def deps do
  [
    {:amqp, "~> 4.1"}
  ]
end

iex> {:ok, conn} = AMQP.Connection.open()
# {:ok, %AMQP.Connection{pid: #PID<0.165.0>}}

iex> {:ok, chan} = AMQP.Channel.open(conn)
# {:ok, %AMQP.Channel{conn: %AMQP.Connection{pid: #PID<0.165.0>}, pid: #PID<0.177.0>}

iex> AMQP.Queue.declare(chan, "test_queue")
# {:ok, %{consumer_count: 0, message_count: 0, queue: "test_queue"}}

iex> AMQP.Exchange.declare(chan, "test_exchange")
# :ok

iex> AMQP.Queue.bind(chan, "test_queue", "test_exchange")
# :ok

iex> AMQP.Basic.publish(chan, "test_exchange", "", "Hello, World!")
# :ok

iex> {:ok, payload, meta} = AMQP.Basic.get(chan, "test_queue")
iex> payload
# "Hello, World!"

iex> AMQP.Queue.subscribe(chan, "test_queue", fn payload, _meta -> IO.puts("Received: #{payload}") end)
# {:ok, "amq.ctag-5L8U-n0HU5doEsNTQpaXWg"}

iex> AMQP.Basic.publish(chan, "test_exchange", "", "Hello, World!")
# :ok
# Received: Hello, World!

defmodule Consumer do
  use GenServer
  use AMQP

  def start_link do
    GenServer.start_link(__MODULE__, [], [])
  end

  @exchange    "gen_server_test_exchange"
  @queue       "gen_server_test_queue"
  @queue_error "#{@queue}_error"

  def init(_opts) do
    {:ok, conn} = Connection.open("amqp://guest:guest@localhost")
    {:ok, chan} = Channel.open(conn)
    setup_queue(chan)

    # Limit unacknowledged messages to 10
    :ok = Basic.qos(chan, prefetch_count: 10)
    # Register the GenServer process as a consumer
    {:ok, _consumer_tag} = Basic.consume(chan, @queue)
    {:ok, chan}
  end

  # Confirmation sent by the broker after registering this process as a consumer
  def handle_info({:basic_consume_ok, %{consumer_tag: consumer_tag}}, chan) do
    {:noreply, chan}
  end

  # Sent by the broker when the consumer is unexpectedly cancelled (such as after a queue deletion)
  def handle_info({:basic_cancel, %{consumer_tag: consumer_tag}}, chan) do
    {:stop, :normal, chan}
  end

  # Confirmation sent by the broker to the consumer process after a Basic.cancel
  def handle_info({:basic_cancel_ok, %{consumer_tag: consumer_tag}}, chan) do
    {:noreply, chan}
  end

  def handle_info({:basic_deliver, payload, %{delivery_tag: tag, redelivered: redelivered}}, chan) do
    # You might want to run payload consumption in separate Tasks in production
    consume(chan, tag, redelivered, payload)
    {:noreply, chan}
  end

  defp setup_queue(chan) do
    {:ok, _} = Queue.declare(chan, @queue_error, durable: true)
    # Messages that cannot be delivered to any consumer in the main queue will be routed to the error queue
    {:ok, _} = Queue.declare(chan, @queue,
                             durable: true,
                             arguments: [
                               {"x-dead-letter-exchange", :longstr, ""},
                               {"x-dead-letter-routing-key", :longstr, @queue_error}
                             ]
                            )
    :ok = Exchange.fanout(chan, @exchange, durable: true)
    :ok = Queue.bind(chan, @queue, @exchange)
  end

  defp consume(channel, tag, redelivered, payload) do
    number = String.to_integer(payload)
    if number <= 10 do
      :ok = Basic.ack channel, tag
      IO.puts "Consumed a #{number}."
    else
      :ok = Basic.reject channel, tag, requeue: false
      IO.puts "#{number} is too big and was rejected."
    end

  rescue
    # Requeue unless it's a redelivered message.
    # This means we will retry consuming a message once in case of exception
    # before we give up and have it moved to the error queue
    #
    # You might also want to catch :exit signal in production code.
    # Make sure you call ack, nack or reject otherwise consumer will stop
    # receiving messages.
    exception ->
      :ok = Basic.reject channel, tag, requeue: not redelivered
      IO.puts "Error converting #{payload} to integer"
  end
end

iex> Consumer.start_link
{:ok, #PID<0.261.0>}
iex> {:ok, conn} = AMQP.Connection.open
{:ok, %AMQP.Connection{pid: #PID<0.165.0>}}
iex> {:ok, chan} = AMQP.Channel.open(conn)
{:ok, %AMQP.Channel{conn: %AMQP.Connection{pid: #PID<0.165.0>}, pid: #PID<0.177.0>}
iex> AMQP.Basic.publish chan, "gen_server_test_exchange", "", "5"
:ok
Consumed a 5.
iex> AMQP.Basic.publish chan, "gen_server_test_exchange", "", "42"
:ok
42 is too big and was rejected.
iex> AMQP.Basic.publish chan, "gen_server_test_exchange", "", "Hello, World!"
:ok
Error converting Hello, World! to integer
Error converting Hello, World! to integer

config :amqp,
  connections: [
    myconn: [url: "amqp://guest:guest@myhost:12345"],
  ],
  channels: [
    mychan: [connection: :myconn]
  ]

iex> {:ok, chan} = AMQP.Application.get_channel(:mychan)
iex> :ok = AMQP.Basic.publish(chan, "", "", "Hello")