cacheWithLimit.ts

/*

Write a class that allows getting and setting key-value pairs, however a time until expiration is associated with each key.

The class has three public methods:

set(key, value, duration): accepts an integer key, an integer value, and a duration in milliseconds. Once the duration has elapsed, the key should be inaccessible. The method should return true if the same un-expired key already exists and false otherwise. Both the value and duration should be overwritten if the key already exists.

get(key): if an un-expired key exists, it should return the associated value. Otherwise it should return -1.

count(): returns the count of un-expired keys.

*/

class TimeLimitedCache {
  cache = new Map<
    number,
    { value: number; timer: ReturnType<typeof setTimeout> }
  >();

  set(key: number, value: number, duration: number): boolean {
    const exists = this.cache.has(key);

    if (exists) {
      clearTimeout(this.cache.get(key)?.timer);
    }

    this.cache.set(key, {
      value,
      timer: setTimeout(() => {
        this.cache.delete(key);
      }, duration),
    });

    return exists;
  }

  get(key: number): number {
    return this.cache.get(key)?.value ?? -1;
  }

  count(): number {
    return this.cache.size;
  }
}

/**
 * const timeLimitedCache = new TimeLimitedCache()
 * timeLimitedCache.set(1, 42, 1000); // false
 * timeLimitedCache.get(1) // 42
 * timeLimitedCache.count() // 1
 */