overleaf/services/web/frontend/translations-loader.js

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/*
* Custom webpack loader for i18next locale JSON files.
*
* It extracts translations used in the frontend (based on the list of keys in
* extracted-locales.json), and merges them with the fallback language (English)
*
* This means that we only load minimal translations data used in the frontend.
*/
const fs = require('fs').promises
const Path = require('path')
const SOURCE_PATH = Path.join(__dirname, '../locales')
const EXTRACTED_TRANSLATIONS_PATH = Path.join(
__dirname,
'./extracted-translation-keys.json'
)
module.exports = function translationsLoader() {
// Mark the loader as asynchronous, and get the done callback function
const callback = this.async()
// Mark the extracted keys file and English translations as a "dependency", so
// that it gets watched for changes in dev
this.addDependency(EXTRACTED_TRANSLATIONS_PATH)
this.addDependency(`${SOURCE_PATH}/en.json`)
const [, locale] = this.resourcePath.match(/(\w{2}(-\w{2})?)\.json$/)
run(locale)
.then(translations => {
callback(null, JSON.stringify(translations))
})
.catch(err => callback(err))
}
async function run(locale) {
const json = await fs.readFile(EXTRACTED_TRANSLATIONS_PATH)
const keys = JSON.parse(json)
const fallbackTranslations = await extract('en', keys)
return extract(locale, keys, fallbackTranslations)
}
async function extract(locale, keys, fallbackTranslations = null) {
const allTranslations = await getAllTranslations(locale)
const extractedTranslations = extractByKeys(keys, allTranslations)
return Object.assign({}, fallbackTranslations, extractedTranslations)
}
async function getAllTranslations(locale) {
const content = await fs.readFile(Path.join(SOURCE_PATH, `${locale}.json`))
return JSON.parse(content)
}
function extractByKeys(keys, translations) {
return keys.reduce((acc, key) => {
const foundString = translations[key]
if (foundString) {
acc[key] = foundString
}
return acc
}, {})
}