Lock traffic data backfill (#3648)

* WIP snapshot

* Don't assume that subscription and trial can't co-exist 🤷

* Don't look up subscription status if payment is overdue

priv/repo/migrations/20231220101920_backfill_accept_traffic_until.exs

@@ -0,0 +1,81 @@
+defmodule Plausible.Repo.Migrations.BackfillAcceptTrafficUntil do
+  use Ecto.Migration
+
+  def change do
+    # trials that are about to expire get extra 14 days
+    # regardless of the effective end date, this still leaves a room for both notifications
+    execute """
+    UPDATE users
+    SET accept_traffic_until = trial_expiry_date + 14
+    WHERE
+      trial_expiry_date IS NOT NULL
+    AND
+      trial_expiry_date >= CURRENT_DATE
+    """
+
+    # free plans
+    execute """
+    UPDATE users AS u
+    SET accept_traffic_until = '2135-01-01'
+    WHERE
+      EXISTS (
+        SELECT 1
+        FROM subscriptions s
+        WHERE
+          user_id = u.id
+        AND
+          paddle_plan_id = 'free_10k'
+      )
+    """
+
+    # abandoned accounts (trial ended and no valid subscriptions) still get a random
+    # phase-out period so that both notifications can be delivered
+    execute """
+    UPDATE users
+    SET accept_traffic_until = CURRENT_DATE + TRUNC(RANDOM() * (20 - 8 + 1) + 8)::int
+    WHERE
+      NOT EXISTS (
+        SELECT 1
+        FROM subscriptions
+        WHERE
+          subscriptions.user_id = users.id
+      )
+    AND
+      trial_expiry_date IS NOT NULL
+    AND
+      trial_expiry_date < CURRENT_DATE
+    """
+
+    # all the non-free subscriptions
+    execute """
+    UPDATE users u1
+    SET accept_traffic_until = s.next_bill_date + 30
+    FROM users u2
+    INNER JOIN LATERAL (
+      SELECT * FROM subscriptions sub WHERE u2.id = sub.user_id ORDER BY sub.inserted_at DESC LIMIT 1
+    ) s ON (true)
+    WHERE
+      u1.id = u2.id
+    AND
+      s.user_id = u1.id
+    AND
+      s.paddle_plan_id != 'free_10k'
+    """
+
+    # subscription for which current period needs payment)
+    execute """
+    UPDATE users u1
+    SET accept_traffic_until = CURRENT_DATE + TRUNC(RANDOM() * (20 - 8 + 1) + 8)::int
+    FROM users u2
+    INNER JOIN LATERAL (
+      SELECT * FROM subscriptions sub WHERE u2.id = sub.user_id ORDER BY sub.inserted_at DESC LIMIT 1
+    ) s ON (true)
+    WHERE
+      s.user_id = u1.id
+    AND
+      u1.id = u2.id
+    AND
+      s.next_bill_date < CURRENT_DATE
+    """
+  end
+end