defmodule StaticBlog do
  @moduledoc """
  A reusable static blog engine for Elixir.

  `StaticBlog` provides the core infrastructure for building, previewing,
  and publishing a static blog. Each consumer project adds this library as
  a dependency, supplies its own content in `priv/posts/`, and configures
  site metadata under the `:static_blog` application key.

  The primary public API is `site_config/0`, `consumer_app/0`,
  `template_module/0`, and `all_posts/0`.

  """

  @doc """
  Returns the consumer application atom.

  This is the OTP application that owns the `priv/posts/` and
  `priv/static/` directories. Configured via
  `config :static_blog, :app, :my_blog`.

  ### Returns

  * The consumer app atom from `config :static_blog, :app`.

  """
  @spec consumer_app() :: atom()
  def consumer_app do
    Application.fetch_env!(:static_blog, :app)
  end

  @doc """
  Returns the site configuration keyword list.

  ### Returns

  * A keyword list of site-wide settings from `config :static_blog, :site`.

  """
  @spec site_config() :: keyword()
  def site_config do
    Application.fetch_env!(:static_blog, :site)
  end

  @doc """
  Returns the template module to use for rendering.

  Defaults to `StaticBlog.Template.Default` if not configured.

  ### Returns

  * A module that implements `StaticBlog.Template`.

  """
  @spec template_module() :: module()
  def template_module do
    Application.get_env(:static_blog, :template, StaticBlog.Template.Default)
  end

  @doc """
  Returns all blog posts.

  If a `:blog_module` is configured, delegates to that module's
  `all_posts/0` function. Otherwise falls back to
  `StaticBlog.RuntimePosts.all/0` which reads from disk at runtime.

  ### Returns

  * A list of `t:StaticBlog.Post.t/0` structs sorted by `:date` descending.

  """
  @spec all_posts() :: [StaticBlog.Post.t()]
  def all_posts do
    case Application.get_env(:static_blog, :blog_module) do
      nil -> StaticBlog.RuntimePosts.all()
      module -> module.all_posts()
    end
  end
end