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.

Create a folder called command. Inside this 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: 24-Feb-2016
# Authors:
#          A00456654 Thursday Rubinstein 
#          A01160611 Anthony Stark
```

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

A remote control

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.

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

Deliverables

Create a compressed tarball file with the full contents of the command directory. 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

✔ Upload Instructions

To deliver the command.tgz file, please provide the following information:

Request PIN

Due date is Wednesday, February 24.

S/W Design and Architecture

Command Pattern

Objectives

Activity Description

Deliverables

✔ Upload Instructions