defmodule Blogex.SEO do
  @moduledoc """
  SEO helpers for generating meta tags and sitemaps.
  """

  @doc """
  Returns a map of meta tag attributes for a blog listing page.
  Useful for setting OpenGraph and Twitter card tags on blog index pages.

      <meta property="og:title" content={@meta.og_title} />
  """
  def meta_tags_for_blog(blog_module, base_url) do
    url = "#{base_url}#{blog_module.base_path()}"

    %{
      title: blog_module.title(),
      description: blog_module.description(),
      og_title: blog_module.title(),
      og_description: blog_module.description(),
      og_type: "website",
      og_url: url,
      og_image: nil,
      twitter_card: "summary"
    }
  end

  @doc """
  Returns a map of meta tag attributes for a post.
  Useful for setting OpenGraph and Twitter card tags in your layout.

      <meta property="og:title" content={@meta.og_title} />
      <meta property="og:image" content={@meta.og_image} />
  """
  def meta_tags(post, base_url, blog_module) do
    url = "#{base_url}#{blog_module.base_path()}/#{post.id}"

    %{
      title: post.title,
      description: post.description,
      og_title: post.title,
      og_description: post.description,
      og_type: "article",
      og_url: url,
      og_image: if(post.image, do: "#{base_url}#{post.image}", else: nil),
      article_published_time: Date.to_iso8601(post.date),
      article_author: post.author,
      article_tags: post.tags,
      twitter_card: "summary_large_image"
    }
  end

  @doc """
  Generates a sitemap.xml string for the given blog modules.

      xml = Blogex.SEO.sitemap([MyApp.EngineeringBlog, MyApp.ReleaseNotes], "https://myapp.com")
  """
  def sitemap(blog_modules, base_url) when is_list(blog_modules) do
    urls =
      blog_modules
      |> Enum.flat_map(fn mod ->
        mod.all_posts()
        |> Enum.map(fn post ->
          url = "#{base_url}#{mod.base_path()}/#{post.id}"
          lastmod = Date.to_iso8601(post.date)

          """
            <url>
              <loc>#{url}</loc>
              <lastmod>#{lastmod}</lastmod>
              <changefreq>monthly</changefreq>
              <priority>0.7</priority>
            </url>
          """
        end)
      end)
      |> Enum.join()

    """
    <?xml version="1.0" encoding="UTF-8"?>
    <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
    #{urls}</urlset>
    """
    |> String.trim()
  end
end