decay.py

import datetime
from decimal import Decimal
import time

import random

INITIAL_RATES = {
    "mandrill": Decimal("0.95"),
    "sendgrid": Decimal("0.05"),
    "sparkpost": Decimal("0"),
}
RATES = INITIAL_RATES.copy()

DECAY_RATE = Decimal("0.50")
RECOVER_RATE = Decimal("0.02")

LAST_TICK = datetime.datetime.now()


def decay(adaptor_key):
    adaptor_rate = RATES[adaptor_key]
    adjusted_rate = adaptor_rate * (1 - DECAY_RATE)
    adjustment = adaptor_rate - adjusted_rate

    remainder = Decimal(sum(RATES.values()) - RATES[adaptor_key])
    for x in RATES:
        if x == adaptor_key:
            continue
        weight = RATES[x] / remainder
        RATES[x] = RATES[x] + (weight * adjustment)

    RATES[adaptor_key] = adjusted_rate


def recover(adaptor_key):
    difference = INITIAL_RATES[adaptor_key] - RATES[adaptor_key]
    RATES[adaptor_key] = RATES[adaptor_key] + (RECOVER_RATE * difference)


def tick():
    global LAST_TICK

    for x in RATES:
        recover(x)

    LAST_TICK = datetime.datetime.now()


def randomly_select_adaptor():
    probablility = random.uniform(0, 1)
    cumulative_probability = Decimal("0.0")
    for choice in RATES:
        cumulative_probability += RATES[choice]
        if probablility < cumulative_probability:
            break
    return choice


def _example_random_mandrill_error():
    if randomly_select_adaptor() == "mandrill":
        print("ERROR")
        decay("mandrill")


while True:
    tick_delta = datetime.datetime.now() - LAST_TICK
    if tick_delta > datetime.timedelta(seconds=1):
        tick()

    time.sleep(0.1)
    print(RATES)

    # Simulate a mandrill outage
    # Everytime mandril is the "chosen" adaptor, it errors
    _example_random_mandrill_error()