Static blog with front page summary

Goal: have a personal blog, and try out another point in the 'modular
app design with elixir' space.

Designing OTP systems with elixir had some interesting ideas.

blogex/test/support/fake_blog.ex

@@ -0,0 +1,100 @@
+defmodule Blogex.Test.FakeBlog do
+  @moduledoc """
+  A test double that implements the same interface as a `use Blogex.Blog`
+  module, but backed by an Agent so tests can control the post data.
+
+  ## Usage in tests
+
+      setup do
+        posts = [PostBuilder.build(id: "hello"), PostBuilder.build(id: "world")]
+        Blogex.Test.FakeBlog.start(posts, blog_id: :engineering, title: "Eng Blog")
+        :ok
+      end
+
+  Then pass `Blogex.Test.FakeBlog` anywhere a blog module is expected.
+  """
+
+  use Agent
+
+  @defaults [
+    blog_id: :test_blog,
+    title: "Test Blog",
+    description: "A blog for tests",
+    base_path: "/blog/test"
+  ]
+
+  def start(posts \\ [], opts \\ []) do
+    opts = Keyword.merge(@defaults, opts)
+
+    state = %{
+      posts: posts,
+      blog_id: opts[:blog_id],
+      title: opts[:title],
+      description: opts[:description],
+      base_path: opts[:base_path]
+    }
+
+    case Agent.start(fn -> state end, name: __MODULE__) do
+      {:ok, pid} -> {:ok, pid}
+      {:error, {:already_started, pid}} ->
+        Agent.update(__MODULE__, fn _ -> state end)
+        {:ok, pid}
+    end
+  end
+
+  def stop, do: Agent.stop(__MODULE__)
+
+  defp get(key), do: Agent.get(__MODULE__, &Map.fetch!(&1, key))
+
+  def blog_id, do: get(:blog_id)
+  def title, do: get(:title)
+  def description, do: get(:description)
+  def base_path, do: get(:base_path)
+
+  def all_posts do
+    get(:posts)
+    |> Enum.filter(& &1.published)
+    |> Enum.sort_by(& &1.date, {:desc, Date})
+  end
+
+  def recent_posts(n \\ 5), do: Enum.take(all_posts(), n)
+
+  def all_tags do
+    all_posts()
+    |> Enum.flat_map(& &1.tags)
+    |> Enum.uniq()
+    |> Enum.sort()
+  end
+
+  def posts_by_tag(tag) do
+    Enum.filter(all_posts(), fn post -> tag in post.tags end)
+  end
+
+  def get_post!(id) do
+    Enum.find(all_posts(), &(&1.id == id)) ||
+      raise Blogex.NotFoundError, "post #{inspect(id)} not found"
+  end
+
+  def get_post(id) do
+    Enum.find(all_posts(), &(&1.id == id))
+  end
+
+  def paginate(page \\ 1, per_page \\ 10) do
+    posts = all_posts()
+    total = length(posts)
+    total_pages = max(ceil(total / per_page), 1)
+
+    entries =
+      posts
+      |> Enum.drop((page - 1) * per_page)
+      |> Enum.take(per_page)
+
+    %{
+      entries: entries,
+      page: page,
+      per_page: per_page,
+      total_entries: total,
+      total_pages: total_pages
+    }
+  end
+end