server_name_spec.rb

require 'rspec'

def next_server_number(server_numbers)
  server_numbers.sort.each.with_index do |s, i|
    return i+1 if s > i+1
  end
  return server_numbers.count + 1
end

describe 'next_server_number' do
  it 'returns 2 for [5, 3, 1]' do
    expect(next_server_number([5, 3, 1])).to eql 2
  end

  it 'returns 4 for [5, 3, 2, 1]' do
    expect(next_server_number([5, 3, 2, 1])).to eql 4
  end

  it 'returns 4 for [3, 2, 1]' do
    expect(next_server_number([3, 2, 1])).to eql 4
  end

  it 'returns 1 for []' do
    expect(next_server_number([])).to eql 1
  end
end


class ServerAllocator
  class << self
    attr_reader :server_types
    def allocate(name)
      sa = get(name)
      sa.get_next_server
    end

    def deallocate(server_name)
      name = server_name.match(/[a-z]+/)[0]
      number = server_name.match(/[0-9]+/)[0].to_i
      sa = get(name)
      sa.remove(number)
    end

    def get(name)
      @server_types ||= {}
      @server_types[name] ||= ServerAllocator.new(name)
    end

    def clear
      @server_types = {}
    end
  end

  attr_reader :server_numbers

  def initialize(name)
    @server_numbers = []
    @name = name;
  end

  def next_server_number
    @server_numbers.sort.each.with_index do |s, i|
      return i+1 if s > i+1
    end
    return @server_numbers.count + 1
  end

  def remove(number)
    @server_numbers.delete(number)

    true
  end

  def allocated?(number)
    @server_numbers.include?(number)
  end

  def get_next_server
    num = next_server_number
    @server_numbers << num
    "#{@name}#{num}"
  end

end

describe ServerAllocator do
  context '.allocate' do
    before(:each) do
      ServerAllocator.clear
    end
    it 'allocates based on one name one time properly' do
      expect(ServerAllocator.allocate('first')).to eql 'first1'
    end

    it 'allocates based on one name multiple times properly' do
      expect(ServerAllocator.allocate('first')).to eql 'first1'
      expect(ServerAllocator.allocate('first')).to eql 'first2'
    end

    it 'allocates based on multiple names multiple times properly' do
      expect(ServerAllocator.allocate('first')).to eql 'first1'
      expect(ServerAllocator.allocate('first')).to eql 'first2'
      expect(ServerAllocator.allocate('second')).to eql 'second1'
      expect(ServerAllocator.allocate('second')).to eql 'second2'
    end
  end

  context '.deallocate' do

    before(:each) do
      ServerAllocator.clear
    end
    it 'deallocates a just allocated item' do
      ServerAllocator.allocate('first')
      expect(ServerAllocator.get('first').allocated?(1)).to eql true

      ServerAllocator.deallocate('first1')
      expect(ServerAllocator.get('first').allocated?(1)).to eql false
    end
  end

  it 'deallocates and allocates properly' do
    ServerAllocator.allocate('first')
    ServerAllocator.allocate('first')
    ServerAllocator.allocate('first')
    ServerAllocator.allocate('first')

    ServerAllocator.deallocate('first2')
    expect(ServerAllocator.get('first').allocated?(2)).to eql false
    expect(ServerAllocator.allocate('first')).to eql 'first2'
    expect(ServerAllocator.allocate('first')).to eql 'first5'
  end
end