Railslove Ruby programming exercise A1

filter.rb

# Railslove Ruby programming exercise A1
#
# To run the following exercise you need to have rspec installed.
# Then watch the output of `rspec filter.rb` and see 3 of 4 failing specs.
#
# The task is to filter a given collection (L#31) for entries that contain unique pairs.
# While filtering return the same structure and keep the ranking.
#
# Write code in the body of the filter method to make the tests pass.
#
# Refactor until you're happy with your solution, by asking the follwing questions:
#   * Is the code understandable/maintainable?
#   * Do I really need all these if/else/elsif statements?
#
require 'ostruct'

class Collection < OpenStruct
  def filter(a = nil, b = nil)
    #
    # your code goes here
    #
    collection
  end
end


# don't touch me
require 'rspec'
RSpec.describe 'Collection' do
  let(:all) do
    [
      { 1 => %w(A B) },
      { 2 => %w(A C) },
      { 3 => %w(D E) },
      { 4 => %w(F G) },
      { 5 => %w(E A) },
      { 6 => %w(C H) },
      { 7 => %w(D B) }
    ]
  end

  subject(:collection) { Collection.new(collection: all) }

  describe '#filter' do
    it 'does not filter with empty params' do
      expect(subject.filter).to eq(all)
    end

    it 'filters one result' do
      expect(subject.filter('H')).to eq([{ 6 => %w(C H) }])
    end

    it 'filters many results' do
      expect(subject.filter('A')).to eq([{ 1 => %w(A B) }, { 2 => %w(A C) }, { 5 => %w(E A) }])
    end

    it 'filters with 2 parameters' do
      expect(subject.filter('A', 'C')).to eq([{ 2 => %w(A C) }])
    end

    it 'filters order independent' do
      expect(subject.filter('C', 'A')).to eq([{ 2 => %w(A C) }])
    end
  end
end