polygerrit-ui/app/embed/diff/gr-diff-cursor/gr-diff-cursor.ts

/**
 * @license
 * Copyright 2016 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */
import {Subscription} from 'rxjs';
import {AbortStop, CursorMoveResult, Stop} from '../../../api/core';
import {
  DiffViewMode,
  GrDiffCursor as GrDiffCursorApi,
  LineNumberEventDetail,
} from '../../../api/diff';
import {ScrollMode, Side} from '../../../constants/constants';
import {toggleClass} from '../../../utils/dom-util';
import {
  GrCursorManager,
  isTargetable,
} from '../../../elements/shared/gr-cursor-manager/gr-cursor-manager';
import {GrDiffLineType} from '../gr-diff/gr-diff-line';
import {GrDiffGroupType} from '../gr-diff/gr-diff-group';
import {GrDiff} from '../gr-diff/gr-diff';

type GrDiffRowType = GrDiffLineType | GrDiffGroupType;

const LEFT_SIDE_CLASS = 'target-side-left';
const RIGHT_SIDE_CLASS = 'target-side-right';

interface Address {
  leftSide: boolean;
  number: number;
}

/** A subset of the GrDiff API that the cursor is using. */
export interface GrDiffCursorable extends HTMLElement {
  isRangeSelected(): boolean;
  createRangeComment(): void;
  getCursorStops(): Stop[];
  path?: string;
}

export class GrDiffCursor implements GrDiffCursorApi {
  private preventAutoScrollOnManualScroll = false;

  set side(side: Side) {
    if (this.sideInternal === side) {
      return;
    }
    if (this.sideInternal && this.diffRow) {
      this.fireCursorMoved(
        'line-cursor-moved-out',
        this.diffRow,
        this.sideInternal
      );
    }
    this.sideInternal = side;
    this.updateSideClass();
    if (this.diffRow) {
      this.fireCursorMoved('line-cursor-moved-in', this.diffRow, this.side);
    }
  }

  get side(): Side {
    return this.sideInternal;
  }

  private sideInternal = Side.RIGHT;

  set diffRow(diffRow: HTMLElement | undefined) {
    if (this.diffRowInternal) {
      this.diffRowInternal.classList.remove(LEFT_SIDE_CLASS, RIGHT_SIDE_CLASS);
      this.fireCursorMoved(
        'line-cursor-moved-out',
        this.diffRowInternal,
        this.side
      );
    }
    this.diffRowInternal = diffRow;

    this.updateSideClass();
    if (this.diffRow) {
      this.fireCursorMoved('line-cursor-moved-in', this.diffRow, this.side);
    }
  }

  get diffRow(): HTMLElement | undefined {
    return this.diffRowInternal;
  }

  private diffRowInternal?: HTMLElement;

  private diffs: GrDiffCursorable[] = [];

  /**
   * If set, the cursor will attempt to move to the line number (instead of
   * the first chunk) the next time the diff renders. It is set back to null
   * when used. It should be only used if you want the line to be focused
   * after initialization of the component and page should scroll
   * to that position. This parameter should be set at most for one gr-diff
   * element in the page.
   */
  initialLineNumber: number | null = null;

  // visible for testing
  cursorManager = new GrCursorManager();

  private targetSubscription?: Subscription;

  constructor() {
    this.cursorManager.cursorTargetClass = 'target-row';
    this.cursorManager.scrollMode = ScrollMode.KEEP_VISIBLE;
    this.cursorManager.focusOnMove = true;

    window.addEventListener('scroll', this._boundHandleWindowScroll);
    this.targetSubscription = this.cursorManager.target$.subscribe(target => {
      this.diffRow = target || undefined;
    });
  }

  dispose() {
    this.cursorManager.unsetCursor();
    if (this.targetSubscription) this.targetSubscription.unsubscribe();
    window.removeEventListener('scroll', this._boundHandleWindowScroll);
  }

  // Don't remove - used by clients embedding gr-diff outside of Gerrit.
  isAtStart() {
    return this.cursorManager.isAtStart();
  }

