Remove local_time gem, and add similar (#2875)

app/javascript/packs/public.js

@@ -1,16 +1,70 @@
 import emojify from 'mastodon/emoji';
 import { length } from 'stringz';
+import { default as dateFormat } from 'date-fns/format';
+import distanceInWordsStrict from 'date-fns/distance_in_words_strict';
 
 window.jQuery = window.$ = require('jquery');
 require('jquery-ujs');
 require.context('../images/', true);
 
+const parseFormat = (format) => format.replace(/%(\w)/g, (_, modifier) => {
+  switch (modifier) {
+  case '%':
+    return '%';
+  case 'a':
+    return 'ddd';
+  case 'A':
+    return 'ddd';
+  case 'b':
+    return 'MMM';
+  case 'B':
+    return 'MMMM';
+  case 'd':
+    return 'DD';
+  case 'H':
+    return 'HH';
+  case 'I':
+    return 'hh';
+  case 'l':
+    return 'H';
+  case 'm':
+    return 'M';
+  case 'M':
+    return 'mm';
+  case 'p':
+    return 'A';
+  case 'S':
+    return 'ss';
+  case 'w':
+    return 'd';
+  case 'y':
+    return 'YY';
+  case 'Y':
+    return 'YYYY';
+  default:
+    return `%${modifier}`;
+  }
+});
+
 $(() => {
   $.each($('.emojify'), (_, content) => {
     const $content = $(content);
     $content.html(emojify($content.html()));
   });
 
+  $('time[data-format]').each((_, content) => {
+    const $content = $(content);
+    const format = parseFormat($content.data('format'));
+    const formattedDate = dateFormat($content.attr('datetime'), format);
+    $content.text(formattedDate);
+  });
+
+  $('time.time-ago').each((_, content) => {
+    const $content = $(content);
+    const timeAgo = distanceInWordsStrict(new Date(), $content.attr('datetime'), { addSuffix: true });
+    $content.text(timeAgo);
+  });
+
   $('.video-player video').on('click', e => {
     if (e.target.paused) {
       e.target.play();