numerica/packages/core/src/converter.ts

import { enUS } from './systems';
import {
	ALLOWED_PARSE_RESULT_TYPES,
	AllowedValue,
	NumberNameSystem,
	ParseResultType,
} from './common';
import { exponentialToNumberString, extractExponentialComponents, numberToExponential } from './exponent';

/**
 * Negative symbol.
 */
const NEGATIVE_SYMBOL = '-' as const;

/**
 * Exponent delimiter.
 */
const EXPONENT_DELIMITER = 'e' as const;

/**
 * Options to use when converting a value to a string.
 */
export interface StringifyOptions<
	TStringifyGroupsOptions extends object,
	TMergeTokensOptions extends object,
> {
	/**
	 * The system to use when converting a value to a string.
	 *
	 * Defaults to en-US (American short count).
	 */
	system?: NumberNameSystem;
	/**
	 * Options to use when stringifying a single group.
	 */
	stringifyGroupsOptions?: TStringifyGroupsOptions;
	/**
	 * Options to use when merging tokens.
	 */
	mergeTokensOptions?: TMergeTokensOptions;
}

/**
 * Converts a numeric value to its name.
 * @param value - The value to convert.
 * @param options - Options to use when converting a value to its name.
 * @returns string The name of the value.
 */
export const stringify = <
	TStringifyGroupsOptions extends object,
	TMergeTokensOptions extends object
>
	(
		value: AllowedValue,
		options = {} as StringifyOptions<TStringifyGroupsOptions, TMergeTokensOptions>,
	): string => {
	if (!(
		(ALLOWED_PARSE_RESULT_TYPES as unknown as string[])
			.includes(typeof (value as unknown))
	)) {
		throw new TypeError(`Value must be a string, number, or bigint. Received: ${typeof value}`);
	}

	if (typeof value === 'number' && Number.isNaN(value)) {
		return 'NaN';
	}

	const valueStr = value.toString().replace(/\s/g, '');
	const { system = enUS.shortCount, stringifyGroupsOptions, mergeTokensOptions } = options;

	if (valueStr.startsWith(NEGATIVE_SYMBOL)) {
		return system.makeNegative(stringify(valueStr.slice(NEGATIVE_SYMBOL.length), options));
	}

	const groups = system.splitIntoGroups(valueStr);
	const groupNames = system.stringifyGroups(groups, stringifyGroupsOptions);
	return system.mergeTokens(groupNames, mergeTokensOptions);
};

/**
 * Options to use when parsing a name of a number to its numeric equivalent.
 */
export interface ParseOptions {
	/**
	 * The system to use when parsing a name of a number to its numeric equivalent.
	 *
	 * Defaults to en-US (American short count).
	 */
	system?: NumberNameSystem;
	/**
	 * The type to parse the value as.
	 */
	type?: ParseResultType;
}

/**
 * Parses a name of a number to its numeric equivalent.
 * @param value - The value to parse.
 * @param options - Options to use when parsing a name of a number to its numeric equivalent.
 * @returns AllowedValue The numeric equivalent of the value.
 */
export const parse = (value: string, options = {} as ParseOptions) => {
	const { system = enUS.shortCount, type: typeRaw = 'string' } = options;
	const type = typeRaw.trim().toLowerCase() as ParseResultType;

	if (!((ALLOWED_PARSE_RESULT_TYPES as unknown as string[]).includes(type))) {
		throw new TypeError(`Return type must be a string, number, or bigint. Received: ${type}`);
	}

	if (value.trim().toLowerCase() === 'nan') {
		return type === 'number' ? NaN : 'NaN';
	}

	const tokens = system.tokenize(value);
	const { groups, negative } = system.parseGroups(tokens);
	const stringValue = system.combineGroups(groups, negative);

	switch (type) {
	case 'number': {
		// Precision might be lost here. Use bigint when not using fractional parts.
		if (stringValue.includes(EXPONENT_DELIMITER)) {
			const { exponent, integer } = extractExponentialComponents(stringValue);
			const exponentValue = Number(exponent);
			const integerValue = Number(integer);

			// max safe integer: 9.007199254740991e+15
			const [maxSafeIntegerSignificand, maxSafeIntegerExponent] = Number.MAX_SAFE_INTEGER.toExponential().split('e');
			if (
				exponentValue >= Number(maxSafeIntegerExponent)
				&& integerValue >= Math.floor(Number(maxSafeIntegerSignificand))
			) {
				// greater than Number.MAX_SAFE_INTEGER
				const logger = console;
				logger.warn(`Value too large to be produced as number: ${value}`);
				logger.warn('Falling back to string...');
				return stringValue;
			}

			// epsilon: 2.220446049250313e-16
			const [epsilonSignificand, epsilonExponent] = Number.EPSILON.toExponential().split('e');
			if (
				exponentValue <= Number(epsilonExponent)
				&& integerValue <= Math.floor(Number(epsilonSignificand))
			) {
				// smaller than Number.EPSILON
				const logger = console;
				logger.warn(`Value too small to be produced as number: ${value}`);
				logger.warn('Falling back to string...');
				return stringValue;
			}
		}
		return Number(stringValue);
	} case 'bigint': {
		const normalizedNumberString = exponentialToNumberString(numberToExponential(stringValue));
		try {
			return BigInt(normalizedNumberString);
		} catch {
			const logger = console;
			logger.warn(`Value too long to be produced as bigint: ${value}`);
			logger.warn('Falling back to string...');
		}

		return stringValue;
	} default:
		break;
	}

	return stringValue;
};