// Functions for parsing and creating a media fragment identifiers.
// A media fragment is used to specify a time range of an audio/video track, e.g. #t=12,18.5.
// See https://www.w3.org/TR/media-frags/

// Creates a media fragment identifier for a given time range (in seconds).
export function createMediaFragmentIdentifier({ start, end }) {
	// Always output the time in seconds, as it is more widely supported than h:m:s syntax.
	const maybeStart = start !== undefined ? start : '';
	const maybeEnd = end !== undefined ? `,${end}` : '';
	const fragmentIdentifier = `t=${maybeStart}${maybeEnd}`;
	return fragmentIdentifier;
}

// Parses the time range from a media fragment identifier.
// Returns an object { start, end }; both numbers are given in seconds (possibly non-integer).
// Note this only supports the usual npt (normal playing time) format, not smpte or wall clock time.
export function parseMediaFragmentIdentifier(fragmentIdentifier) {
	// Strip possible leading hash character '#'.
	if (fragmentIdentifier.startsWith('#')) {
		fragmentIdentifier = fragmentIdentifier.substring(1);
	}

	const temporalDimensionRegex = /(?:^|&)(?:t|%74)=([^&]+)(?=&|$)/g;
	const temporalDimensionMatches = [...fragmentIdentifier.matchAll(temporalDimensionRegex)];
	if (temporalDimensionMatches.length === 0) {
		throw new Error('No time dimension defined');
	}
	// If there are multiple occurrences (e.g. t=1&t=2), take the last one.
	const temporalDimensionMatch = temporalDimensionMatches[temporalDimensionMatches.length - 1];
	const temporalDimensionValue = decodeURIComponent(temporalDimensionMatch[1]);

	const nptRegex = /^(?:npt:)?(?:(?:(\d+):)??(?:(\d+):)?(\d+(?:\.\d*)?))?(?:,(?:(\d+):)??(?:(\d+):)?(\d+(?:\.\d*)?))?$/;
	const nptMatch = temporalDimensionValue.match(nptRegex);
	if (!nptMatch) {
		throw new Error('Unable to parse fragment identifier.');
	}

	const start = (nptMatch[3] ? Number.parseFloat(nptMatch[3]) : 0)
			+ (nptMatch[2] ? Number.parseInt(nptMatch[2]) * 60 : 0)
			+ (nptMatch[1] ? Number.parseInt(nptMatch[1]) * 60 * 60 : 0);

	let end;
	if (nptMatch[6]) {
		end = Number.parseFloat(nptMatch[6])
			+ (nptMatch[5] ? Number.parseInt(nptMatch[5]) * 60 : 0)
			+ (nptMatch[4] ? Number.parseInt(nptMatch[4]) * 60 * 60 : 0);
	}

	return { start, end };
}