ExpiringCount.ts

// The Counter class tracks expiring event counts for specific labels.
// Events are added with a timestamp using `put`. 
// Use `get_count` to get the count of valid events for a label.
// Use `get_total_count` to get the count of all valid events across labels.
// Events older than the expiration window are discarded automatically.

class Counter {
  expirationWindow: number;
  elements: { [key: string]: number[] } = {};

  constructor(expirationWindow: number) {
    this.expirationWindow = expirationWindow;
  }

  // Adds a timestamp for the given label
  put(label: string, timestamp: number): void {
    if (!this.elements[label]) {
      this.elements[label] = [];
    }
    this.elements[label].push(timestamp);
  }

  // Returns the count of valid timestamps for the given label
  get_count(label: string, timestamp: number): number {
    if (!this.elements[label]) return 0;

    // Remove expired timestamps
    this.elements[label] = this.elements[label].filter(
      (time) => timestamp - time <= this.expirationWindow
    );

    // If no valid timestamps remain, clean up the label
    if (this.elements[label].length === 0) {
      delete this.elements[label];
      return 0;
    }

    return this.elements[label].length;
  }

  // Returns the total count of valid timestamps across all labels
  get_total_count(timestamp: number): number {
    let totalCount = 0;

    for (const label of Object.keys(this.elements)) {
      totalCount += this.get_count(label, timestamp);
    }

    return totalCount;
  }
}

// Example usage
const counter = new Counter(3);

counter.put("a", 1);
counter.put("a", 2);
counter.put("b", 3);
counter.put("c", 4);
counter.put("d", 5);

console.log(counter.get_count("a", 4)); // Output: 2 (timestamps: [1, 2])
console.log(counter.get_total_count(4)); // Output: 5 (timestamps: [1, 2, 3, 4, 5])
console.log(counter.get_count("a", 6)); // Output: 0 (timestamps expired, only [b, c, d] remain)
console.log(counter.get_total_count(6)); // Output: 3 (timestamps: [3, 4, 5])
console.log(counter.get_count("6", 6)); // Output: 0 (not a valid label)