/** Count Unicode scalar values, matching Python string length semantics. */
export function codePointLength(text: string): number {
	let length = 0;
	for (let index = 0; index < text.length; length += 1) {
		const codePoint = text.codePointAt(index);
		if (codePoint === undefined) break;
		index += codePoint > 0xffff ? 2 : 1;
	}
	return length;
}

/** Slice by Unicode scalar offsets rather than UTF-16 code units. */
export function sliceCodePoints(text: string, start: number, end?: number): string {
	const normalizedStart = Math.max(0, Math.trunc(start));
	const normalizedEnd = end === undefined ? Number.POSITIVE_INFINITY : Math.max(normalizedStart, Math.trunc(end));
	let ordinal = 0;
	let startOffset = text.length;
	let endOffset = text.length;
	for (let index = 0; index < text.length;) {
		if (ordinal === normalizedStart) startOffset = index;
		if (ordinal === normalizedEnd) {
			endOffset = index;
			break;
		}
		const codePoint = text.codePointAt(index);
		if (codePoint === undefined) break;
		index += codePoint > 0xffff ? 2 : 1;
		ordinal += 1;
	}
	if (normalizedStart === ordinal) startOffset = text.length;
	return text.slice(startOffset, endOffset);
}