tubestation/devtools/client/shared/components/VirtualizedTree.js

/* 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/. */
/* eslint-env browser */
"use strict";

const { Component, createFactory } = require("devtools/client/shared/vendor/react");
const PropTypes = require("devtools/client/shared/vendor/react-prop-types");
const dom = require("devtools/client/shared/vendor/react-dom-factories");
const { scrollIntoView } = require("devtools/client/shared/scroll");
const { preventDefaultAndStopPropagation } = require("devtools/client/shared/events");

loader.lazyRequireGetter(this, "focusableSelector", "devtools/client/shared/focus", true);

const AUTO_EXPAND_DEPTH = 0;
const NUMBER_OF_OFFSCREEN_ITEMS = 1;

/**
 * A fast, generic, expandable and collapsible tree component.
 *
 * This tree component is fast: it can handle trees with *many* items. It only
 * renders the subset of those items which are visible in the viewport. It's
 * been battle tested on huge trees in the memory panel. We've optimized tree
 * traversal and rendering, even in the presence of cross-compartment wrappers.
 *
 * This tree component doesn't make any assumptions about the structure of your
 * tree data. Whether children are computed on demand, or stored in an array in
 * the parent's `_children` property, it doesn't matter. We only require the
 * implementation of `getChildren`, `getRoots`, `getParent`, and `isExpanded`
 * functions.
 *
 * This tree component is well tested and reliable. See
 * devtools/client/shared/components/test/mochitest/test_tree_* and its usage in
 * the performance and memory panels.
 *
 * This tree component doesn't make any assumptions about how to render items in
 * the tree. You provide a `renderItem` function, and this component will ensure
 * that only those items whose parents are expanded and which are visible in the
 * viewport are rendered. The `renderItem` function could render the items as a
 * "traditional" tree or as rows in a table or anything else. It doesn't
 * restrict you to only one certain kind of tree.
 *
 * The only requirement is that every item in the tree render as the same
 * height. This is required in order to compute which items are visible in the
 * viewport in constant time.
 *
 * ### Example Usage
 *
 * Suppose we have some tree data where each item has this form:
 *
 *     {
 *       id: Number,
 *       label: String,
 *       parent: Item or null,
 *       children: Array of child items,
 *       expanded: bool,
 *     }
 *
 * Here is how we could render that data with this component:
 *
 *     class MyTree extends Component {
 *       static get propTypes() {
 *         // The root item of the tree, with the form described above.
 *         return {
 *           root: PropTypes.object.isRequired
 *         };
 *       }
 *
 *       render() {
 *         return Tree({
 *           itemHeight: 20, // px
 *
 *           getRoots: () => [this.props.root],
 *
 *           getParent: item => item.parent,
 *           getChildren: item => item.children,
 *           getKey: item => item.id,
 *           isExpanded: item => item.expanded,
 *
 *           renderItem: (item, depth, isFocused, arrow, isExpanded) => {
 *             let className = "my-tree-item";
 *             if (isFocused) {
 *               className += " focused";
 *             }
 *             return dom.div(
 *               {
 *                 className,
 *                 // Apply 10px nesting per expansion depth.
 *                 style: { marginLeft: depth * 10 + "px" }
 *               },
 *               // Here is the expando arrow so users can toggle expansion and
 *               // collapse state.
 *               arrow,
 *               // And here is the label for this item.
 *               dom.span({ className: "my-tree-item-label" }, item.label)
 *             );
 *           },
 *
 *           onExpand: item => dispatchExpandActionToRedux(item),
 *           onCollapse: item => dispatchCollapseActionToRedux(item),
 *         });
 *       }
 *     }
 */
class Tree extends Component {
  static get propTypes() {
    return {
      // Required props

      // A function to get an item's parent, or null if it is a root.
      //
      // Type: getParent(item: Item) -> Maybe<Item>
      //
      // Example:
      //
      //     // The parent of this item is stored in its `parent` property.
      //     getParent: item => item.parent
      getParent: PropTypes.func.isRequired,

      // A function to get an item's children.
      //
      // Type: getChildren(item: Item) -> [Item]
      //
      // Example:
      //
      //     // This item's children are stored in its `children` property.
      //     getChildren: item => item.children
      getChildren: PropTypes.func.isRequired,

