feat(data-structures/unstable): add RollingCounter

[tomas-zijdemans]

This data structure tracks counts across a fixed number of segments using a ring buffer. The caller controls when the window advances by calling rotate(), making it useful for rate limiting (I'm working on a new module for that), circuit breaker ++

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.84%. Comparing base (8d3e9c3) to head (710936b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7028   +/-   ##
=======================================
  Coverage   93.83%   93.84%           
=======================================
  Files         624      625    +1     
  Lines       49629    49693   +64     
  Branches     8721     8733   +12     
=======================================
+ Hits        46571    46635   +64     
  Misses       2478     2478           
  Partials      580      580           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[kt3k]

Is it common to call this data structure Sliding Window Counter? Is there any prior example library?

I research a bit about rate limiting algorithms, but this data structure seems more similar to one for sliding window log to me (sliding window counter seems using only 2 fixed windows and combining them with weighted interpolation)

[tomas-zijdemans]

Is it common to call this data structure Sliding Window Counter? Is there any prior example library?

I research a bit about rate limiting algorithms, but this data structure seems more similar to one for sliding window log to me (sliding window counter seems using only 2 fixed windows and combining them with weighted interpolation)

I agree. I was looking at a Go package. Renaming to RollingCounter. It's a ring of counters that rotates.

So usage could look like:

// Circuit breaker
const failures = new RollingCounter(10);
const requests = new RollingCounter(10);


// Rate limiter
const permits = new RollingCounter(segmentsPerWindow);