feat: add reconsumer module

lib/kafee/reconsumer.ex

@@ -0,0 +1,63 @@
+defmodule Kafee.Reconsumer do
+  @moduledoc """
+  Reconsumer is a `Task` that queries and filters
+  messages from Kafka for ad hoc re-consumption. This
+  is mainly used for debugging or fixing an out of band
+  issue that arose in the system.
+
+  ## Querying
+
+  This module is based on a built query for the Kafka messages.
+  It's based off of `Ecto.Query` and allows you to filter out
+  messages based off of timestamp, offset, partition, topic, and key.
+
+  To start, you want to create a query from an already existing `Kafee.Consumer`.
+  This will pull in all of the consumer configuration set, like connection
+  details, group id, topics, and handler function.
+
+      MyConsumer
+      |> Kafee.Reconsumer.from_consumer()
+
+  Next up, you can refine the query by adding or ignoring topics.
+
+      MyConsumer
+      |> Kafee.Reconsumer.from_consumer()
+      |> Kafee.Reconsumer.add_topic(["good_topic_1"])
+      |> Kafee.Reconsumer.remove_topic(["bad_topic_1", "bad_topic_2"])
+
+  You'll then want to filter out the messages based off of the criteria you have.
+
+      MyConsumer
+      |> Kafee.Reconsumer.from_consumer()
+      |> Kafee.Reconsumer.add_topic(["good_topic_1"])
+      |> Kafee.Reconsumer.remove_topic(["bad_topic_1", "bad_topic_2"])
+      |> Kafee.Reconsumer.filter_timestamp_window(~U[2020-01-01 00:00:00Z], ~U[2020-01-02 00:00:00Z])
+      |> Kafee.Reconsumer.filter_key("my_key")
+
+  Lastly, you can run the query.
+
+      MyConsumer
+      |> Kafee.Reconsumer.from_consumer()
+      |> Kafee.Reconsumer.add_topic(["good_topic_1"])
+      |> Kafee.Reconsumer.remove_topic(["bad_topic_1", "bad_topic_2"])
+      |> Kafee.Reconsumer.filter_timestamp_window(~U[2020-01-01 00:00:00Z], ~U[2020-01-02 00:00:00Z])
+      |> Kafee.Reconsumer.filter_key("my_key")
+      |> Kafee.Reconsumer.run()
+
+  ### Assumptions
+
+  When the query is created from the consumer, we take the existing consumer group name and
+  append a random generated string. This is to ensure that the reconsumer does not interfere
+  with the existing consumer group. Once the reconsumer is done, we will automatially delete the
+  consumer group to avoid any lingering consumer group issues.
+
+  When setting time windows, we set the initial offset for the consumer groups _close to_ (but not exactly)
+  to the needed offset. This should optimize the query to only pull in the messages that are needed.
+
+  ## Running
+
+  Once you have your reconsumer query set up, you can call the `run/0` function.
+  This will run the reconsumer synchronously. We recommend wrapping this up in a
+  `Task`, use [`Flame`](https://github.com/phoenixframework/flame), or run via a Kubernetes job.
+  """
+end