Change how list query parameters are constructed

lib/gmail/base.ex

@@ -30,27 +30,39 @@ defmodule Gmail.Base do
     if Enum.empty?(params) do
       path
     else
-      query =
+      {query, list_params} =
         params
-        |> Map.keys
-        |> Enum.filter(fn key -> key in available_options end)
-        |> Enum.reduce(Map.new, fn key, query ->
-          string_key = Utils.camelize(key)
-          val = if is_list(params[key]) do
-            Enum.join(params[key], ",")
-          else
-            params[key]
-          end
-          Map.put(query, string_key, val)
-        end)
-      if Enum.empty?(query) do
+        |> Enum.reduce({ Map.new, Map.new}, fn {key, value}, {q, lps} ->
+            if key in available_options do
+              string_key = Utils.camelize(key)
+              if is_list(value) do
+                {q, Map.put(lps, string_key, value)}
+              else
+                {Map.put(q, string_key, value), lps}
+              end
+            else
+              {q, lps}
+            end
+          end)
+      if Enum.empty?(query) && Enum.empty?(list_params) do
         path
       else
-        path <> "?" <> URI.encode_query(query)
+        path <> "?" <> URI.encode_query(query) <> queryify_arrays(list_params)
       end
     end
   end
 
+  @spec queryify_arrays(map) :: String.t
+  defp queryify_arrays(params) do
+        params
+        |> Map.keys
+        |> Enum.reduce("", fn key, query_string ->
+            string_key = "&" <> key <> "="
+            query_string <> string_key <> Enum.join(params[key], string_key)
+           end)
+        |> URI.encode
+  end
+
   @spec handle_error({atom, map}) :: {atom, String.t} | {atom, map}
   @spec handle_error({atom, String.t}) :: {atom, String.t} | {atom, map}
   def handle_error(response) do

test/gmail/thread_test.exs

@@ -227,7 +227,7 @@ defmodule Gmail.ThreadTest do
   } do
     Bypass.expect bypass, fn conn ->
       assert "/gmail/v1/users/#{user_id}/threads/#{thread_id}" == conn.request_path
-      assert URI.encode_query(%{"format" => "metadata", "metadataHeaders" => "header1,header1"}) == conn.query_string
+      assert URI.encode("format=metadata&metadataHeaders=header1&metadataHeaders=header1") == conn.query_string
       assert "GET" == conn.method
       assert {"authorization", "Bearer #{access_token}"} in conn.req_headers
       {:ok, json} = Poison.encode(thread)
@@ -237,6 +237,25 @@ defmodule Gmail.ThreadTest do
     assert expected_result == thread
   end
 
+  test "gets threads, specifying multiple labels", %{
+    access_token: access_token,
+    expected_search_results: expected_search_results,
+    list_results: list_results,
+    bypass: bypass,
+    user_id: user_id
+  } do
+    Bypass.expect bypass, fn conn ->
+      assert "/gmail/v1/users/#{user_id}/threads" == conn.request_path
+      assert URI.encode("&labelIds=sample&labelIds=blah") == conn.query_string
+      assert "GET" == conn.method
+      assert {"authorization", "Bearer #{access_token}"} in conn.req_headers
+      {:ok, json} = Poison.encode(list_results)
+      Plug.Conn.resp(conn, 200, json)
+    end
+    {:ok, results, _} = Gmail.User.threads(user_id, %{label_ids: ["sample", "blah"]})
+    assert expected_search_results == results
+  end
+
   test "reports :not_found for a thread that doesn't exist", %{
     thread_not_found: thread_not_found,
     thread_id: thread_id,