UX: Make sentiment trends more readable in time series data

Instead of a stacked chart showing a separate series for positive and negative, this PR introduces a simplification to the overall sentiment dashboard. It comprises the sentiment into a single series of the difference between `positive - negative` instead. This should allow for the data to be more easy to scan and look for trends.

Author: keegangeorge

config/locales/server.en.yml

@@ -400,9 +400,7 @@ en:
 
     sentiment:
       reports:
-        overall_sentiment:
-          positive: "Positive"
-          negative: "Negative"
+        overall_sentiment: "Overall sentiment (Positive - Negative)"
         post_emotion:
           sadness: "Sadness 😢"
           surprise: "Surprise 😱"

lib/sentiment/sentiment_dashboard_report.rb

@@ -5,7 +5,7 @@ module Sentiment
     class SentimentDashboardReport
       def self.register!(plugin)
         plugin.add_report("overall_sentiment") do |report|
-          report.modes = [:stacked_chart]
+          report.modes = [:chart]
           threshold = 0.6
 
           sentiment_count_sql = Proc.new { |sentiment| <<~SQL }
@@ -38,20 +38,17 @@ def self.register!(plugin)
               threshold: threshold,
             )
 
-          data_points = %w[positive negative]
-
           return report if grouped_sentiments.empty?
 
           report.data =
-            data_points.map do |point|
+            grouped_sentiments.map do |gs|
               {
-                req: "sentiment_#{point}",
-                color: point == "positive" ? report.colors[:lime] : report.colors[:purple],
-                label: I18n.t("discourse_ai.sentiment.reports.overall_sentiment.#{point}"),
-                data:
-                  grouped_sentiments.map do |gs|
-                    { x: gs.posted_at, y: gs.public_send("#{point}_count") }
-                  end,
+                color: report.colors[:lime],
+                label: I18n.t("discourse_ai.sentiment.reports.overall_sentiment"),
+                data: {
+                  x: gs.posted_at,
+                  y: gs.public_send("positive_count") - gs.public_send("negative_count"),
+                },
               }
             end
         end