Add mix elasticsearch.install task

This will be helpful for making projects initialize their own version of
elasticsearch for development purposes.

.gitignore

@@ -18,3 +18,5 @@ erl_crash.dump
 
 # Also ignore archive artifacts (built via "mix archive.build").
 *.ez
+
+vendor/

lib/mix/elasticsearch.install.ex

@@ -0,0 +1,47 @@
+defmodule Mix.Tasks.Elasticsearch.Install do
+  @moduledoc """
+  Downloads a version of Elasticsearch with `curl` to a directory of your
+  choosing.
+  """
+
+  def run(args) do
+    with {[{:version, version}], [location], _} <- OptionParser.parse(args, switches: [ version: :string ]) do
+      download_elasticsearch(version, location)
+      download_kibana(version, location)
+    else
+      _ ->
+        Mix.raise """
+        Invalid options. See `mix help elasticsearch.install`
+        """
+    end
+  end
+
+  defp download_elasticsearch(version, location) do
+    name = "elasticsearch-#{version}" 
+    tar = "#{name}.tar.gz"
+
+    System.cmd("curl", ["-L", "-O", "https://artifacts.elastic.co/downloads/elasticsearch/#{tar}"], cd: location)
+    unpack(tar, name, "elasticsearch", location)
+  end
+
+  defp download_kibana(version, location) do
+    name =
+      case :os.type do
+        {:unix, :darwin} ->
+          "kibana-#{version}-darwin-x86_64"
+        other ->
+          Mix.raise "Unsupported system for Kibana: #{inspect other}"
+      end
+
+    tar = "#{name}.tar.gz"
+
+    System.cmd("curl", ["-L", "-O", "https://artifacts.elastic.co/downloads/kibana/#{tar}"], cd: location)
+    unpack(tar, name, "kibana", location)
+  end
+
+  defp unpack(tar, name, alias, location) do
+    System.cmd("tar", ["-zxvf", tar], cd: location)
+    System.cmd("rm", [tar], cd: location)
+    System.cmd("mv", [name, alias], cd: location)
+  end
+end