  // Don't remove - used by clients embedding gr-diff outside of Gerrit.
  isAtEnd() {
    return this.cursorManager.isAtEnd();
  }

  moveLeft() {
    this.side = Side.LEFT;
    if (this._isTargetBlank()) {
      this.moveUp();
    }
  }

  moveRight() {
    this.side = Side.RIGHT;
    if (this._isTargetBlank()) {
      this.moveUp();
    }
  }

  moveDown() {
    if (this._getViewMode() === DiffViewMode.SIDE_BY_SIDE) {
      return this.cursorManager.next({
        filter: (row: Element) => this._rowHasSide(row),
      });
    } else {
      return this.cursorManager.next();
    }
  }

  moveUp() {
    if (this._getViewMode() === DiffViewMode.SIDE_BY_SIDE) {
      return this.cursorManager.previous({
        filter: (row: Element) => this._rowHasSide(row),
      });
    } else {
      return this.cursorManager.previous();
    }
  }

  moveToVisibleArea() {
    if (this._getViewMode() === DiffViewMode.SIDE_BY_SIDE) {
      this.cursorManager.moveToVisibleArea((row: Element) =>
        this._rowHasSide(row)
      );
    } else {
      this.cursorManager.moveToVisibleArea();
    }
  }

  moveToNextChunk(clipToTop?: boolean): CursorMoveResult {
    const result = this.cursorManager.next({
      filter: (row: HTMLElement) => this._isFirstRowOfChunk(row),
      getTargetHeight: target =>
        (target?.parentNode as HTMLElement)?.scrollHeight || 0,
      clipToTop,
    });
    this._fixSide();
    return result;
  }

  moveToPreviousChunk(): CursorMoveResult {
    const result = this.cursorManager.previous({
      filter: (row: HTMLElement) => this._isFirstRowOfChunk(row),
    });
    this._fixSide();
    return result;
  }

  moveToNextCommentThread(): CursorMoveResult {
    if (this.isAtEnd()) {
      return CursorMoveResult.CLIPPED;
    }
    const result = this.cursorManager.next({
      filter: (row: HTMLElement) => this._rowHasThread(row),
    });
    this._fixSide();
    return result;
  }

  moveToPreviousCommentThread(): CursorMoveResult {
    const result = this.cursorManager.previous({
      filter: (row: HTMLElement) => this._rowHasThread(row),
    });
    this._fixSide();
    return result;
  }

  moveToLineNumber(
    number: number,
    side: Side,
    path?: string,
    intentionalMove?: boolean
  ) {
    const row = this._findRowByNumberAndFile(number, side, path);
    if (row) {
      this.side = side;
      this.cursorManager.setCursor(row, undefined, intentionalMove);
    }
  }

  /**
   * Get the line number element targeted by the cursor row and side.
   */
  getTargetLineElement(): HTMLElement | null {
    let lineElSelector = '.lineNum';

    if (!this.diffRow) {
      return null;
    }

    if (this._getViewMode() === DiffViewMode.SIDE_BY_SIDE) {
      lineElSelector += this.side === Side.LEFT ? '.left' : '.right';
    }

    return this.diffRow.querySelector(lineElSelector);
  }

  getTargetDiffElement(): GrDiff | null {
    if (!this.diffRow) return null;

    const hostOwner = this.diffRow.getRootNode() as ShadowRoot;
    if (hostOwner?.host?.tagName === 'GR-DIFF') {
      return hostOwner.host as GrDiff;
    }
    return null;
  }

  moveToFirstChunk() {
    this.cursorManager.moveToStart();
    if (this.diffRow && !this._isFirstRowOfChunk(this.diffRow)) {
      this.moveToNextChunk(true);
    } else {
      this._fixSide();
    }
  }

  moveToLastChunk() {
    this.cursorManager.moveToEnd();
    if (this.diffRow && !this._isFirstRowOfChunk(this.diffRow)) {
      this.moveToPreviousChunk();
    } else {
      this._fixSide();
    }
  }

