(fix) Backfill visitor referrer if missing

lib/revstack/tracking/service.ex

@@ -26,7 +26,8 @@ defmodule Revstack.Tracking.Service do
     method = Map.get(attrs, :method)
 
     with {:ok, visitor} <- find_or_create_visitor(ip, user_agent, referrer),
-         {:ok, _page_visit} <- create_page_visit(visitor, path, full_url, query_string, method) do
+         {:ok, _page_visit} <-
+           create_page_visit(visitor, path, full_url, query_string, method, referrer) do
       maybe_enrich_location(visitor)
       {:ok, visitor}
     end
@@ -39,7 +40,9 @@ defmodule Revstack.Tracking.Service do
   def find_or_create_visitor(ip_address, user_agent \\ nil, referrer \\ nil) do
     case Visitor.by_ip(ip_address, authorize?: false) do
       {:ok, visitor} ->
-        Visitor.record_visit(visitor, authorize?: false)
+        with {:ok, visitor} <- maybe_backfill_referrer(visitor, referrer) do
+          Visitor.record_visit(visitor, authorize?: false)
+        end
 
       {:error, _} ->
         Visitor.create(
@@ -56,19 +59,42 @@ defmodule Revstack.Tracking.Service do
   @doc """
   Creates a page visit record for a visitor.
   """
-  def create_page_visit(visitor, path, full_url \\ nil, query_string \\ nil, method \\ nil) do
+  def create_page_visit(
+        visitor,
+        path,
+        full_url \\ nil,
+        query_string \\ nil,
+        method \\ nil,
+        referrer \\ nil
+      ) do
     VisitorPageVisit.create(
       %{
         visitor_id: visitor.id,
         path: path,
         full_url: full_url,
         query_string: query_string,
-        method: method
+        method: method,
+        referrer: referrer
       },
       authorize?: false
     )
   end
 
+  defp maybe_backfill_referrer(visitor, referrer) do
+    cond do
+      present_referrer?(visitor.referrer) ->
+        {:ok, visitor}
+
+      present_referrer?(referrer) ->
+        Visitor.backfill_referrer(visitor, %{referrer: referrer}, authorize?: false)
+
+      true ->
+        {:ok, visitor}
+    end
+  end
+
+  defp present_referrer?(value), do: is_binary(value) and String.trim(value) != ""
+
   @doc """
   Triggers location enrichment for a visitor if location data is missing.
   Runs asynchronously to avoid blocking page rendering.

lib/revstack/tracking/visitor.ex

@@ -15,6 +15,7 @@ defmodule Revstack.Tracking.Visitor do
     define :read, action: :read
     define :by_ip, action: :by_ip, args: [:ip_address]
     define :record_visit, action: :record_visit
+    define :backfill_referrer, action: :backfill_referrer
     define :enrich_location, action: :enrich_location
     define :destroy, action: :destroy
   end
@@ -53,6 +54,12 @@ defmodule Revstack.Tracking.Visitor do
       change increment(:visit_count)
     end
 
+    update :backfill_referrer do
+      require_atomic? false
+
+      accept [:referrer]
+    end
+
     update :enrich_location do
       require_atomic? false
 

lib/revstack/tracking/visitor_page_visit.ex

@@ -26,6 +26,7 @@ defmodule Revstack.Tracking.VisitorPageVisit do
         :full_url,
         :query_string,
         :method,
+        :referrer,
         :visitor_id
       ]
 
@@ -80,6 +81,11 @@ defmodule Revstack.Tracking.VisitorPageVisit do
       public? true
     end
 
+    attribute :referrer, :string do
+      allow_nil? true
+      public? true
+    end
+
     attribute :visited_at, :utc_datetime do
       allow_nil? false
       public? true

lib/revstack_web/plugs/visitor_tracking.ex

@@ -17,7 +17,7 @@ defmodule RevstackWeb.Plugs.VisitorTracking do
   def call(conn, _opts) do
     ip = Service.extract_ip(conn)
     user_agent = get_user_agent(conn)
-    referrer = get_referrer(conn)
+    referrer = get_referrer(conn) || Plug.Conn.get_session(conn, :visitor_referrer)
 
     conn
     |> Plug.Conn.assign(:visitor_ip, ip)
@@ -54,5 +54,15 @@ defmodule RevstackWeb.Plugs.VisitorTracking do
     conn
     |> Plug.Conn.get_req_header("referer")
     |> List.first()
+    |> normalize_blank()
   end
+
+  defp normalize_blank(value) when is_binary(value) do
+    case String.trim(value) do
+      "" -> nil
+      trimmed -> trimmed
+    end
+  end
+
+  defp normalize_blank(_value), do: nil
 end

