = Object.keys(drafts)
          .reduce((count, file) => count + drafts[file].length, 0);

      let label = 'Reply';
      if (draftCount > 0) {
        label += ' (' + draftCount + ')';
      }
      return label;
    }

    _handleOpenReplyDialog(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) {
        return;
      }
      this._getLoggedIn().then(isLoggedIn => {
        if (!isLoggedIn) {
          this.fire('show-auth-required');
          return;
        }

        e.preventDefault();
        this._openReplyDialog(this.$.replyDialog.FocusTarget.ANY);
      });
    }

    _handleOpenDownloadDialogShortcut(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this.$.downloadOverlay.open();
    }

    _handleEditTopic(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this.$.metadata.editTopic();
    }

    _handleRefreshChange(e) {
      if (this.shouldSuppressKeyboardShortcut(e)) { return; }
      e.preventDefault();
      Gerrit.Nav.navigateToChange(this._change);
    }

    _handleToggleChangeStar(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this.$.changeStar.toggleStar();
    }

    _handleUpToDashboard(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this._determinePageBack();
    }

    _handleExpandAllMessages(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this.messagesList.handleExpandCollapse(true);
    }

    _handleCollapseAllMessages(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      e.preventDefault();
      this.messagesList.handleExpandCollapse(false);
    }

    _handleOpenDiffPrefsShortcut(e) {
      if (this.shouldSuppressKeyboardShortcut(e) ||
          this.modifierPressed(e)) { return; }

      if (this._diffPrefsDisabled) { return; }

      e.preventDefault();
      this.$.fileList.openDiffPrefs();
    }

    _determinePageBack() {
      // Default backPage to root if user came to change view page
      // via an email link, etc.
      Gerrit.Nav.navigateToRelativeUrl(this.backPage ||
          Gerrit.Nav.getUrlForRoot());
    }

    _handleLabelRemoved(splices, path) {
      for (const splice of splices) {
        for (const removed of splice.removed) {
          const changePath = path.split('.');
          const labelPath = changePath.splice(0, changePath.length - 2);
          const labelDict = this.get(labelPath);
          if (labelDict.approved &&
              labelDict.approved._account_id === removed._account_id) {
            this._reload();
            return;
          }
        }
      }
    }

    _labelsChanged(changeRecord) {
      if (!changeRecord) { return; }
      if (changeRecord.value && changeRecord.value.indexSplices) {
        this._handleLabelRemoved(changeRecord.value.indexSplices,
            changeRecord.path);
      }
      this.$.jsAPI.handleEvent(this.$.jsAPI.EventType.LABEL_CHANGE, {
        change: this._change,
      });
    }

    /**
     * @param {string=} opt_section
     */
    _openReplyDialog(opt_section) {
      this.$.replyOverlay.open().then(() => {
        this._resetReplyOverlayFocusStops();
        this.$.replyDialog.open(opt_section);
        Polymer.dom.flush();
        this.$.replyOverlay.center();
      });
    }

    _handleReloadChange(e) {
      return this._reload().then(() => {
        // If the change was rebased or submitted, we need to reload the page
        // with the latest patch.
        const action = e.detail.action;
        if (action === 'rebase' || action === 'submit') {
          Gerrit.Nav.navigateToChange(this._change);
        }
      });
    }

    _handleGetChangeDetailError(response) {
      this.fire('page-error', {response});
    }

    _getLoggedIn() {
      return this.$.restAPI.getLoggedIn();
    }

    _getServerConfig() {
      return this.$.restAPI.getConfig();
    }

    _getProjectConfig() {
      if (!this._change) return;
      return this.$.restAPI.getProjectConfig(this._change.project).then(
          config => {
            this._projectConfig = config;
          });
    }

    _getPreferences() {
      return this.$.restAPI.getPreferences();
    }

    _prepareCommitMsgForLinkify(msg) {
      // TODO(wyatta) switch linkify sequence, see issue 5526.
      // This is a zero-with space. It is added to prevent the linkify library
      // from including R= or CC= as part of the email address.
      return msg.replace(REVIEWERS_REGEX, '$1=\u200B');
    }

