Simulate a Leaky Bucket Rate Limiter in Python

import time
from collections import deque


class LeakyBucket:
    """Simulates a leaky bucket rate limiter with a fixed drain rate."""
    def __init__(self, capacity, drain_rate_per_sec):
        self.capacity = capacity
        self.drain_rate = drain_rate_per_sec
        self.water = 0.0
        self.last_refill = time.monotonic()

    def add_request(self, amount=1):
        """Return True if request fits, False if bucket overflows."""
        now = time.monotonic()
        elapsed = now - self.last_refill
        self.water = max(0.0, self.water - elapsed * self.drain_rate)
        self.last_refill = now

        if self.water + amount <= self.capacity:
            self.water += amount
            return True
        return False


if __name__ == "__main__":
    bucket = LeakyBucket(capacity=3, drain_rate_per_sec=1)
    for i in range(6):
        accepted = bucket.add_request()
        print(f"Request {i}: {'accepted' if accepted else 'rejected'} (water={bucket.water:.2f})")
    time.sleep(1.5)
    accepted = bucket.add_request()
    print(f"Request after drain: {'accepted' if accepted else 'rejected'} (water={bucket.water:.2f})")