Add Daring Fireball scraper

lib/frenzy/pipeline/scrape_stage.ex

@@ -10,7 +10,7 @@ defmodule Frenzy.Pipeline.ScrapeStage do
         {:ok, %{item_params | content: content}}
 
       {:error, reason} ->
-        Logger.warn("Unable to get article content: #{reason}")
+        Logger.warn("Unable to get article content for #{url}: #{reason}")
         item_params
     end
   end
@@ -47,8 +47,16 @@ defmodule Frenzy.Pipeline.ScrapeStage do
        when status_code in [301, 302] do
     {"Location", new_url} = Enum.find(headers, fn {name, _value} -> name == "Location" end)
 
+    headers
+    |> Enum.find(fn {name, _value} -> name == "Location" end)
+    |> case do
+      {"Location", new_url} ->
         Logger.debug("Got 301 redirect from #{url} to #{new_url}")
         get_article_content(new_url)
+
+      _ ->
+        {:error, "Missing Location header for redirect"}
+    end
   end
 
   defp handle_response(_url, %HTTPoison.Response{status_code: 403}) do

lib/frenzy/pipeline/site/daring_fireball_scrape_stage.ex

@@ -0,0 +1,102 @@
+defmodule Frenzy.Pipeline.Site.DaringFireballScrapeStage do
+  require Logger
+  alias Frenzy.Pipeline.Stage
+  @behaviour Stage
+
+  @impl Stage
+  def apply(_opts, %{url: url} = item_params) do
+    case get_article_content(url) do
+      {:ok, content} ->
+        {:ok, %{item_params | content: content}}
+
+      {:error, reason} ->
+        Logger.warn("Unable to get Daring Fireball article content for #{url}: #{reason}")
+        item_params
+    end
+  end
+
+  @impl Stage
+  def validate_opts(opts), do: {:ok, opts}
+
+  defp get_article_content(url) when is_binary(url) and url != "" do
+    Logger.debug("Get Daring Fireball article from #{url}")
+
+    url
+    |> HTTPoison.get()
+    |> case do
+      {:ok, response} ->
+        handle_response(url, response)
+
+      {:error, %HTTPoison.Error{reason: reason}} ->
+        {:error, "HTTPoison error: #{reason}"}
+    end
+  end
+
+  defp get_article_content(_url), do: {:error, "URL must be a non-empty string"}
+
+  defp handle_response(url, %HTTPoison.Response{status_code: 200, body: body}) do
+    html_tree = Floki.parse(body)
+
+    case get_article_element(html_tree) || get_link_element(html_tree) do
+      nil ->
+        {:error, "no matching element"}
+
+      elem ->
+        readable_html =
+          elem
+          |> Floki.filter_out(:comment)
+          |> Readability.readable_html()
+
+        {:ok, readable_html}
+    end
+  end
+
+  defp handle_response(_url, %HTTPoison.Response{status_code: 404}) do
+    {:error, "404 not found"}
+  end
+
+  defp handle_response(url, %HTTPoison.Response{status_code: status_code, headers: headers})
+       when status_code in [301, 302] do
+    {"Location", new_url} = Enum.find(headers, fn {name, _value} -> name == "Location" end)
+
+    headers
+    |> Enum.find(fn {name, _value} -> name == "Location" end)
+    |> case do
+      {"Location", new_url} ->
+        Logger.debug("Got 301 redirect from #{url} to #{new_url}")
+        get_article_content(new_url)
+
+      _ ->
+        {:error, "Missing Location header for redirect"}
+    end
+  end
+
+  defp handle_response(_url, %HTTPoison.Response{status_code: 403}) do
+    {:error, "403 Forbidden"}
+  end
+
+  defp handle_response(_url, %HTTPoison.Response{status_code: status_code} = response) do
+    {:error, "No handler for response #{inspect(response)}"}
+  end
+
+  defp get_article_element(html_tree) do
+    case Floki.find(html_tree, "div.article") do
+      [article_elem | _] ->
+        # articles include extra information in the div.article element
+        Floki.filter_out(article_elem, "h1, .dateline, #PreviousNext")
+
+      _ ->
+        nil
+    end
+  end
+
+  defp get_link_element(html_tree) do
+    case Floki.find(html_tree, "dl.linkedlist dd") do
+      [dd_elem | _] ->
+        dd_elem
+
+      _ ->
+        nil
+    end
+  end
+end