      // A function which takes an item and ArrowExpander component instance and
      // returns a component, or text, or anything else that React considers
      // renderable.
      //
      // Type: renderItem(item: Item,
      //                  depth: Number,
      //                  isFocused: Boolean,
      //                  arrow: ReactComponent,
      //                  isExpanded: Boolean) -> ReactRenderable
      //
      // Example:
      //
      //     renderItem: (item, depth, isFocused, arrow, isExpanded) => {
      //       let className = "my-tree-item";
      //       if (isFocused) {
      //         className += " focused";
      //       }
      //       return dom.div(
      //         {
      //           className,
      //           style: { marginLeft: depth * 10 + "px" }
      //         },
      //         arrow,
      //         dom.span({ className: "my-tree-item-label" }, item.label)
      //       );
      //     },
      renderItem: PropTypes.func.isRequired,

      // A function which returns the roots of the tree (forest).
      //
      // Type: getRoots() -> [Item]
      //
      // Example:
      //
      //     // In this case, we only have one top level, root item. You could
      //     // return multiple items if you have many top level items in your
      //     // tree.
      //     getRoots: () => [this.props.rootOfMyTree]
      getRoots: PropTypes.func.isRequired,

      // A function to get a unique key for the given item. This helps speed up
      // React's rendering a *TON*.
      //
      // Type: getKey(item: Item) -> String
      //
      // Example:
      //
      //     getKey: item => `my-tree-item-${item.uniqueId}`
      getKey: PropTypes.func.isRequired,

      // A function to get whether an item is expanded or not. If an item is not
      // expanded, then it must be collapsed.
      //
      // Type: isExpanded(item: Item) -> Boolean
      //
      // Example:
      //
      //     isExpanded: item => item.expanded,
      isExpanded: PropTypes.func.isRequired,

      // The height of an item in the tree including margin and padding, in
      // pixels.
      itemHeight: PropTypes.number.isRequired,

      // Optional props

      // The currently focused item, if any such item exists.
      focused: PropTypes.any,

      // Handle when a new item is focused.
      onFocus: PropTypes.func,

      // The currently active (keyboard) item, if any such item exists.
      active: PropTypes.any,

      // Handle when item is activated with a keyboard (using Space or Enter)
      onActivate: PropTypes.func,

      // The currently shown item, if any such item exists.
      shown: PropTypes.any,

      // Indicates if pressing ArrowRight key should only expand expandable node
      // or if the selection should also move to the next node.
      preventNavigationOnArrowRight: PropTypes.bool,

      // The depth to which we should automatically expand new items.
      autoExpandDepth: PropTypes.number,

      // Note: the two properties below are mutually exclusive. Only one of the
      // label properties is necessary.
      // ID of an element whose textual content serves as an accessible label for
      // a tree.
      labelledby: PropTypes.string,
      // Accessibility label for a tree widget.
      label: PropTypes.string,

      // Optional event handlers for when items are expanded or collapsed. Useful
      // for dispatching redux events and updating application state, maybe lazily
      // loading subtrees from a worker, etc.
      //
      // Type:
      //     onExpand(item: Item)
      //     onCollapse(item: Item)
      //
      // Example:
      //
      //     onExpand: item => dispatchExpandActionToRedux(item)
      onExpand: PropTypes.func,
      onCollapse: PropTypes.func,
    };
  }

  static get defaultProps() {
    return {
      autoExpandDepth: AUTO_EXPAND_DEPTH,
      preventNavigationOnArrowRight: true,
    };
  }

  constructor(props) {
    super(props);

    this.state = {
      scroll: 0,
      height: window.innerHeight,
      seen: new Set(),
      mouseDown: false,
    };

    this._onExpand = oncePerAnimationFrame(this._onExpand).bind(this);
    this._onCollapse = oncePerAnimationFrame(this._onCollapse).bind(this);
    this._onScroll = oncePerAnimationFrame(this._onScroll).bind(this);
    this._focusPrevNode = oncePerAnimationFrame(this._focusPrevNode).bind(this);
    this._focusNextNode = oncePerAnimationFrame(this._focusNextNode).bind(this);
    this._focusParentNode = oncePerAnimationFrame(this._focusParentNode).bind(this);
    this._focusFirstNode = oncePerAnimationFrame(this._focusFirstNode).bind(this);
    this._focusLastNode = oncePerAnimationFrame(this._focusLastNode).bind(this);

    this._autoExpand = this._autoExpand.bind(this);
    this._preventArrowKeyScrolling = this._preventArrowKeyScrolling.bind(this);
    this._updateHeight = this._updateHeight.bind(this);
    this._onResize = this._onResize.bind(this);
    this._dfs = this._dfs.bind(this);
    this._dfsFromRoots = this._dfsFromRoots.bind(this);
    this._focus = this._focus.bind(this);
    this._activate = this._activate.bind(this);
    this._onKeyDown = this._onKeyDown.bind(this);
  }

  componentDidMount() {
    window.addEventListener("resize", this._onResize);
    this._autoExpand();
    this._updateHeight();
    this._scrollItemIntoView();
  }

  componentWillReceiveProps(nextProps) {
    this._autoExpand();
    this._updateHeight();
  }

  shouldComponentUpdate(nextProps, nextState) {
    const { scroll, height, seen, mouseDown } = this.state;

    return scroll !== nextState.scroll ||
           height !== nextState.height ||
           seen !== nextState.seen ||
           mouseDown === nextState.mouseDown;
  }

  componentDidUpdate() {
    this._scrollItemIntoView();
  }

  componentWillUnmount() {
    window.removeEventListener("resize", this._onResize);
  }

  _scrollItemIntoView() {
    const { shown } = this.props;
    if (!shown) {
      return;
    }

    this._scrollIntoView(shown);
  }

  _autoExpand() {
    if (!this.props.autoExpandDepth) {
      return;
    }

    // Automatically expand the first autoExpandDepth levels for new items. Do
    // not use the usual DFS infrastructure because we don't want to ignore
    // collapsed nodes.
    const autoExpand = (item, currentDepth) => {
      if (currentDepth >= this.props.autoExpandDepth ||
          this.state.seen.has(item)) {
        return;
      }

      this.props.onExpand(item);
      this.state.seen.add(item);

      const children = this.props.getChildren(item);
      const length = children.length;
      for (let i = 0; i < length; i++) {
        autoExpand(children[i], currentDepth + 1);
      }
    };

    const roots = this.props.getRoots();
    const length = roots.length;
    for (let i = 0; i < length; i++) {
      autoExpand(roots[i], 0);
    }
  }

  _preventArrowKeyScrolling(e) {
    switch (e.key) {
      case "ArrowUp":
      case "ArrowDown":
      case "ArrowLeft":
      case "ArrowRight":
        preventDefaultAndStopPropagation(e);
        break;
    }
  }

  /**
   * Updates the state's height based on clientHeight.
   */
  _updateHeight() {
    this.setState({ height: this.refs.tree.clientHeight });
  }

  /**
   * Perform a pre-order depth-first search from item.
   */
  _dfs(item, maxDepth = Infinity, traversal = [], _depth = 0) {
    traversal.push({ item, depth: _depth });

    if (!this.props.isExpanded(item)) {
      return traversal;
    }

    const nextDepth = _depth + 1;

    if (nextDepth > maxDepth) {
      return traversal;
    }

    const children = this.props.getChildren(item);
    const length = children.length;
    for (let i = 0; i < length; i++) {
      this._dfs(children[i], maxDepth, traversal, nextDepth);
    }

    return traversal;
  }

  /**
   * Perform a pre-order depth-first search over the whole forest.
   */
  _dfsFromRoots(maxDepth = Infinity) {
    const traversal = [];

    const roots = this.props.getRoots();
    const length = roots.length;
    for (let i = 0; i < length; i++) {
      this._dfs(roots[i], maxDepth, traversal);
    }

    return traversal;
  }

  /**
   * Expands current row.
   *
   * @param {Object} item
   * @param {Boolean} expandAllChildren
   */
  _onExpand(item, expandAllChildren) {
    if (this.props.onExpand) {
      this.props.onExpand(item);

      if (expandAllChildren) {
        const children = this._dfs(item);
        const length = children.length;
        for (let i = 0; i < length; i++) {
          this.props.onExpand(children[i].item);
        }
      }
    }
  }

  /**
   * Collapses current row.
   *
   * @param {Object} item
   */
  _onCollapse(item) {
    if (this.props.onCollapse) {
      this.props.onCollapse(item);
    }
  }

  /**
   * Scroll item into view. Depending on whether the item is already rendered,
   * we might have to calculate the position of the item based on its index and
   * the item height.
   *
   * @param {Object} item
   *        The item to be scrolled into view.
   * @param {Number|undefined} index
   *        The index of the item in a full DFS traversal (ignoring collapsed
   *        nodes) or undefined.
   * @param {Object} options
   *        Optional information regarding item's requested alignement when
   *        scrolling.
   */
  _scrollIntoView(item, index, options = {}) {
    const treeElement = this.refs.tree;
    if (!treeElement) {
      return;
    }

    const element = document.getElementById(this.props.getKey(item));
    if (element) {
      scrollIntoView(element, { ...options, container: treeElement });
      return;
    }

    if (index == null) {
      // If index is not provided, determine item index from traversal.
      const traversal = this._dfsFromRoots();
      index = traversal.findIndex(({ item: i }) => i === item);
    }

    if (index == null || index < 0) {
      return;
    }

    const { itemHeight } = this.props;
    const { clientHeight, scrollTop } = treeElement;
    const elementTop = index * itemHeight;
    let scrollTo;
    if (scrollTop >= elementTop + itemHeight) {
      scrollTo = elementTop;
    } else if (scrollTop + clientHeight <= elementTop) {
      scrollTo = elementTop + itemHeight - clientHeight;
    }

    if (scrollTo != undefined) {
      treeElement.scrollTo({
        left: 0,
        top: scrollTo,
      });
    }
  }

  /**
   * Sets the passed in item to be the focused item.
   *
   * @param {Number} index
   *        The index of the item in a full DFS traversal (ignoring collapsed
   *        nodes). Ignored if `item` is undefined.
   *
   * @param {Object|undefined} item
   *        The item to be focused, or undefined to focus no item.
   */
  _focus(index, item, options = {}) {
    if (item !== undefined && !options.preventAutoScroll) {
      this._scrollIntoView(item, index, options);
    }

    if (this.props.active != null) {
      this._activate(null);
      if (this.refs.tree !== this.activeElement) {
        this.refs.tree.focus();
      }
    }

    if (this.props.onFocus) {
      this.props.onFocus(item);
    }
  }

  _activate(item) {
    if (this.props.onActivate) {
      this.props.onActivate(item);
    }
  }

  /**
   * Update state height and tree's scrollTop if necessary.
   */
  _onResize() {
    // When tree size changes without direct user action, scroll top cat get re-set to 0
    // (for example, when tree height changes via CSS rule change). We need to ensure that
    // the tree's scrollTop is in sync with the scroll state.
    if (this.state.scroll !== this.refs.tree.scrollTop) {
      this.refs.tree.scrollTo({ left: 0, top: this.state.scroll });
    }

    this._updateHeight();
  }

  /**
   * Fired on a scroll within the tree's container, updates
   * the stored position of the view port to handle virtual view rendering.
   *
   * @param {Event} e
   */
  _onScroll(e) {
    this.setState({
      scroll: Math.max(this.refs.tree.scrollTop, 0),
      height: this.refs.tree.clientHeight,
    });
  }

  /**
   * Handles key down events in the tree's container.
   *
   * @param {Event} e
   */
  /* eslint-disable complexity */
  _onKeyDown(e) {
    if (this.props.focused == null) {
      return;
    }

    // Allow parent nodes to use navigation arrows with modifiers.
    if (e.altKey || e.ctrlKey || e.shiftKey || e.metaKey) {
      return;
    }

    this._preventArrowKeyScrolling(e);

    switch (e.key) {
      case "ArrowUp":
        this._focusPrevNode();
        break;

      case "ArrowDown":
        this._focusNextNode();
        break;

      case "ArrowLeft":
        if (this.props.isExpanded(this.props.focused)
            && this.props.getChildren(this.props.focused).length) {
          this._onCollapse(this.props.focused);
        } else {
          this._focusParentNode();
        }
        break;

      case "ArrowRight":
        if (this.props.getChildren(this.props.focused).length &&
            !this.props.isExpanded(this.props.focused)) {
          this._onExpand(this.props.focused);
        } else if (!this.props.preventNavigationOnArrowRight) {
          this._focusNextNode();
        }
        break;

