strategy tutorial

strategy.rb

class BaseContext
  attr_accessor :strategy

  def initialize(strategy)
    @strategy = strategy
  end

  def execute(*args)
    @strategy.new.execute(*args).round(2)
  end
end

class AverageStrategy
  def execute(grades)
    grades.sum(0.0) / grades.size
  end
end

class WeightedStrategy
  WEIGHTS = [0.1, 0.1, 0.2, 0.3, 0.3]

  def execute(grades)
    [grades, WEIGHTS].transpose.map { |weight_and_grade| weight_and_grade.inject(:*) }.sum
  end
end

class AllButLowerStrategy
  def execute(grades)
    AverageStrategy.new.execute(grades.max(grades.size - 1))
  end
end

class HighestPairStrategy
  def execute(grades)
    AverageStrategy.new.execute(grades.max(2))
  end
end

rand_grades = ->(num_grades) { num_grades.times.map { (rand * 100).round(2) } }

dataset = {
  paul: rand_grades.call(5),
  duncan: rand_grades.call(5),
  leto: rand_grades.call(5),
  wang_miao: rand_grades.call(5),
  da_shi: rand_grades.call(5),
  luo_ji: rand_grades.call(5)
}

apply_strategy = ->(dataset, context) { dataset.to_h { |student, grades| [student, context.execute(grades)] } }

context = BaseContext.new(AverageStrategy)

strategies = [WeightedStrategy, AllButLowerStrategy, HighestPairStrategy]

answer_matrix = { "AverageStrategy" => apply_strategy.call(dataset, context) }

strategies.map do |next_strategy|
  context.strategy = next_strategy

  answer_matrix[next_strategy.to_s] = apply_strategy.call(dataset, context)
end

ap dataset
ap answer_matrix

answer_matrix.each do |strategy, data|
  ap "#{strategy} - Passing grades: #{data.select { |_student, grade| grade >= 60.0 }}"
end