  /**
   * Move the cursor either to initialLineNumber or the first chunk and
   * reset scroll behavior.
   *
   * This may grab the focus from the app.
   *
   * If you do not want to move the cursor or grab focus, and just want to
   * reset the scroll behavior, use reInitAndUpdateStops() instead.
   */
  reInitCursor() {
    this._updateStops();
    if (!this.diffRow) {
      // does not scroll during init unless requested
      this.cursorManager.scrollMode = this.initialLineNumber
        ? ScrollMode.KEEP_VISIBLE
        : ScrollMode.NEVER;
      if (this.initialLineNumber) {
        this.moveToLineNumber(this.initialLineNumber, this.side);
        this.initialLineNumber = null;
      } else {
        this.moveToFirstChunk();
      }
    }
    this.resetScrollMode();
  }

  resetScrollMode() {
    this.cursorManager.scrollMode = ScrollMode.KEEP_VISIBLE;
  }

  private _boundHandleWindowScroll = () => {
    if (this.preventAutoScrollOnManualScroll) {
      this.cursorManager.scrollMode = ScrollMode.NEVER;
      this.cursorManager.focusOnMove = false;
      this.preventAutoScrollOnManualScroll = false;
    }
  };

  reInitAndUpdateStops() {
    this.resetScrollMode();
    this._updateStops();
  }

  private boundHandleDiffLoadingChanged = () => {
    this._updateStops();
  };

  private _boundHandleDiffRenderStart = () => {
    this.preventAutoScrollOnManualScroll = true;
  };

  private _boundHandleDiffRenderContent = () => {
    this._updateStops();
    // When done rendering, turn focus on move and automatic scrolling back on
    this.cursorManager.focusOnMove = true;
    this.preventAutoScrollOnManualScroll = false;
  };

  private _boundHandleDiffLineSelected = (event: Event) => {
    const customEvent = event as CustomEvent;
    this.moveToLineNumber(
      customEvent.detail.number,
      customEvent.detail.side,
      customEvent.detail.path
    );
  };

  createCommentInPlace() {
    const diffWithRangeSelected = this.diffs.find(diff =>
      diff.isRangeSelected()
    );
    if (diffWithRangeSelected) {
      diffWithRangeSelected.createRangeComment();
    } else {
      const line = this.getTargetLineElement();
      const diff = this.getTargetDiffElement();
      if (diff && line) {
        diff.addDraftAtLine(line);
      }
    }
  }

  /**
   * Get an object describing the location of the cursor. Such as
   * {leftSide: false, number: 123} for line 123 of the revision, or
   * {leftSide: true, number: 321} for line 321 of the base patch.
   * Returns null if an address is not available.
   */
  getAddress(): Address | null {
    if (!this.diffRow) {
      return null;
    }
    // Get the line-number cell targeted by the cursor. If the mode is unified
    // then prefer the revision cell if available.
    return this.getAddressFor(this.diffRow, this.side);
  }

  private getAddressFor(diffRow: HTMLElement, side: Side): Address | null {
    let cell;
    if (this._getViewMode() === DiffViewMode.UNIFIED) {
      cell = diffRow.querySelector('.lineNum.right');
      if (!cell) {
        cell = diffRow.querySelector('.lineNum.left');
      }
    } else {
      cell = diffRow.querySelector('.lineNum.' + side);
    }
    if (!cell) {
      return null;
    }

    const number = cell.getAttribute('data-value');
    if (!number || number === 'FILE') {
      return null;
    }

    return {
      leftSide: cell.matches('.left'),
      number: Number(number),
    };
  }

  _getViewMode() {
    if (!this.diffRow) {
      return null;
    }

    if (this.diffRow.classList.contains('side-by-side')) {
      return DiffViewMode.SIDE_BY_SIDE;
    } else {
      return DiffViewMode.UNIFIED;
    }
  }

  _rowHasSide(row: Element) {
    const selector =
      (this.side === Side.LEFT ? '.left' : '.right') + ' + .content';
    return !!row.querySelector(selector);
  }

  _isFirstRowOfChunk(row: HTMLElement) {
    const parentClassList = (row.parentNode as HTMLElement).classList;
    const isInChunk =
      parentClassList.contains('section') && parentClassList.contains('delta');
    const previousRow = row.previousSibling as HTMLElement;
    const firstContentRow =
      !previousRow || previousRow.classList.contains('moveControls');
    return isInChunk && firstContentRow;
  }

  _rowHasThread(row: HTMLElement): boolean {
    const slots = [
      ...row.querySelectorAll<HTMLSlotElement>('.thread-group > slot'),
    ];
    return slots.some(slot => slot.assignedElements().length > 0);
  }

