Use ranking to improve order of results

lib/pleroma/hashtag.ex

@@ -149,9 +149,39 @@ defmodule Pleroma.Hashtag do
       # This is much more efficient than multiple OR clauses
       search_patterns = Enum.map(search_terms, &"%#{&1}%")
 
-      from(ht in Hashtag,
-        where: fragment("LOWER(?) LIKE ANY(?)", ht.name, ^search_patterns),
-        order_by: [asc: ht.name],
+      # Create ranking query that prioritizes exact matches and closer matches
+      # Use a subquery to properly handle computed columns in ORDER BY
+      base_query =
+        from(ht in Hashtag,
+          where: fragment("LOWER(?) LIKE ANY(?)", ht.name, ^search_patterns),
+          select: %{
+            name: ht.name,
+            # Ranking: exact matches get highest priority (0), then prefix matches (1), then contains (2)
+            match_rank:
+              fragment(
+                """
+                  CASE
+                    WHEN LOWER(?) = ANY(?) THEN 0
+                    WHEN LOWER(?) LIKE ANY(?) THEN 1
+                    ELSE 2
+                  END
+                """,
+                ht.name,
+                ^search_terms,
+                ht.name,
+                ^Enum.map(search_terms, &"#{&1}%")
+              ),
+            # Secondary sort by name length (shorter names first)
+            name_length: fragment("LENGTH(?)", ht.name)
+          }
+        )
+
+      from(result in subquery(base_query),
+        order_by: [
+          asc: result.match_rank,
+          asc: result.name_length,
+          asc: result.name
+        ],
         limit: ^limit,
         offset: ^offset
       )

test/pleroma/hashtag_test.exs

@@ -39,7 +39,6 @@ defmodule Pleroma.HashtagTest do
     end
 
     test "searches hashtags by multiple words in query" do
-      # Create some hashtags
       {:ok, _} = Hashtag.get_or_create_by_name("computer")
       {:ok, _} = Hashtag.get_or_create_by_name("laptop")
       {:ok, _} = Hashtag.get_or_create_by_name("desktop")
@@ -80,19 +79,48 @@ defmodule Pleroma.HashtagTest do
       assert length(results) == 2
     end
 
-    test "handles many search terms efficiently" do
-      # Create hashtags
+    test "handles matching many search terms" do
       {:ok, _} = Hashtag.get_or_create_by_name("computer")
       {:ok, _} = Hashtag.get_or_create_by_name("laptop")
       {:ok, _} = Hashtag.get_or_create_by_name("phone")
       {:ok, _} = Hashtag.get_or_create_by_name("tablet")
 
-      # Search with many terms - should be efficient with PostgreSQL ANY operator
       results = Hashtag.search("new fast computer laptop phone tablet device")
       assert "computer" in results
       assert "laptop" in results
       assert "phone" in results
       assert "tablet" in results
     end
+
+    test "ranks results by match quality" do
+      {:ok, _} = Hashtag.get_or_create_by_name("my_computer")
+      {:ok, _} = Hashtag.get_or_create_by_name("computer_science")
+      {:ok, _} = Hashtag.get_or_create_by_name("computer")
+
+      results = Hashtag.search("computer")
+
+      # Exact match first
+      assert Enum.at(results, 0) == "computer"
+
+      # Prefix match would be next
+      assert Enum.at(results, 1) == "computer_science"
+
+      # worst match is last
+      assert Enum.at(results, 2) == "my_computer"
+    end
+
+    test "prioritizes shorter names when ranking is equal" do
+      # Create hashtags with same ranking but different lengths
+      {:ok, _} = Hashtag.get_or_create_by_name("car")
+      {:ok, _} = Hashtag.get_or_create_by_name("racecar")
+      {:ok, _} = Hashtag.get_or_create_by_name("nascar")
+
+      # Search for "car" - shorter names should come first
+      results = Hashtag.search("car")
+      # Shortest exact match first
+      assert Enum.at(results, 0) == "car"
+      assert "racecar" in results
+      assert "nascar" in results
+    end
   end
 end