import { describe, expect, it } from 'vitest';
import {
  addShanghaiDays,
  previousShanghaiMonth,
  shanghaiLaggedIssueWindow,
  shanghaiMonthLastInstant,
  shanghaiMonthRange,
  shanghaiPeriodYmds,
  shanghaiT1DayWindow,
  shanghaiYmd,
  startOfShanghaiDay,
} from './shanghai-date';

describe('shanghaiYmd / startOfShanghaiDay', () => {
  it('UTC 16:00 已是北京次日 00:00，账单日取北京日历日', () => {
    const utc = new Date('2026-08-30T16:00:00.000Z');
    expect(shanghaiYmd(utc)).toBe('2026-08-31');
    expect(startOfShanghaiDay(utc).toISOString()).toBe('2026-08-30T16:00:00.000Z');
  });

  it('UTC 15:59 仍是北京当日', () => {
    const utc = new Date('2026-08-30T15:59:59.000Z');
    expect(shanghaiYmd(utc)).toBe('2026-08-30');
    expect(startOfShanghaiDay(utc).toISOString()).toBe('2026-08-29T16:00:00.000Z');
  });

  it('不依赖服务器本地时区：输入 ISO 即得到北京自然日 00:00', () => {
    const noonUtc = new Date('2026-08-30T04:00:00.000Z'); // 北京 12:00
    expect(shanghaiYmd(noonUtc)).toBe('2026-08-30');
    expect(startOfShanghaiDay(noonUtc).toISOString()).toBe('2026-08-29T16:00:00.000Z');
  });
});

describe('shanghaiT1DayWindow', () => {
  it('北京 8 月 30 日 08:00 出账：出账日 30 日，窗口为 29 日全天', () => {
    const { start, end, billDate } = shanghaiT1DayWindow(new Date('2026-08-30T00:00:00.000Z'));
    expect(shanghaiYmd(billDate)).toBe('2026-08-30');
    expect(shanghaiYmd(start)).toBe('2026-08-29');
    expect(end.toISOString()).toBe(billDate.toISOString());
  });

  it('北京 8 月 31 日 00:05：出账日仍是 31 日，不是 UTC 的 30 日', () => {
    const { billDate } = shanghaiT1DayWindow(new Date('2026-08-30T16:05:00.000Z'));
    expect(shanghaiYmd(billDate)).toBe('2026-08-31');
  });
});

describe('shanghaiLaggedIssueWindow', () => {
  it('酒厂 T+3：出账日是今天，纳入 3 天前完成的订单', () => {
    const { start, end, billDate } = shanghaiLaggedIssueWindow(
      new Date('2026-08-31T00:00:00.000Z'),
      3,
    );
    expect(shanghaiYmd(billDate)).toBe('2026-08-31');
    expect(shanghaiYmd(start)).toBe('2026-08-28');
    expect(shanghaiYmd(end)).toBe('2026-08-29');
  });
});

describe('addShanghaiDays', () => {
  it('跨月跨年按北京日历加减', () => {
    expect(shanghaiYmd(addShanghaiDays(new Date('2026-08-31T16:00:00.000Z'), 1))).toBe(
      '2026-09-02',
    );
    expect(shanghaiYmd(addShanghaiDays(new Date('2026-01-01T00:00:00.000Z'), -1))).toBe(
      '2025-12-31',
    );
  });
});

describe('shanghaiMonthRange', () => {
  it('8 月账期为北京 8/1 00:00 至 9/1 00:00（不含）', () => {
    const { start, endExclusive } = shanghaiMonthRange(2026, 8);
    expect(start.toISOString()).toBe('2026-07-31T16:00:00.000Z');
    expect(endExclusive.toISOString()).toBe('2026-08-31T16:00:00.000Z');
    expect(shanghaiYmd(shanghaiMonthLastInstant(2026, 8))).toBe('2026-08-31');
  });

  it('UTC 月末 23:59:59 不会把账期止日滚成下月', () => {
    const periodStart = new Date('2026-08-01T00:00:00.000Z');
    expect(shanghaiPeriodYmds(periodStart)).toEqual({
      periodStart: '2026-08-01',
      periodEnd: '2026-08-31',
    });
  });
});

describe('previousShanghaiMonth', () => {
  it('北京 9 月 1 日 08:00（UTC 9/1 00:00）取 8 月', () => {
    expect(previousShanghaiMonth(new Date('2026-09-01T00:00:00.000Z'))).toEqual({
      year: 2026,
      month: 8,
    });
  });

  it('北京 9 月 1 日 00:30（UTC 8/31 16:30）取 8 月，不因 UTC 仍是 8 月而错到 7 月', () => {
    expect(previousShanghaiMonth(new Date('2026-08-31T16:30:00.000Z'))).toEqual({
      year: 2026,
      month: 8,
    });
  });
});