emoji: Rank "popular" > custom > other emoji

Fixes part of zulip#1068.

lib/model/emoji.dart

@@ -237,6 +237,17 @@ class EmojiStoreImpl with EmojiStore {
     ];
   }
 
+  static final _popularEmojiCodes = (() {
+    assert(_popularCandidates.every((c) =>
+      c.emojiType == ReactionType.unicodeEmoji));
+    return Set.of(_popularCandidates.map((c) => c.emojiCode));
+  })();
+
+  static bool _isPopularEmoji(EmojiCandidate candidate) {
+    return candidate.emojiType == ReactionType.unicodeEmoji
+      && _popularEmojiCodes.contains(candidate.emojiCode);
+  }
+
   EmojiCandidate _emojiCandidateFor({
     required ReactionType emojiType,
     required String emojiCode,
@@ -406,7 +417,8 @@ class EmojiAutocompleteQuery extends ComposeAutocompleteQuery {
   EmojiAutocompleteResult? testCandidate(EmojiCandidate candidate) {
     final matchQuality = match(candidate);
     if (matchQuality == null) return null;
-    return EmojiAutocompleteResult(candidate, _rankResult(matchQuality));
+    return EmojiAutocompleteResult(candidate,
+      _rankResult(matchQuality, candidate));
   }
 
   // Compare get_emoji_matcher in Zulip web:shared/src/typeahead.ts .
@@ -459,17 +471,24 @@ class EmojiAutocompleteQuery extends ComposeAutocompleteQuery {
 
   /// A measure of the result's quality in the context of the query,
   /// ranked from 0 (best) to one less than [_numResultRanks].
-  static int _rankResult(EmojiMatchQuality matchQuality) {
+  static int _rankResult(EmojiMatchQuality matchQuality, EmojiCandidate candidate) {
     // Compare sort_emojis in Zulip web:
     //   https://github.com/zulip/zulip/blob/83a121c7e/web/shared/src/typeahead.ts#L322-L382
     //
     // Behavior differences we should or might copy, TODO(#1068):
-    //  * Web ranks popular emoji > custom emoji > others; we don't yet.
     //  * Web ranks matches starting at a word boundary ahead of
     //    other non-prefix matches; we don't yet.
+    //  * Relatedly, web favors popular emoji only upon a word-aligned match.
     //  * Web ranks each name of a Unicode emoji separately.
     //
     // Behavior differences that web should probably fix, TODO(web):
+    //  * Among popular emoji with non-exact matches,
+    //    web doesn't prioritize prefix over word-aligned; we do.
+    //    (This affects just one case: for query "o",
+    //    we put :octopus: before :working_on_it:.)
+    //  * Web only counts an emoji as "popular" for ranking if the query
+    //    is a prefix of a single word in the name; so "thumbs_" or "working_on_i"
+    //    lose the ranking boost for :thumbs_up: and :working_on_it: respectively.
     //  * Web starts with only case-sensitive exact matches ("perfect matches"),
     //    and puts case-insensitive exact matches just ahead of prefix matches;
     //    it also distinguishes prefix matches by case-sensitive vs. not.
@@ -480,15 +499,24 @@ class EmojiAutocompleteQuery extends ComposeAutocompleteQuery {
     //    because emoji with the same name will mostly both match or both not;
     //    but it breaks if the Unicode emoji was a literal match.
 
+    final isPopular = EmojiStoreImpl._isPopularEmoji(candidate);
+    final isCustomEmoji = switch (candidate.emojiType) {
+      // The web implementation calls this condition `is_realm_emoji`,
+      // but its actual semantics is it's true for the Zulip extra emoji too.
+      // See `zulip_emoji` in web:src/emoji.ts .
+      ReactionType.realmEmoji || ReactionType.zulipExtraEmoji => true,
+      ReactionType.unicodeEmoji => false,
+    };
     return switch (matchQuality) {
       EmojiMatchQuality.exact  => 0,
-      EmojiMatchQuality.prefix => 1,
-      EmojiMatchQuality.other  => 2,
+      EmojiMatchQuality.prefix => isPopular ? 1 : isCustomEmoji ? 3 : 4,
+      // TODO word-boundary vs. not
+      EmojiMatchQuality.other  => isPopular ? 2 : isCustomEmoji ? 5 : 6,
     };
   }
 
