sim.py

"""
Gas Station Refueling example

Covers:
- Resources: Resource
- Resources: Container
- Waiting for other processes

Scenario:
  An airport gas station has a limited number of gas pumps that share a common
  fuel reservoir. Planes randomly arrive at the gas station, request one
  of the fuel pumps and start refueling from that reservoir.

  A gas station control process observes the gas station's fuel level
  and calls a tank truck for refueling if the station's level drops
  below a threshold.
"""
import itertools
import random
import logging
import simpy
import pandas as pd

# Parameters
RANDOM_SEED = 42
STATION_TANK_SIZE = 700000              # Size of the gas station tank (liters)
THRESHOLD = 25                          # Station tank minimum level (% of full)
PLANE_TANK_SIZE = 150000                # Size of plane fuel tanks (liters)
PLANE_TANK_LEVEL = [30000, 100000]      # Min/max levels of plane fuel tanks (liters)
REFUELING_SPEED = 1600                  # Rate of refuelling plane fuel tank (liters / second)
TANK_TRUCK_TIME = 1000                  # Time it takes tank truck to arrive (seconds)
T_INTER = [4000, 8000]                  # Interval between plane arrivals [min, max] (seconds)
SIM_TIME = 1000000                      # Simulation time (seconds)


times = []

def plane(name, env, gas_station, station_tank):
    # TODO: Docstring
    plane_tank_level = random.randint(*PLANE_TANK_LEVEL)
    logging.debug(f'{env.now:6.1f} s: {name} arrived at gas station')

    start_time = env.now

    with gas_station.request() as req:
        # Request one of the gas pumps
        yield req

        # Get the required amount of fuel
        fuel_required = PLANE_TANK_SIZE - plane_tank_level
        yield station_tank.get(fuel_required)

        # The "actual" refueling process takes some time
        yield env.timeout(fuel_required / REFUELING_SPEED)

        times.append((env.now, env.now - start_time, fuel_required))

        logging.debug(f'{env.now:6.1f} s: {name} refueled with {fuel_required:.1f}L')


def gas_station_control(env, station_tank):
    """Periodically check the level of the gas station tank and call the tank
    truck if the level falls below a threshold."""
    while True:
        # TODO: Add a condition to check if the station tank level is below the threshold

        # We need to call the tank truck now!
        logging.debug(f'{env.now:6.1f} s: Calling tank truck')
        # Wait for the tank truck to arrive and refuel the station tank
        yield env.process(tank_truck(env, station_tank))

        yield env.timeout(10)  # Check every 10 seconds


def tank_truck(env, station_tank):
    """Arrives at the gas station after a certain delay and refuels it."""
    yield env.timeout(TANK_TRUCK_TIME)
    amount = station_tank.capacity - station_tank.level
    station_tank.put(amount)
    logging.debug(
        f'{env.now:6.1f} s: Tank truck arrived and refuelled station with {amount:.1f}L'
    )

def plane_generator(env, gas_station, station_tank):
    """Generate new planes that arrive at the gas station."""
    for i in itertools.count():
        yield env.timeout(random.randint(*T_INTER))
        env.process(plane(f'Plane {i}', env, gas_station, station_tank))

# Setup and start the simulation
random.seed(RANDOM_SEED)

# Create environment and start processes
env = simpy.Environment()
gas_station = simpy.Resource(env, 2)
station_tank = simpy.Container(env, STATION_TANK_SIZE, init=STATION_TANK_SIZE)
env.process(gas_station_control(env, station_tank))
env.process(plane_generator(env, gas_station, station_tank))

# Execute!
# TODO run simulation for the time you want

pd.DataFrame(times, columns=['entry_time', 'duration', 'fuel_litres']).to_csv('sim.csv', index=False)