    /**
     * Utility function to make the necessary modifications to a change in the
     * case an edit exists.
     *
     * @param {!Object} change
     * @param {?Object} edit
     */
    _processEdit(change, edit) {
      if (!edit) { return; }
      change.revisions[edit.commit.commit] = {
        _number: this.EDIT_NAME,
        basePatchNum: edit.base_patch_set_number,
        commit: edit.commit,
        fetch: edit.fetch,
      };
      // If the edit is based on the most recent patchset, load it by
      // default, unless another patch set to load was specified in the URL.
      if (!this._patchRange.patchNum &&
          change.current_revision === edit.base_revision) {
        change.current_revision = edit.commit.commit;
        this.set('_patchRange.patchNum', this.EDIT_NAME);
        // Because edits are fibbed as revisions and added to the revisions
        // array, and revision actions are always derived from the 'latest'
        // patch set, we must copy over actions from the patch set base.
        // Context: Issue 7243
        change.revisions[edit.commit.commit].actions =
            change.revisions[edit.base_revision].actions;
      }
    }

    _getChangeDetail() {
      const detailCompletes = this.$.restAPI.getChangeDetail(
          this._changeNum, this._handleGetChangeDetailError.bind(this));
      const editCompletes = this._getEdit();
      const prefCompletes = this._getPreferences();

      return Promise.all([detailCompletes, editCompletes, prefCompletes])
          .then(([change, edit, prefs]) => {
            this._prefs = prefs;

            if (!change) {
              return '';
            }
            this._processEdit(change, edit);
            // Issue 4190: Coalesce missing topics to null.
            if (!change.topic) { change.topic = null; }
            if (!change.reviewer_updates) {
              change.reviewer_updates = null;
            }
            const latestRevisionSha = this._getLatestRevisionSHA(change);
            const currentRevision = change.revisions[latestRevisionSha];
            if (currentRevision.commit && currentRevision.commit.message) {
              this._latestCommitMessage = this._prepareCommitMsgForLinkify(
                  currentRevision.commit.message);
            } else {
              this._latestCommitMessage = null;
            }

            const lineHeight = getComputedStyle(this).lineHeight;

            // Slice returns a number as a string, convert to an int.
            this._lineHeight =
                parseInt(lineHeight.slice(0, lineHeight.length - 2), 10);

            this._change = change;
            if (!this._patchRange || !this._patchRange.patchNum ||
                this.patchNumEquals(this._patchRange.patchNum,
                    currentRevision._number)) {
              // CommitInfo.commit is optional, and may need patching.
              if (!currentRevision.commit.commit) {
                currentRevision.commit.commit = latestRevisionSha;
              }
              this._commitInfo = currentRevision.commit;
              this._selectedRevision = currentRevision;
              // TODO: Fetch and process files.
            } else {
              this._selectedRevision =
                Object.values(this._change.revisions).find(
                    revision => revision._number ===
                      parseInt(this._patchRange.patchNum, 10));
            }
          });
    }

    _isSubmitEnabled(revisionActions) {
      return !!(revisionActions && revisionActions.submit &&
        revisionActions.submit.enabled);
    }

    _getEdit() {
      return this.$.restAPI.getChangeEdit(this._changeNum, true);
    }

    _getLatestCommitMessage() {
      return this.$.restAPI.getChangeCommitInfo(this._changeNum,
          this.computeLatestPatchNum(this._allPatchSets)).then(commitInfo => {
        if (!commitInfo) return Promise.resolve();
        this._latestCommitMessage =
                    this._prepareCommitMsgForLinkify(commitInfo.message);
      });
    }

    _getLatestRevisionSHA(change) {
      if (change.current_revision) {
        return change.current_revision;
      }
      // current_revision may not be present in the case where the latest rev is
      // a draft and the user doesn’t have permission to view that rev.
      let latestRev = null;
      let latestPatchNum = -1;
      for (const rev in change.revisions) {
        if (!change.revisions.hasOwnProperty(rev)) { continue; }

        if (change.revisions[rev]._number > latestPatchNum) {
          latestRev = rev;
          latestPatchNum = change.revisions[rev]._number;
        }
      }
      return latestRev;
    }

    _getCommitInfo() {
      return this.$.restAPI.getChangeCommitInfo(
          this._changeNum, this._patchRange.patchNum).then(
          commitInfo => {
            this._commitInfo = commitInfo;
          });
    }

