parsing / combination exercise

parse_brackets.rb

# Run using rspec parse_brackets.rb

# Uses array combination/permutation method from 
# http://trevoke.net/blog/2009/12/17/inter-array-permutations-in-ruby/

# Takes an array of arrays and returns permutations of them
# e.g., fancy_array_permutation[["one", "two"], ["three", "four"]]
#       returns: ["onethree", "onefour", "twothree", "twofour"]
def fancy_array_permutation array
  return array[0] if array.size == 1
  first = array.shift
  return first.product( fancy_array_permutation(array) ).map {|x| x.flatten.join}
end

def parse(name)
  curr_token = ""
  tokens = [] # Array of token option arrays.
  
  name.each_char do |char| # Each character...
    if char == '['
      tokens << [curr_token] unless curr_token.empty?
      curr_token = ""
    elsif char == ']'
      tokens << [curr_token, ""]
      curr_token = ""
    else
      curr_token << char
    end
  end
  
  tokens << [curr_token] unless curr_token.empty? # Process last word
  
  fancy_array_permutation tokens # Return combinations of words
end

describe "parse" do 

  it 'should list all permutations, text in brackets is optional' do
    strings = parse('foo[bar]')
    strings.should include('foo')
    strings.should include('foobar')
    strings.should_not include('bar')
    strings.size.should == 2
  end
  
  it 'should list all permutations, text in brackets is optional' do
    strings = parse('[foo]bar[baz]')
    strings.should include('foobar')
    strings.should include('bar')
    strings.should include('barbaz')
    strings.should include('foobarbaz')
    strings.should_not include('foo')
    strings.should_not include('baz')
    strings.size.should == 4
  end

  it 'should list all permutations, text in brackets is optional' do
    strings = parse('[foo][bar][baz]')
    strings.should include('foobarbaz')
    strings.should include('foobar')
    strings.should include('foobaz')
    strings.should include('barbaz')
    strings.should include('foo')
    strings.should include('bar')
    strings.should include('baz')
    strings.should include('')
    strings.size.should == 8 # or 7, if "" is not a valid permutation
  end

end