Clear threshold timestamps when decrementing

If we're invalidating a bunch of signatures and it goes through a
threshold like 100,000 for a debate or 10,000 for a response then
we need to clear the relevant timestamp so that it doesn't appear
in the wrong lists in both the public and admin websites.

Author: pixeltrix

app/models/petition.rb

@@ -358,6 +358,15 @@ def increment_signature_count!(time = Time.current)
   def decrement_signature_count!(time = Time.current)
     updates = []
 
+    if below_threshold_for_debate?
+      updates << "debate_threshold_reached_at = NULL"
+      updates << "debate_state = 'pending'"
+    end
+
+    if below_threshold_for_response?
+      updates << "response_threshold_reached_at = NULL"
+    end
+
     updates << "signature_count = greatest(signature_count - 1, 1)"
     updates << "updated_at = :now"
 
@@ -384,6 +393,18 @@ def at_threshold_for_debate?
     end
   end
 
+  def below_threshold_for_response?
+    if response_threshold_reached_at?
+      signature_count <= Site.threshold_for_response
+    end
+  end
+
+  def below_threshold_for_debate?
+    if debate_threshold_reached_at?
+      signature_count <= Site.threshold_for_debate
+    end
+  end
+
   def signatures_by_country
     country_petition_journals.joins(:location).preload(:location).to_a.sort_by(&:name)
   end

spec/models/petition_spec.rb

@@ -1301,7 +1301,10 @@
       FactoryGirl.create(:open_petition, {
         signature_count: signature_count,
         last_signed_at: 2.days.ago,
-        updated_at: 2.days.ago
+        updated_at: 2.days.ago,
+        response_threshold_reached_at: 2.days.ago,
+        debate_threshold_reached_at: 2.days.ago,
+        debate_state: 'awaiting'
       })
     end
 
@@ -1325,6 +1328,37 @@
         }.not_to change{ petition.signature_count }
       end
     end
+
+    context "when the signature count crosses below the threshold for a response" do
+      let(:signature_count) { 10 }
+
+      before do
+        expect(Site).to receive(:threshold_for_response).and_return(10)
+      end
+
+      it "resets the timestamp" do
+        petition.decrement_signature_count!
+        expect(petition.response_threshold_reached_at).to be_nil
+      end
+    end
+
+    context "when the signature count crosses below the threshold for a debate" do
+      let(:signature_count) { 100 }
+
+      before do
+        expect(Site).to receive(:threshold_for_debate).and_return(100)
+      end
+
+      it "records the time it happened" do
+        petition.decrement_signature_count!
+        expect(petition.debate_threshold_reached_at).to be_nil
+      end
+
+      it "sets the debate_state to 'pending'" do
+        petition.decrement_signature_count!
+        expect(petition.debate_state).to eq("pending")
+      end
+    end
   end
 
   describe "at_threshold_for_moderation?" do