    _reloadDraftsWithCallback(e) {
      return this._reloadDrafts().then(() => e.detail.resolve());
    }

    /**
     * Fetches a new changeComment object, and data for all types of comments
     * (comments, robot comments, draft comments) is requested.
     */
    _reloadComments() {
      return this.$.commentAPI.loadAll(this._changeNum)
          .then(comments => {
            this._changeComments = comments;
            this._diffDrafts = Object.assign({}, this._changeComments.drafts);
            this._commentThreads = this._changeComments.getAllThreadsForChange()
                .map(c => Object.assign({}, c));
          });
    }

    /**
     * Fetches a new changeComment object, but only updated data for drafts is
     * requested.
     */
    _reloadDrafts() {
      return this.$.commentAPI.reloadDrafts(this._changeNum)
          .then(comments => {
            this._changeComments = comments;
            this._diffDrafts = Object.assign({}, this._changeComments.drafts);
          });
    }

    /**
     * Reload the change.
     *
     * @param {boolean=} opt_isLocationChange Reloads the related changes
     *     when true and ends reporting events that started on location change.
     * @return {Promise} A promise that resolves when the core data has loaded.
     *     Some non-core data loading may still be in-flight when the core data
     *     promise resolves.
     */
    _reload(opt_isLocationChange) {
      this._loading = true;
      this._relatedChangesCollapsed = true;
      this.$.reporting.time(CHANGE_RELOAD_TIMING_LABEL);
      this.$.reporting.time(CHANGE_DATA_TIMING_LABEL);

      // Array to house all promises related to data requests.
      const allDataPromises = [];

      // Resolves when the change detail and the edit patch set (if available)
      // are loaded.
      const detailCompletes = this._getChangeDetail();
      allDataPromises.push(detailCompletes);

      // Resolves when the loading flag is set to false, meaning that some
      // change content may start appearing.
      const loadingFlagSet = detailCompletes
          .then(() => { this._loading = false; })
          .then(() => {
            this.$.reporting.timeEnd(CHANGE_RELOAD_TIMING_LABEL);
            if (opt_isLocationChange) {
              this.$.reporting.changeDisplayed();
            }
          });

      // Resolves when the project config has loaded.
      const projectConfigLoaded = detailCompletes
          .then(() => this._getProjectConfig());
      allDataPromises.push(projectConfigLoaded);

      // Resolves when change comments have loaded (comments, drafts and robot
      // comments).
      const commentsLoaded = this._reloadComments();
      allDataPromises.push(commentsLoaded);

      let coreDataPromise;

      // If the patch number is specified
      if (this._patchRange && this._patchRange.patchNum) {
        // Because a specific patchset is specified, reload the resources that
        // are keyed by patch number or patch range.
        const patchResourcesLoaded = this._reloadPatchNumDependentResources();
        allDataPromises.push(patchResourcesLoaded);

        // Promise resolves when the change detail and patch dependent resources
        // have loaded.
        const detailAndPatchResourcesLoaded =
            Promise.all([patchResourcesLoaded, loadingFlagSet]);

        // Promise resolves when mergeability information has loaded.
        const mergeabilityLoaded = detailAndPatchResourcesLoaded
            .then(() => this._getMergeability());
        allDataPromises.push(mergeabilityLoaded);

        // Promise resovles when the change actions have loaded.
        const actionsLoaded = detailAndPatchResourcesLoaded
            .then(() => this.$.actions.reload());
        allDataPromises.push(actionsLoaded);

        // The core data is loaded when both mergeability and actions are known.
        coreDataPromise = Promise.all([mergeabilityLoaded, actionsLoaded]);
      } else {
        // Resolves when the file list has loaded.
        const fileListReload = loadingFlagSet
            .then(() => this.$.fileList.reload());
        allDataPromises.push(fileListReload);

        const latestCommitMessageLoaded = loadingFlagSet.then(() => {
          // If the latest commit message is known, there is nothing to do.
          if (this._latestCommitMessage) { return Promise.resolve(); }
          return this._getLatestCommitMessage();
        });
        allDataPromises.push(latestCommitMessageLoaded);

