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import { describe, it, expect } from "vitest";

// Pure pagination logic extracted from imap.ts for unit testing
function paginate(allUids: number[], offset: number, limit: number) {
  const allNewestFirst = [...allUids].reverse();
  const total = allNewestFirst.length;
  const page = allNewestFirst.slice(offset, offset + limit);
  return {
    page,
    total,
    offset,
    hasMore: offset + limit < total,
    nextOffset: offset + limit < total ? offset + limit : null,
  };
}

describe("pagination", () => {
  const uids = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; // oldest → newest

  it("first page returns newest-first", () => {
    const r = paginate(uids, 0, 3);
    expect(r.page).toEqual([10, 9, 8]);
    expect(r.total).toBe(10);
    expect(r.hasMore).toBe(true);
    expect(r.nextOffset).toBe(3);
  });

  it("second page continues from offset", () => {
    const r = paginate(uids, 3, 3);
    expect(r.page).toEqual([7, 6, 5]);
    expect(r.hasMore).toBe(true);
  });

  it("last page has hasMore=false", () => {
    const r = paginate(uids, 9, 3);
    expect(r.page).toEqual([1]);
    expect(r.hasMore).toBe(false);
    expect(r.nextOffset).toBeNull();
  });

  it("offset beyond total returns empty page", () => {
    const r = paginate(uids, 20, 3);
    expect(r.page).toEqual([]);
    expect(r.hasMore).toBe(false);
  });

  it("limit larger than total returns all", () => {
    const r = paginate(uids, 0, 100);
    expect(r.page).toHaveLength(10);
    expect(r.hasMore).toBe(false);
  });

  it("empty uid list", () => {
    const r = paginate([], 0, 10);
    expect(r.page).toEqual([]);
    expect(r.total).toBe(0);
    expect(r.hasMore).toBe(false);
  });

  it("exactly fills a page — hasMore false", () => {
    const r = paginate(uids, 0, 10);
    expect(r.hasMore).toBe(false);
    expect(r.page).toHaveLength(10);
  });

  it("offset=0 limit=1 paginates through all one by one", () => {
    for (let i = 0; i < 10; i++) {
      const r = paginate(uids, i, 1);
      expect(r.page).toEqual([10 - i]);
      expect(r.hasMore).toBe(i < 9);
    }
  });
});