  /**
   * If we jumped to a row where there is no content on the current side then
   * switch to the alternate side.
   */
  _fixSide() {
    if (
      this._getViewMode() === DiffViewMode.SIDE_BY_SIDE &&
      this._isTargetBlank()
    ) {
      this.side = this.side === Side.LEFT ? Side.RIGHT : Side.LEFT;
    }
  }

  _isTargetBlank() {
    if (!this.diffRow) {
      return false;
    }

    const actions = this._getActionsForRow();
    return (
      (this.side === Side.LEFT && !actions.left) ||
      (this.side === Side.RIGHT && !actions.right)
    );
  }

  private fireCursorMoved(
    event: 'line-cursor-moved-out' | 'line-cursor-moved-in',
    row: HTMLElement,
    side: Side
  ) {
    const address = this.getAddressFor(row, side);
    if (address) {
      const {leftSide, number} = address;
      row.dispatchEvent(
        new CustomEvent<LineNumberEventDetail>(event, {
          detail: {
            lineNum: number,
            side: leftSide ? Side.LEFT : Side.RIGHT,
          },
          composed: true,
          bubbles: true,
        })
      );
    }
  }

  private updateSideClass() {
    if (!this.diffRow) {
      return;
    }
    toggleClass(this.diffRow, LEFT_SIDE_CLASS, this.side === Side.LEFT);
    toggleClass(this.diffRow, RIGHT_SIDE_CLASS, this.side === Side.RIGHT);
  }

  _isActionType(type: GrDiffRowType) {
    return (
      type !== GrDiffLineType.BLANK && type !== GrDiffGroupType.CONTEXT_CONTROL
    );
  }

  _getActionsForRow() {
    const actions = {left: false, right: false};
    if (this.diffRow) {
      actions.left = this._isActionType(
        this.diffRow.getAttribute('left-type') as GrDiffRowType
      );
      actions.right = this._isActionType(
        this.diffRow.getAttribute('right-type') as GrDiffRowType
      );
    }
    return actions;
  }

  _updateStops() {
    this.cursorManager.stops = this.diffs.reduce(
      (stops: Stop[], diff) => stops.concat(diff.getCursorStops()),
      []
    );
  }

  replaceDiffs(diffs: GrDiffCursorable[]) {
    for (const diff of this.diffs) {
      this.removeEventListeners(diff);
    }
    this.diffs = [];
    for (const diff of diffs) {
      this.addEventListeners(diff);
    }
    this.diffs.push(...diffs);
    this._updateStops();
  }

  unregisterDiff(diff: GrDiffCursorable) {
    // This can happen during destruction - just don't unregister then.
    if (!this.diffs) return;
    const i = this.diffs.indexOf(diff);
    if (i !== -1) {
      this.diffs.splice(i, 1);
    }
  }

  private removeEventListeners(diff: GrDiffCursorable) {
    diff.removeEventListener(
      'loading-changed',
      this.boundHandleDiffLoadingChanged
    );
    diff.removeEventListener('render-start', this._boundHandleDiffRenderStart);
    diff.removeEventListener(
      'render-content',
      this._boundHandleDiffRenderContent
    );
    diff.removeEventListener(
      'line-selected',
      this._boundHandleDiffLineSelected
    );
  }

  private addEventListeners(diff: GrDiffCursorable) {
    diff.addEventListener(
      'loading-changed',
      this.boundHandleDiffLoadingChanged
    );
    diff.addEventListener('render-start', this._boundHandleDiffRenderStart);
    diff.addEventListener('render-content', this._boundHandleDiffRenderContent);
    diff.addEventListener('line-selected', this._boundHandleDiffLineSelected);
  }

  _findRowByNumberAndFile(
    targetNumber: number,
    side: Side,
    path?: string
  ): HTMLElement | undefined {
    let stops: Array<HTMLElement | AbortStop>;
    if (path) {
      const diff = this.diffs.filter(diff => diff.path === path)[0];
      stops = diff.getCursorStops();
    } else {
      stops = this.cursorManager.stops;
    }
    // Sadly needed for type narrowing to understand that the result is always
    // targetable.
    const targetableStops: HTMLElement[] = stops.filter(isTargetable);
    const selector = `.lineNum.${side}[data-value="${targetNumber}"]`;
    return targetableStops.find(stop => stop.querySelector(selector));
  }
}