   /// The number of possible values returned by [_rankResult].
-  static const _numResultRanks = 3;
+  static const _numResultRanks = 7;
 
   @override
   String toString() {

test/model/emoji_test.dart

@@ -245,9 +245,9 @@ void main() {
       await Future(() {});
       check(done).isTrue();
       check(view.results).deepEquals([
-        isUnicodeResult(names: ['bookmark']),
         isRealmResult(emojiName: 'happy'),
         isZulipResult(),
+        isUnicodeResult(names: ['bookmark']),
       ]);
     });
 
@@ -287,15 +287,17 @@ void main() {
     }
 
     test('results end-to-end', () async {
+      // (See more detailed rank tests below, on EmojiAutocompleteQuery.)
+
       final unicodeEmoji = {
         '1f4d3': ['notebook'], '1f516': ['bookmark'], '1f4d6': ['book']};
 
       // Empty query -> base ordering.
       check(await resultsOf('', unicodeEmoji: unicodeEmoji)).deepEquals([
+        isZulipResult(),
         isUnicodeResult(names: ['notebook']),
         isUnicodeResult(names: ['bookmark']),
         isUnicodeResult(names: ['book']),
-        isZulipResult(),
       ]);
 
       // With query, exact match precedes prefix match precedes other.
@@ -468,17 +470,56 @@ void main() {
       check(rankOf(query, a)!).isLessThan(rankOf(query, b)!);
     }
 
+    void checkSameRank(String query, EmojiCandidate a, EmojiCandidate b) {
+      check(rankOf(query, a)!).equals(rankOf(query, b)!);
+    }
+
+    final octopus = unicode(['octopus'], emojiCode: '1f419');
+    final workingOnIt = unicode(['working_on_it'], emojiCode: '1f6e0');
+
     test('ranks exact before prefix before other match', () {
       checkPrecedes('o', unicode(['o']), unicode(['onion']));
       checkPrecedes('o', unicode(['onion']), unicode(['book']));
     });
 
+    test('ranks popular before realm before other Unicode', () {
+      checkPrecedes('o', octopus, realmCandidate('open_book'));
+      checkPrecedes('o', realmCandidate('open_book'), unicode(['ok']));
+    });
+
+    test('ranks Zulip extra emoji same as realm emoji', () {
+      checkSameRank('z', zulipCandidate(), realmCandidate('zounds'));
+    });
+
+    test('ranks exact-vs-not more significant than popular/custom/other', () {
+      // Generic Unicode exact beats popular prefix…
+      checkPrecedes('o', unicode(['o']), octopus);
+      // … which really does count as popular, beating realm prefix.
+      checkPrecedes('o', octopus, realmCandidate('open_book'));
+    });
+
+    test('ranks popular-vs-not more significant than prefix/other', () {
+      // Popular other beats realm prefix.
+      checkPrecedes('o', workingOnIt, realmCandidate('open_book'));
+    });
+
+    test('ranks prefix/other more significant than custom/other', () {
+      // Generic Unicode prefix beats realm other.
+      checkPrecedes('o', unicode(['ok']), realmCandidate('yo'));
+    });
+
     test('full list of ranks', () {
       check([
-        rankOf('o', unicode(['o'])),              // exact
-        rankOf('o', unicode(['onion'])),          // prefix
-        rankOf('o', unicode(['book'])),           // other
-      ]).deepEquals([0, 1, 2]);
+        rankOf('o', unicode(['o'])),              // exact (generic)
+        rankOf('o', octopus),                     // prefix popular
+        rankOf('o', workingOnIt),                 // other popular
+        rankOf('o', realmCandidate('open_book')), // prefix realm
+        rankOf('z', zulipCandidate()),            //  == prefix :zulip:
+        rankOf('o', unicode(['ok'])),             // prefix generic
+        rankOf('o', realmCandidate('yo')),        // other realm
+        rankOf('p', zulipCandidate()),            //  == other :zulip:
+        rankOf('o', unicode(['book'])),           // other generic
+      ]).deepEquals([0, 1, 2, 3, 3, 4, 5, 5, 6]);
     });
   });
 }