// ── Date utilities ──
// Uses moment.js which is bundled with Obsidian.
// Period format helpers following O-vault conventions.

import { moment } from 'obsidian';

export interface PeriodInfo {
	day: string;       // yyyy-MM-dd
	week: string;      // GGGG-[W]WW
	month: string;     // yyyy-MM
	quarter: string;   // yyyy-[Q]Q
	year: string;      // yyyy
}

export interface CalendarDay {
	date: moment.Moment;
	dayOfMonth: number;
	isToday: boolean;
	isCurrentMonth: boolean;
	isoWeekNumber: number;
}

export interface CalendarWeek {
	weekNumber: number;
	days: CalendarDay[];
}

/**
 * Get period info for a given date.
 */
export function getPeriodInfo(date: moment.Moment): PeriodInfo {
	return {
		day: date.format('YYYY-MM-DD'),
		week: date.format('GGGG-[W]WW'),
		month: date.format('YYYY-MM'),
		quarter: date.format('YYYY-[Q]Q'),
		year: date.format('YYYY'),
	};
}

/**
 * Get quarter string from a moment date (e.g. "2026-Q3").
 */
export function getQuarterString(date: moment.Moment): string {
	return date.format('YYYY-[Q]Q');
}

/**
 * Get the current date's period info.
 */
export function getTodayPeriod(): PeriodInfo {
	return getPeriodInfo(moment());
}

/**
 * Build a month grid as an array of weeks.
 * Each week has 7 days, starting on the configured first day of week.
 * ISO week numbers are calculated from the Monday of that week row.
 */
export function getMonthGrid(
	year: number,
	month: number,   // 0-indexed (0 = January)
	firstDayOfWeek: number,  // 0 = Sunday, 1 = Monday
): CalendarWeek[] {
	const firstOfMonth = moment({ year, month, day: 1 });
	const lastOfMonth = moment(firstOfMonth).endOf('month');

	// Find the first day to display (may go back into previous month)
	const startDate = moment(firstOfMonth)
		.subtract((firstOfMonth.day() - firstDayOfWeek + 7) % 7, 'days');

	const today = moment().startOf('day');
	const weeks: CalendarWeek[] = [];
	let currentDay = moment(startDate);

	while (currentDay.isBefore(lastOfMonth) || currentDay.month() === month) {
		const weekDays: CalendarDay[] = [];

		for (let i = 0; i < 7; i++) {
			weekDays.push({
				date: moment(currentDay),
				dayOfMonth: currentDay.date(),
				isToday: currentDay.isSame(today, 'day'),
				isCurrentMonth: currentDay.month() === month,
				isoWeekNumber: currentDay.isoWeek(),
			});
			currentDay.add(1, 'day');
		}

		weeks.push({
			weekNumber: weekDays[0].isoWeekNumber,
			days: weekDays,
		});

		// Safety: break after 6 weeks
		if (weeks.length >= 6) break;
	}

	return weeks;
}

/**
 * Format a date label for the breadcrumb (e.g. "June 1st, 2026").
 */
export function formatDateLabel(date: moment.Moment): string {
	return date.format('MMMM Do, YYYY');
}

/**
 * Format a month label (e.g. "June 2026").
 */
export function formatMonthLabel(date: moment.Moment): string {
	return date.format('MMMM YYYY');
}

/**
 * Get readable quarter label (e.g. "Q3 2026").
 */
export function formatQuarterLabel(date: moment.Moment): string {
	return date.format('[Q]Q YYYY');
}

/**
 * Navigate a date by a given period and amount.
 */
export function navigateDate(
	date: moment.Moment,
	period: 'day' | 'week' | 'month' | 'quarter' | 'year',
	delta: number,
): moment.Moment {
	if (period === 'quarter') {
		return moment(date).add(delta * 3, 'months');
	}
	return moment(date).add(delta, period);
}

/**
 * Create a note filename from a date using the given format string.
 */
export function formatPeriodName(date: moment.Moment, format: string): string {
	return date.format(format);
}

/**
 * Get ISO week number for a given date.
 */
export function getISOWeek(date: moment.Moment): number {
	return date.isoWeek();
}