Migration to allow users to be anonymised

This is the first step in a larger piece of work.

We will use DateTime to store when a user is deactivated, this will
replace the `active` attribute:

- when the deactivated_at is nil the user is active
- when the deactivated_at has a date time the user has been deactivated

We have no way to know when a user was deactivated (hence the work!) so
we'll use the updated_at to be our best guess.

At this point the application is broken, but we'll keep this commit
separate and fix that next.

db/migrate/20241212115356_add_user_anonymisation.rb

@@ -0,0 +1,23 @@
+class AddUserAnonymisation < ActiveRecord::Migration[6.1]
+  def up
+    add_column :users, :deactivated_at, :datetime
+    add_column :users, :anonymised_at, :datetime
+
+    User.where(active: false).each do |user|
+      user.update_column(:deactivated_at, user.updated_at)
+    end
+
+    remove_column :users, :active
+  end
+
+  def down
+    add_column :users, :active, :boolean, default: true
+
+    User.where(deactivated_at: nil).each do |user|
+      user.update_column(:active, true)
+    end
+
+    remove_column :users, :deactivated_at, :datetime
+    remove_column :users, :anonymised_at, :datetime
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2024_12_04_220209) do
+ActiveRecord::Schema.define(version: 2024_12_12_115356) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
@@ -358,7 +358,6 @@
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
     t.uuid "organisation_id"
-    t.boolean "active", default: true
     t.string "encrypted_password", default: "", null: false
     t.string "reset_password_token"
     t.datetime "reset_password_sent_at"
@@ -370,6 +369,8 @@
     t.boolean "otp_required_for_login", default: true
     t.string "mobile_number"
     t.datetime "mobile_number_confirmed_at"
+    t.datetime "deactivated_at"
+    t.datetime "anonymised_at"
     t.index ["organisation_id"], name: "index_users_on_organisation_id"
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
   end