How to Implement an Error Budget Policy in Python

from datetime import datetime, timedelta

class ErrorBudgetPolicy:
    FREEZE_WINDOW_HOURS = 24
    MAX_FREEZES_PER_MONTH = 3

    def __init__(self, budget_percentage=99.9):
        self.budget_percentage = budget_percentage
        self.freeze_count = 0
        self.last_freeze_start = None
        self.freeze_enabled = True

    def should_freeze(self, deploy_time):
        if not self.freeze_enabled:
            return False
        if self.freeze_count >= self.MAX_FREEZES_PER_MONTH:
            return False
        if self.last_freeze_start and deploy_time < self.last_freeze_start + timedelta(hours=self.FREEZE_WINDOW_HOURS):
            return False
        # Mock: freeze if error rate exceeds budget allowance
        error_rate = 0.02  # simulated 2% error rate
        allowed_error = 1 - (self.budget_percentage / 100)
        return error_rate > allowed_error

    def apply_freeze(self, deploy_time):
        self.freeze_count += 1
        self.last_freeze_start = deploy_time
        self.freeze_enabled = False
        return {"frozen": True, "freeze_expires": deploy_time + timedelta(hours=self.FREEZE_WINDOW_HOURS)}

def simulate_deploy():
    policy = ErrorBudgetPolicy(budget_percentage=99.9)
    deploy_time = datetime.now()
    print("Initial policy:", policy)

    if policy.should_freeze(deploy_time):
        result = policy.apply_freeze(deploy_time)
        print("Deploy frozen -", result)
    else:
        print("Deploy allowed")

if __name__ == "__main__":
    simulate_deploy()