import { describe, expect, it } from 'vitest';
import { nextIndex, swipeStep } from './carousel';

// 广告轮播纯逻辑（Task 10 Step 1）：推进/环形回绕/单条静止 + 滑动手势判定
//（阈值 40px、水平分量须严格大于垂直分量）。

describe('nextIndex', () => {
  it('advances forward and wraps from the tail to the head (ring)', () => {
    expect(nextIndex(3, 0)).toBe(1);
    expect(nextIndex(3, 1)).toBe(2);
    expect(nextIndex(3, 2)).toBe(0); // 末→首
  });

  it('keeps a single item pinned at 0 (never switches)', () => {
    expect(nextIndex(1, 0)).toBe(0);
    expect(nextIndex(1, 0, -1)).toBe(0);
    expect(nextIndex(0, 0)).toBe(0); // 空表防御：同 0
  });

  it('steps backwards wrapping from the head to the tail', () => {
    expect(nextIndex(3, 0, -1)).toBe(2);
    expect(nextIndex(3, 2, -1)).toBe(1);
    expect(nextIndex(5, 4, -1)).toBe(3);
  });
});

describe('swipeStep', () => {
  it('maps an unambiguous horizontal swipe to its direction', () => {
    expect(swipeStep(-80, 5)).toBe(1); // 左滑 → 下一张
    expect(swipeStep(80, -5)).toBe(-1); // 右滑 → 上一张
  });

  it('ignores movement under the 40px threshold', () => {
    expect(swipeStep(-39, 0)).toBe(0);
    expect(swipeStep(39, 2)).toBe(0);
  });

  it('accepts exactly 40px (>= threshold)', () => {
    expect(swipeStep(-40, 0)).toBe(1);
    expect(swipeStep(40, 0)).toBe(-1);
  });

  it('ignores diagonal or vertically dominant movement', () => {
    expect(swipeStep(60, 70)).toBe(0); // 垂直分量更大（斜向）
    expect(swipeStep(50, 50)).toBe(0); // 等分量：水平须严格大于垂直
    expect(swipeStep(-100, 100)).toBe(0);
  });
});