Fixed massive writes to creature.variables on calc

Now only writes changed variables, preventing oplog from being
polluted with massive updates

app/imports/api/engine/computation/CreatureComputation.js

@@ -2,7 +2,7 @@ import { EJSON } from 'meteor/ejson';
 import createGraph from 'ngraph.graph';
 
 export default class CreatureComputation {
-  constructor(properties){
+  constructor(properties, creature){
     // Set up fields
     this.originalPropsById =  {};
     this.propsById =  {};
@@ -11,6 +11,7 @@ export default class CreatureComputation {
     this.props =  properties;
     this.dependencyGraph = createGraph();
     this.errors = [];
+    this.creature = creature;
 
     // Store properties for easy access later
     properties.forEach(prop => {

app/imports/api/engine/computation/buildCreatureComputation.js

@@ -54,7 +54,7 @@ function getCreature(creatureId){
 
 export function buildComputationFromProps(properties, creature){
 
-  const computation = new CreatureComputation(properties);
+  const computation = new CreatureComputation(properties, creature);
   // Dependency graph where edge(a, b) means a depends on b
   // The graph includes all dependencies even of inactive properties
   // such that any properties changing without changing their dependencies

app/imports/api/engine/computation/writeComputation/writeScope.js

@@ -1,10 +1,31 @@
 import Creatures from '/imports/api/creature/creatures/Creatures.js';
+import { EJSON } from 'meteor/ejson';
 
-export default function writeScope(creatureId, scope){
-  // Remove large properties that aren't likely to be accessed
+export default function writeScope(creatureId, computation) {
+  const scope = computation.scope;
+  const variables = computation.creature.variables || {};
+  let $set;
   for (const key in scope){
+    // Remove large properties that aren't likely to be accessed
     delete scope[key].parent;
     delete scope[key].ancestors;
+    
+    // Remove empty keys
+    for (const subKey in scope[key]) {
+      if (scope[key][subKey] === undefined) {
+        delete scope[key][subKey]
+      }
+    }
+    
+    // Only update changed fields
+    if (!EJSON.equals(variables[key], scope[key])) {
+      if (!$set) $set = {};
+
+      // Set the changed key in the creature variables
+      $set[`variables.${key}`] = scope[key];
+    }
+  }
+  if ($set) {
+    Creatures.update(creatureId, {$set});
   }
-  Creatures.update(creatureId, {$set: {variables: scope}});
 }

app/imports/api/engine/computeCreature.js

@@ -10,7 +10,7 @@ export default function computeCreature(creatureId){
   try {
     computeCreatureComputation(computation);
     writeAlteredProperties(computation);
-    writeScope(creatureId, computation.scope);
+    writeScope(creatureId, computation);
   } catch (e){
     const errorText = e.reason || e.message || e.toString();
     computation.errors.push({