app: cache the duration estimate for published procedures

app/helpers/procedure_helper.rb

@@ -84,7 +84,8 @@ module ProcedureHelper
   end
 
   def estimated_fill_duration_minutes(procedure)
-    minutes = (procedure.active_revision.estimated_fill_duration / 60.0).round
+    seconds = procedure.active_revision.estimated_fill_duration
+    minutes = (seconds / 60.0).round
     [1, minutes].max
   end
 end

app/models/procedure_revision.rb

@@ -180,8 +180,18 @@ class ProcedureRevision < ApplicationRecord
     tdcs_as_json
   end
 
-  # Estimated duration to fill the form, in seconds
+  # Estimated duration to fill the form, in seconds.
+  #
+  # If the revision is locked (i.e. published), the result is cached (because type de champs can no longer be mutated).
   def estimated_fill_duration
+    Rails.cache.fetch("#{cache_key_with_version}/estimated_fill_duration", expires_in: 12.hours, force: !locked?) do
+      compute_estimated_fill_duration
+    end
+  end
+
+  private
+
+  def compute_estimated_fill_duration
     tdc_durations = types_de_champ_public.fillable.map do |tdc|
       duration = tdc.estimated_fill_duration(self)
       tdc.mandatory ? duration : duration / 2
@@ -189,8 +199,6 @@ class ProcedureRevision < ApplicationRecord
     tdc_durations.sum
   end
 
-  private
-
   def children_types_de_champ_as_json(tdcs_as_json, parent_tdcs)
     parent_tdcs.each do |parent_tdc|
       tdc_as_json = tdcs_as_json.find { |json| json["id"] == parent_tdc.stable_id }

spec/models/procedure_revision_spec.rb

@@ -592,5 +592,38 @@ describe ProcedureRevision do
         expect(subject).to eq row_duration * 2.5
       end
     end
+
+    describe 'caching behavior' do
+      let(:procedure) { create(:procedure, :published, types_de_champ: types_de_champ) }
+
+      before { Rails.cache = ActiveSupport::Cache::MemoryStore.new }
+      after { Rails.cache = ActiveSupport::Cache::NullStore.new }
+
+      context 'when a type de champ belonging to a draft revision is updated' do
+        let(:draft_revision) { procedure.draft_revision }
+
+        before do
+          draft_revision.estimated_fill_duration
+          draft_revision.types_de_champ.first.update!(type_champ: TypeDeChamp.type_champs.fetch(:piece_justificative))
+        end
+
+        it 'returns an up-to-date estimate' do
+          expect(draft_revision.estimated_fill_duration).to eq \
+              TypesDeChamp::TypeDeChampBase::FILL_DURATION_LONG \
+            + TypesDeChamp::TypeDeChampBase::FILL_DURATION_MEDIUM \
+            + TypesDeChamp::TypeDeChampBase::FILL_DURATION_LONG \
+        end
+      end
+
+      context 'when the revision is published (and thus immutable)' do
+        let(:published_revision) { procedure.published_revision }
+
+        it 'caches the estimate' do
+          expect(published_revision).to receive(:compute_estimated_fill_duration).once
+          published_revision.estimated_fill_duration
+          published_revision.estimated_fill_duration
+        end
+      end
+    end
   end
 end