class String

  # Converts a string to camelcase. This method leaves the first character
  # as given. This allows other methods to be used first, such as #uppercase
  # and #lowercase.
  #
  #   "camel_case".camelcase          #=> "camelCase"
  #   "Camel_case".camelcase          #=> "CamelCase"
  #
  # Custom +separators+ can be used to specify the patterns used to determine
  # where capitalization should occur. By default these are underscores (`_`)
  # and space characters (`\s`).
  #
  #   "camel/case".camelcase('/')     #=> "camelCase"
  #
  # If the first separator is a symbol, either `:lower` or `:upper`, then
  # the first characters of the string will be downcased or upcased respectively.
  #
  #   "camel_case".camelcase(:upper)  #=> "CamelCase"
  #
  # Note that this implementation is different from ActiveSupport's.
  # If that is what you are looking for you may want {#modulize}.
  #
  def camelcase(*separators)
    case separators.first
    when Symbol, TrueClass, FalseClass, NilClass
      first_letter = separators.shift
    end

    separators = ['_', '\s'] if separators.empty?

    str = self.dup

    separators.each do |s|
      str = str.gsub(/(?:#{s}+)([a-z])/){ $1.upcase }
    end

    case first_letter
    when :upper, true
      str = str.gsub(/(\A|\s)([a-z])/){ $1 + $2.upcase }
    when :lower, false
      str = str.gsub(/(\A|\s)([A-Z])/){ $1 + $2.downcase }
    end

    str
  end

  # Same as +#camelcase+ but converts first letter to uppercase.
  #
  #   "camel_case".upper_camelcase   #=> "CamelCase"
  #   "Camel_case".upper_camelcase   #=> "CamelCase"
  #
  # @deprecated
  #   Use `#camelcase(:upper)` instead.
  #
  def upper_camelcase(*separators)
    camelcase(:upper, *separators)
  end

  # Same as +#camelcase+ but converts first letter to lowercase.
  #
  #   "camel_case".lower_camelcase   #=> "camelCase"
  #   "Camel_case".lower_camelcase   #=> "camelCase"
  #
  # @deprecated
  #   Use `#camelcase(:lower)` instead.
  #
  def lower_camelcase(*separators)
    camelcase(:lower, *separators)
  end

end