2 files changed, 94 insertions, 8 deletions
diff --git a/lib/pleroma/user.ex b/lib/pleroma/user.ex
index c5c74d132..f0193207c 100644
--- a/lib/pleroma/user.ex
+++ b/lib/pleroma/user.ex
@@ -92,6 +92,7 @@ defmodule Pleroma.User do
     field(:local, :boolean, default: true)
     field(:follower_address, :string)
     field(:following_address, :string)
+    field(:levenshtein_distance, :integer, virtual: true)
     field(:search_rank, :float, virtual: true)
     field(:search_type, :integer, virtual: true)
     field(:tags, {:array, :string}, default: [])
diff --git a/lib/pleroma/user/search.ex b/lib/pleroma/user/search.ex
index cec59c372..3878e81bf 100644
--- a/lib/pleroma/user/search.ex
+++ b/lib/pleroma/user/search.ex
@@ -8,6 +8,8 @@ defmodule Pleroma.User.Search do
   import Ecto.Query
 
   @limit 20
+  @levenshtein_max_query_length 5
+  @search_rank_threshold 0
 
   def search(query_string, opts \\ []) do
     resolve = Keyword.get(opts, :resolve, false)
@@ -31,7 +33,10 @@ defmodule Pleroma.User.Search do
 
   defp format_query(query_string) do
     # Strip the beginning @ off if there is a query
-    query_string = String.trim_leading(query_string, "@")
+    query_string =
+      query_string
+      |> String.trim()
+      |> String.trim_leading("@")
 
     with [name, domain] <- String.split(query_string, "@") do
       encoded_domain =
@@ -47,15 +52,33 @@ defmodule Pleroma.User.Search do
     end
   end
 
+  defp levenshtein_applicable?(query_string) do
+    String.length(query_string) <= @levenshtein_max_query_length
+  end
+
   defp search_query(query_string, for_user, following) do
-    for_user
-    |> base_query(following)
-    |> filter_blocked_user(for_user)
-    |> filter_invisible_users()
-    |> filter_blocked_domains(for_user)
-    |> fts_search(query_string)
-    |> trigram_rank(query_string)
+    query =
+      for_user
+      |> base_query(following)
+      |> filter_blocked_user(for_user)
+      |> filter_invisible_users()
+      |> filter_blocked_domains(for_user)
+
+    query =
+      if levenshtein_applicable?(query_string) do
+        query
+        |> levenshtein_distance(query_string)
+        |> fts_levenshtein_search(query_string)
+        |> trigram_levenshtein_rank(query_string)
+      else
+        query
+        |> fts_search(query_string)
+        |> trigram_rank(query_string)
+      end
+
+    query
     |> boost_search_rank(for_user)
+    |> filter_by_search_rank()
     |> subquery()
     |> order_by(desc: :search_rank)
     |> maybe_restrict_local(for_user)
@@ -78,6 +101,25 @@ defmodule Pleroma.User.Search do
     )
   end
 
+  defp fts_levenshtein_search(query, query_string) do
+    tsquery = to_tsquery(query_string)
+
+    from(
+      u in subquery(query),
+      where:
+        fragment(
+          """
+          ? <= 2 OR
+            (to_tsvector('simple', ?) || to_tsvector('simple', ?)) @@ to_tsquery('simple', ?)
+          """,
+          u.levenshtein_distance,
+          u.name,
+          u.nickname,
+          ^tsquery
+        )
+    )
+  end
+
   defp to_tsquery(query_string) do
     String.trim_trailing(query_string, "@" <> local_domain())
     |> String.replace(~r/[!-\/|@|[-`|{-~|:-?]+/, " ")
@@ -87,6 +129,45 @@ defmodule Pleroma.User.Search do
     |> Enum.join(" | ")
   end
 
+  # Trigram-based rank with bonus for close Levenshtein distance b/w query and nickname
+  defp trigram_levenshtein_rank(query, query_string) do
+    from(
+      u in subquery(query),
+      select_merge: %{
+        search_rank:
+          fragment(
+            "similarity(?, trim(? || ' ' || coalesce(?, ''))) + \
+                            (CASE WHEN ? = 0 THEN 1.0 \
+                              WHEN ? = 1 AND length(?) > 1 THEN 0.5
+                              WHEN ? = 2 AND length(?) > 3 THEN 0.2
+                              ELSE 0 END)",
+            ^query_string,
+            u.nickname,
+            u.name,
+            u.levenshtein_distance,
+            u.levenshtein_distance,
+            ^query_string,
+            u.levenshtein_distance,
+            ^query_string
+          )
+      }
+    )
+  end
+
+  defp levenshtein_distance(query, query_string) do
+    from(
+      u in query,
+      select_merge: %{
+        levenshtein_distance:
+          fragment(
+            "levenshtein(?, regexp_replace(?, '@.+', ''))",
+            ^query_string,
+            u.nickname
+          )
+      }
+    )
+  end
+
   defp trigram_rank(query, query_string) do
     from(
       u in query,
@@ -185,4 +266,8 @@ defmodule Pleroma.User.Search do
   end
 
   defp boost_search_rank(query, _for_user), do: query
+
+  defp filter_by_search_rank(query) do
+    from(u in subquery(query), where: u.search_rank > @search_rank_threshold)
+  end
 end