numerica/packages/core/src/systems/en-US/stringify.ts

import {
	Group,
	GROUP_DIGITS_INDEX,
	GROUP_PLACE_INDEX,
	GroupPlace,
} from '../../common';
import { numberToExponential } from '../../exponent';
import {
	CENTILLIONS_PREFIXES,
	CentillionsPrefix,
	DECILLIONS_PREFIXES,
	DecillionsPrefix,
	DECIMAL_POINT,
	EMPTY_GROUP_DIGITS,
	EXPONENT_DELIMITER,
	GROUPING_SYMBOL,
	HUNDRED,
	ILLION_SUFFIX,
	MILLIA_PREFIX,
	MILLIONS_PREFIXES,
	MILLIONS_SPECIAL_PREFIXES,
	MillionsPrefix,
	MillionsSpecialPrefix, NEGATIVE,
	ONES,
	OnesName,
	SHORT_MILLIA_DELIMITER,
	TEN_PLUS_ONES,
	TenPlusOnesName,
	TENS,
	TENS_ONES_SEPARATOR,
	TensName,
	THOUSAND,
} from './common';

/**
 * Builds a name for numbers in tens and ones.
 * @param tens - Tens digit.
 * @param ones - Ones digit.
 * @param addTensDashes - Whether to add dashes between the tens and ones.
 * @returns string The name for the number.
 */
const makeTensName = (tens: number, ones: number, addTensDashes = false) => {
	if (tens === 0) {
		return ONES[ones];
	}

	if (tens === 1) {
		return TEN_PLUS_ONES[ones] as unknown as TenPlusOnesName;
	}

	if (ones === 0) {
		return TENS[tens];
	}

	return `${TENS[tens] as Exclude<TensName, 'zero' | 'ten'>}${addTensDashes ? TENS_ONES_SEPARATOR : ' '}${ONES[ones] as Exclude<OnesName, 'zero'>}` as const;
};

/**
 * Builds a name for numbers in hundreds, tens, and ones.
 * @param hundreds - Hundreds digit.
 * @param tens - Tens digit.
 * @param ones - Ones digit.
 * @param addTensDashes - Whether to add dashes between the tens and ones.
 * @returns string The name for the number.
 */
const makeHundredsName = (hundreds: number, tens: number, ones: number, addTensDashes = false) => {
	if (hundreds === 0) {
		return makeTensName(tens, ones, addTensDashes);
	}

	if (tens === 0 && ones === 0) {
		return `${ONES[hundreds]} ${HUNDRED}` as const;
	}

	return `${ONES[hundreds]} ${HUNDRED} ${makeTensName(tens, ones, addTensDashes)}` as const;
};

/**
 * Builds a name for numbers in the millions.
 * @param millions - Millions digit.
 * @param milliaCount - Number of millia- groups.
 * @returns string The millions prefix.
 */
const makeMillionsPrefix = (millions: number, milliaCount: GroupPlace) => {
	if (milliaCount > 0) {
		return MILLIONS_PREFIXES[millions] as MillionsPrefix;
	}

	return MILLIONS_SPECIAL_PREFIXES[millions] as MillionsSpecialPrefix;
};

/**
 * Builds a name for numbers in the decillions.
 * @param decillions - Decillions digit.
 * @param millions - Millions digit.
 * @param milliaCount - Number of millia- groups.
 * @returns string The decillions prefix.
 */
const makeDecillionsPrefix = (decillions: number, millions: number, milliaCount: GroupPlace) => {
	if (decillions === 0) {
		return makeMillionsPrefix(millions, milliaCount);
	}

	const onesPrefix = MILLIONS_PREFIXES[millions] as MillionsPrefix;
	const tensName = DECILLIONS_PREFIXES[decillions] as DecillionsPrefix;
	return `${onesPrefix}${tensName}` as const;
};

/**
 * Builds a name for numbers in the centillions.
 * @param centillions - Centillions digit.
 * @param decillions - Decillions digit.
 * @param millions - Millions digit.
 * @param milliaCount - Number of millia- groups.
 * @returns string The centillions prefix.
 */
const makeCentillionsPrefix = (
	centillions: number,
	decillions: number,
	millions: number,
	milliaCount: GroupPlace,
) => {
	if (centillions === 0) {
		return makeDecillionsPrefix(decillions, millions, milliaCount);
	}

	const onesPrefix = MILLIONS_PREFIXES[millions] as MillionsPrefix;
	const tensName = DECILLIONS_PREFIXES[decillions] as DecillionsPrefix;
	const hundredsName = CENTILLIONS_PREFIXES[centillions] as CentillionsPrefix;
	return `${hundredsName}${onesPrefix}${decillions > 0 ? tensName : ''}` as const;
};

const repeatString = (s: string, count: GroupPlace) => {
	let result = '';
	for (let i = BigInt(0); i < count; i += BigInt(1)) {
		result += s;
	}
	return result;
};

