alialsahaf.rb

class Polynomial
  attr_accessor :polynomial
  def initialize(polynomial)
    raise ArgumentError, 'Need at least 2 coefficients' if polynomial.size < 2
    @polynomial = polynomial.reverse
  end

  def to_s
    join(terms)
  end

  private

  # returns an array that contains the terms of the polynomial
  def terms
    degree = @polynomial.size - 1
    exponent = degree
    terms = []
    degree.downto 0 do |position|
      terms << term_at(position , exponent)
      exponent -= 1
    end
    return terms
  end

  # returns a string that contains the polynomial in a pretty format
  def join(terms)
    # checking if all the terms are zeros to display it as '0'
    all_zeros = terms.all? {|coefficient| coefficient == '0'}
    if all_zeros
      '0'
    else
      # delete all terms with 0 as coefficient as away to omitting them form being displayed
      terms.delete '0'
      # joining all terms by '+' sign then omitting '+' sign in '+-' like in '+-10x' => '-10x'
      terms.join('+').gsub(/\+\-/ , '-')
    end
  end

  # making sure that the coefficients '1x' and '-1x' displayed as 'x' and '-x'
  def pretty(coefficient)
    if coefficient == '1'
      ''
    elsif coefficient == '-1'
      '-'
    else
      coefficient
    end
  end

  # returns a string that contains the term in pretty format
  def term_at(position, exponent)
    coefficient = @polynomial[position].to_s
    # returning '1' instead of '1x^0'
    if position == 0
      coefficient
    # returning '0' instead of '0x^2'
    elsif coefficient == '0'
      '0'
    # returning '10x' if the exponent is 1 or '10x^2'
    else
      exponent == 1 ? "#{pretty coefficient}x" : "#{pretty coefficient}x^#{exponent}"
    end
  end

end