import { expect, it } from "vitest";
import { PageHeights } from "../src/lib/virt";

it("估算高度:offset/total/pageAt/range(带 overscan、夹边)", () => {
  const ph = new PageHeights(10, 100);
  expect(ph.offset(3)).toBe(300);
  expect(ph.total()).toBe(1000);
  expect(ph.pageAt(350)).toBe(3);
  expect(ph.pageAt(-10)).toBe(0);
  expect(ph.pageAt(99_999)).toBe(9);
  expect(ph.range(0, 100, 2)).toEqual([0, 3]);
  expect(ph.range(950, 100, 2)).toEqual([7, 10]);
});

it("set 修正高度并平移后续 offset;返回增量;幂等", () => {
  const ph = new PageHeights(10, 100);
  expect(ph.set(2, 150)).toBe(50);
  expect(ph.offset(2)).toBe(200); // 自身 offset 不受自己影响
  expect(ph.offset(3)).toBe(350); // 后续整体 +50
  expect(ph.total()).toBe(1050);
  expect(ph.pageAt(349)).toBe(2);
  expect(ph.pageAt(351)).toBe(3);
  expect(ph.set(2, 150)).toBe(0);
});

it("setEst:重估默认页高,返回视口上方「未量高」页数,已量高页保留", () => {
  const ph = new PageHeights(5, 100); // cum 顶部: 0,100,200,300,400
  ph.set(0, 160); // 页0 实测 160 → cum 顶部: 0,160,260,360,460
  expect(ph.setEst(140, 260)).toBe(1); // 顶部<260 且未量高:页1(160)。页0 已量高排除,页2(260)不<260
  expect(ph.total()).toBe(160 + 4 * 140); // 页0 实测保留,其余按新估高
  expect(ph.setEst(140, 9999)).toBe(0); // 同值幂等:est 不变直接 0
});

it("n=0 时一切归空", () => {
  const ph = new PageHeights(0, 100);
  expect(ph.total()).toBe(0);
  expect(ph.range(0, 100, 2)).toEqual([0, 0]);
  expect(ph.set(0, 50)).toBe(0);
});