# Ruby version 2.5.0
# RSPEC version 3.8
#   Running the tests in a console: rspec theorem.rb

# #flatten_array is a recursive method that takes in an array of arbitrary
# nesting elements and returns a flattened array.
#
# Parameters:
#   arr:Array The array to flatten
#   result:Array The flattened array
module Theorem
  def self.flatten_array(arr, result = [])
    # return arr if the array is empty or not
    # an array.
    return arr if arr.empty? || !arr.is_a?(Array)

    # Iterate over each item in the array
    arr.each do |a|
      if a.class != Array
        # If it isn't an array then we append the 
        # value to the result
        result << a
      else
        # If it is an array then we call the 
        # flatten_array method recursively to
        # perform the same process
        self.flatten_array(a, result)
      end
    end

    result
  end
end

describe Theorem do
  it 'should returned a flattened array' do
    result = Theorem.flatten_array [1,[2,3],4,[5,[6,7]],8,[9,[10]]]

    expect(result[0]).to eq 1
    expect(result[9]).to eq 10
  end

  it 'should return a flattened array even if an element is empty' do
    result = Theorem.flatten_array [1,[2,3],4,[],5]

    expect(result[0]).to eq 1
    expect(result[4]).to eq 5
  end

  it 'should return arr parameter value if arr is empty' do
    result = Theorem.flatten_array []

    expect(result.class).to eq Array
  end

  it 'should returned arr parameter value if arr is not not an array' do
    result = Theorem.flatten_array "This is a string"

    expect(result).to eq "This is a string"
  end
end