fake_redis.rb

class FakeRedis
  attr_reader :counts, :vars

  def initialize(counts: {}, vars: {})
    @counts = counts
    @vars = vars
  end

  def set(var, val)
    @vars[var] = val
    
    if @counts[val]
        @counts[val] = @counts[val] + 1
    else
        @counts[val] = 1
    end  
  end

  def get(var)
    if @vars[var]
        puts @vars[var]
    else
        puts "NULL"
    end
  end

  def unset(var)
    val = @vars[var]
    @vars.delete(var)
    
    @counts[val] = @counts[val] - 1 if val
  end

  def numequal_to(val)
    puts @counts[val] || 0
  end
end

transactions = []
base_pr = FakeRedis.new
current_pr = base_pr

while true do
  comm = STDIN.gets
  args = comm.split(" ")

  case args[0]
  when "SET"
    current_pr.set(args[1], args[2])
  when "GET"
    current_pr.get(args[1])
  when "UNSET"
    current_pr.unset(args[1])
  when "NUMEQUALTO"
    current_pr.numequal_to(args[1])
  when "END"
    exit
  when "BEGIN"
    new_pr = FakeRedis.new(
        counts: current_pr.counts.dup,
        vars: current_pr.vars.dup
    )

    transactions << new_pr
    current_pr = new_pr
  when "ROLLBACK"
    if transactions.empty?
        puts "NO TRANSACTION"
    elsif transactions.length == 1
        transactions.pop
        current_pr = base_pr
    else
        transactions.pop
        current_pr = transactions.last
    end
  when "COMMIT"
    if transactions.empty?
        puts "NO TRANSACTION"
    else
        current_pr = transactions.last
        base_pr = current_pr
        transactions = []
    end
  else
    p "Failed with args #{args}"
  end
end