Migrate "i18n-provider" to new context API (#8213)

The "i18n-provider" module has been replaced by a new `i18n.js` module
in the `contexts` directory which provides the `t` function via the new
React Context API.

The legacy context API is still used throughout the codebase, so a
legacy context provider has also been added as a shim until we migrate
away from the old API. The migration does require changing every single
place where the `t` function is used, so it is a non-trivial amount of
work. This shim allows us to tackle it one piece at a time without
breaking anything.

This was placed in a new `contexts` directory because it didn't seem
to belong in any existing categories. It certainly isn't a higher-order
component.

.storybook/preview.js

@@ -1,7 +1,7 @@
 import React from 'react'
 import { addDecorator, addParameters } from '@storybook/react'
 import { withKnobs } from '@storybook/addon-knobs/react'
-import I18nProvider from '../ui/app/helpers/higher-order-components/i18n-provider'
+import I18nProvider from '../ui/app/contexts/i18n'
 import { Provider } from 'react-redux'
 import configureStore from '../ui/app/store/store'
 import '../ui/app/css/index.scss'

ui/app/contexts/i18n.js

@@ -0,0 +1,61 @@
+import React, { Component, createContext, useMemo } from 'react'
+import PropTypes from 'prop-types'
+import { useSelector } from 'react-redux'
+import { getMessage } from '../helpers/utils/i18n-helper'
+import { getCurrentLocale } from '../ducks/metamask/metamask'
+import { getCurrentLocaleMessages, getEnLocaleMessages } from '../ducks/locale/locale'
+
+export const I18nContext = createContext((key) => `[${key}]`)
+
+export const I18nProvider = (props) => {
+  const currentLocale = useSelector(getCurrentLocale)
+  const current = useSelector(getCurrentLocaleMessages)
+  const en = useSelector(getEnLocaleMessages)
+
+  const t = useMemo(() => {
+    return (key, ...args) => (
+      getMessage(currentLocale, current, key, ...args) ||
+      getMessage(currentLocale, en, key, ...args)
+    )
+  }, [currentLocale, current, en])
+
+  return (
+    <I18nContext.Provider value={t}>
+      { props.children }
+    </I18nContext.Provider>
+  )
+}
+
+I18nProvider.propTypes = {
+  children: PropTypes.node,
+}
+
+I18nProvider.defaultProps = {
+  children: undefined,
+}
+
+export class LegacyI18nProvider extends Component {
+  static propTypes = {
+    children: PropTypes.node,
+  }
+
+  static defaultProps = {
+    children: undefined,
+  }
+
+  static contextType = I18nContext
+
+  static childContextTypes = {
+    t: PropTypes.func,
+  }
+
+  getChildContext () {
+    return {
+      t: this.context,
+    }
+  }
+
+  render () {
+    return this.props.children
+  }
+}

ui/app/ducks/locale/locale.js

@@ -11,3 +11,7 @@ export default function reduceLocaleMessages (state = {}, { type, value }) {
       return state
   }
 }
+
+export const getCurrentLocaleMessages = (state) => state.localeMessages.current
+
+export const getEnLocaleMessages = (state) => state.localeMessages.en

ui/app/ducks/metamask/metamask.js

@@ -379,3 +379,5 @@ export default function reduceMetamask (state = {}, action) {
       return metamaskState
   }
 }
+
+export const getCurrentLocale = (state) => state.metamask.currentLocale

ui/app/helpers/higher-order-components/i18n-provider.js

@@ -1,46 +0,0 @@
-import { Component } from 'react'
-import { connect } from 'react-redux'
-import PropTypes from 'prop-types'
-import { getMessage } from '../utils/i18n-helper'
-
-class I18nProvider extends Component {
-  getChildContext () {
-    const { localeMessages, currentLocale } = this.props
-    const { current, en } = localeMessages
-    return {
-      /**
-       * Returns a localized message for the given key
-       * @param {string} key - The message key
-       * @param {string[]} args - A list of message substitution replacements
-       * @returns {string|undefined|null} - The localized message if available
-       */
-      t (key, ...args) {
-        return getMessage(currentLocale, current, key, ...args) || getMessage(currentLocale, en, key, ...args)
-      },
-    }
-  }
-
-  render () {
-    return this.props.children
-  }
-}
-
-I18nProvider.propTypes = {
-  localeMessages: PropTypes.object,
-  currentLocale: PropTypes.string,
-  children: PropTypes.object,
-}
-
-I18nProvider.childContextTypes = {
-  t: PropTypes.func,
-}
-
-const mapStateToProps = (state) => {
-  const { localeMessages, metamask: { currentLocale } } = state
-  return {
-    currentLocale,
-    localeMessages,
-  }
-}
-
-export default connect(mapStateToProps)(I18nProvider)

ui/app/pages/index.js

@@ -5,7 +5,7 @@ import { HashRouter } from 'react-router-dom'
 import * as Sentry from '@sentry/browser'
 import ErrorPage from './error'
 import Routes from './routes'
-import I18nProvider from '../helpers/higher-order-components/i18n-provider'
+import { I18nProvider, LegacyI18nProvider } from '../contexts/i18n'
 import MetaMetricsProvider from '../helpers/higher-order-components/metametrics/metametrics.provider'
 
 class Index extends PureComponent {
@@ -27,10 +27,12 @@ class Index extends PureComponent {
       return (
         <Provider store={store}>
           <I18nProvider>
-            <ErrorPage
-              error={error}
-              errorId={errorId}
-            />
+            <LegacyI18nProvider>
+              <ErrorPage
+                error={error}
+                errorId={errorId}
+              />
+            </LegacyI18nProvider>
           </I18nProvider>
         </Provider>
       )
@@ -41,7 +43,9 @@ class Index extends PureComponent {
         <HashRouter hashType="noslash">
           <MetaMetricsProvider>
             <I18nProvider>
-              <Routes />
+              <LegacyI18nProvider>
+                <Routes />
+              </LegacyI18nProvider>
             </I18nProvider>
           </MetaMetricsProvider>
         </HashRouter>