class SlideEngine {
  constructor(deckSelector) {
    this.deck = document.querySelector(deckSelector);
    this.slides = [...this.deck.children];
    this.current = 0;
    this.total = this.slides.length;
    this.bindEvents();
  }

  navigate(direction) {
    const next = this.current + direction;
    if (next < 0 || next >= this.total) return;

    this.slides[this.current].classList.remove('active');
    this.current = next;
    this.slides[this.current].classList.add('active');

    this.updateProgress();
    this.updateNotes();
  }

  updateProgress() {
    const pct = ((this.current + 1) / this.total) * 100;
    document.getElementById('progress')
      .style.width = pct + '%';
  }
}