basic.ex

defmodule AMQP.Basic do
  @moduledoc """
  Functions to publish, consume and acknowledge messages.
  """

  import AMQP.Core
  alias AMQP.{Channel, Utils}

  @type error :: {:error, reason :: :blocked | :closing}

  @type exchange :: String.t
  @type queue :: String.t
  @type routing_key :: String.t
  @type payload :: String.t
  @type delivery_tag :: integer
  @type consumer_tag :: String.t

  @doc """
  Publishes a message to an Exchange.

  This method publishes a message to a specific exchange. The message will be routed
  to queues as defined by the exchange configuration and distributed to any subscribers.

  The parameter `exchange` specifies the name of the exchange to publish to. If set to
  empty string, it publishes to the default exchange.
  The `routing_key` parameter specifies the routing key for the message.

  The `payload` parameter specifies the message content as a binary.

  In addition to the previous parameters, the following options can be used:

  # Options

    * `:mandatory` - If set, returns an error if the broker can't route the message to a queue (default `false`);
    * `:immediate` - If set, returns an error if the broker can't deliver te message to a consumer immediately (default `false`);
    * `:content_type` - MIME Content type;
    * `:content_encoding` - MIME Content encoding;
    * `:headers` - Message headers. Can be used with headers Exchanges;
    * `:persistent` - If set, uses persistent delivery mode. Messages marked as `persistent` that are delivered to `durable` \
                      queues will be logged to disk;
    * `:correlation_id` - application correlation identifier;
    * `:priority` - message priority, ranging from 0 to 9;
    * `:reply_to` - name of the reply queue;
    * `:expiration` - how long the message is valid (in milliseconds);
    * `:message_id` - message identifier;
    * `:timestamp` - timestamp associated with this message (epoch time);
    * `:type` - message type as a string;
    * `:user_id` - creating user ID. RabbitMQ will validate this against the active connection user;
    * `:app_id` - publishing application ID.

  ## Examples

      iex> AMQP.Basic.publish chan, \"my_exchange\", \"my_routing_key\", \"Hello World!\", persistent: true
      :ok

  """
  @spec publish(Channel.t, exchange, routing_key, payload, keyword) :: :ok | error
  def publish(%Channel{pid: pid}, exchange, routing_key, payload, options \\ []) do
    basic_publish =
      basic_publish(exchange:    exchange,
                    routing_key: routing_key,
                    mandatory:   Keyword.get(options, :mandatory, false),
                    immediate:   Keyword.get(options, :immediate, false))
    p_basic =
      p_basic(content_type:     Keyword.get(options, :content_type,     :undefined),
              content_encoding: Keyword.get(options, :content_encoding, :undefined),
              headers:          Keyword.get(options, :headers,          :undefined) |> Utils.to_type_tuple,
              delivery_mode:    if(options[:persistent], do: 2, else: 1),
              priority:         Keyword.get(options, :priority,         :undefined),
              correlation_id:   Keyword.get(options, :correlation_id,   :undefined),
              reply_to:         Keyword.get(options, :reply_to,         :undefined),
              expiration:       Keyword.get(options, :expiration,       :undefined),
              message_id:       Keyword.get(options, :message_id,       :undefined),
              timestamp:        Keyword.get(options, :timestamp,        :undefined),
              type:             Keyword.get(options, :type,             :undefined),
              user_id:          Keyword.get(options, :user_id,          :undefined),
              app_id:           Keyword.get(options, :app_id,           :undefined),
              cluster_id:       Keyword.get(options, :cluster_id,       :undefined))

    case :amqp_channel.call(pid, basic_publish, amqp_msg(props: p_basic, payload: payload)) do
      :ok -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Sets the message prefetch count or prefetech size (in bytes). If `global` is set to `true` this
  applies to the entire Connection, otherwise it applies only to the specified Channel.
  """
  @spec qos(Channel.t, keyword) :: :ok | error
  def qos(%Channel{pid: pid}, options \\ []) do
    basic_qos = basic_qos(prefetch_size:  Keyword.get(options, :prefetch_size,  0),
                          prefetch_count: Keyword.get(options, :prefetch_count, 0),
                          global:         Keyword.get(options, :global,         false))

