Support --platform and --platform_version args

Fixes #13

Author: neonichu

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    cocoapods-playgrounds (1.0.0)
+    cocoapods-playgrounds (1.1.0)
       cocoapods (~> 1.0.0)
 
 GEM

lib/cocoapods-playgrounds/command/playgrounds.rb

@@ -1,6 +1,10 @@
+require 'xcodeproj'
+
 module Pod
   class Command
     class Playgrounds < Command
+      DEFAULT_PLATFORM_NAME = :ios
+
       self.summary = 'Generates a Swift Playground for any Pod.'
 
       self.description = <<-DESC
@@ -11,14 +15,23 @@ class Playgrounds < Command
 
       def self.options
         [
-          ['--no-install', 'Skip running `pod install`']
+          ['--no-install', 'Skip running `pod install`'],
+          ['--platform', "Platform to generate for (default: #{DEFAULT_PLATFORM_NAME})"],
+          ['--platform_version', 'Platform version to generate for ' \
+            "(default: #{default_version_for_platform(DEFAULT_PLATFORM_NAME)})"]
         ]
       end
 
+      def self.default_version_for_platform(platform)
+        Xcodeproj::Constants.const_get("LAST_KNOWN_#{platform.upcase}_SDK")
+      end
+
       def initialize(argv)
         arg = argv.shift_argument
         @names = arg.split(',') if arg
         @install = argv.flag?('install', true)
+        @platform = argv.option('platform', DEFAULT_PLATFORM_NAME).to_sym
+        @platform_version = argv.option('platform_version', Playgrounds.default_version_for_platform(@platform))
         super
       end
 
@@ -29,7 +42,7 @@ def validate!
 
       def run
         # TODO: Pass platform and deployment target from configuration
-        generator = WorkspaceGenerator.new(@names)
+        generator = WorkspaceGenerator.new(@names, :cocoapods, @platform, @platform_version)
         generator.generate(@install)
       end
     end