test_user_buffer.rb

# Requirements: Pass the unit tests at the bottom (in a non-trivial
# way) and be cleanly translatable to Java. That means no block and
# yield magic allowed nor setting values in the condition statements
# of loops.

require 'test/unit'

class UserBuffer
    def initialize(arr)
      @file = arr
      @last_values = {}
    end

    def read_user
      if @last_values.empty?
        user_id,item_id,value = get_split_line

      else
        user_id, item_id, value = @last_values[:user_id], @last_values[:item_id], @last_values[:value]
      end

      output_user_id = user_id

      ratings = {}

      while true
        if user_id == output_user_id && !(output_user_id.nil? && user_id.nil?)
          ratings[item_id] = value
          user_id, item_id, value = get_split_line
        else
          if !user_id.nil?
            @last_values = {:user_id => user_id, :item_id => item_id, :value => value}
          else
            @last_values = {}
          end
          break
        end
      end

      if output_user_id
        {
          :user_id => output_user_id,
          :ratings => ratings
        }
      end
    end

    def get_split_line
      foo = @file.shift
      if foo
        foo.split(" ")
      else
        [nil,nil,nil]
      end
    end
  end
  
class TestCase < Test::Unit::TestCase
  

  def test_reads_one_line_file
    file = ["1 2 3"]
    b = UserBuffer.new(file)
    h = b.read_user
    assert_equal '1', h[:user_id]
    assert_equal({'2' => '3'}, h[:ratings])
  end

  def test_reads_two_lines_one_user
    file = ['1 2 3', '1 3 4']
    b = UserBuffer.new(file)
    h = b.read_user
    assert_equal '1', h[:user_id]
    assert_equal '3', h[:ratings]['2']
    assert_equal '4', h[:ratings]['3']
  end

  def test_two_lines_two_users
    file = ['1 2 3', '2 3 4']
    b = UserBuffer.new(file)
    h = b.read_user
    assert_equal '1', h[:user_id], "first user id"
    assert_equal '3', h[:ratings]['2'], "rating value for first user is 3"
    assert_equal 1, h[:ratings].size, "only one rating for first user"

    h = b.read_user
    assert_equal '2', h[:user_id], 'second user id'
    assert_equal '4', h[:ratings]['3'], 'rating value for second user is 4'
    assert_equal 1, h[:ratings].size, 'only one rating for second user'
  end

  def test_one_line_file_three_reads
    file = ['1 2 3']
    b = UserBuffer.new(file)
    assert_not_nil b.read_user
    assert_nil b.read_user
    assert_nil b.read_user
  end

  def test_three_two_users_two_ratings_at_end
    file = ['1 2 3', '2 3 4', '2 2 1']
    b = UserBuffer.new(file)
    b.read_user
    h = b.read_user
    assert_equal '2', h[:user_id], 'second user id'
    assert_equal '4', h[:ratings]['3'], 'rating for 4'
    assert_equal '1', h[:ratings]['2'], 'rating for 2'
    assert_equal 2, h[:ratings].size, 'two ratings'

    assert_nil b.read_user
  end

  def test_longer
    file = ['1 2 3', '1 7 8', '1 9 3', '1 10 11', '2 4 3', '2 3 3', '3 9 2', '3 10 2', '3 4 2']
    b = UserBuffer.new(file)
    h = b.read_user
    assert_equal 4, h[:ratings].size
    assert_equal '1', h[:user_id]

    h = b.read_user
    assert_equal 2, h[:ratings].size
    assert_equal '2', h[:user_id]

    h = b.read_user
    assert_equal 3, h[:ratings].size
    assert_equal '3', h[:user_id]

    h = b.read_user
    assert_nil h
  end
end