        // Promise resolves when mergeability information has loaded.
        const mergeabilityLoaded = loadingFlagSet
            .then(() => this._getMergeability());
        allDataPromises.push(mergeabilityLoaded);

        // Core data is loaded when mergeability has been loaded.
        coreDataPromise = mergeabilityLoaded;
      }

      if (opt_isLocationChange) {
        const relatedChangesLoaded = coreDataPromise
            .then(() => this.$.relatedChanges.reload());
        allDataPromises.push(relatedChangesLoaded);
      }

      Promise.all(allDataPromises).then(() => {
        this.$.reporting.timeEnd(CHANGE_DATA_TIMING_LABEL);
        if (opt_isLocationChange) {
          this.$.reporting.changeFullyLoaded();
        }
      });

      return coreDataPromise;
    }

    /**
     * Kicks off requests for resources that rely on the patch range
     * (`this._patchRange`) being defined.
     */
    _reloadPatchNumDependentResources() {
      return Promise.all([
        this._getCommitInfo(),
        this.$.fileList.reload(),
      ]);
    }

    _getMergeability() {
      if (!this._change) {
        this._mergeable = null;
        return Promise.resolve();
      }
      // If the change is closed, it is not mergeable. Note: already merged
      // changes are obviously not mergeable, but the mergeability API will not
      // answer for abandoned changes.
      if (this._change.status === this.ChangeStatus.MERGED ||
          this._change.status === this.ChangeStatus.ABANDONED) {
        this._mergeable = false;
        return Promise.resolve();
      }

      this._mergeable = null;
      return this.$.restAPI.getMergeable(this._changeNum).then(m => {
        this._mergeable = m.mergeable;
      });
    }

    _computeCanStartReview(change) {
      return !!(change.actions && change.actions.ready &&
          change.actions.ready.enabled);
    }

    _computeReplyDisabled() { return false; }

    _computeChangePermalinkAriaLabel(changeNum) {
      return 'Change ' + changeNum;
    }

    _computeCommitClass(collapsed, commitMessage) {
      if (this._computeCommitToggleHidden(commitMessage)) { return ''; }
      return collapsed ? 'collapsed' : '';
    }

    _computeRelatedChangesClass(collapsed) {
      return collapsed ? 'collapsed' : '';
    }

    _computeCollapseText(collapsed) {
      // Symbols are up and down triangles.
      return collapsed ? '\u25bc Show more' : '\u25b2 Show less';
    }

    /**
     * Returns the text to be copied when
     * click the copy icon next to change subject
     *
     * @param {!Object} change
     */
    _computeCopyTextForTitle(change) {
      return `${change._number}: ${change.subject}` +
       ` | https://${location.host}${this._computeChangeUrl(change)}`;
    }

    _toggleCommitCollapsed() {
      this._commitCollapsed = !this._commitCollapsed;
      if (this._commitCollapsed) {
        window.scrollTo(0, 0);
      }
    }

    _toggleRelatedChangesCollapsed() {
      this._relatedChangesCollapsed = !this._relatedChangesCollapsed;
      if (this._relatedChangesCollapsed) {
        window.scrollTo(0, 0);
      }
    }

    _computeCommitToggleHidden(commitMessage) {
      if (!commitMessage) { return true; }
      return commitMessage.split('\n').length < MIN_LINES_FOR_COMMIT_COLLAPSE;
    }

    _getOffsetHeight(element) {
      return element.offsetHeight;
    }

    _getScrollHeight(element) {
      return element.scrollHeight;
    }

    /**
     * Get the line height of an element to the nearest integer.
     */
    _getLineHeight(element) {
      const lineHeightStr = getComputedStyle(element).lineHeight;
      return Math.round(lineHeightStr.slice(0, lineHeightStr.length - 2));
    }

