import { beforeEach, expect, test, vi } from 'vitest';
import { createCarousel } from '../src/index.ts';

// Minimal IO shim — records instances so tests can fire entries manually.
class IOShim {
  static last: IOShim | null = null;
  cb: IntersectionObserverCallback;
  elements: Element[] = [];
  constructor(cb: IntersectionObserverCallback) {
    this.cb = cb;
    IOShim.last = this;
  }
  observe(el: Element) {
    this.elements.push(el);
  }
  unobserve() {}
  disconnect() {}
  // helper: emit "slide i is the one intersecting" (ratio 1), others 0
  emit(i: number) {
    this.cb(
      this.elements.map((target, idx) => ({
        target,
        isIntersecting: idx === i,
        intersectionRatio: idx === i ? 1 : 0,
      })) as unknown as IntersectionObserverEntry[],
      this as unknown as IntersectionObserver,
    );
  }
}
vi.stubGlobal('IntersectionObserver', IOShim);

function makeTrack(n: number): HTMLElement {
  const track = document.createElement('div');
  for (let i = 0; i < n; i++) {
    const slide = document.createElement('div');
    slide.className = 'slide';
    track.append(slide);
  }
  track.scrollTo = vi.fn();
  return track;
}

let track: HTMLElement;
beforeEach(() => {
  track = makeTrack(3);
});

test('count reflects slide children', () => {
  const c = createCarousel(track);
  expect(c.count).toBe(3);
});

test('next/prev clamp to range and scroll to target offset', () => {
  const c = createCarousel(track);
  c.next();
  expect(track.scrollTo).toHaveBeenCalled();
});

test('change fires with new index when a slide intersects', () => {
  const c = createCarousel(track);
  const seen: number[] = [];
  c.on('change', (i) => seen.push(i));
  (IOShim.last as IOShim).emit(2); // user swiped to slide 2
  expect(seen).toEqual([2]);
  expect(c.index).toBe(2);
});

test('change does not re-fire for the same index', () => {
  const c = createCarousel(track);
  const seen: number[] = [];
  c.on('change', (i) => seen.push(i));
  (IOShim.last as IOShim).emit(1);
  (IOShim.last as IOShim).emit(1);
  expect(seen).toEqual([1]);
});

test('unsubscribe stops delivery; destroy disconnects observer', () => {
  const c = createCarousel(track);
  const seen: number[] = [];
  const off = c.on('change', (i) => seen.push(i));
  off();
  (IOShim.last as IOShim).emit(2);
  expect(seen).toEqual([]);
  const spy = vi.spyOn(IOShim.last as IOShim, 'disconnect');
  c.destroy();
  expect(spy).toHaveBeenCalled();
});