    case :amqp_channel.call(pid, basic_qos) do
      basic_qos_ok() -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Acknowledges one or more messages. If `multiple` is set to `true`, all messages up to the one
  specified by `delivery_tag` are considered acknowledged by the server.
  """
  @spec ack(Channel.t, delivery_tag, keyword) :: :ok | error
  def ack(%Channel{pid: pid}, delivery_tag, options \\ []) do
    basic_ack = basic_ack(delivery_tag: delivery_tag,
                          multiple: Keyword.get(options, :multiple, false))

    case :amqp_channel.call(pid, basic_ack) do
      :ok -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Rejects (and, optionally, requeues) a message.
  """
  @spec reject(Channel.t, delivery_tag, keyword) :: :ok | error
  def reject(%Channel{pid: pid}, delivery_tag, options \\ []) do
    basic_reject = basic_reject(delivery_tag: delivery_tag,
                                requeue: Keyword.get(options, :requeue, true))

    case :amqp_channel.call(pid, basic_reject) do
      :ok -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Negative acknowledge of one or more messages. If `multiple` is set to `true`, all messages up to the
  one specified by `delivery_tag` are considered as not acknowledged by the server. If `requeue` is set
  to `true`, the message will be returned to the queue and redelivered to the next available consumer.

  This is a RabbitMQ specific extension to AMQP 0.9.1. It is equivalent to reject, but allows rejecting
  multiple messages using the `multiple` option.
  """
  @spec nack(Channel.t, delivery_tag, keyword) :: :ok | error
  def nack(%Channel{pid: pid}, delivery_tag, options \\ []) do
    basic_nack = basic_nack(delivery_tag: delivery_tag,
                            multiple: Keyword.get(options, :multiple, false),
                            requeue: Keyword.get(options, :requeue,   true))

    case :amqp_channel.call(pid, basic_nack) do
      :ok -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Polls a queue for an existing message.

  Returns the tuple `{:empty, meta}` if the queue is empty or the tuple {:ok, payload, meta} if at least
  one message exists in the queue. The returned meta map includes the entry `message_count` with the
  current number of messages in the queue.

  Receiving messages by polling a queue is not as as efficient as subscribing a consumer to a queue,
  so consideration should be taken when receiving large volumes of messages.

  Setting the `no_ack` option to true will tell the broker that the receiver will not send an acknowledgement of
  the message. Once it believes it has delivered a message, then it is free to assume that the consuming application
  has taken responsibility for it. In general, a lot of applications will not want these semantics, rather, they
  will want to explicitly acknowledge the receipt of a message and have `no_ack` with the default value of false.
  """
  @spec get(Channel.t, queue, keyword) :: {:ok, String.t, map} | {:empty, map} | error
  def get(%Channel{pid: pid}, queue, options \\ []) do
    case :amqp_channel.call pid, basic_get(queue: queue, no_ack: Keyword.get(options, :no_ack, false)) do
      {basic_get_ok(delivery_tag: delivery_tag,
                    redelivered: redelivered,
                    exchange: exchange,
                    routing_key: routing_key,
                    message_count: message_count),
       amqp_msg(props: p_basic(content_type: content_type,
                               content_encoding: content_encoding,
                               headers: headers,
                               delivery_mode: delivery_mode,
                               priority: priority,
                               correlation_id: correlation_id,
                               reply_to: reply_to,
                               expiration: expiration,
                               message_id: message_id,
                               timestamp: timestamp,
                               type: type,
                               user_id: user_id,
                               app_id: app_id,
                               cluster_id: cluster_id), payload: payload)} ->
        {:ok, payload, %{delivery_tag: delivery_tag,
                         redelivered: redelivered,
                         exchange: exchange,
                         routing_key: routing_key,
                         message_count: message_count,
                         content_type: content_type,
                         content_encoding: content_encoding,
                         headers: headers,
                         persistent: delivery_mode == 2,
                         priority: priority,
                         correlation_id: correlation_id,
                         reply_to: reply_to,
                         expiration: expiration,
                         message_id: message_id,
                         timestamp: timestamp,
                         type: type,
                         user_id: user_id,
                         app_id: app_id,
                         cluster_id: cluster_id}}
      basic_get_empty(cluster_id: cluster_id) ->
        {:empty, %{cluster_id: cluster_id}}
      error -> {:error, error}
    end
  end

  @doc """
  Asks the server to redeliver all unacknowledged messages on a specified channel.

