add privacy-first analytics with progressive event collection

Three-layer pipeline: Plug for all HTTP requests (no JS needed), LiveView
hook for SPA navigations, JS hook for screen width. ETS-backed buffer
batches writes to SQLite every 10s. Daily-rotating salt for visitor hashing.
Includes admin dashboard with date ranges, visitor trends, top pages,
sources, devices, and e-commerce conversion funnel. Oban cron for 12-month
data retention.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/berrypod_web/live/admin/analytics_test.exs

@@ -0,0 +1,106 @@
+defmodule BerrypodWeb.Admin.AnalyticsTest do
+  use BerrypodWeb.ConnCase, async: false
+
+  import Phoenix.LiveViewTest
+  import Berrypod.AccountsFixtures
+
+  alias Berrypod.Analytics.{Buffer, Event}
+  alias Berrypod.Repo
+
+  setup do
+    send(Buffer, :flush)
+    :timer.sleep(50)
+
+    user = user_fixture()
+    %{user: user}
+  end
+
+  describe "unauthenticated" do
+    test "redirects to login", %{conn: conn} do
+      {:error, redirect} = live(conn, ~p"/admin/analytics")
+      assert {:redirect, %{to: path}} = redirect
+      assert path == ~p"/users/log-in"
+    end
+  end
+
+  describe "analytics dashboard" do
+    setup %{conn: conn, user: user} do
+      %{conn: log_in_user(conn, user)}
+    end
+
+    test "renders the analytics page", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/admin/analytics")
+
+      assert html =~ "Analytics"
+      assert html =~ "Unique visitors"
+      assert html =~ "Total pageviews"
+      assert html =~ "Bounce rate"
+      assert html =~ "Visit duration"
+    end
+
+    test "shows zero state with no data", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/admin/analytics")
+
+      assert html =~ "No data for this period"
+    end
+
+    test "shows data when events exist", %{conn: conn} do
+      now = DateTime.utc_now() |> DateTime.truncate(:second)
+
+      Repo.insert_all(Event, [
+        [
+          id: Ecto.UUID.generate(),
+          name: "pageview",
+          pathname: "/",
+          visitor_hash: :crypto.strong_rand_bytes(8),
+          session_hash: :crypto.strong_rand_bytes(8),
+          browser: "Chrome",
+          os: "macOS",
+          inserted_at: now
+        ]
+      ])
+
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      assert has_element?(view, "rect")
+    end
+
+    test "changes period", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      html = render_click(view, "change_period", %{"period" => "7d"})
+      assert html =~ "Analytics"
+    end
+
+    test "changes tab to sources", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      html = render_click(view, "change_tab", %{"tab" => "sources"})
+      assert html =~ "Top sources"
+      assert html =~ "Top referrers"
+    end
+
+    test "changes tab to countries", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      html = render_click(view, "change_tab", %{"tab" => "countries"})
+      assert html =~ "Countries"
+    end
+
+    test "changes tab to devices", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      html = render_click(view, "change_tab", %{"tab" => "devices"})
+      assert html =~ "Browsers"
+      assert html =~ "Operating systems"
+      assert html =~ "Screen sizes"
+    end
+
+    test "changes tab to funnel", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/admin/analytics")
+
+      html = render_click(view, "change_tab", %{"tab" => "funnel"})
+      assert html =~ "Conversion funnel"
+    end
+  end
+end

test/berrypod_web/plugs/analytics_test.exs

@@ -0,0 +1,115 @@
+defmodule BerrypodWeb.Plugs.AnalyticsTest do
+  use BerrypodWeb.ConnCase, async: false
+
+  import Ecto.Query
+
+  alias Berrypod.Analytics.{Buffer, Event}
+  alias Berrypod.Repo
+
+  setup do
+    send(Buffer, :flush)
+    :timer.sleep(50)
+    :ok
+  end
+
+  describe "analytics plug" do
+    test "records a pageview on GET request", %{conn: conn} do
+      conn
+      |> put_req_header("user-agent", "Mozilla/5.0 Chrome/120.0")
+      |> get(~p"/")
+
+      send(Buffer, :flush)
+      :timer.sleep(50)
+
+      events =
+        from(e in Event, where: e.pathname == "/" and e.name == "pageview")
+        |> Repo.all()
+
+      assert length(events) >= 1
+      event = hd(events)
+      assert event.browser == "Chrome"
+    end
+
+    test "does not record on POST request", %{conn: conn} do
+      count_before = Repo.aggregate(Event, :count)
+
+      conn
+      |> put_req_header("user-agent", "Mozilla/5.0 Chrome/120.0")
+      |> post(~p"/checkout", %{})
+
+      send(Buffer, :flush)
+      :timer.sleep(50)
+
+      count_after = Repo.aggregate(Event, :count)
+      # POST to /checkout shouldn't create a pageview event via the plug
+      # (it may fail with a redirect, but the plug should have skipped)
+      assert count_after == count_before
+    end
+
+    test "skips bots", %{conn: conn} do
+      count_before = Repo.aggregate(Event, :count)
+
+      conn
+      |> put_req_header("user-agent", "Googlebot/2.1 (+http://www.google.com/bot.html)")
+      |> get(~p"/")
+
+      send(Buffer, :flush)
+      :timer.sleep(50)
+
+      count_after = Repo.aggregate(Event, :count)
+      assert count_after == count_before
+    end
+
+    test "stores analytics data in session", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("user-agent", "Mozilla/5.0 Firefox/121.0")
+        |> get(~p"/")
+
+      assert get_session(conn, "analytics_visitor_hash") |> is_binary()
+      assert get_session(conn, "analytics_browser") == "Firefox"
+    end
+
+    test "extracts referrer", %{conn: conn} do
+      conn
+      |> put_req_header("user-agent", "Mozilla/5.0 Chrome/120.0")
+      |> put_req_header("referer", "https://www.google.com/search?q=test")
+      |> get(~p"/")
+
+      send(Buffer, :flush)
+      :timer.sleep(50)
+
+      event =
+        from(e in Event,
+          where: e.referrer == "google.com",
+          order_by: [desc: e.inserted_at],
+          limit: 1
+        )
+        |> Repo.one()
+
+      assert event
+      assert event.referrer_source == "Google"
+    end
+
+    test "extracts UTM params", %{conn: conn} do
+      conn
+      |> put_req_header("user-agent", "Mozilla/5.0 Chrome/120.0")
+      |> get(~p"/?utm_source=newsletter&utm_medium=email&utm_campaign=spring")
+
+      send(Buffer, :flush)
+      :timer.sleep(50)
+
+      event =
+        from(e in Event,
+          where: e.utm_source == "newsletter",
+          order_by: [desc: e.inserted_at],
+          limit: 1
+        )
+        |> Repo.one()
+
+      assert event
+      assert event.utm_medium == "email"
+      assert event.utm_campaign == "spring"
+    end
+  end
+end