commands/box: Introduce a StateFile for keeping track of downloaded boxes

plugins/commands/box/command/add.rb

@@ -40,6 +40,7 @@ module VagrantPlugins
             :box_url      => argv[1],
             :box_force    => options[:force],
             :box_download_insecure => options[:insecure],
+            :box_state_file => StateFile.new(@env.home_path.join('boxes.json'))
           })
 
           # Success, exit status 0

plugins/commands/box/plugin.rb

@@ -11,5 +11,7 @@ module VagrantPlugins
         Command::Root
       end
     end
+
+    autoload :StateFile, File.expand_path("../state_file", __FILE__)
   end
 end

plugins/commands/box/state_file.rb

@@ -0,0 +1,39 @@
+require "json"
+
+module VagrantPlugins
+  module CommandBox
+    # This is a helper to deal with the boxes state file that Vagrant
+    # uses to track the boxes that have been downloaded.
+    class StateFile
+      def initialize(path)
+        @path = path
+
+        @data = {}
+        @data = JSON.parse(@path.read) if @path.exist?
+        @data["boxes"] ||= {}
+      end
+
+      # Add a downloaded box to the state file.
+      #
+      # @param [Box] box The Box object that was added
+      # @param [String] url The URL from where the box was downloaded
+      def add_box(box, url)
+        box_key = "#{box.name}-#{box.provider}"
+
+        @data["boxes"][box_key] = {
+          "url"           => url,
+          "downloaded_at" => Time.now.utc.to_s
+        }
+
+        save!
+      end
+
+      # This saves the state back into the state file.
+      def save!
+        @path.open("w+") do |f|
+          f.write(JSON.dump(@data))
+        end
+      end
+    end
+  end
+end