  If `requeue` is set to `true` the server will attempt to requeue the message,
  potentially delivering it to another subscriber. Otherwise it will be redelivered
  to the original recipient.
  """
  @spec recover(Channel.t, keyword) :: :ok | error
  def recover(%Channel{pid: pid}, options \\ []) do
    basic_recover = basic_recover(requeue: Keyword.get(options, :requeue, false))

    case :amqp_channel.call(pid, basic_recover) do
      basic_recover_ok() -> :ok
      error -> {:error, error}
    end
  end

  @doc """
  Registers a queue consumer process. The `pid` of the process can be set using
  the `consumer_pid` argument and defaults to the calling process.

  The consumer process will receive the following data structures:

    * `{:basic_deliver, payload, meta}` - This is sent for each message consumed, where \
  `payload` contains the message content and `meta` contains all the metadata set when \
  sending with Basic.publish or additional info set by the broker;
    * `{:basic_consume_ok, %{consumer_tag: consumer_tag}}` - Sent when the consumer \
  process is registered with Basic.consume. The caller receives the same information \
  as the return of Basic.consume;
    * `{:basic_cancel, %{consumer_tag: consumer_tag, no_wait: no_wait}}` - Sent by the \
  broker when the consumer is unexpectedly cancelled (such as after a queue deletion)
    * `{:basic_cancel_ok, %{consumer_tag: consumer_tag}}` - Sent to the consumer process after a call to Basic.cancel

  """
  @spec consume(Channel.t, String.t, pid | nil, keyword) :: {:ok, String.t} | error
  def consume(%Channel{} = chan, queue, consumer_pid \\ nil, options \\ []) do
    basic_consume =
      basic_consume(queue: queue,
                    consumer_tag: Keyword.get(options, :consumer_tag, ""),
                    no_local:     Keyword.get(options, :no_local,     false),
                    no_ack:       Keyword.get(options, :no_ack,       false),
                    exclusive:    Keyword.get(options, :exclusive,    false),
                    nowait:       Keyword.get(options, :no_wait,      false),
                    arguments:    Keyword.get(options, :arguments,    []))

    consumer_pid = consumer_pid || self()

    adapter_pid = spawn fn ->
      Process.flag(:trap_exit, true)
      Process.monitor(consumer_pid)
      Process.monitor(chan.pid)
      do_start_consumer(chan, consumer_pid)
    end

    case :amqp_channel.subscribe(chan.pid, basic_consume, adapter_pid) do
      basic_consume_ok(consumer_tag: consumer_tag) -> {:ok, consumer_tag}
      error -> {:error, error}
    end
  end

  defp do_start_consumer(chan, consumer_pid) do
    receive do
      basic_consume_ok(consumer_tag: consumer_tag) ->
        send consumer_pid, {:basic_consume_ok, %{consumer_tag: consumer_tag}}
        do_consume(chan, consumer_pid, consumer_tag)
    end
  end

  defp do_consume(chan, consumer_pid, consumer_tag) do
    receive do
      {basic_deliver(consumer_tag: consumer_tag,
                     delivery_tag: delivery_tag,
                     redelivered: redelivered,
                     exchange: exchange,
                     routing_key: routing_key),
       amqp_msg(props: p_basic(content_type: content_type,
                               content_encoding: content_encoding,
                               headers: headers,
                               delivery_mode: delivery_mode,
                               priority: priority,
                               correlation_id: correlation_id,
                               reply_to: reply_to,
                               expiration: expiration,
                               message_id: message_id,
                               timestamp: timestamp,
                               type: type,
                               user_id: user_id,
                               app_id: app_id,
                               cluster_id: cluster_id), payload: payload)} ->
        send consumer_pid, {:basic_deliver, payload, %{consumer_tag: consumer_tag,
                                                       delivery_tag: delivery_tag,
                                                       redelivered: redelivered,
                                                       exchange: exchange,
                                                       routing_key: routing_key,
                                                       content_type: content_type,
                                                       content_encoding: content_encoding,
                                                       headers: headers,
                                                       persistent: delivery_mode == 2,
                                                       priority: priority,
                                                       correlation_id: correlation_id,
                                                       reply_to: reply_to,
                                                       expiration: expiration,
                                                       message_id: message_id,
                                                       timestamp: timestamp,
                                                       type: type,
                                                       user_id: user_id,
                                                       app_id: app_id,
                                                       cluster_id: cluster_id}}
        do_consume(chan, consumer_pid, consumer_tag)
      basic_consume_ok(consumer_tag: consumer_tag) ->
        send consumer_pid, {:basic_consume_ok, %{consumer_tag: consumer_tag}}
        do_consume(chan, consumer_pid, consumer_tag)
      basic_cancel_ok(consumer_tag: consumer_tag) ->
        send consumer_pid, {:basic_cancel_ok, %{consumer_tag: consumer_tag}}
      basic_cancel(consumer_tag: consumer_tag, nowait: no_wait) ->
        send consumer_pid, {:basic_cancel, %{consumer_tag: consumer_tag, no_wait: no_wait}}
      {:DOWN, _ref, :process, ^consumer_pid, reason} ->
        cancel(chan, consumer_tag)
        exit(reason)
      {:DOWN, _ref, :process, _pid, reason} ->
        exit(reason)
    end
  end

