fake_enumerable.rb

module FakeEnumerable
  def map
    res = []
    each do |item|
      res << yield(item)
    end
    res
  end

  def select
    res = []
    each do |item|
      res << item if yield(item)
    end
    res
  end

  def sort_by(&block)
    temp_array = []
    each do |item|
      temp_array << [item, yield(item)]
    end
    temp_array.sort_by { |x, y| y }.map { |x, y| x }
  end

  def reduce(*args, &block)
    initial_given = false
    sym_given = false

    acc, sym = case args.size
    when 0
      raise LocalJumpError unless block_given?
      [nil, nil]
    when 1
      if block_given?
        initial_given = true
        [args.first, nil]
      else
        sym_given = true
        [nil, args.first]
      end
    when 2
      initial_given = true
      sym_given = true
      args
    end

    transformation = ->(acc, elt) { acc.send(sym, elt) } if sym_given

    first_pass = true
    each do |item|
      acc = 
        if first_pass && !initial_given
          item
        else
          if sym_given
            transformation.call(acc, item)
          else
            yield(acc, item)
          end
        end

      first_pass = false
    end

    acc
  end
end