Fixed locale switching to correct base codes

lib/phoenix_kit/migrations/postgres.ex

@@ -248,7 +248,7 @@ defmodule PhoenixKit.Migrations.Postgres do
   use Ecto.Migration
 
   @initial_version 1
-  @current_version 27
+  @current_version 28
   @default_prefix "public"
 
   @doc false

lib/phoenix_kit/migrations/postgres/v28.ex

@@ -0,0 +1,83 @@
+defmodule PhoenixKit.Migrations.Postgres.V28 do
+  @moduledoc """
+  Migration V28: Add preferred_locale field to users table for dialect preferences.
+
+  This migration adds support for user-specific language dialect preferences,
+  allowing authenticated users to choose their preferred variant (e.g., en-GB vs en-US)
+  while URLs continue to show simplified base language codes (/en/ instead of /en-US/).
+
+  ## Changes
+  - Adds `preferred_locale` column to `phoenix_kit_users` table (nullable string, size 10)
+  - Creates index on `preferred_locale` for potential locale-based queries
+  - Supports full dialect codes (en-US, es-MX, zh-Hans-CN, etc.)
+
+  ## Requirements
+  - PostgreSQL database
+  - PhoenixKit V27 or higher
+
+  ## Purpose
+  Enable simplified URL structure with dialect preferences:
+  - URLs show base codes: `/en/`, `/es/`, `/fr/`
+  - Users can save preferred dialects: "en-GB", "es-MX", "pt-BR"
+  - Guest users get default dialect mapping (en → en-US)
+  - Translation system uses full dialect codes internally
+
+  ## Usage
+  Once migrated, users can update their locale preference:
+
+      PhoenixKit.Users.Auth.update_user_locale(user, "en-GB")
+
+  When visiting `/en/dashboard`, the system will:
+  1. Detect base code "en" from URL
+  2. Resolve to user's preferred_locale ("en-GB")
+  3. Use "en-GB" for translations while URL stays `/en/`
+
+  ## Validation
+  - Format validation: matches ~r/^[a-z]{2}(-[A-Z]{2})?$/
+  - Existence validation: must be in predefined language list
+  - NULL allowed: defaults to system dialect mapping
+
+  ## Size Rationale
+  - Size 10 supports extended codes like "zh-Hans-CN" (10 chars)
+  - Covers all standard language-REGION codes (5 chars: "en-US")
+  - Allows future BCP 47 extensions if needed
+
+  ## Notes
+  - Idempotent: Safe to run multiple times
+  - No default value: NULL indicates "use system default"
+  - Index improves potential analytics queries
+  - Backward compatible: existing users have NULL (use defaults)
+  """
+
+  use Ecto.Migration
+
+  def up(%{prefix: prefix} = _opts) do
+    alter table(:phoenix_kit_users, prefix: prefix) do
+      add :preferred_locale, :string, size: 10
+    end
+
+    # Create index for potential locale-based queries
+    create index(:phoenix_kit_users, [:preferred_locale], prefix: prefix)
+
+    # Update version comment on phoenix_kit table for version tracking
+    execute "COMMENT ON TABLE #{prefix_table_name("phoenix_kit", prefix)} IS '28'"
+  end
+
+  def down(%{prefix: prefix} = _opts) do
+    # Remove index
+    drop index(:phoenix_kit_users, [:preferred_locale], prefix: prefix)
+
+    # Remove column
+    alter table(:phoenix_kit_users, prefix: prefix) do
+      remove :preferred_locale
+    end
+
+    # Update version comment on phoenix_kit table to previous version
+    execute "COMMENT ON TABLE #{prefix_table_name("phoenix_kit", prefix)} IS '27'"
+  end
+
+  # Helper functions
+
+  defp prefix_table_name(table_name, nil), do: table_name
+  defp prefix_table_name(table_name, prefix), do: "#{prefix}.#{table_name}"
+end