  @doc """
  End a queue consumer.

  This method cancels a consumer. This does not affect already delivered messages, but it does
  mean the server will not send any more messages for that consumer. The client may receive an
  arbitrary number of messages in between sending the cancel method and receiving the reply.
  """
  @spec cancel(Channel.t, String.t, keyword) :: {:ok, String.t} | error
  def cancel(%Channel{pid: pid}, consumer_tag, options \\ []) do
    basic_cancel = basic_cancel(consumer_tag: consumer_tag, nowait: Keyword.get(options, :no_wait, false))

    case :amqp_channel.call(pid, basic_cancel) do
      basic_cancel_ok(consumer_tag: consumer_tag) -> {:ok, consumer_tag}
      error -> {:error, error}
    end
  end

  @doc """
  Registers a handler to deal with returned messages. The registered
  process will receive `{:basic_return, payload, meta}` data structures.
  """
  @spec return(Channel.t, pid) :: :ok
  def return(%Channel{pid: pid}, return_handler_pid) do
    adapter_pid = spawn fn ->
      Process.flag(:trap_exit, true)
      Process.monitor(return_handler_pid)
      Process.monitor(pid)
      handle_return_messages(pid, return_handler_pid)
    end

    :amqp_channel.register_return_handler(pid, adapter_pid)
  end

  @doc """
  Removes the return handler, if it exists. Does nothing if there is no
  such handler.
  """
  @spec cancel_return(Channel.t) :: :ok
  def cancel_return(%Channel{pid: pid}) do
    :amqp_channel.unregister_return_handler(pid)
  end

  defp handle_return_messages(chan_pid, return_handler_pid) do
    receive do
      {basic_return(reply_code: reply_code,
                    reply_text: reply_text,
                    exchange: exchange,
                    routing_key: routing_key),
       amqp_msg(props: p_basic(content_type: content_type,
                               content_encoding: content_encoding,
                               headers: headers,
                               delivery_mode: delivery_mode,
                               priority: priority,
                               correlation_id: correlation_id,
                               reply_to: reply_to,
                               expiration: expiration,
                               message_id: message_id,
                               timestamp: timestamp,
                               type: type,
                               user_id: user_id,
                               app_id: app_id,
                               cluster_id: cluster_id), payload: payload)} ->
        send return_handler_pid, {:basic_return, payload, %{reply_code: reply_code,
                                                            reply_text: reply_text,
                                                            exchange: exchange,
                                                            routing_key: routing_key,
                                                            content_type: content_type,
                                                            content_encoding: content_encoding,
                                                            headers: headers,
                                                            persistent: delivery_mode == 2,
                                                            priority: priority,
                                                            correlation_id: correlation_id,
                                                            reply_to: reply_to,
                                                            expiration: expiration,
                                                            message_id: message_id,
                                                            timestamp: timestamp,
                                                            type: type,
                                                            user_id: user_id,
                                                            app_id: app_id,
                                                            cluster_id: cluster_id}}

        handle_return_messages(chan_pid, return_handler_pid)

      {:DOWN, _ref, :process, _pid, reason} ->
        exit(reason)
    end
  end
end