Refactor GitHub api layer for easier and more flexible testing

- removed bypass from all tests except lib/code_corps/github/api_test.exs
- introduced `with_mock_api` macro to mock out an api layer module for usage in misc github tests
- implementd proper bypass tests in `api_test`
- removed github_case since it's bypass facilities are now only existing in `api_test`
- fixed several minor bugs and issues revealed through this process

config/config.exs

@@ -68,6 +68,7 @@ config :code_corps, :corsica_log_level, [rejected: :warn]
 {:ok, pem} = (System.get_env("GITHUB_APP_PEM") || "") |> Base.decode64()
 
 config :code_corps,
+  github: CodeCorps.GitHub.API,
   github_app_id: System.get_env("GITHUB_APP_ID"),
   github_app_client_id: System.get_env("GITHUB_APP_CLIENT_ID"),
   github_app_client_secret: System.get_env("GITHUB_APP_CLIENT_SECRET"),

config/test.exs

@@ -61,4 +61,6 @@ pem = case System.get_env("GITHUB_APP_PEM") do
   encoded_pem -> encoded_pem |> Base.decode64!
 end
 
-config :code_corps, github_app_pem: pem
+config :code_corps,
+  github: CodeCorps.GitHub.SuccessAPI,
+  github_app_pem: pem

lib/code_corps/github/api.ex

@@ -0,0 +1,41 @@
+defmodule CodeCorps.GitHub.API do
+  alias CodeCorps.{
+    GitHub,
+    GitHub.APIError,
+    GitHub.HTTPClientError
+  }
+
+  @spec request(GitHub.method, String.t, GitHub.headers, GitHub.body, list) :: GitHub.response
+  def request(method, url, headers, body, options) do
+    method
+    |> :hackney.request(url, headers, body, options)
+    |> marshall_response()
+  end
+
+  @typep http_success :: {:ok, integer, [{String.t, String.t}], String.t}
+  @typep http_failure :: {:error, term}
+
+  @spec marshall_response(http_success | http_failure) :: GitHub.response
+  defp marshall_response({:ok, status, _headers, body}) when status in 200..299 do
+    case body |> Poison.decode do
+      {:ok, json} ->
+        {:ok, json}
+      {:error, {_decoding_error, _decoding_value}} ->
+        marshall_response({:error, :body_decoding_error})
+    end
+  end
+  defp marshall_response({:ok, 404, _headers, body}) do
+    {:error, APIError.new({404, %{"message" => body}})}
+  end
+  defp marshall_response({:ok, status, _headers, body}) when status in 400..599 do
+    case body |> Poison.decode do
+      {:ok, json} ->
+        {:error, APIError.new({status, json})}
+      {:error, {_decoding_error, _decoding_value}} ->
+        marshall_response({:error, :body_decoding_error})
+    end
+  end
+  defp marshall_response({:error, reason}) do
+    {:error, HTTPClientError.new(reason: reason)}
+  end
+end