priv/repo/migrations/20260413202952_add_referrer_to_visitor_page_visits.exs

@@ -0,0 +1,21 @@
+defmodule Revstack.Repo.Migrations.AddReferrerToVisitorPageVisits do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:visitor_page_visits) do
+      add(:referrer, :text)
+    end
+  end
+
+  def down do
+    alter table(:visitor_page_visits) do
+      remove(:referrer)
+    end
+  end
+end

priv/resource_snapshots/repo/visitor_page_visits/20260413202952.json

@@ -0,0 +1,159 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": true,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "path",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "full_url",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "query_string",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "method",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "referrer",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "visited_at",
+      "type": "utc_datetime"
+    },
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"(now() AT TIME ZONE 'utc')\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "inserted_at",
+      "type": "utc_datetime_usec"
+    },
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"(now() AT TIME ZONE 'utc')\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "updated_at",
+      "type": "utc_datetime_usec"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": {
+        "deferrable": false,
+        "destination_attribute": "id",
+        "destination_attribute_default": null,
+        "destination_attribute_generated": null,
+        "index?": false,
+        "match_type": null,
+        "match_with": null,
+        "multitenancy": {
+          "attribute": null,
+          "global": null,
+          "strategy": null
+        },
+        "name": "visitor_page_visits_visitor_id_fkey",
+        "on_delete": null,
+        "on_update": null,
+        "primary_key?": true,
+        "schema": null,
+        "table": "visitors"
+      },
+      "scale": null,
+      "size": null,
+      "source": "visitor_id",
+      "type": "uuid"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "create_table_options": null,
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "CA26469D09F600007777880AC5713745DD76FBCAF8FE41A0B74034325D189045",
+  "identities": [],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.Revstack.Repo",
+  "schema": null,
+  "table": "visitor_page_visits"
+}

test/revstack/tracking/service_test.exs

@@ -49,6 +49,28 @@ defmodule Revstack.Tracking.ServiceTest do
 
       assert visitor.referrer == "https://google.com"
     end
+
+    test "backfills referrer for existing visitor when missing" do
+      {:ok, visitor1} = Service.find_or_create_visitor("203.0.113.6", "TestAgent", nil)
+      assert is_nil(visitor1.referrer)
+
+      {:ok, visitor2} =
+        Service.find_or_create_visitor("203.0.113.6", "TestAgent", "https://google.com")
+
+      assert visitor2.id == visitor1.id
+      assert visitor2.referrer == "https://google.com"
+    end
+
+    test "does not overwrite existing referrer for existing visitor" do
+      {:ok, visitor1} =
+        Service.find_or_create_visitor("203.0.113.7", "TestAgent", "https://google.com")
+
+      {:ok, visitor2} =
+        Service.find_or_create_visitor("203.0.113.7", "TestAgent", "https://bing.com")
+
+      assert visitor2.id == visitor1.id
+      assert visitor2.referrer == "https://google.com"
+    end
   end
 
   describe "create_page_visit/5" do
@@ -78,6 +100,22 @@ defmodule Revstack.Tracking.ServiceTest do
       assert visit.method == "GET"
     end
 
+    test "stores referrer on page visit" do
+      {:ok, visitor} = Service.find_or_create_visitor("203.0.113.13")
+
+      assert {:ok, visit} =
+               Service.create_page_visit(
+                 visitor,
+                 "/services",
+                 "http://localhost/services",
+                 nil,
+                 "GET",
+                 "https://example.com/source"
+               )
+
+      assert visit.referrer == "https://example.com/source"
+    end
+
     test "creates multiple page visits for same visitor" do
       {:ok, visitor} = Service.find_or_create_visitor("203.0.113.12")
 
@@ -96,7 +134,7 @@ defmodule Revstack.Tracking.ServiceTest do
                Service.track_page_visit(%{
                  ip_address: "203.0.113.20",
                  user_agent: "TestUA",
-                 referrer: nil,
+                 referrer: "https://example.com/source",
                  path: "/",
                  full_url: "http://localhost/",
                  query_string: nil,
@@ -109,6 +147,7 @@ defmodule Revstack.Tracking.ServiceTest do
       visits = VisitorPageVisit.for_visitor!(visitor.id, authorize?: false)
       assert length(visits) == 1
       assert hd(visits).path == "/"
+      assert hd(visits).referrer == "https://example.com/source"
     end
 
     test "tracks multiple pages for the same visitor" do