// One definition of a PageUp/PageDown page for the palette and every popover list (owner
// request). The DOM-bound halves are covered where they are wired (CommandPalette, Combobox,
// ActionMenu); this pins the arithmetic both lean on.
import { describe, expect, it } from "vitest";
import { PAGE_FALLBACK, pageStep, pageTarget } from "./listPaging";

const box = (top: number, height: number) =>
  ({ getBoundingClientRect: () => ({ top, bottom: top + height, height }) }) as unknown as Element;

describe("pageStep", () => {
  it("is the rows wholly in view minus one", () => {
    // A 100px list with 30px rows: 0–30, 30–60, 60–90 fit; 90–120 is cut off.
    const rows = [0, 30, 60, 90, 120].map((top) => box(top, 30));
    expect(pageStep(box(0, 100), rows)).toBe(2);
  });

  it("never stands still, and falls back without layout", () => {
    expect(pageStep(box(0, 20), [box(0, 30)])).toBe(1);
    expect(pageStep(box(0, 0), [box(0, 30)])).toBe(PAGE_FALLBACK);
    expect(pageStep(null, [])).toBe(PAGE_FALLBACK);
  });
});

describe("pageTarget", () => {
  it("moves a page and stops at both ends instead of wrapping", () => {
    expect(pageTarget(0, 10, 25)).toBe(10);
    expect(pageTarget(20, 10, 25)).toBe(24);
    expect(pageTarget(24, 10, 25)).toBe(24);
    expect(pageTarget(3, -10, 25)).toBe(0);
    expect(pageTarget(0, 10, 0)).toBeNull();
  });

  it("passes over a row it may not land on, then looks back — never past the start", () => {
    const off = new Set([10, 11]);
    const usable = (i: number) => !off.has(i);
    expect(pageTarget(0, 10, 25, usable)).toBe(12); // on past the landing row first
    off.add(24);
    off.add(23);
    expect(pageTarget(15, 10, 25, usable)).toBe(22); // at the end: back toward the start
    expect(pageTarget(22, 10, 25, usable)).toBeNull(); // nothing between the start and the end
    expect(pageTarget(15, -10, 25, (i) => i > 12)).toBe(13);
  });
});