Command Pattern

Objectives

During this activity:

• Students will write and test Ruby code that implements the Command pattern.

This activity helps students develop the following skills, values and attitudes: ability to analyze and synthesize, capacity for identifying and solving problems, and efficient use of computer systems.

Activity Description

This activity can be developed individually or in pairs.

This example was taken from [FREEMAN] pp. 191-223.

1. Create a directory called command and a subdirectory src within it. Inside the src folder create two files called: control.rb, and control_test.rb.

   Both Ruby source files must start with a comment containing title, date, and the authors' personal information. For example:

   # Command Pattern
   # Date: 20-Sep-2017
   # Authors:
   #          A00456654 Thursday Rubinstein 
   #          A01160611 Anthony Stark
   

2. You are required to write part of the software for the control remote shown in the following image, using the Command pattern.

   

   You are given the following Ruby code. Place it in the control.rb source file and study it carefully.

   # File: control.rb
   
   class RemoteControlWithUndo
   
     def initialize
       @on_commands = []
       @off_commands = []
       no_command = NoCommand.new
       7.times do
         @on_commands << no_command
         @off_commands << no_command
       end
       @undo_command = no_command
     end
   
     def set_command(slot, on_command, off_command)
       @on_commands[slot] = on_command
       @off_commands[slot] = off_command
     end
   
     def on_button_was_pushed(slot)
       @on_commands[slot].execute
       @undo_command = @on_commands[slot]
     end
   
     def off_button_was_pushed(slot)
       @off_commands[slot].execute
       @undo_command = @off_commands[slot]
     end
   
     def undo_button_was_pushed()
       @undo_command.undo
     end
   
     def inspect
       string_buff = ["\n------ Remote Control -------\n"]
       @on_commands.zip(@off_commands) \
           .each_with_index do |commands, i|
         on_command, off_command = commands
         string_buff << \
         "[slot #{i}] #{on_command.class}  " \
           "#{off_command.class}\n"
       end
       string_buff << "[undo] #{@undo_command.class}\n"
       string_buff.join
     end
   
   end
   
   class NoCommand
   
     def execute
     end
   
     def undo
     end
   
   end
   
   class Light
   
     attr_reader :level
   
     def initialize(location)
       @location = location
       @level = 0
     end
   
     def on
       @level = 100
       puts "Light is on"
     end
   
     def off
       @level = 0
       puts "Light is off"
     end
   
     def dim(level)
       @level = level
       if level == 0
         off
       else
         puts "Light is dimmed to #{@level}%"
       end
     end
   
   end
   
   class CeilingFan
   
     # Access these constants from outside this class as
     # CeilingFan::HIGH, CeilingFan::MEDIUM, and so on.
     HIGH   = 3
     MEDIUM = 2
     LOW    = 1
     OFF    = 0
   
     attr_reader :speed
   
     def initialize (location)
       @location = location
       @speed = OFF
     end
   
     def high
       @speed = HIGH;
       puts "#{@location} ceiling fan is on high"
     end
   
     def medium
       @speed = MEDIUM
       puts "#{@location} ceiling fan is on medium"
     end
   
     def low
       @speed = LOW
       puts "#{@location} ceiling fan is on low"
     end
   
     def off
       @speed = OFF
       puts "#{@location} ceiling fan is off"
     end
   
   end
   

   Write the following command classes placing them in the control.rb source file: LightOnCommand, LightOffCommand, CeilingFanHighCommand, CeilingFanMediumCommand, and CeilingFanOffCommand. All these classes should have these three methods: initialize, execute and undo. Check the unit tests in the next step to understand the expected behavior of each method.

3. The following unit tests verify the correct behavior of your classes. Place the test class in the control_test.rb source file.

   # File: control_test.rb
   
   require 'minitest/autorun'
   require 'stringio'
   require 'control'
   
   class ControlTest < Minitest::Test
   
     def setup
       set_stdout
       @rc = RemoteControlWithUndo.new
       set_light
       set_fan
     end
   
     def teardown
       reset_stdout
     end
   
     def set_stdout
       @out = StringIO.new
       @old_stdout = $stdout
       $stdout = @out
     end
   
     def reset_stdout
       $stdout = @old_stdout
     end
   
     def set_light
       light = Light.new("Living Room")
       light_on = LightOnCommand.new(light)
       light_off = LightOffCommand.new(light)
       @rc.set_command(0, light_on, light_off)
     end
   