const getGroupName = (place: GroupPlace, shortenMillia: boolean) => {
	if (place === BigInt(0)) {
		return '' as const;
	}

	if (place === BigInt(1)) {
		return THOUSAND;
	}

	const bigGroupPlace = place - BigInt(1);
	const groupGroups = bigGroupPlace
		.toString()
		.split('')
		.reduceRight<Group[]>(
			(acc, c, i, cc) => {
				const firstGroup = acc.at(0);
				const currentPlace = BigInt(Math.floor((cc.length - i - 1) / 3));
				const newGroup = [EMPTY_GROUP_DIGITS, currentPlace] as Group;
				if (typeof firstGroup === 'undefined') {
					newGroup[GROUP_DIGITS_INDEX] = c;
					return [newGroup];
				}

				if (firstGroup[0].length > 2) {
					newGroup[GROUP_DIGITS_INDEX] = c;
					return [newGroup, ...acc];
				}

				newGroup[GROUP_DIGITS_INDEX] = c + firstGroup[0];
				return [
					newGroup,
					...acc.slice(1),
				];
			},
			[],
		)
		.map(([groupDigits, groupPlace]) => [groupDigits.padStart(3, '0'), groupPlace] as const)
		.filter(([groupDigits]) => groupDigits !== EMPTY_GROUP_DIGITS)
		.map(([groupDigits, groupPlace]) => {
			const [hundreds, tens, ones] = groupDigits.split('').map(Number);
			if (groupPlace < 1) {
				return makeCentillionsPrefix(hundreds, tens, ones, groupPlace);
			}

			const milliaSuffix = (
				shortenMillia && groupPlace > 1
					? `${MILLIA_PREFIX}${SHORT_MILLIA_DELIMITER}${groupPlace}`
					: repeatString(MILLIA_PREFIX, groupPlace)
			);

			if (groupDigits === '001') {
				return milliaSuffix;
			}

			return makeCentillionsPrefix(hundreds, tens, ones, groupPlace) + milliaSuffix;
		})
		.join('');

	if (groupGroups.endsWith(DECILLIONS_PREFIXES[1])) {
		return `${groupGroups}${ILLION_SUFFIX}` as const;
	}

	if (bigGroupPlace > 10) {
		return `${groupGroups}t${ILLION_SUFFIX}` as const;
	}

	return `${groupGroups}${ILLION_SUFFIX}` as const;
};

export interface MakeGroupsOptions {
	addTensDashes?: boolean;
	shortenMillia?: boolean;
}

export const makeGroups = (groups: Group[], options?: MakeGroupsOptions): string[] => {
	const filteredGroups = groups.filter(([digits, place]) => (
		place === BigInt(0) || digits !== EMPTY_GROUP_DIGITS
	));

	return filteredGroups.map(
		([group, place]) => {
			const makeHundredsArgs = group
				.padStart(3, '0')
				.split('')
				.map((s) => Number(s)) as [number, number, number];

			const groupDigitsName = makeHundredsName(
				...makeHundredsArgs,
				options?.addTensDashes ?? false,
			);
			const groupName = getGroupName(place, options?.shortenMillia ?? false);
			if (groupName.length > 0) {
				return `${groupDigitsName} ${groupName}`;
			}
			return groupDigitsName;
		},
	);
};

/**
 * Group a number string into groups of three digits, starting from the decimal point.
 * @param value - The number string to group.
 */
export const group = (value: string): Group[] => {
	const [significand, exponentString] = numberToExponential(
		value,
		{
			decimalPoint: DECIMAL_POINT,
			groupingSymbol: GROUPING_SYMBOL,
			exponentDelimiter: EXPONENT_DELIMITER,
		},
	)
		.split(EXPONENT_DELIMITER);
	const exponent = Number(exponentString);
	const significantDigits = significand.replace(DECIMAL_POINT, '');
	return significantDigits.split('').reduce<Group[]>(
		(acc, c, i) => {
			const currentPlace = BigInt(Math.floor((exponent - i) / 3));
			const lastGroup = acc.at(-1) ?? [EMPTY_GROUP_DIGITS, currentPlace];
			const currentPlaceInGroup = 2 - ((exponent - i) % 3);
			if (lastGroup[GROUP_PLACE_INDEX] === currentPlace) {
				const lastGroupDigits = lastGroup[0].split('');
				lastGroupDigits[currentPlaceInGroup] = c;
				return [...acc.slice(0, -1) ?? [], [
					lastGroupDigits.join(''),
					currentPlace,
				]];
			}
			return [...acc, [c.padEnd(3, '0'), currentPlace]];
		},
		[],
	);
};

/**
 * Formats the final tokenized string.
 * @param tokens - The tokens to finalize.
 */
export const finalize = (tokens: string[]) => (
	tokens
		.map((t) => t.trim())
		.join(' ')
		.trim()
);

/**
 * Makes a negative string.
 * @param s - The string to make negative.
 */
export const makeNegative = (s: string) => (
	`${NEGATIVE} ${s}`
);