FEATURE: prioritize group search order based on prefix match (#16093)

Our @mention user search prioritized users based on prefix matches.

So if searching for `sa` we will display `sam`, `asam` in that order

Previously, we did not prioritize group matches based on prefix. This change ensures better parity.

Implementation notes:

1. User search only prioritizes based on username prefix, not name prefix. TBD if we want to change that.
2. @mention on client side will show 0 group matches if we fill up all the spots with user matches. TBD if we want to unconditionally show the first / second group match.

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

spec/models/group_spec.rb

@@ -923,21 +923,36 @@ describe Group do
   end
 
   describe '.search_groups' do
-    fab!(:group) { Fabricate(:group, name: 'tEsT_more_things', full_name: 'Abc something awesome') }
-    let(:messageable_group) { Fabricate(:group, name: "MessageableGroup", messageable_level: Group::ALIAS_LEVELS[:everyone]) }
+
+    def search_group_names(name)
+      Group.search_groups(name, sort: :auto).map(&:name)
+    end
 
     it 'should return the right groups' do
-      group
+      group_name = Fabricate(:group, name: 'tEsT_more_things', full_name: 'Abc something awesome').name
 
-      expect(Group.search_groups('te')).to eq([group])
-      expect(Group.search_groups('TE')).to eq([group])
-      expect(Group.search_groups('es')).to eq([group])
-      expect(Group.search_groups('ES')).to eq([group])
-      expect(Group.search_groups('ngs')).to eq([group])
-      expect(Group.search_groups('sOmEthi')).to eq([group])
-      expect(Group.search_groups('abc')).to eq([group])
-      expect(Group.search_groups('sOmEthi')).to eq([group])
-      expect(Group.search_groups('test2')).to eq([])
+      expect(search_group_names('te')).to eq([group_name])
+      expect(search_group_names('TE')).to eq([group_name])
+      expect(search_group_names('es')).to eq([group_name])
+      expect(search_group_names('ES')).to eq([group_name])
+      expect(search_group_names('ngs')).to eq([group_name])
+      expect(search_group_names('sOmEthi')).to eq([group_name])
+      expect(search_group_names('abc')).to eq([group_name])
+      expect(search_group_names('sOmEthi')).to eq([group_name])
+      expect(search_group_names('test2')).to eq([])
+    end
+
+    it "should prioritize prefix matches on group's name or fullname" do
+      Fabricate(:group, name: 'pears_11', full_name: 'fred apple')
+      Fabricate(:group, name: 'apples', full_name: 'jane orange')
+      Fabricate(:group, name: 'oranges2', full_name: 'nothing')
+      Fabricate(:group, name: 'oranges1', full_name: 'ms fred')
+
+      expect(search_group_names('ap')).to eq(['apples', 'pears_11'])
+      expect(search_group_names('fr')).to eq(['pears_11', 'oranges1'])
+      expect(search_group_names('oran')).to eq(['oranges1', 'oranges2', 'apples'])
+
+      expect(search_group_names('pearsX11')).to eq([])
     end
   end