reports: fix error when report is empty.

Fix an exception when a report is empty, for example when performing a
tag search that returns no results:

* https://betabooru.donmai.us/reports/posts?search[group]=uploader&search[tags]=does_not_exist

app/components/time_series_component.rb

@@ -18,7 +18,7 @@ class TimeSeriesComponent < ApplicationComponent
 
   def chart_height
     if x_axis != "date"
-      dataframe[x_axis].size * 30
+      dataframe[x_axis]&.size.to_i * 30
     end
   end
 

app/components/time_series_component/time_series_component.html.erb

@@ -6,7 +6,9 @@
   <% end %>
 </div>
 
-<% if mode == :chart && x_axis.present? %>
+<% if dataframe.empty? %>
+  <p>No results found. Try modifying your search or expanding your time range.</p>
+<% elsif mode == :chart && x_axis.present? %>
   <div class="line-chart" style="width: 100%; height: max(90vh, <%= chart_height.to_i %>px);"></div>
 
   <script type="text/javascript">

app/controllers/reports_controller.rb

@@ -147,7 +147,7 @@ class ReportsController < ApplicationController
         @x_axis = @group
       end
 
-      @dataframe[@group] = @dataframe[@group].map(&:pretty_name) if @group.in?(%w[creator updater uploader banner approver user])
+      @dataframe[@group] = @dataframe[@group].map(&:pretty_name) if @group.in?(%w[creator updater uploader banner approver user]) && @dataframe.names.include?(@group)
       @dataframe["date"] = @dataframe["date"].map(&:to_date) if @dataframe["date"]
       @dataframe = @dataframe.crosstab("date", @group) if @group && @period.present?
     end

app/logical/danbooru/data_frame.rb

@@ -4,7 +4,7 @@
 module Danbooru
   class DataFrame
     attr_reader :df
-    delegate :head, :shape, :types, :rename, :each_row, :[], :[]=, to: :df
+    delegate :head, :shape, :names, :types, :rename, :empty?, :each_row, :[], :[]=, to: :df
 
     def initialize(...)
       @df = Rover::DataFrame.new(...)
@@ -17,6 +17,8 @@ module Danbooru
         foreign_key = association.foreign_key
         name = association.name.to_s
 
+        next table if !table.names.include?(foreign_key)
+
         ids = table[foreign_key].to_a.uniq.compact_blank
         records = association.klass.where(primary_key => ids).index_by(&primary_key.to_sym)
 
@@ -27,6 +29,8 @@ module Danbooru
     end
 
     def crosstab(index, pivot)
+      return self if empty?
+
       new_df = DataFrame.new(index => df[index].uniq)
 
       df[pivot].uniq.to_a.each do |value|

test/functional/reports_controller_test.rb

@@ -26,6 +26,18 @@ class ReportsControllerTest < ActionDispatch::IntegrationTest
           assert_response :success
         end
 
+        should "work with the period and group params" do
+          get report_path("posts", search: { period: "month", group: "uploader" })
+
+          assert_response :success
+        end
+
+        should "work with the group param when the dataset is empty" do
+          get report_path("posts", search: { tags: "does_not_exist", group: "uploader" })
+
+          assert_response :success
+        end
+
         should "work when filtering by a nested association" do
           get report_path("posts", search: { uploader: { name: @post.uploader.name }})