Limit rate of events based on time for Unity.

RateLimiter.cs

/* Original code[1] Copyright (c) 2009 Antti Huima[2]
   Modified code[3] Copyright (c) 2020 Shane Celis[4]
   Licensed under the MIT License[5]

   Original code posted to this question[6] and answer[7] on stackoverflow.com.

   This comment generated by code-cite[8].

   [1]: https://stackoverflow.com/a/668327
   [2]: https://stackoverflow.com/users/64376/antti-huima
   [3]: https://gist.github.com/shanecelis/d4a26d21d9dc531bbd3e2bf33cb00259
   [4]: http://twitter.com/shanecelis
   [5]: https://opensource.org/licenses/MIT
   [6]: https://stackoverflow.com/a/668327
   [7]: https://github.com/shanecelis/code-cite
*/

using UnityEngine;

/** Limit rate of events based on time for Unity.

```
private RateLimiter limiter = new RateLimiter(1/60f); // Allow 1 event per 60 seconds
                                                      // or 1 event per minute.
// ...
// Called 60 times a second.
void Update() {
  if (limiter.Allow()) {
    Debug.Log("Without a limiter this message would be logged 60 times a second.");
  }
}
```
 */
public class RateLimiter {
  public float eventsPerSecond; // units: events / second
  private float lastCheck = -1f; // units: seconds
  private float allowance; // units: events / second

  public RateLimiter(float eventsPerSecond) {
    this.eventsPerSecond = eventsPerSecond;
    allowance = eventsPerSecond;
  }

  // https://stackoverflow.com/questions/667508/whats-a-good-rate-limiting-algorithm
  /** Can allow an event within the limiter's constraints? */
  public bool Allow() {
    if (lastCheck < 0)
      lastCheck = Time.time - 1f/eventsPerSecond;
    float current = Time.time;
    float timePassed = current - lastCheck;
    lastCheck = current;
    float eventAllowance = timePassed * eventsPerSecond; // units: events
    allowance += eventAllowance / timePassed; // units: events / second
    if (allowance > eventsPerSecond)
      allowance = eventsPerSecond;
    if (eventAllowance < 1f) {
      return false;
    } else {
      allowance -= 1f / timePassed;
      return true;
    }
  }

}