export const DASHBOARD_LOCALE = "en-US";

/** Noon anchor avoids off-by-one labels around timezone boundaries for ISO date strings. */
export function parseIsoCalendarDate(isoDate: string): Date {
	return new Date(`${isoDate}T12:00:00`);
}

export type DashboardDateStyle = "month" | "day-month" | "full";

export function formatDate(isoDate: string, style: DashboardDateStyle): string {
	const date = parseIsoCalendarDate(isoDate);
	if (style === "month") {
		return date.toLocaleDateString(DASHBOARD_LOCALE, { month: "short" });
	}
	if (style === "day-month") {
		return date.toLocaleDateString(DASHBOARD_LOCALE, {
			day: "numeric",
			month: "short",
		});
	}
	return date.toLocaleDateString(DASHBOARD_LOCALE, {
		day: "numeric",
		month: "short",
		year: "numeric",
	});
}

/** X-axis for range charts: weekday when showing ~a week, otherwise month + day. */
export function formatChartAxisTick(
	isoDate: string,
	periodDays: number
): string {
	const date = parseIsoCalendarDate(isoDate);
	if (periodDays <= 7) {
		return date.toLocaleDateString(DASHBOARD_LOCALE, { weekday: "short" });
	}
	return formatDate(isoDate, "day-month");
}

export type ChartTooltipWeekdayStyle = "short" | "long";

/** Tooltip label for a chart point (weekday + month + day). */
export function formatChartTooltipDate(
	isoDate: string,
	weekdayStyle: ChartTooltipWeekdayStyle = "short"
): string {
	const date = parseIsoCalendarDate(isoDate);
	return date.toLocaleDateString(DASHBOARD_LOCALE, {
		weekday: weekdayStyle,
		day: "numeric",
		month: "short",
	});
}

export function formatCompactCurrency(
	value: number,
	options?: { maximumFractionDigits?: number }
) {
	const { maximumFractionDigits = 0 } = options ?? {};
	return new Intl.NumberFormat(DASHBOARD_LOCALE, {
		currency: "USD",
		maximumFractionDigits,
		notation: "compact",
		style: "currency",
	}).format(value);
}

/** Full-precision USD (e.g. average order value). */
export function formatFullCurrency(value: number) {
	return new Intl.NumberFormat(DASHBOARD_LOCALE, {
		currency: "USD",
		minimumFractionDigits: 2,
		maximumFractionDigits: 2,
		style: "currency",
	}).format(value);
}

export function formatCompactNumber(value: number) {
	return new Intl.NumberFormat(DASHBOARD_LOCALE, {
		maximumFractionDigits: 1,
		notation: "compact",
	}).format(value);
}

/** Whole numbers with grouping (visits, sessions, counts). */
export function formatInteger(value: number) {
	return new Intl.NumberFormat(DASHBOARD_LOCALE, {
		maximumFractionDigits: 0,
	}).format(value);
}

/** Percentage with fixed decimal places (e.g. conversion rate). */
export function formatPercent(value: number, fractionDigits = 2) {
	return `${value.toFixed(fractionDigits)}%`;
}