First Pass at Transactions

database.rb

class Database
  def initialize
    @count_versions = [Hash.new(0)]
    @db_versions = [Hash.new()]
  end

  # CRUD COMMANDS

  def set(key, value)
    @db_versions[-1][key] = value
    @count_versions[-1][value] += 1
    puts "Current state of database: #{@db_versions.inspect}"

    return nil
  end

  def get(key)
    puts "Current state of database: #{@db_versions.inspect}"
    @db_versions[-1].fetch(key, "NULL")
  end

  def count(value)
    @count_versions[-1].fetch(value, 0)
  end

  #TRANSACTION MANAGEMENT

  def begin()
    @db_versions.push(Hash.new())
    @count_versions.push(Hash.new(0))
    puts "Current state of database: #{@db_versions.inspect}"

    return nil
  end

  def rollback()
    if @db_versions.length == 1
      return "No transaction in progress"
    end
    
    @db_versions.pop
    @count_versions.pop
    puts "Current state of database: #{@db_versions.inspect}"

    return nil
  end

  def commit()
    if @db_versions.length == 1
      return "No transaction in progress"
    end

    @db_versions[-2] = @db_versions[-2].merge(@db_versions[-1])
    @count_versions[-2] = @count_versions[-2].merge(@count_versions[-1])
    @db_versions.pop
    @count_versions.pop
    puts "Current state of database: #{@db_versions.inspect}"

    return nil
  end
end