Add support for sending user emoji using autocomplete (#205)

* Add support for sending user emoji using autocomplete

What's included:
- An implementation for detecting user emojis
- Addition of user emojis to the emoji autocomplete in the command bar
- Translation of shortcodes into image tags on message sending

What's not included:
- Loading emojis from the active room, loading the user's global emoji packs, loading emoji from spaces
- Selecting custom emoji using the emoji picker

This is a predominantly proof-of-concept change, and everything here may be subject to
architectural review and reworking.

* Amending PR:  Allow sending multiple of the same emoji

* Amending PR:  Add support for emojis in edited messages

* Amend PR:  Apply requested revisions

This commit consists of several small changes, including:
- Fix crash when the user doesn't have the im.ponies.user_emotes account data entry
- Add mx-data-emoticon attribute to command bar emoji
- Rewrite alt text in the command bar interface
- Remove "vertical-align" attribute from sent emoji

* Amending PR:  Fix bugs (listed below)

- Fix bug where sending emoji w/ markdown off resulted in a crash
- Fix bug where alt text in the command bar was wrong

* Amending PR:  Add support for replacement of twemoji shortcodes

* Amending PR: Fix & refactor getAllEmoji -> getShortcodeToEmoji

* Amending PR: Fix bug: Sending two of the same emoji corrupts message

* Amending PR:  Stylistic fixes

src/app/organisms/emoji-board/custom-emoji.js

@@ -0,0 +1,77 @@
+import { emojis } from './emoji';
+
+// Custom emoji are stored in one of three places:
+// - User emojis, which are stored in account data
+// - Room emojis, which are stored in state events in a room
+// - Emoji packs, which are rooms of emojis referenced in the account data or in a room's
+//   cannonical space
+//
+// Emojis and packs referenced from within a user's account data should be available
+// globally, while emojis and packs in rooms and spaces should only be available within
+// those spaces and rooms
+
+// Retrieve a list of user emojis
+//
+// Result is a list of objects, each with a shortcode and an mxc property
+//
+// Accepts a reference to a matrix client as the only argument
+function getUserEmoji(mx) {
+  const accountDataEmoji = mx.getAccountData('im.ponies.user_emotes');
+  if (!accountDataEmoji) {
+    return [];
+  }
+
+  const { images } = accountDataEmoji.event.content;
+  const mapped = Object.entries(images).map((e) => ({
+    shortcode: e[0],
+    mxc: e[1].url,
+  }));
+  return mapped;
+}
+
+// Returns all user emojis and all standard unicode emojis
+//
+// Accepts a reference to a matrix client as the only argument
+//
+// Result is a map from shortcode to the corresponding emoji.  If two emoji share a
+// shortcode, only one will be presented, with priority given to custom emoji.
+//
+// Will eventually be expanded to include all emojis revelant to a room and the user
+function getShortcodeToEmoji(mx) {
+  const allEmoji = new Map();
+
+  emojis.forEach((emoji) => {
+    if (emoji.shortcodes.constructor.name === 'Array') {
+      emoji.shortcodes.forEach((shortcode) => {
+        allEmoji.set(shortcode, emoji);
+      });
+    } else {
+      allEmoji.set(emoji.shortcodes, emoji);
+    }
+  });
+
+  getUserEmoji(mx).forEach((emoji) => {
+    allEmoji.set(emoji.shortcode, emoji);
+  });
+
+  return allEmoji;
+}
+
+// Produces a special list of emoji specifically for auto-completion
+//
+// This list contains each emoji once, with all emoji being deduplicated by shortcode.
+// However, the order of the standard emoji will have been preserved, and alternate
+// shortcodes for the standard emoji will not be considered.
+//
+// Standard emoji are guaranteed to be earlier in the list than custom emoji
+function getEmojiForCompletion(mx) {
+  const allEmoji = new Map();
+  getUserEmoji(mx).forEach((emoji) => {
+    allEmoji.set(emoji.shortcode, emoji);
+  });
+
+  return emojis.filter((e) => !allEmoji.has(e.shortcode))
+    .concat(Array.from(allEmoji.values()));
+}
+
+export { getUserEmoji, getShortcodeToEmoji, getEmojiForCompletion };