Add Upgrade Guide

README.md

@@ -16,41 +16,35 @@ def deps do
 end
 ```
 
-2. Configure [Goth](https://github.com/peburrows/goth) (Kane's underlying token storage and retrieval library) with your Google JSON credentials:
-
-```elixir
-config :goth,
-  json: "path/to/google/json/creds.json" |> File.read!
-```
-
-3. Ensure Kane is started before your application:
-
-```elixir
-def application do
-  [applications: [:kane]]
-end
-```
+2. Configure [Goth](https://github.com/peburrows/goth) (Kane's underlying token storage and retrieval library) with your Google JSON credentials.
 
 ## Usage
 
 Pull, process and acknowledge messages via a pre-existing subscription:
 
 ```elixir
+{:ok, token} = Goth.fetch(MyApp.Goth)
+
+kane = %Kane{
+  project_id: my_app_gcp_credentials["project_id"],
+  token: token
+}
+
 subscription = %Kane.Subscription{
                   name: "my-sub",
                   topic: %Kane.Topic{
                     name: "my-topic"
                   }
                 }
 
-{:ok, messages} = Kane.Subscription.pull(subscription)
+{:ok, messages} = Kane.Subscription.pull(kane, subscription)
 
 Enum.each messages, fn(mess)->
   process_message(mess)
 end
 
 # acknowledge message receipt in bulk
-Kane.Subscription.ack(subscription, messages)
+Kane.Subscription.ack(kane, subscription, messages)
 ```
 
 Send message via pre-existing subscription:
@@ -59,7 +53,7 @@ Send message via pre-existing subscription:
 topic   = %Kane.Topic{name: "my-topic"}
 message = %Kane.Message{data: %{"hello": "world"}, attributes: %{"random" => "attr"}}
 
-result  = Kane.Message.publish(message, topic)
+result  = Kane.Message.publish(kane, message, topic)
 
 case result do
   {:ok, _return}    -> IO.puts("It worked!")

UPGRADE_GUIDE.md

@@ -0,0 +1,53 @@
+## Upgrading from Kane 0.9
+
+Earlier versions of Kane relied on global application environment configuration which is deprecated in favour of a more direct and explicit approach in Kane vX.X+. Kane is following the same principle changes of [Goth 1.3+](https://github.com/peburrows/goth/blob/master/UPGRADE_GUIDE.md).
+
+Below is a step-by-step upgrade path from Goth 0.x to X.X:
+
+Upgrade Goth to [1.3+](https://github.com/peburrows/goth/blob/master/UPGRADE_GUIDE.md). Previous versions of Kane, heavily depended on the global configuration of Goth.
+
+So, your `mix.exs` should be looking like this:
+
+```elixir
+def deps do
+  [
+    {:goth, "~> 1.3"},
+    {:kane, "~> X.X"}
+  ]
+end
+```
+
+You might have a code similar to this:
+
+
+```elixir
+subscription = %Kane.Subscription{
+                  name: "my-sub",
+                  topic: %Kane.Topic{
+                    name: "my-topic"
+                  }
+                }
+
+{:ok, messages} = Kane.Subscription.pull(subscription)
+```
+
+Now you need explicity fetch the token and the project's id:
+
+```elixir
+defmodule MyApp do
+  def kane do
+    {:ok, token} = Goth.fetch(MyApp.Goth)
+    project_id = Application.fetch_env!(:my_app, :gcp_credentials)["project_id"]
+
+    %Kane{
+      project_id: project_id,
+      token: token
+    }
+  end
+end
+
+# then
+{:ok, messages} = Kane.Subscription.pull(MyApp.kane(), subscription)
+```
+
+For more information on earlier versions of Kane, [see v0.9.0 documentation on hexdocs.pm](https://hexdocs.pm/kane/0.9.0).