export class PriorityQueue<T> {
  private readonly values: { node: T; priority: number }[] = [];

  enqueue(node: T, priority: number) {
    this.values.push({ node, priority });
    this._bubbleUp();
  }

  dequeue() {
    if (this.values.length === 0) return null;

    const min = this.values[0];
    const end = this.values.pop();

    if (this.values.length > 0) {
      this.values[0] = end!;
      this._sinkDown();
    }

    return min;
  }

  size() {
    return this.values.length;
  }

  _bubbleUp() {
    let idx = this.values.length - 1;
    const element = this.values[idx];

    while (idx > 0) {
      const parentIdx = Math.floor((idx - 1) / 2);
      const parent = this.values[parentIdx];

      if (element.priority >= parent.priority) break;

      this.values[parentIdx] = element;
      this.values[idx] = parent;
      idx = parentIdx;
    }
  }

  _sinkDown() {
    let idx = 0;
    const length = this.values.length;
    const element = this.values[0];

    while (true) {
      const leftChildIdx = 2 * idx + 1;
      const rightChildIdx = 2 * idx + 2;
      let leftChild, rightChild;
      let swap = null;

      if (leftChildIdx < length) {
        leftChild = this.values[leftChildIdx];
        if (leftChild.priority < element.priority) {
          swap = leftChildIdx;
        }
      }

      if (rightChildIdx < length) {
        rightChild = this.values[rightChildIdx];
        if (
          (swap === null && rightChild.priority < element.priority) ||
          (swap !== null && rightChild.priority < leftChild!.priority)
        ) {
          swap = rightChildIdx;
        }
      }

      if (swap === null) break;

      this.values[idx] = this.values[swap];
      this.values[swap] = element;
      idx = swap;
    }
  }
}