// @if TARGET='app'
let fs = require('fs');
// @endif

const isProduction = process.env.NODE_ENV === 'production';
let knownMessages = null;
let localStorageAvailable;
try {
  localStorageAvailable = Boolean(window.localStorage);
} catch (e) {
  localStorageAvailable = false;
}

window.i18n_messages = window.i18n_messages || {};

// @if TARGET='app'
function saveMessage(message) {
  const messagesFilePath = __static + '/app-strings.json';

  if (knownMessages === null) {
    try {
      knownMessages = JSON.parse(fs.readFileSync(messagesFilePath, 'utf-8'));
    } catch (err) {
      throw new Error('Error parsing i18n messages file: ' + messagesFilePath + ' err: ' + err);
    }
  }

  if (!knownMessages[message]) {
    const END = '--end--';
    delete knownMessages[END];
    knownMessages[message] = removeContextMetadata(message);
    knownMessages[END] = END;

    fs.writeFile(messagesFilePath, JSON.stringify(knownMessages, null, 2) + '\n', 'utf-8', err => {
      if (err) {
        throw err;
      }
    });
  }
}
// @endif

/*
 I dislike the below code (and note that it ships all the way to the distributed app),
 but this seems better than silently having this limitation and future devs not knowing.
 */
// @if TARGET='web'
function saveMessage(message) {
  if (!isProduction && knownMessages === null) {
    console.log('Note that i18n messages are not saved in web dev mode.');
    knownMessages = {};
  }
}
// @endif

function removeContextMetadata(message) {
  // Example string entries with context-metadata:
  //   "About --[About section in Help Page]--": "About",
  //   "About --[tab title in Channel Page]--": "About",
  const CONTEXT_BEGIN = '--[';
  const CONTEXT_FINAL = ']--';

  // If the resolved string still contains the context-metadata, then it's one of the following:
  // 1. In development mode, where 'en.json' in the server hasn't been updated with the string yet.
  // 2. Translator made a mistake of not ignoring the context string.
  // In either case, we'll revert to the English version.

  const begin = message.lastIndexOf(CONTEXT_BEGIN);
  if (begin > 0 && message.endsWith(CONTEXT_FINAL)) {
    // Strip away context:
    message = message.substring(0, begin);
    // No trailing spaces should be allowed in the string database anyway, because that is hard to translate
    // (can't see in Transifex; might not make sense in other languages; etc.).
    // With that, we can add a space before the context-metadata to make it neat, and trim both cases here:
    message = message.trimEnd();
  }

  return message;
}

export function __(message, tokens) {
  const language = localStorageAvailable
    ? window.localStorage.getItem('language') || 'en'
    : window.navigator.language.slice(0, 2) || 'en';

  if (!isProduction) {
    saveMessage(message);
  }

  let translatedMessage = window.i18n_messages[language] ? window.i18n_messages[language][message] || message : message;
  translatedMessage = removeContextMetadata(translatedMessage);

  if (!tokens) {
    return translatedMessage;
  }

  return translatedMessage.replace(/%([^%]+)%/g, function($1, $2) {
    return tokens.hasOwnProperty($2) ? tokens[$2] : $2;
  });
}