feat: let toshihiko support promise

lib/toshihiko.js

@@ -11,6 +11,8 @@ const EventEmitter = require("eventemitter2").EventEmitter2;
 
 const common = require("../util/common");
 
+const emptyFunc = function() {};
+
 class Toshihiko extends EventEmitter {
     constructor(Adapter, options) {
         super();
@@ -34,7 +36,35 @@ class Toshihiko extends EventEmitter {
     }
 
     execute() {
+        const promise = common.promisify();
+
+        let trueCallback = emptyFunc;
+        let cbIdx;
+        for(let i = 0; i < arguments.length; i++) {
+            if(typeof arguments[i] === "function") {
+                trueCallback = arguments[i];
+                cbIdx = i;
+            }
+        }
+        let callback = function(err, res, extra) {
+            if(err) {
+                promise.reject(err);
+            } else {
+                promise.resolve(res);
+            }
+
+            trueCallback(err, res, extra);
+        };
+        if(cbIdx === undefined){
+            arguments[arguments.length] = callback;
+            arguments.length++;
+        } else {
+            arguments[cbIdx] = callback;
+        }
+
         this.adapter.execute.apply(this.adapter, arguments);
+
+        return promise.q;
     }
 
     define(collectionName, schema, options) {