      case "Home":
        this._focusFirstNode();
        break;

      case "End":
        this._focusLastNode();
        break;

      case "Enter":
      case " ":
        // On space or enter make focused tree node active. This means keyboard focus
        // handling is passed on to the tree node itself.
        if (this.refs.tree === this.activeElement) {
          preventDefaultAndStopPropagation(e);
          if (this.props.active !== this.props.focused) {
            this._activate(this.props.focused);
          }
        }
        break;

      case "Escape":
        preventDefaultAndStopPropagation(e);
        if (this.props.active != null) {
          this._activate(null);
        }

        if (this.refs.tree !== this.activeElement) {
          this.refs.tree.focus();
        }
        break;
    }
  }
  /* eslint-enable complexity */

  get activeElement() {
    return this.refs.tree.ownerDocument.activeElement;
  }

  _focusFirstNode() {
    const traversal = this._dfsFromRoots();
    this._focus(0, traversal[0].item, { alignTo: "top" });
  }

  _focusLastNode() {
    const traversal = this._dfsFromRoots();
    const lastIndex = traversal.length - 1;
    this._focus(lastIndex, traversal[lastIndex].item, { alignTo: "bottom" });
  }

  /**
   * Sets the previous node relative to the currently focused item, to focused.
   */
  _focusPrevNode() {
    // Start a depth first search and keep going until we reach the currently
    // focused node. Focus the previous node in the DFS, if it exists. If it
    // doesn't exist, we're at the first node already.

    let prev;
    let prevIndex;

    const traversal = this._dfsFromRoots();
    const length = traversal.length;
    for (let i = 0; i < length; i++) {
      const item = traversal[i].item;
      if (item === this.props.focused) {
        break;
      }
      prev = item;
      prevIndex = i;
    }

    if (prev === undefined) {
      return;
    }

    this._focus(prevIndex, prev, { alignTo: "top" });
  }

  /**
   * Handles the down arrow key which will focus either the next child
   * or sibling row.
   */
  _focusNextNode() {
    // Start a depth first search and keep going until we reach the currently
    // focused node. Focus the next node in the DFS, if it exists. If it
    // doesn't exist, we're at the last node already.

    const traversal = this._dfsFromRoots();
    const length = traversal.length;
    let i = 0;

    while (i < length) {
      if (traversal[i].item === this.props.focused) {
        break;
      }
      i++;
    }

    if (i + 1 < traversal.length) {
      this._focus(i + 1, traversal[i + 1].item, { alignTo: "bottom" });
    }
  }

  /**
   * Handles the left arrow key, going back up to the current rows'
   * parent row.
   */
  _focusParentNode() {
    const parent = this.props.getParent(this.props.focused);
    if (!parent) {
      return;
    }

    const traversal = this._dfsFromRoots();
    const length = traversal.length;
    let parentIndex = 0;
    for (; parentIndex < length; parentIndex++) {
      if (traversal[parentIndex].item === parent) {
        break;
      }
    }

    this._focus(parentIndex, parent, { alignTo: "top" });
  }

  render() {
    const traversal = this._dfsFromRoots();

    // 'begin' and 'end' are the index of the first (at least partially) visible item
    // and the index after the last (at least partially) visible item, respectively.
    // `NUMBER_OF_OFFSCREEN_ITEMS` is removed from `begin` and added to `end` so that
    // the top and bottom of the page are filled with the `NUMBER_OF_OFFSCREEN_ITEMS`
    // previous and next items respectively, which helps the user to see fewer empty
    // gaps when scrolling quickly.
    const { itemHeight, active, focused } = this.props;
    const { scroll, height } = this.state;
    const begin = Math.max(((scroll / itemHeight) | 0) - NUMBER_OF_OFFSCREEN_ITEMS, 0);
    const end = Math.ceil((scroll + height) / itemHeight) + NUMBER_OF_OFFSCREEN_ITEMS;
    const toRender = traversal.slice(begin, end);
    const topSpacerHeight = begin * itemHeight;
    const bottomSpacerHeight = Math.max(traversal.length - end, 0) * itemHeight;

    const nodes = [
      dom.div({
        key: "top-spacer",
        role: "presentation",
        style: {
          padding: 0,
          margin: 0,
          height: topSpacerHeight + "px",
        },
      }),
    ];

