Theming components

Theming Strategies

The storybook gives you different possibilities to apply a theme to your components. These possibilities are named strategies.

The following strategies are available:

1. sandbox class: set your theme as a CSS class, on the sandbox container, with a custom prefix
2. assign: pass the theme as an assign to your components, with a custom key.
3. function: call a custom module/function along with the current theme.

Here is how you can use these strategies. In your storybook.ex:

use PhoenixStorybook,
  themes_strategies: [
    sandbox_class: "prefix", # will set a class prefixed by `prefix-` on the sandbox container
    assign: :theme,
    function: {MyApp.ThemeHelper, :register_theme}
  ]

If the themes_strategies key is undefined, the default sandbox_class: "theme" strategy is applied.

CSS theming

By default, the storybook is applying a theme-* CSS class to your components/page containers and you should do as well to your application HTML body element.

It will allow you to style raw HTML elements

body.theme-colorful {
  font-family: // ...
}

.theme-colorful h1 {
  font-family: // ...
  font-size: // ...
}

Using a Registry

This chapter explain how you can leverage on a Registry with the function theming strategy.

An effective way to store the current theme setting so that it can be available to all your components, but still have different values for different (concurrent) users is to associate it to the current LiveView pid.

Registry is a native Elixir module that handles decentralized storage, linked to specific processes. We will leverage on this to associate a theme to the current LiveView pid.

First start a Registry from your Application module.

defmodule PhenixStorybook.Application do
  def start(_type, _args) do
    children = [
      {Registry, keys: :duplicate, name: ThemeRegistry}
    ]
  end
end

Then create a LiveView Hook that will fetch the theme from wherever it is relevant for your application: database, user session, URL params... and store it in the Registry (it's working because the Hook is running under the same pid than the LiveView).

defmodule ThemeHook do
  def on_mount(:default, params, _session, socket) do
    theme = current_user_theme(socket, params)
    Registry.register(ThemeRegistry, :theme, theme)
    {:cont, socket}
  end
end

Mount the hook in your router.

defmodule Router do
  live_session :default, on_mount: [ThemeHook] do
    scope "/" do
      # ...
    end
  end
end

Write a helper module, to be used from your components to fetch the current theme from the Registry and merge it in the component's assigns.

defmodule ThemeHelpers do
  def set_theme(assigns) do
    pid_and_themes = Registry.lookup(ThemeRegistry, :theme)

    case find_by_pid(pid_and_themes, self()) do
      {_pid, theme} -> Map.put_new(assigns, :theme, theme)
      _ -> raise("theme not found in registry")
    end
  end

  defp find_by_pid(pid_and_themes, current_pid) do
    Enum.find(pid_and_themes, fn {pid, _} -> pid == current_pid end)
  end
end