Add data structure invariants for tree data

Summary:
1. Only leaf nodes have text.
2. Leaf nodes cannot have children.
3. Parent and child relationships should be mirrored.
4. Sibling relationship (``prevSibling`` & ``nextSibling``) should be mirrored.
5. All children of a parent must have sibling relationships.
6. The first node has no prev sibling.
7. The last node has no next sibling.
8. The data structure is a tree - fully connected & acyclic on the ``parent -> child`` and ``nextSibling`` edges.

We do these checks as:
* Go through each node in the block map and check that it is a valid node with respect to its properties and pointers to and from other nodes
* Find the first (unique) node of the tree and check that the tree is connected

Reviewed By: mitermayer

Differential Revision: D9193098

fbshipit-source-id: 0dd6177e3cb8d15c9ee76ce48fa14d191f3ec93c

Author: niveditc

src/component/utils/exploration/DraftTreeInvariants.js

@@ -0,0 +1,165 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @format
+ * @flow strict-local
+ *
+ * This is unstable and not part of the public API and should not be used by
+ * production systems. This file may be update/removed without notice.
+ */
+import type {BlockMap} from 'BlockMap';
+import type ContentBlockNode from 'ContentBlockNode';
+
+const warning = require('warning');
+
+const DraftTreeInvariants = {
+  /**
+   * Check if the block is valid
+   */
+  isValidBlock(block: ContentBlockNode, blockMap: BlockMap): boolean {
+    const key = block.getKey();
+    // is its parent's child
+    const parentKey = block.getParentKey();
+    if (parentKey != null) {
+      const parent = blockMap.get(parentKey);
+      if (!parent.getChildKeys().includes(key)) {
+        warning(true, 'Tree is missing parent -> child pointer on %s', key);
+        return false;
+      }
+    }
+
+    // is its children's parent
+    const children = block.getChildKeys().map(k => blockMap.get(k));
+    if (!children.every(c => c.getParentKey() === key)) {
+      warning(true, 'Tree is missing child -> parent pointer on %s', key);
+      return false;
+    }
+
+    // is its previous sibling's next sibling
+    const prevSiblingKey = block.getPrevSiblingKey();
+    if (prevSiblingKey != null) {
+      const prevSibling = blockMap.get(prevSiblingKey);
+      if (prevSibling.getNextSiblingKey() !== key) {
+        warning(
+          true,
+          "Tree is missing nextSibling pointer on %s's prevSibling",
+          key,
+        );
+        return false;
+      }
+    }
+
+    // is its next sibling's previous sibling
+    const nextSiblingKey = block.getNextSiblingKey();
+    if (nextSiblingKey != null) {
+      const nextSibling = blockMap.get(nextSiblingKey);
+      if (nextSibling.getPrevSiblingKey() !== key) {
+        warning(
+          true,
+          "Tree is missing prevSibling pointer on %s's nextSibling",
+          key,
+        );
+        return false;
+      }
+    }
+
+    // no 2-node cycles
+    if (nextSiblingKey !== null && prevSiblingKey !== null) {
+      if (prevSiblingKey === nextSiblingKey) {
+        warning(true, 'Tree has a two-node cycle at %s', key);
+        return false;
+      }
+    }
+
+    // if it's a leaf node, it has text but no children
+    if (block.text != '') {
+      if (block.getChildKeys().size > 0) {
+        warning(true, 'Leaf node %s has children', key);
+        return false;
+      }
+    }
+    return true;
+  },
+
+  /**
+   * Checks that this is a connected tree on all the blocks
+   * starting from the first block, traversing nextSibling and child pointers
+   * should be a tree (preorder traversal - parent, then children)
+   * num of connected node === number of blocks
+   */
+  isConnectedTree(blockMap: BlockMap): boolean {
+    // exactly one node has no previous sibling + no parent
+    const eligibleFirstNodes = blockMap
+      .toArray()
+      .filter(
+        block =>
+          block.getParentKey() == null && block.getPrevSiblingKey() == null,
+      );
+    if (eligibleFirstNodes.length !== 1) {
+      warning(true, 'Tree is not connected. More or less than one first node');
+      return false;
+    }
+    const firstNode = eligibleFirstNodes.shift();
+    let nodesSeen = 0;
+    let currentKey = firstNode.getKey();
+    const visitedStack = [];
+    while (currentKey != null) {
+      const currentNode = blockMap.get(currentKey);
+      const childKeys = currentNode.getChildKeys();
+      const nextSiblingKey = currentNode.getNextSiblingKey();
+      // if the node has children, add parent's next sibling to stack and go to children
+      if (childKeys.size > 0) {
+        if (nextSiblingKey != null) {
+          visitedStack.unshift(nextSiblingKey);
+        }
+        const children = childKeys.map(k => blockMap.get(k));
+        const firstNode = children.find(
+          block => block.getPrevSiblingKey() == null,
+        );
+        if (firstNode == null) {
+          warning(true, '%s has no first child', currentKey);
+          return false;
+        }
+        currentKey = firstNode.getKey();
+        // TODO(T32490138): Deal with multi-node cycles here
+      } else {
+        if (currentNode.getNextSiblingKey() != null) {
+          currentKey = currentNode.getNextSiblingKey();
+        } else {
+          currentKey = visitedStack.shift();
+        }
+      }
+      nodesSeen++;
+    }
+
+    if (nodesSeen !== blockMap.size) {
+      warning(
+        true,
+        'Tree is not connected. %s nodes were seen instead of %s',
+        nodesSeen,
+        blockMap.size,
+      );
+      return false;
+    }
+
+    return true;
+  },
+
+  /**
+   * Checks that the block map is a connected tree with valid blocks
+   */
+  isValidTree(blockMap: BlockMap): boolean {
+    const blocks = blockMap.toArray();
+    if (!blocks.every(block => this.isValidBlock(block, blockMap))) {
+      return false;
+    }
+    return this.isConnectedTree(blockMap);
+  },
+};
+
+module.exports = DraftTreeInvariants;