feat(hooks): download default gulpfile

If user has ionic.config.js and no gulpfile, prompt to download the
default gulpfile so they can still build.

Author: tlancina

lib/cli.js

@@ -176,10 +176,48 @@ function runWithGulp(argv, taskInstance){
     });
   }
 
+  //No gulpfile
   if (/serve|build|run|emulate|upload/.test(cmdName) && argv.v2) {
     console.warn('WARN: No gulpfile found!');
     console.warn('If your app requires a build step, you may want to ensure it runs before ' + cmdName + '.\n');
+
+    if (fs.existsSync('ionic.config.js')) {
+      var inquirer = require('inquirer');
+      var deferred = Q.defer();
+
+      console.info('Looks like you are using the deprecated ionic.config.js and have no gulpfile!');
+      console.info('As of beta.21 the Ionic CLI relies on gulp hooks to build your web assets\n');
+      inquirer.prompt([{
+        type: 'confirm',
+        name: 'downloadGulp',
+        message: 'Would you like to download the default gulpfile?'.cyan,
+      }],
+      function(answers){
+        answers.downloadGulp ? deferred.resolve() : deferred.reject();
+      });
+      var downloadGulp = false;
+      return deferred.promise.then(
+        function(){
+          downloadGulp = true;
+          return downloadDefaultGulpfile();
+        },
+        function(){
+          return Q.fcall(taskInstance.run.bind(taskInstance), Cli, argv);
+        }
+      ).then(
+        function(){
+          if (downloadGulp) {
+            console.success('Successfully downloaded gulpfile. Try running \'' + cmdName + '\' again.');
+          }
+        },
+        function(err) {
+          console.error('There was an error downloading the default gulpfile: ' + err);
+          process.exit(1);
+        }
+      );
+    }
   }
+
   return Q.fcall(taskInstance.run.bind(taskInstance), Cli, argv);
 }
 
@@ -207,6 +245,34 @@ function loadGulpfile(){
   return false;
 }
 
+function downloadDefaultGulpfile(){
+  var https = require('https');
+  var fileStream = fs.createWriteStream('gulpfile.js');
+  var deferred = Q.defer();
+  var project = IonicProject.load();
+  var branch = project.get('typescript') ? 'typescript' : 'master';
+  var url = 'https://cdn.rawgit.com/driftyco/ionic2-app-base/' + branch + '/gulpfile.js';
+
+  console.info(('Downloading default gulpfile from: ' + url));
+
+  fileStream.on('open', function () {
+    https.get(url, function (res) {
+      res.on('error', function (err) {
+        deferred.reject(err);
+      });
+
+      res.pipe(fileStream);
+    });
+  }).on('error', function (err) {
+    deferred.reject(err);
+  }).on('finish', function () {
+    deferred.resolve();
+  });
+
+  return deferred.promise;
+}
+
+
 function logEvents(gulpInst, finalTaskNames) {
   gulpInst.on('task_start', function(e) {
     // TODO: batch these