use enum to check verbosity strings

Author: HanaPearlman

lib/core/wireprotocol/query.js

@@ -9,7 +9,7 @@ const maxWireVersion = require('../utils').maxWireVersion;
 const applyCommonQueryOptions = require('./shared').applyCommonQueryOptions;
 const command = require('./command');
 const decorateWithExplain = require('../../utils').decorateWithExplain;
-const Explain = require('../../explain');
+const Explain = require('../../explain').Explain;
 
 function query(server, ns, cmd, cursorState, options, callback) {
   options = options || {};

lib/core/wireprotocol/write_command.js

@@ -4,7 +4,7 @@ const MongoError = require('../error').MongoError;
 const collectionNamespace = require('./shared').collectionNamespace;
 const command = require('./command');
 const decorateWithExplain = require('../../utils').decorateWithExplain;
-const Explain = require('../../explain');
+const Explain = require('../../explain').Explain;
 
 function writeCommand(server, type, opsField, ns, ops, options, callback) {
   if (ops.length === 0) throw new MongoError(`${type} must contain at least one document`);

lib/cursor.js

@@ -12,7 +12,7 @@ const Map = require('./core').BSON.Map;
 const maybePromise = require('./utils').maybePromise;
 const executeOperation = require('./operations/execute_operation');
 const formattedOrderClause = require('./utils').formattedOrderClause;
-const Explain = require('./explain');
+const Explain = require('./explain').Explain;
 const Aspect = require('./operations/operation').Aspect;
 
 const each = require('./operations/cursor_ops').each;

lib/explain.js

@@ -1,5 +1,14 @@
 'use strict';
 
+const MongoError = require('./core/error').MongoError;
+
+const ExplainVerbosity = {
+  queryPlanner: 'queryPlanner',
+  queryPlannerExtended: 'queryPlannerExtended',
+  executionStats: 'executionStats',
+  allPlansExecution: 'allPlansExecution'
+};
+
 /**
  * @class
  * @property {string} verbosity The verbosity mode for the explain output
@@ -25,16 +34,22 @@ class Explain {
   /**
    * Construct an Explain given an options object.
    *
-   * @param {object} options The options object from which to extract the explain.
+   * @param {object} [options] The options object from which to extract the explain.
+   * @param {'queryPlanner'|'queryPlannerExtended'|'executionStats'|'allPlansExecution'|boolean} [options.explain] The verbosity mode for the explain output
    * @return {Explain}
    */
   static fromOptions(options) {
     if (options == null || options.explain === undefined) {
       return;
     }
 
-    return new Explain(options.explain);
+    const explain = options.explain;
+    if (typeof explain === 'boolean' || explain in ExplainVerbosity) {
+      return new Explain(options.explain);
+    }
+
+    throw new MongoError(`explain must be one of ${Object.keys(ExplainVerbosity)} or a boolean`);
   }
 }
 
-module.exports = Explain;
+module.exports = { Explain };

lib/operations/operation.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const Explain = require('../explain');
+const Explain = require('../explain').Explain;
 const MongoError = require('../core').MongoError;
 
 const Aspect = {