const numberPattern = /^\d+$/;
const letterPattern = /^[a-z]$/i;

// ranges: 3 is exactly 3, 2- is at least 2, -4 is at most 4, 2-4 is between 2 and 4 inclusive
// comma is accepted as a legacy separator for closed ranges, e.g. age=22,30 from older links
// values not matching the pattern invalidate the range, which keeps them safe to use in queries
export function parseRange(rangeString, { pattern = numberPattern, parse = Number } = {}) {
	const parts = String(rangeString ?? '').trim().split(/[-,]/);

	if (parts.length > 2 || parts.every((part) => part === '') || parts.some((part) => part !== '' && !pattern.test(part))) {
		return null;
	}

	const [minString, maxString = minString] = parts; // no separator means an exact value

	return {
		min: minString ? parse(minString) : null,
		max: maxString ? parse(maxString) : null,
	};
}

// single letter cup sizes, matching the cup filter's regex character class
export function parseLetterRange(rangeString) {
	return parseRange(rangeString, {
		pattern: letterPattern,
		parse: (letter) => letter.toUpperCase(),
	});
}

export function formatRange(range) {
	if (!range || (range.min === null && range.max === null)) {
		return undefined;
	}

	if (range.min === range.max) {
		return String(range.min);
	}

	return `${range.min ?? ''}-${range.max ?? ''}`;
}

// years are a range like 2015-2020 or 2020-, or a list like 2015,2019 from older links
export function parseYears(yearsString) {
	if (yearsString?.includes('-')) {
		return { years: [], yearRange: parseRange(yearsString) };
	}

	return {
		years: yearsString?.split(',').map((year) => Number(year)).filter(Boolean) || [],
		yearRange: null,
	};
}

export function formatYears({ years, yearRange }) {
	return formatRange(yearRange) || years?.filter(Boolean).join(',') || undefined;
}