    /**
     * New max height for the related changes section, shorter than the existing
     * change info height.
     */
    _updateRelatedChangeMaxHeight() {
      // Takes into account approximate height for the expand button and
      // bottom margin.
      const EXTRA_HEIGHT = 30;
      let newHeight;
      const hasCommitToggle =
          !this._computeCommitToggleHidden(this._latestCommitMessage);

      if (window.matchMedia(`(max-width: ${BREAKPOINT_RELATED_SMALL})`)
          .matches) {
        // In a small (mobile) view, give the relation chain some space.
        newHeight = SMALL_RELATED_HEIGHT;
      } else if (window.matchMedia(`(max-width: ${BREAKPOINT_RELATED_MED})`)
          .matches) {
        // Since related changes are below the commit message, but still next to
        // metadata, the height should be the height of the metadata minus the
        // height of the commit message to reduce jank. However, if that doesn't
        // result in enough space, instead use the MINIMUM_RELATED_MAX_HEIGHT.
        // Note: extraHeight is to take into account margin/padding.
        const medRelatedHeight = Math.max(
            this._getOffsetHeight(this.$.mainChangeInfo) -
            this._getOffsetHeight(this.$.commitMessage) - 2 * EXTRA_HEIGHT,
            MINIMUM_RELATED_MAX_HEIGHT);
        newHeight = medRelatedHeight;
      } else {
        if (hasCommitToggle) {
          // Make sure the content is lined up if both areas have buttons. If
          // the commit message is not collapsed, instead use the change info
          // height.
          newHeight = this._getOffsetHeight(this.$.commitMessage);
        } else {
          newHeight = this._getOffsetHeight(this.$.commitAndRelated) -
              EXTRA_HEIGHT;
        }
      }
      const stylesToUpdate = {};

      // Get the line height of related changes, and convert it to the nearest
      // integer.
      const lineHeight = this._getLineHeight(this.$.relatedChanges);

      // Figure out a new height that is divisible by the rounded line height.
      const remainder = newHeight % lineHeight;
      newHeight = newHeight - remainder;

      stylesToUpdate['--relation-chain-max-height'] = newHeight + 'px';

      // Update the max-height of the relation chain to this new height.
      if (hasCommitToggle) {
        stylesToUpdate['--related-change-btn-top-padding'] = remainder + 'px';
      }

      this.updateStyles(stylesToUpdate);
    }

    _computeShowRelatedToggle() {
      // Make sure the max height has been applied, since there is now content
      // to populate.
      if (!util.getComputedStyleValue('--relation-chain-max-height', this)) {
        this._updateRelatedChangeMaxHeight();
      }
      // Prevents showMore from showing when click on related change, since the
      // line height would be positive, but related changes height is 0.
      if (!this._getScrollHeight(this.$.relatedChanges)) {
        return this._showRelatedToggle = false;
      }

      if (this._getScrollHeight(this.$.relatedChanges) >
          (this._getOffsetHeight(this.$.relatedChanges) +
          this._getLineHeight(this.$.relatedChanges))) {
        return this._showRelatedToggle = true;
      }
      this._showRelatedToggle = false;
    }

    _updateToggleContainerClass(showRelatedToggle) {
      if (showRelatedToggle) {
        this.$.relatedChangesToggle.classList.add('showToggle');
      } else {
        this.$.relatedChangesToggle.classList.remove('showToggle');
      }
    }

    _startUpdateCheckTimer() {
      if (!this._serverConfig ||
          !this._serverConfig.change ||
          this._serverConfig.change.update_delay === undefined ||
          this._serverConfig.change.update_delay <= MIN_CHECK_INTERVAL_SECS) {
        return;
      }

      this._updateCheckTimerHandle = this.async(() => {
        this.fetchChangeUpdates(this._change, this.$.restAPI).then(result => {
          let toastMessage = null;
          if (!result.isLatest) {
            toastMessage = ReloadToastMessage.NEWER_REVISION;
          } else if (result.newStatus === this.ChangeStatus.MERGED) {
            toastMessage = ReloadToastMessage.MERGED;
          } else if (result.newStatus === this.ChangeStatus.ABANDONED) {
            toastMessage = ReloadToastMessage.ABANDONED;
          } else if (result.newStatus === this.ChangeStatus.NEW) {
            toastMessage = ReloadToastMessage.RESTORED;
          } else if (result.newMessages) {
            toastMessage = ReloadToastMessage.NEW_MESSAGE;
          }

          if (!toastMessage) {
            this._startUpdateCheckTimer();
            return;
          }

          this._cancelUpdateCheckTimer();
          this.fire('show-alert', {
            message: toastMessage,
            // Persist this alert.
            dismissOnNavigation: true,
            action: 'Reload',
            callback: function() {
              // Load the current change without any patch range.
              Gerrit.Nav.navigateToChange(this._change);
            }.bind(this),
          });
        });
      }, this._serverConfig.change.update_delay * 1000);
    }

