parking-lot-sim.rb

# A Parking Lot Simulation by Brandon Bayer
#
# To run the simulation:
#   Create a Lot object and a Car object
#     - lot = ParkingLot.new
#     - car = Car.new
#
#   Use the following Car methods
#     - Car#get_ticket(Lot)
#     - Car#enter(Lot)
#     - Car#return_ticket
#     - Car#pay(cost)
#     - Car#exit
#
# NOTE: You must use the Car methods to cause the car
#       to interact with the parking lot. If you directly
#       call the parking lot methods, the simulation may not work correctly
#
# NOTE 2: The simulation will not work correctly if you pass
#         unexpected arguments to the methods (there is no argument verification)

require 'time'

# Parking lots!
class ParkingLot
  attr_reader :number_of_spaces
  attr_reader :available_spaces

  def initialize(number_of_spaces = 10)
    @number_of_spaces = number_of_spaces
    @hourly_rate = 5  # dollars
    @amount_owed = 0
    @available_spaces = @number_of_spaces
  end

  # Get a ticket from the lot. Returns a ticket if open spots
  def get_ticket
    if @available_spaces == 0
      p "Sorry, there is currently no room in this parking lot."
      nil
    else
      Ticket.new
    end
  end

  # Return a ticket to the lot. Reports elasped time and cost
  def return_ticket(ticket)
    elapsed_hours = (Time.now - ticket.timestamp)/600
    p "Your total time in the parking lot is #{elapsed_hours.round(2)} hours"
    @amount_owed = calculate_cost(@hourly_rate, elapsed_hours)
    true
  end

  # Calculate the parking fee based on elasped time
  def calculate_cost(hourly_rate, elapsed_hours)
    if elapsed_hours < 1
      p "This is your lucky day, you don't have to pay!"
    else
      cost = (elapsed_hours * hourly_rate).floor
      p "Your parking fee is $#{cost}"
    end
    cost ||= 0
  end

  # Accept payment and return any change
  def pay(paid)
    # Make sure they owe something
    if @amount_owed == 0
      p "Well, thanks for the offer, but you don't owe anything!"
      return paid
    end

    remaining_balance = @amount_owed - paid

    if remaining_balance == 0
      @amount_owed = 0
      p "Thank you! Have a phenomonal day!"
      true
    elsif remaining_balance > 0
      @amount_owed = remaining_balance
      p "Thank you, but you still owe $#{remaining_balance}"
      false
    elsif remaining_balance < 0
      @amount_owed = 0
      p "Thank you! Your change is $#{-remaining_balance}."
      p "Have an outstanding day!"
      remaining_balance *= -1 # Return the change
    end
  end

  # Lets a car into the parking lot
  def enter(car)
    if @available_spaces == 0
      p "Oops, sorry, there is currently no more room in this lot"
      return false
    elsif car.ticket.nil?
      p "Hey, not so fast! You must first take a ticket"
      return false
    end

    @available_spaces -= 1
    p "You've entered the lot, please stay as long as you like!!"
    true
  end

  # Lets a car out of the parking lot as long as they have paid
  def exit(car)
    if car.ticket && @amount_owed > 0
      p "Whoa there, buddy! You must pay before leaving!"
      return false
    end

    @available_spaces += 1
    p "You have exited the lot. Please come back soon!"
    true
  end
end


# Cars!
class Car
  attr_accessor :ticket
  @in_parking_lot = false

  # Attempts to enter a lot, returns the outcome
  def enter(lot)
    @lot = lot
    if @in_parking_lot
      p "Are you serious? You are already in the lot"
      return false
    end

    if success = @lot.enter(self)
      @in_parking_lot = true
    end
    success
  end

  # Attempts to exit a lot, returns the outcome
  def exit
    if !@in_parking_lot
      p "Are you crazy? You can't exit before you enter!"
      return false
    end

    if @lot.exit(self)
      @in_parking_lot = false
      return true
    end
    false
  end

  # Attempts to get a ticket, returns the ticket or false
  def get_ticket(lot)
    @lot = lot
    if @in_parking_lot
      p "Um, sir, you already have a ticket!"
      return false
    end

    @ticket = @lot.get_ticket
  end

  # Attempts to return a ticket
  def return_ticket
    if @ticket.nil? && !@in_parking_lot
      p "Hello? What do you think you are trying to do?"
      return false
    end

    @lot.return_ticket(@ticket)
    @ticket = nil
    true
  end

  # Pays the specified amount to the lot, returns success or change
  def pay(amount)
    @lot.pay(amount)
  end
end


# Tickets!
class Ticket
  attr_reader :timestamp

  def initialize
    @timestamp = Time.now
    p "Thank you! Your entry time is #{@time}"
  end
end