@huggingface/jinja/src/utils.ts

A minimalistic JavaScript implementation of the Jinja templating engine, specifically designed for parsing and rendering ML chat templates.

/**
 * Function that mimics Python's range() function.
 * @param start The start value of the range.
 * @param stop The stop value of the range. If not provided, start will be 0 and stop will be the provided start value.
 * @param step The step value of the range. Defaults to 1.
 * @returns The range of numbers.
 */
export function range(start: number, stop?: number, step = 1): number[] {
	if (stop === undefined) {
		stop = start;
		start = 0;
	}

	const result: number[] = [];
	for (let i = start; i < stop; i += step) {
		result.push(i);
	}
	return result;
}

/**
 * Function that mimics Python's array slicing.
 * @param array The array to slice.
 * @param start The start index of the slice. Defaults to 0.
 * @param stop The last index of the slice. Defaults to `array.length`.
 * @param step The step value of the slice. Defaults to 1.
 * @returns The sliced array.
 */
export function slice<T>(array: T[], start?: number, stop?: number, step = 1): T[] {
	const direction = Math.sign(step);

	if (direction >= 0) {
		start = (start ??= 0) < 0 ? Math.max(array.length + start, 0) : Math.min(start, array.length);
		stop = (stop ??= array.length) < 0 ? Math.max(array.length + stop, 0) : Math.min(stop, array.length);
	} else {
		start = (start ??= array.length - 1) < 0 ? Math.max(array.length + start, -1) : Math.min(start, array.length - 1);
		stop = (stop ??= -1) < -1 ? Math.max(array.length + stop, -1) : Math.min(stop, array.length - 1);
	}

	const result: T[] = [];
	for (let i = start; direction * i < direction * stop; i += step) {
		result.push(array[i]);
	}
	return result;
}

/**
 * Function that mimics Python's string.title() function.
 * @param value The string to title case.
 * @returns The title cased string.
 */
export function titleCase(value: string): string {
	return value.replace(/\b\w/g, (c) => c.toUpperCase());
}

export function strftime_now(format: string): string {
	return strftime(new Date(), format);
}

/**
 * A minimalistic implementation of Python's strftime function.
 */
export function strftime(date: Date, format: string): string {
	// Set locale to undefined to use the default locale
	const monthFormatterLong = new Intl.DateTimeFormat(undefined, { month: "long" });
	const monthFormatterShort = new Intl.DateTimeFormat(undefined, { month: "short" });

	const pad2 = (n: number): string => (n < 10 ? "0" + n : n.toString());

	return format.replace(/%[YmdbBHM%]/g, (token) => {
		switch (token) {
			case "%Y":
				return date.getFullYear().toString();
			case "%m":
				return pad2(date.getMonth() + 1);
			case "%d":
				return pad2(date.getDate());
			case "%b":
				return monthFormatterShort.format(date);
			case "%B":
				return monthFormatterLong.format(date);
			case "%H":
				return pad2(date.getHours());
			case "%M":
				return pad2(date.getMinutes());
			case "%%":
				return "%";
			default:
				return token;
		}
	});
}

function escapeRegExp(s: string): string {
	return s.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

/**
 * Function that mimics Python's string.replace() function.
 */
export function replace(str: string, oldvalue: string, newvalue: string, count?: number | null): string {
	if (count === 0) return str;
	let remaining = count == null || count < 0 ? Infinity : count;
	// NB: Use a Unicode-aware global regex so unpaired surrogates won't match
	const pattern = oldvalue.length === 0 ? new RegExp("(?=)", "gu") : new RegExp(escapeRegExp(oldvalue), "gu");
	return str.replaceAll(pattern, (match) => {
		if (remaining > 0) {
			--remaining;
			return newvalue;
		}
		return match;
	});
}