find_callable.rb

class FindCallable
  class << self
    def call
      new.call
    end
  end

  INPUT = 'index_delicous_fruit_recipes_on_apple_id_and_banana_id_and_citron_id_and_durian_id'

  PASSTHROUGH = lambda do |string|
    string
  end

  DROP_VERB = lambda do |string|
    head, tail = string.split('_on_')

    _verb, *objects = head.split('_')

    [objects.join('_'), tail].join('_on_')
  end

  SHORTEN_PREPOSITION = lambda do |string|
    head, tail = string.split('_on_')

    prepositional_objects = tail.split('_and_').map do |object|
      object.
      split('_').
      map { |word| word[0] }.
      join('_')
    end.join('_and_')

    [head, prepositional_objects].join('_on_')
  end

  ALGORITHMS = [
    PASSTHROUGH,
    DROP_VERB,
    SHORTEN_PREPOSITION,
  ]

  def call
    [60, 80, 100].map do |max_length|
      # In practice one would just want the actually callable returned, but for
      # illustrative purposes it may helpful to more directly "see" which
      # callable will be used.
      process_index = ALGORITHMS.find_index do |a|
        a.call(INPUT).length <= max_length
      end

      {
        max_length: max_length,
        process_index: process_index,
        output: ALGORITHMS[process_index].call(INPUT),
      }
    end
  end
end