From ea170c747756b4a54c3106a8c42383ac5c5e4e44 Mon Sep 17 00:00:00 2001
From: Mike McNeil <git+mikermcneil@sailsjs.com>
Date: Wed, 9 May 2018 23:42:59 -0500
Subject: [PATCH] spec out handleUndo

---
 machine-def.struct.js | 38 +++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/machine-def.struct.js b/machine-def.struct.js
index 5e6f82c..fa3d7cf 100644
--- a/machine-def.struct.js
+++ b/machine-def.struct.js
@@ -12,13 +12,35 @@ module.exports = {
   moreInfoUrl: 'http://hello.com',
 
 
-  sideEffects: 'idempotent', // either omit or set as "cacheable" or "idempotent"
+  habitat: 'sails', // either omit or set as "request", "sails", "node", or "browser".
 
 
-  habitat: 'sails', // either omit or set as "request" or "sails"
+  //sync: true, // either omit or set as `true`
 
 
-  sync: true, // either omit or set as `true`
+  // sideEffects: 'idempotent', // either omit or set as "cacheable" or "idempotent"
+
+
+  handleUndo: async function(inputs){ // either omit or set as a function
+    // ^^ should never be defined for a "cacheable" machine
+
+    // Reverse `fn`'s side effect.
+    // (Note that this is not a GLOBAL UNDO!!!  In this example, this code could
+    // not attempt to handle any changes that might have befallen the global var
+    // from other logic.  It can really only attempt to reverse the side effects
+    // of running `fn` with these inputs, and even then only assuming `fn`
+    // triggered its success exit.)
+    
+    // Realistically, it's not super possible w/ this example, but we can at
+    // least fudge it a little bit:
+    if (global.foo) {
+      // if we knew how much to subtract, we could do that here, for example
+    }
+
+    // (In reality, this example isn't really reversible, so we would not
+    // want to define a handleUndo function at all!)
+
+  },
 
 
   inputs: {
@@ -35,15 +57,18 @@ module.exports = {
   },
 
 
-  fn: function (inputs, exits) {
+  fn: async function (inputs, exits) {
 
+    // Import any dependencies here
     var _ = require('@sailshq/lodash');
 
+    // Do asynchronous things with callbacks if you like
+    // (or better yet, use `await`!)
     setTimeout(function (){
 
       try {
 
-        var luckyNum = Math.random();
+        let luckyNum = Math.random();
         if (luckyNum > 0.5) {
           throw new Error('whatever');
         }
@@ -62,6 +87,9 @@ module.exports = {
 
       // --• OK so if we made it here, `luckyNum` must be between 0.1 and 0.5 (exclusive).
 
+      // Maybe do some kind of side effect.
+      global.foo = (global.foo || 0) + luckyNum;
+
       // Exit `success` with no output.
       return exits.success();
       // > NOTE: