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import libLanguages from '../lib/languages.js'

import parser from 'accept-language-parser'

const languageCodes = Object.keys(libLanguages)

const chineseRegions = ['CN', 'HK']

function translationExists(language) {

if (language.code === 'zh') {

return chineseRegions.includes(language.region)

}

return languageCodes.includes(language.code)

}

function getLanguageCode(language) {

return language.code === 'zh' && chineseRegions.includes(language.region) ? 'cn' : language.code

}

function getUserLanguage(browserLanguages) {

try {

let userLanguage = getLanguageCode(browserLanguages[0])

let numTopPreferences = 1

for (let lang = 0; lang < browserLanguages.length; lang++) {

// If language has multiple regions, Chrome adds the non-region language to list

if (lang > 0 && browserLanguages[lang].code !== browserLanguages[lang - 1].code)

numTopPreferences++

if (translationExists(browserLanguages[lang]) && numTopPreferences < 3) {

userLanguage = getLanguageCode(browserLanguages[lang])

break

}

}

return userLanguage

} catch {

return undefined

}

}

export default function detectLanguage(req, res, next) {

// determine language code from the URL, or default to English

// /en/articles/foo

// ^^

// /_next/data/development/en/articles/foo

// ^^

const maybeLanguage = req.path.split('/')[req.path.startsWith('/_next/data/') ? 4 : 1]

req.language = languageCodes.includes(maybeLanguage) ? maybeLanguage : 'en'

// Detecting browser language by user preference

const browserLanguages = parser.parse(req.headers['accept-language'])

req.userLanguage = getUserLanguage(browserLanguages)

return next()

}