chapter_7.rb

# Pg 145 & 146 (book) diagrams are helpful
# 

############## Page 148 ##############
class Schedule
  def scheduled?(schedulable, start_date, end_date)
    puts "This #{schedulable.class} " +
         "is not scheduled\n" +
         "  between #{start_date} and #{end_date}"
    false
  end
end

############## Page 149 ##############
class Bicycle
  attr_reader :schedule, :size, :chain, :tire_size

  # Inject the Schedule and provide a default
  def initialize(args={})
    @schedule = args[:schedule] || Schedule.new
    # ...
  end

  # Return true if this bicycle is available
  # during this (now Bicycle specific) interval.
  def schedulable?(start_date, end_date)
    !scheduled?(start_date - lead_days, end_date)
  end

  # Return the schedule's answer
  def scheduled?(start_date, end_date)
    schedule.scheduled?(self, start_date, end_date)
  end

  # Return the number of lead_days before a bicycle
  # can be scheduled.
  def lead_days
    1
  end

  # ...
end

require 'date'
starting = Date.parse("2015/09/04")
ending   = Date.parse("2015/09/10")

b = Bicycle.new
b.schedulable?(starting, ending)
# This Bicycle is not scheduled
#   between 2015-09-03 and 2015-09-10
#  => true

############## Page 150 ##############
module Schedulable
  attr_writer :schedule

  def schedule
    @schedule ||= ::Schedule.new
  end

  def schedulable?(start_date, end_date)
    !scheduled?(start_date - lead_days, end_date)
  end

  def scheduled?(start_date, end_date)
    schedule.scheduled?(self, start_date, end_date)
  end

  # includers may override
  def lead_days
    0
  end

end

############## Page 151 ##############
class Bicycle
  include Schedulable

  def lead_days
    1
  end

  # ...
end

require 'date'
starting = Date.parse("2015/09/04")
ending   = Date.parse("2015/09/10")

b = Bicycle.new
b.schedulable?(starting, ending)
# This Bicycle is not scheduled
#    between 2015-09-03 and 2015-09-10
#  => true

############## Page 152 ##############
class Vehicle
  include Schedulable

  def lead_days
    3
  end

  # ...
end

class Mechanic
  include Schedulable

  def lead_days
    4
  end

  # ...
end

v = Vehicle.new
v.schedulable?(starting, ending)
# This Vehicle is not scheduled
#   between 2015-09-01 and 2015-09-10
#  => true

m = Mechanic.new
m.schedulable?(starting, ending)
# This Mechanic is not scheduled
#   between 2015-08-31 and 2015-09-10
#  => true

##
# Liskov Substitution Principle (LSP)
## In plain English: In order for a type system to be sane, 
## sub-types must be substitutable for their supertypes. 
# Template method pattern:
## This pattern is what allows you to seperate the abstract
## from the concrete. The abstract code defines the algorithms
## and the concrete inheritors of that abstraction contribute.
# Shallow, narrow hierarchies are easy to understand. Shallow,
## wide are more complicated, but still understandable. Deep
##  hierarchies are difficult to understand and to maintain.