add url prefix settings with validation and redirects

Customisable route prefixes for products, collections, orders:
- get_url_prefixes/0 and get_url_prefix/1 for retrieval
- update_url_prefix/2 with format validation and conflict checks
- Automatic redirects from old to new prefix URLs
- list_product_slugs/0 and list_category_slugs/0 helpers
- Redirects.clear_cache/0 for test isolation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod/products.ex

@@ -352,6 +352,29 @@ defmodule Berrypod.Products do
     end)
   end
 
+  @doc """
+  Returns a list of all product slugs.
+
+  Used for URL prefix redirects when admin changes the products prefix.
+  """
+  def list_product_slugs do
+    from(p in Product,
+      where: p.visible == true and p.status == "active",
+      select: p.slug
+    )
+    |> Repo.all()
+  end
+
+  @doc """
+  Returns a list of all category slugs.
+
+  Used for URL prefix redirects when admin changes the collections prefix.
+  """
+  def list_category_slugs do
+    list_categories()
+    |> Enum.map(& &1.slug)
+  end
+
   @doc """
   Recomputes denormalized fields from a product's variants.
   Called after variant sync to keep cached fields up to date.

lib/berrypod/redirects.ex

@@ -48,6 +48,15 @@ defmodule Berrypod.Redirects do
     :ok
   end
 
+  @doc "Clears the redirect cache without re-warming. Used in tests."
+  def clear_cache do
+    if :ets.whereis(@table) != :undefined do
+      :ets.delete_all_objects(@table)
+    end
+
+    :ok
+  end
+
   defp invalidate_cache(from_path) do
     :ets.delete(@table, from_path)
   end
@@ -90,6 +99,10 @@ defmodule Berrypod.Redirects do
     attrs = Map.put(attrs, :to_path, to_path)
     from_path = attrs[:from_path] || attrs["from_path"]
 
+    # Don't create self-redirects
+    if from_path == to_path do
+      {:ok, :skipped}
+    else
       # Flatten any existing redirects that point to our from_path
       flatten_incoming(from_path, to_path)
 
@@ -105,6 +118,7 @@ defmodule Berrypod.Redirects do
           error
       end
     end
+  end
 
   @doc """
   Creates a manual redirect (from admin UI).

lib/berrypod/settings.ex

@@ -307,6 +307,142 @@ defmodule Berrypod.Settings do
     end
   end
 
+  # ── URL prefixes ─────────────────────────────────────────────
+
+  @valid_prefix_types ~w(products collections orders)a
+  @default_prefixes %{products: "products", collections: "collections", orders: "orders"}
+
+  @doc """
+  Gets the current URL prefixes map.
+
+  Returns a map like `%{"products" => "p", "collections" => "c"}`.
+  Missing keys use defaults.
+  """
+  def get_url_prefixes do
+    get_setting("url_prefixes") || %{}
+  end
+
+  @doc """
+  Gets the current prefix for a specific type.
+
+  ## Examples
+
+      iex> get_url_prefix(:products)
+      "p"  # if customised, or "products" by default
+  """
+  def get_url_prefix(type) when type in @valid_prefix_types do
+    prefixes = get_url_prefixes()
+    Map.get(prefixes, Atom.to_string(type)) || @default_prefixes[type]
+  end
+
+  @doc """
+  Updates a single URL prefix.
+
+  Creates redirects from old prefix URLs to new ones if products/collections exist.
+  Invalidates the R module cache.
+
+  ## Examples
+
+      iex> update_url_prefix(:products, "p")
+      {:ok, %{"products" => "p"}}
+  """
+  def update_url_prefix(type, new_prefix)
+      when type in @valid_prefix_types and is_binary(new_prefix) do
+    new_prefix = String.downcase(String.trim(new_prefix))
+
+    # Validate prefix format
+    cond do
+      new_prefix == "" ->
+        {:error, :empty_prefix}
+
+      not Regex.match?(~r/^[a-z0-9-]+$/, new_prefix) ->
+        {:error, :invalid_format}
+
+      reserved_prefix?(new_prefix) ->
+        {:error, :reserved_prefix}
+
+      true ->
+        old_prefix = get_url_prefix(type)
+        prefixes = get_url_prefixes()
+
+        # If same as current, no-op
+        if old_prefix == new_prefix do
+          {:ok, prefixes}
+        else
+          # Update the prefixes map
+          # If new prefix matches default, remove the key (use default)
+          new_prefixes =
+            if new_prefix == @default_prefixes[type] do
+              Map.delete(prefixes, Atom.to_string(type))
+            else
+              Map.put(prefixes, Atom.to_string(type), new_prefix)
+            end
+
+          # Save to database
+          {:ok, _} = put_setting("url_prefixes", new_prefixes, "json")
+
+          # Create redirects for existing items
+          create_prefix_redirects(type, old_prefix, new_prefix)
+
+          # Invalidate R module cache
+          BerrypodWeb.R.invalidate_all_sync()
+
+          {:ok, new_prefixes}
+        end
+    end
+  end
+
+  @doc """
+  Resets a URL prefix to its default value.
+  """
+  def reset_url_prefix(type) when type in @valid_prefix_types do
+    update_url_prefix(type, @default_prefixes[type])
+  end
+
+  # Check if prefix conflicts with reserved routes
+  defp reserved_prefix?(prefix) do
+    reserved = ~w(admin api auth checkout coming-soon health live phoenix static _)
+    prefix in reserved
+  end
+
+  # Create redirects from old prefix to new prefix for existing items
+  defp create_prefix_redirects(:products, old_prefix, new_prefix) do
+    Berrypod.Products.list_product_slugs()
+    |> Enum.each(fn slug ->
+      Berrypod.Redirects.create_auto(%{
+        from_path: "/#{old_prefix}/#{slug}",
+        to_path: "/#{new_prefix}/#{slug}",
+        source: "auto_prefix_change"
+      })
+    end)
+  end
+
+  defp create_prefix_redirects(:collections, old_prefix, new_prefix) do
+    Berrypod.Products.list_category_slugs()
+    |> Enum.each(fn slug ->
+      Berrypod.Redirects.create_auto(%{
+        from_path: "/#{old_prefix}/#{slug}",
+        to_path: "/#{new_prefix}/#{slug}",
+        source: "auto_prefix_change"
+      })
+    end)
+
+    # Also redirect "all" and "sale" virtual collections
+    for slug <- ["all", "sale"] do
+      Berrypod.Redirects.create_auto(%{
+        from_path: "/#{old_prefix}/#{slug}",
+        to_path: "/#{new_prefix}/#{slug}",
+        source: "auto_prefix_change"
+      })
+    end
+  end
+
+  defp create_prefix_redirects(:orders, _old_prefix, _new_prefix) do
+    # Orders use order numbers, which we can't enumerate easily
+    # The DynamicRoutes plug handles the redirect at runtime
+    :ok
+  end
+
   # Private helpers
 
   defp fetch_setting(key) do