slug.js

import slugify from '@sindresorhus/slugify';
import {SLUG_SEPARATOR} from '../../config';

/* url-safe processor */

export const urlsafeSlugProcessor = string =>
	slugify(string, {
		customReplacements: [	// runs before any other transformations
			['$', 'DOLLAR'], // `$destroy` & co
			['-', 'DASH'], // conflicts with `separator`
		],
		separator: SLUG_SEPARATOR,
		decamelize: false,
		lowercase: false
	})
		.replace(/DOLLAR/g, '$')
		.replace(/DASH/g, '-');

/* unicode-preserver processor */

const alphaNumRegex = /[a-zA-Z0-9]/;
const unicodeRegex = /\p{Letter}/u;
const isNonAlphaNumUnicode =
	string => !alphaNumRegex.test(string) && unicodeRegex.test(string);

export const unicodeSafeProcessor = string =>
	string.split('')
		.reduce((accum, char, index, array) => {
			const type = isNonAlphaNumUnicode(char) ? 'pass' : 'process';

			if (index === 0) {
				accum.current = {type, string: char};
			} else if (type === accum.current.type) {
				accum.current.string += char;
			} else {
				accum.chunks.push(accum.current);
				accum.current = {type, string: char};
			}

			if (index === array.length - 1) {
				accum.chunks.push(accum.current);
			}

			return accum;
		}, {chunks: [], current: {type: '', string: ''}})
		.chunks
		.reduce((accum, chunk) => {
			const processed = chunk.type === 'process'
				? urlsafeSlugProcessor(chunk.string)
				: chunk.string;

			processed.length > 0 && accum.push(processed);

			return accum;
		}, [])
		.join(SLUG_SEPARATOR);

/* processor */

export const makeSlugProcessor = (preserveUnicode = false) => preserveUnicode
	? unicodeSafeProcessor
	: urlsafeSlugProcessor;

/* session processor */

export const makeSessionSlugProcessor = (preserveUnicode = false) => {
	const processor = makeSlugProcessor(preserveUnicode);
	const seen = new Set();

	return string => {
		const slug = processor(string);

		if (seen.has(slug)) throw new Error(`Duplicate slug ${slug}`);
		seen.add(slug);

		return slug;
	};
};