first commit

common/resources/client/i18n/handle-plural-message.tsx

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+import memoize from 'nano-memoize';
+import {MessageDescriptor} from './message-descriptor';
+
+// this will get memoized by enclosing function (<Trans> or useTrans)
+export function handlePluralMessage(
+  localeCode: string,
+  {message, values}: MessageDescriptor
+): string {
+  // find plural config e.g. [one 1 item|other :count items]
+  const match = message.match(/\[(.+?)]/);
+  const count = values?.count;
+  if (match && match[1] && !Number.isNaN(count)) {
+    // get config without brackets and split by pipe e.g. [one 1 item, other :count items]
+    const [pluralPlaceholder, pluralConfig] = match;
+    const choices = pluralConfig.split('|');
+    if (!choices.length) return message;
+
+    // use Intl.PluralRules to determine which choice to use, based on special "count" value
+    const rules = getRules(localeCode);
+    const choiceName = rules.select(count as number);
+
+    // find the correct choice from config, or use first one
+    let choiceConfig = choices.find(c => {
+      return c.startsWith(choiceName);
+    });
+    if (!choiceConfig) {
+      choiceConfig = choices[0];
+    }
+
+    // get rid of plural prefix e.g. one 1 item => 1 item
+    const choice = choiceConfig.substring(choiceConfig.indexOf(' ') + 1);
+
+    return message.replace(pluralPlaceholder, choice);
+  }
+  return message;
+}
+
+const getRules = memoize((localeCode: string) => {
+  return new Intl.PluralRules(localeCode);
+});