import { describe, it, expect, vi, afterEach } from 'vitest';
import {
	getWeekStart,
	prevWeek,
	nextWeek,
	weekDays,
	isToday,
	formatWeekRange,
	formatDayLabel
} from './week';

describe('getWeekStart', () => {
	it('returns Monday for a Monday input', () => {
		// 2026-03-30 is a Monday
		const d = new Date('2026-03-30T12:00:00Z');
		expect(getWeekStart(d)).toBe('2026-03-30');
	});

	it('returns Monday for a Wednesday input', () => {
		// 2026-04-01 is a Wednesday → week starts 2026-03-30
		const d = new Date('2026-04-01T12:00:00Z');
		expect(getWeekStart(d)).toBe('2026-03-30');
	});

	it('returns Monday for a Sunday input (edge case — goes back 6 days)', () => {
		// 2026-04-05 is a Sunday → week starts 2026-03-30
		const d = new Date('2026-04-05T12:00:00Z');
		expect(getWeekStart(d)).toBe('2026-03-30');
	});

	it('returns Monday for a Saturday input', () => {
		// 2026-04-04 is a Saturday → week starts 2026-03-30
		const d = new Date('2026-04-04T12:00:00Z');
		expect(getWeekStart(d)).toBe('2026-03-30');
	});

	it('handles year boundary correctly (Dec 28 2025 → week starts Dec 22 2025)', () => {
		const d = new Date('2025-12-28T12:00:00Z');
		expect(getWeekStart(d)).toBe('2025-12-22');
	});
});

describe('prevWeek', () => {
	it('returns the Monday 7 days before', () => {
		expect(prevWeek('2026-03-30')).toBe('2026-03-23');
	});

	it('handles month boundary', () => {
		expect(prevWeek('2026-04-06')).toBe('2026-03-30');
	});

	it('handles year boundary', () => {
		expect(prevWeek('2026-01-05')).toBe('2025-12-29');
	});
});

describe('nextWeek', () => {
	it('returns the Monday 7 days after', () => {
		expect(nextWeek('2026-03-30')).toBe('2026-04-06');
	});

	it('handles month boundary', () => {
		expect(nextWeek('2026-03-30')).toBe('2026-04-06');
	});

	it('handles year boundary', () => {
		expect(nextWeek('2025-12-29')).toBe('2026-01-05');
	});
});

describe('weekDays', () => {
	it('returns exactly 7 dates', () => {
		expect(weekDays('2026-03-30')).toHaveLength(7);
	});

	it('starts on the given weekStart', () => {
		const days = weekDays('2026-03-30');
		expect(days[0]).toBe('2026-03-30');
	});

	it('ends 6 days after weekStart', () => {
		const days = weekDays('2026-03-30');
		expect(days[6]).toBe('2026-04-05');
	});

	it('has consecutive daily dates', () => {
		const days = weekDays('2026-03-30');
		for (let i = 1; i < 7; i++) {
			const prev = new Date(days[i - 1] + 'T00:00:00Z');
			const curr = new Date(days[i] + 'T00:00:00Z');
			expect(curr.getTime() - prev.getTime()).toBe(86400000);
		}
	});

	it('handles month boundary correctly', () => {
		const days = weekDays('2026-03-30');
		expect(days[1]).toBe('2026-03-31');
		expect(days[2]).toBe('2026-04-01');
	});
});

describe('isToday', () => {
	afterEach(() => {
		vi.useRealTimers();
	});

	it('returns true for today (UTC)', () => {
		vi.useFakeTimers();
		vi.setSystemTime(new Date('2026-04-03T10:00:00Z'));
		expect(isToday('2026-04-03')).toBe(true);
	});

	it('returns false for yesterday', () => {
		vi.useFakeTimers();
		vi.setSystemTime(new Date('2026-04-03T10:00:00Z'));
		expect(isToday('2026-04-02')).toBe(false);
	});

	it('returns false for tomorrow', () => {
		vi.useFakeTimers();
		vi.setSystemTime(new Date('2026-04-03T10:00:00Z'));
		expect(isToday('2026-04-04')).toBe(false);
	});
});

describe('formatWeekRange', () => {
	it('returns a non-empty string', () => {
		expect(formatWeekRange('2026-03-30')).toBeTruthy();
	});

	it('contains both start and end month info', () => {
		const range = formatWeekRange('2026-03-30');
		// Start is March 30, end is April 5 — range should span both months
		expect(range).toContain('–');
	});
});

describe('formatDayLabel', () => {
	it('returns a non-empty string', () => {
		expect(formatDayLabel('2026-03-30')).toBeTruthy();
	});

	it('contains a comma separator', () => {
		expect(formatDayLabel('2026-03-30')).toContain(',');
	});
});