    for (let i = 0; i < toRender.length; i++) {
      const index = begin + i;
      const first = index == 0;
      const last = index == traversal.length - 1;
      const { item, depth } = toRender[i];
      const key = this.props.getKey(item);
      nodes.push(TreeNode({
        // We make a key unique depending on whether the tree node is in active or
        // inactive state to make sure that it is actually replaced and the tabbable
        // state is reset.
        key: `${key}-${active === item ? "active" : "inactive"}`,
        index,
        first,
        last,
        item,
        depth,
        id: key,
        renderItem: this.props.renderItem,
        focused: focused === item,
        active: active === item,
        expanded: this.props.isExpanded(item),
        hasChildren: !!this.props.getChildren(item).length,
        onExpand: this._onExpand,
        onCollapse: this._onCollapse,
        // Since the user just clicked the node, there's no need to check if
        // it should be scrolled into view.
        onClick: () => this._focus(begin + i, item, { preventAutoScroll: true }),
      }));
    }

    nodes.push(dom.div({
      key: "bottom-spacer",
      role: "presentation",
      style: {
        padding: 0,
        margin: 0,
        height: bottomSpacerHeight + "px",
      },
    }));

    return dom.div(
      {
        className: "tree",
        ref: "tree",
        role: "tree",
        tabIndex: "0",
        onKeyDown: this._onKeyDown,
        onKeyPress: this._preventArrowKeyScrolling,
        onKeyUp: this._preventArrowKeyScrolling,
        onScroll: this._onScroll,
        onMouseDown: () => this.setState({ mouseDown: true }),
        onMouseUp: () => this.setState({ mouseDown: false }),
        onFocus: () => {
          if (focused || this.state.mouseDown) {
            return;
          }

          // Only set default focus to the first tree node if focused node is
          // not yet set and the focus event is not the result of a mouse
          // interarction.
          this._focus(begin, toRender[0].item);
        },
        onBlur: e => {
          if (active != null) {
            const { relatedTarget } = e;
            if (!this.refs.tree.contains(relatedTarget)) {
              this._activate(null);
            }
          }
        },
        onClick: () => {
          // Focus should always remain on the tree container itself.
          this.refs.tree.focus();
        },
        "aria-label": this.props.label,
        "aria-labelledby": this.props.labelledby,
        "aria-activedescendant": focused && this.props.getKey(focused),
        style: {
          padding: 0,
          margin: 0,
        },
      },
      nodes
    );
  }
}

/**
 * An arrow that displays whether its node is expanded (▼) or collapsed
 * (▶). When its node has no children, it is hidden.
 */
class ArrowExpanderClass extends Component {
  static get propTypes() {
    return {
      item: PropTypes.any.isRequired,
      visible: PropTypes.bool.isRequired,
      expanded: PropTypes.bool.isRequired,
      onCollapse: PropTypes.func.isRequired,
      onExpand: PropTypes.func.isRequired,
    };
  }

  shouldComponentUpdate(nextProps, nextState) {
    return this.props.item !== nextProps.item
      || this.props.visible !== nextProps.visible
      || this.props.expanded !== nextProps.expanded;
  }

  render() {
    const attrs = {
      className: "arrow theme-twisty",
      // To collapse/expand the tree rows use left/right arrow keys.
      tabIndex: "-1",
      "aria-hidden": true,
      onClick: this.props.expanded
        ? () => this.props.onCollapse(this.props.item)
        : e => this.props.onExpand(this.props.item, e.altKey),
    };

    if (this.props.expanded) {
      attrs.className += " open";
    }

    if (!this.props.visible) {
      attrs.style = {
        visibility: "hidden",
      };
    }

    return dom.div(attrs);
  }
}

class TreeNodeClass extends Component {
  static get propTypes() {
    return {
      id: PropTypes.any.isRequired,
      focused: PropTypes.bool.isRequired,
      active: PropTypes.bool.isRequired,
      item: PropTypes.any.isRequired,
      expanded: PropTypes.bool.isRequired,
      hasChildren: PropTypes.bool.isRequired,
      onExpand: PropTypes.func.isRequired,
      index: PropTypes.number.isRequired,
      first: PropTypes.bool,
      last: PropTypes.bool,
      onClick: PropTypes.func,
      onCollapse: PropTypes.func.isRequired,
      depth: PropTypes.number.isRequired,
      renderItem: PropTypes.func.isRequired,
    };
  }