     def set_fan
       fan = CeilingFan.new("Living Room")
       fan_medium = CeilingFanMediumCommand.new(fan)
       fan_high = CeilingFanHighCommand.new(fan)
       fan_off = CeilingFanOffCommand.new(fan)
       @rc.set_command(1, fan_medium, fan_off)
       @rc.set_command(2, fan_high, fan_off)
     end
   
     def test_light
       @rc.on_button_was_pushed(0)
       @rc.off_button_was_pushed(0)
       p @rc
       @rc.undo_button_was_pushed
       @rc.off_button_was_pushed(0)
       @rc.on_button_was_pushed(0)
       p @rc
       @rc.undo_button_was_pushed
       assert_equal                                                 \
         "Light is on\n"                                            \
         "Light is off\n"                                           \
         "\n------ Remote Control -------\n"                        \
         "[slot 0] LightOnCommand  LightOffCommand\n"               \
         "[slot 1] CeilingFanMediumCommand  CeilingFanOffCommand\n" \
         "[slot 2] CeilingFanHighCommand  CeilingFanOffCommand\n"   \
         "[slot 3] NoCommand  NoCommand\n"                          \
         "[slot 4] NoCommand  NoCommand\n"                          \
         "[slot 5] NoCommand  NoCommand\n"                          \
         "[slot 6] NoCommand  NoCommand\n"                          \
         "[undo] LightOffCommand\n\n"                               \
         "Light is on\n"                                            \
         "Light is off\n"                                           \
         "Light is on\n"                                            \
         "\n------ Remote Control -------\n"                        \
         "[slot 0] LightOnCommand  LightOffCommand\n"               \
         "[slot 1] CeilingFanMediumCommand  CeilingFanOffCommand\n" \
         "[slot 2] CeilingFanHighCommand  CeilingFanOffCommand\n"   \
         "[slot 3] NoCommand  NoCommand\n"                          \
         "[slot 4] NoCommand  NoCommand\n"                          \
         "[slot 5] NoCommand  NoCommand\n"                          \
         "[slot 6] NoCommand  NoCommand\n"                          \
         "[undo] LightOnCommand\n\n"                                \
         "Light is off\n", @out.string
     end
   
     def test_fan
       @rc.on_button_was_pushed(1)
       @rc.off_button_was_pushed(1)
       p @rc
       @rc.undo_button_was_pushed
       @rc.on_button_was_pushed(2)
       p @rc
       @rc.undo_button_was_pushed
       assert_equal                                                 \
         "Living Room ceiling fan is on medium\n"                   \
         "Living Room ceiling fan is off\n"                         \
         "\n------ Remote Control -------\n"                        \
         "[slot 0] LightOnCommand  LightOffCommand\n"               \
         "[slot 1] CeilingFanMediumCommand  CeilingFanOffCommand\n" \
         "[slot 2] CeilingFanHighCommand  CeilingFanOffCommand\n"   \
         "[slot 3] NoCommand  NoCommand\n"                          \
         "[slot 4] NoCommand  NoCommand\n"                          \
         "[slot 5] NoCommand  NoCommand\n"                          \
         "[slot 6] NoCommand  NoCommand\n"                          \
         "[undo] CeilingFanOffCommand\n\n"                          \
         "Living Room ceiling fan is on medium\n"                   \
         "Living Room ceiling fan is on high\n"                     \
         "\n------ Remote Control -------\n"                        \
         "[slot 0] LightOnCommand  LightOffCommand\n"               \
         "[slot 1] CeilingFanMediumCommand  CeilingFanOffCommand\n" \
         "[slot 2] CeilingFanHighCommand  CeilingFanOffCommand\n"   \
         "[slot 3] NoCommand  NoCommand\n"                          \
         "[slot 4] NoCommand  NoCommand\n"                          \
         "[slot 5] NoCommand  NoCommand\n"                          \
         "[slot 6] NoCommand  NoCommand\n"                          \
         "[undo] CeilingFanHighCommand\n\n"                         \
         "Living Room ceiling fan is on medium\n", @out.string
     end
   
   end
   

4. Write and generate your program’s documentation as described in: Documenting Ruby Programs.

Deliverables

Create a compressed tarball file with the full contents of the command directory (including the generated HTML documentation in the doc subdirectory). Call this file command.tgz. From a terminal, you can use the following command to create this file (make sure to run it at the same level where the command folder resides):

tar czf command.tgz command

Only one team member needs to upload the file.

Due date is Wednesday, September 20.

Evaluation

This activity will be evaluated using the following criteria:

50%	Implementation of program requirements.
50%	Documentation.
1	The program and/or documentation was plagiarized.