#434

backend/app/services/counts_pivot_layout.rb

@@ -0,0 +1,28 @@
+# Coordinates carry their aggregation depth; SQL NULL remains an ordinary axis value.
+class CountsPivotLayout
+  def self.depths(keys, sorts, measures: true)
+    return [] if keys.length < 2 || sorts.first&.first == 'count' ||
+        sorts.first&.first&.start_with?('measure_')
+
+    relevant = sorts.map(&:first).select { keys.include?(_1) || (measures && (_1 == 'count' ||
+        _1.start_with?('measure_'))) }
+    order = (relevant + keys).uniq
+    (1...keys.length).select { order.first(_1).sort == keys.first(_1).sort }
+  end
+
+  def self.headers(values, depths, next_values: nil, grand: false)
+    result = []
+    values.each_with_index do |tuple, index|
+      result << { values: tuple, kind: 'data' }
+      following = values[index + 1] || next_values
+      depths.reverse_each do |depth|
+        prefix = tuple.first(depth)
+        next if following && following.first(depth) == prefix
+
+        result << { values: prefix, kind: 'subtotal' }
+      end
+    end
+    result << { values: [], kind: 'grand_total' } if grand
+    result
+  end
+end