  constructor(props) {
    super(props);

    this._onKeyDown = this._onKeyDown.bind(this);
  }

  componentDidMount() {
    // Make sure that none of the focusable elements inside the tree node container are
    // tabbable if the tree node is not active. If the tree node is active and focus is
    // outside its container, focus on the first focusable element inside.
    const elms = this.getFocusableElements();
    if (elms.length === 0) {
      return;
    }

    if (!this.props.active) {
      elms.forEach(elm => elm.setAttribute("tabindex", "-1"));
      return;
    }

    if (!elms.includes(this.refs.treenode.ownerDocument.activeElement)) {
      elms[0].focus();
    }
  }

  /**
   * Get a list of all elements that are focusable with a keyboard inside the tree node.
   */
  getFocusableElements() {
    return Array.from(this.refs.treenode.querySelectorAll(focusableSelector));
  }

  /**
   * Wrap and move keyboard focus to first/last focusable element inside the tree node to
   * prevent the focus from escaping the tree node boundaries.
   * element).
   *
   * @param  {DOMNode} current  currently focused element
   * @param  {Boolean} back     direction
   * @return {Boolean}          true there is a newly focused element.
   */
  _wrapMoveFocus(current, back) {
    const elms = this.getFocusableElements();
    let next;

    if (elms.length === 0) {
      return false;
    }

    if (back) {
      if (elms.indexOf(current) === 0) {
        next = elms[elms.length - 1];
        next.focus();
      }
    } else if (elms.indexOf(current) === elms.length - 1) {
      next = elms[0];
      next.focus();
    }

    return !!next;
  }

  _onKeyDown(e) {
    const { target, key, shiftKey } = e;

    if (key !== "Tab") {
      return;
    }

    const focusMoved = this._wrapMoveFocus(target, shiftKey);
    if (focusMoved) {
      // Focus was moved to the begining/end of the list, so we need to prevent the
      // default focus change that would happen here.
      e.preventDefault();
    }

    e.stopPropagation();
  }

  render() {
    const arrow = ArrowExpander({
      item: this.props.item,
      expanded: this.props.expanded,
      visible: this.props.hasChildren,
      onExpand: this.props.onExpand,
      onCollapse: this.props.onCollapse,
    });

    const classList = [ "tree-node", "div" ];
    if (this.props.index % 2) {
      classList.push("tree-node-odd");
    }
    if (this.props.first) {
      classList.push("tree-node-first");
    }
    if (this.props.last) {
      classList.push("tree-node-last");
    }
    if (this.props.active) {
      classList.push("tree-node-active");
    }

    let ariaExpanded;
    if (this.props.hasChildren) {
      ariaExpanded = false;
    }
    if (this.props.expanded) {
      ariaExpanded = true;
    }

    return dom.div(
      {
        id: this.props.id,
        className: classList.join(" "),
        role: "treeitem",
        ref: "treenode",
        "aria-level": this.props.depth + 1,
        onClick: this.props.onClick,
        onKeyDownCapture: this.props.active ? this._onKeyDown : undefined,
        "aria-expanded": ariaExpanded,
        "data-expanded": this.props.expanded ? "" : undefined,
        "data-depth": this.props.depth,
        style: {
          padding: 0,
          margin: 0,
        },
      },

      this.props.renderItem(this.props.item,
                            this.props.depth,
                            this.props.focused,
                            arrow,
                            this.props.expanded),
    );
  }
}

const ArrowExpander = createFactory(ArrowExpanderClass);
const TreeNode = createFactory(TreeNodeClass);

/**
 * Create a function that calls the given function `fn` only once per animation
 * frame.
 *
 * @param {Function} fn
 * @returns {Function}
 */
function oncePerAnimationFrame(fn) {
  let animationId = null;
  let argsToPass = null;
  return function(...args) {
    argsToPass = args;
    if (animationId !== null) {
      return;
    }

    animationId = requestAnimationFrame(() => {
      fn.call(this, ...argsToPass);
      animationId = null;
      argsToPass = null;
    });
  };
}

module.exports = Tree;