add connection behaviour and architecture docs

README.md

@@ -291,3 +291,14 @@ Bug reports and pull requests are welcome on GitHub at https://github.com/coinga
 ## License
 
 The library is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).
+
+## Architecture
+```mermaid
+  graph TD;
+      A[ApplicationSupervisor] --> B[ConsumerSupervisor];
+      A --> C[ConnectionServer - GenServer];
+      C -- sends requests to start consumers --> B;
+      B -- dynamic supervisor of multiple -->D[ConsumerServer - GenServer];
+      D -- monitors --> E[ConsumerExecutor];
+      E -- sends messages to --> C;
+```

lib/coney/connection.ex

@@ -0,0 +1,23 @@
+defmodule Coney.Connection do
+  alias AMQP
+
+  @callback open(settings :: map()) :: {:ok, Connection.t()} | {:error, any()}
+
+  @callback create_channel(Connection.t()) :: Channel.t()
+
+  @callback subscribe(Channel.t(), pid(), consumer :: any()) ::
+              {:ok, String.t()} | {:error, :blocked} | {:error, :closing}
+
+  @callback publish(
+              conn :: Connection.t(),
+              exchange :: String.t(),
+              routing_key :: String.t(),
+              message :: any()
+            ) :: :ok | {:error, any()}
+
+  @callback confirm(Channel.t(), tag :: any()) :: :ok | {:error, any()}
+
+  @callback reject(Channel.t(), tag :: any(), opts :: Keyword.t()) :: :ok | {:error, any()}
+
+  @callback init_topology(Connection.t(), topology :: map()) :: :ok | {:error, Basic.error()}
+end

lib/coney/fake_connection.ex

@@ -1,4 +1,6 @@
 defmodule Coney.FakeConnection do
+  @behaviour Coney.Connection
+
   def open(_) do
     :conn
   end

lib/coney/rabbit_connection.ex

@@ -1,6 +1,8 @@
 defmodule Coney.RabbitConnection do
   use AMQP
 
+  @behaviour Coney.Connection
+
   require Logger
 
   def open(%{url: url, timeout: timeout} = settings) do