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>

lib/berrypod_web/analytics_hook.ex

@@ -0,0 +1,100 @@
+defmodule BerrypodWeb.AnalyticsHook do
+  @moduledoc """
+  LiveView on_mount hook for analytics — Layer 2 of the progressive pipeline.
+
+  Reads analytics data from the session (set by the Plugs.Analytics plug) and
+  tracks subsequent SPA navigations via handle_params. Skips the initial mount
+  since the plug already recorded that pageview.
+
+  Also handles the `analytics:screen` event from the JS hook (Layer 3) to
+  capture screen width for device classification.
+  """
+
+  import Phoenix.Component, only: [assign: 3]
+  import Phoenix.LiveView, only: [attach_hook: 4, connected?: 1]
+
+  alias Berrypod.Analytics
+
+  def on_mount(:track, _params, session, socket) do
+    socket =
+      socket
+      |> assign(:analytics_visitor_hash, session["analytics_visitor_hash"])
+      |> assign(:analytics_browser, session["analytics_browser"])
+      |> assign(:analytics_os, session["analytics_os"])
+      |> assign(:analytics_referrer, session["analytics_referrer"])
+      |> assign(:analytics_referrer_source, session["analytics_referrer_source"])
+      |> assign(:analytics_utm_source, session["analytics_utm_source"])
+      |> assign(:analytics_utm_medium, session["analytics_utm_medium"])
+      |> assign(:analytics_utm_campaign, session["analytics_utm_campaign"])
+      |> assign(:analytics_screen_size, session["analytics_screen_size"])
+      |> assign(:analytics_country_code, session["country_code"])
+      |> assign(:analytics_initial_mount, true)
+
+    socket =
+      if connected?(socket) and socket.assigns.analytics_visitor_hash do
+        socket
+        |> attach_hook(:analytics_params, :handle_params, &handle_analytics_params/3)
+        |> attach_hook(:analytics_events, :handle_event, &handle_analytics_event/3)
+      else
+        socket
+      end
+
+    {:cont, socket}
+  end
+
+  defp handle_analytics_params(_params, uri, socket) do
+    # Skip the initial mount — the plug already recorded this pageview
+    if socket.assigns.analytics_initial_mount do
+      {:cont, assign(socket, :analytics_initial_mount, false)}
+    else
+      # Skip if admin user is browsing
+      if admin?(socket) do
+        {:cont, socket}
+      else
+        pathname = URI.parse(uri).path
+
+        Analytics.track_pageview(%{
+          pathname: pathname,
+          visitor_hash: socket.assigns.analytics_visitor_hash,
+          referrer: socket.assigns.analytics_referrer,
+          referrer_source: socket.assigns.analytics_referrer_source,
+          utm_source: socket.assigns.analytics_utm_source,
+          utm_medium: socket.assigns.analytics_utm_medium,
+          utm_campaign: socket.assigns.analytics_utm_campaign,
+          country_code: socket.assigns.analytics_country_code,
+          screen_size: socket.assigns.analytics_screen_size,
+          browser: socket.assigns.analytics_browser,
+          os: socket.assigns.analytics_os
+        })
+
+        # Clear referrer/UTMs after first SPA navigation — they only apply to the entry
+        {:cont,
+         socket
+         |> assign(:analytics_referrer, nil)
+         |> assign(:analytics_referrer_source, nil)
+         |> assign(:analytics_utm_source, nil)
+         |> assign(:analytics_utm_medium, nil)
+         |> assign(:analytics_utm_campaign, nil)}
+      end
+    end
+  end
+
+  defp handle_analytics_event("analytics:screen", %{"width" => width}, socket)
+       when is_integer(width) do
+    screen_size = classify_screen(width)
+    {:cont, assign(socket, :analytics_screen_size, screen_size)}
+  end
+
+  defp handle_analytics_event(_event, _params, socket), do: {:cont, socket}
+
+  defp classify_screen(width) when width < 768, do: "mobile"
+  defp classify_screen(width) when width < 1024, do: "tablet"
+  defp classify_screen(_width), do: "desktop"
+
+  defp admin?(socket) do
+    case socket.assigns[:current_scope] do
+      %{user: %{}} -> true
+      _ -> false
+    end
+  end
+end