    _cancelUpdateCheckTimer() {
      if (this._updateCheckTimerHandle) {
        this.cancelAsync(this._updateCheckTimerHandle);
      }
      this._updateCheckTimerHandle = null;
    }

    _handleVisibilityChange() {
      if (document.hidden && this._updateCheckTimerHandle) {
        this._cancelUpdateCheckTimer();
      } else if (!this._updateCheckTimerHandle) {
        this._startUpdateCheckTimer();
      }
    }

    _handleTopicChanged() {
      this.$.relatedChanges.reload();
    }

    _computeHeaderClass(editMode) {
      const classes = ['header'];
      if (editMode) { classes.push('editMode'); }
      return classes.join(' ');
    }

    _computeEditMode(patchRangeRecord, paramsRecord) {
      if ([patchRangeRecord, paramsRecord].some(arg => arg === undefined)) {
        return undefined;
      }

      if (paramsRecord.base && paramsRecord.base.edit) { return true; }

      const patchRange = patchRangeRecord.base || {};
      return this.patchNumEquals(patchRange.patchNum, this.EDIT_NAME);
    }

    _handleFileActionTap(e) {
      e.preventDefault();
      const controls = this.$.fileListHeader.$.editControls;
      const path = e.detail.path;
      switch (e.detail.action) {
        case GrEditConstants.Actions.DELETE.id:
          controls.openDeleteDialog(path);
          break;
        case GrEditConstants.Actions.OPEN.id:
          Gerrit.Nav.navigateToRelativeUrl(
              Gerrit.Nav.getEditUrlForDiff(this._change, path,
                  this._patchRange.patchNum));
          break;
        case GrEditConstants.Actions.RENAME.id:
          controls.openRenameDialog(path);
          break;
        case GrEditConstants.Actions.RESTORE.id:
          controls.openRestoreDialog(path);
          break;
      }
    }

    _computeCommitMessageKey(number, revision) {
      return `c${number}_rev${revision}`;
    }

    _patchNumChanged(patchNumStr) {
      if (!this._selectedRevision) {
        return;
      }
      // If patchNumStr is"edit", then patchNum is undefined hence an OR
      const patchNum = parseInt(patchNumStr, 10) || patchNumStr;
      if (patchNum === this._selectedRevision._number) {
        return;
      }
      this._selectedRevision = Object.values(this._change.revisions).find(
          revision => revision._number === patchNum);
    }

    /**
     * If an edit exists already, load it. Otherwise, toggle edit mode via the
     * navigation API.
     */
    _handleEditTap() {
      const editInfo = Object.values(this._change.revisions).find(info =>
        info._number === this.EDIT_NAME);

      if (editInfo) {
        Gerrit.Nav.navigateToChange(this._change, this.EDIT_NAME);
        return;
      }

      // Avoid putting patch set in the URL unless a non-latest patch set is
      // selected.
      let patchNum;
      if (!this.patchNumEquals(this._patchRange.patchNum,
          this.computeLatestPatchNum(this._allPatchSets))) {
        patchNum = this._patchRange.patchNum;
      }
      Gerrit.Nav.navigateToChange(this._change, patchNum, null, true);
    }

    _handleStopEditTap() {
      Gerrit.Nav.navigateToChange(this._change, this._patchRange.patchNum);
    }

    _resetReplyOverlayFocusStops() {
      this.$.replyOverlay.setFocusStops(this.$.replyDialog.getFocusStops());
    }

    _handleToggleStar(e) {
      this.$.restAPI.saveChangeStarred(e.detail.change._number,
          e.detail.starred);
    }

    _getRevisionInfo(change) {
      return new Gerrit.RevisionInfo(change);
    }

    _computeCurrentRevision(currentRevision, revisions) {
      return currentRevision && revisions && revisions[currentRevision];
    }

    _computeDiffPrefsDisabled(disableDiffPrefs, loggedIn) {
      return disableDiffPrefs || !loggedIn;
    }
  }

  customElements.define(GrChangeView.is, GrChangeView);
})();