Fix EndOf cycle final_date off-by-one

EndOf#final_date subtracted 1 period before adding period_count,
causing V1E12M to expire at end of month 11 instead of month 12.
Remove the offset so the notation matches user expectations:
V1E12M from Dec 1 now correctly expires Dec 31 (not Nov 30).

Fixed: EndOf cycle expiration was 1 month early (QUAL-6189)

Author: rymiwe

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.1.13] - Unreleased
 
+### Fixed
+
+- EndOf cycle `final_date` was off by one period — `V1E12M` now correctly expires at the end of the 12th month, not the 11th
+
 ## [0.1.12] - 2025-09-05
 
 ### Added

lib/sof/cycles/end_of.rb

@@ -2,7 +2,7 @@
 
 # Captures the logic for enforcing the EndOf cycle variant
 #   E.g. "V1E18MF2020-01-05" means:
-#     You're good until the end of the 17th subsequent month from 2020-01-05.
+#     You're good until the end of the 18th month from 2020-01-05.
 #     Complete 1 by that date to reset the cycle.
 #
 # Some of the calculations are quite different from other cycles.
@@ -62,15 +62,15 @@ def satisfied_by?(_ = nil, anchor: Date.current)
       #
       # @param [nil] _ Unused parameter, maintained for compatibility
       # @return [Date] The final date of the cycle calculated as the end of the
-      #   nth subsequent period after the FROM date, where n = (period count - 1)
+      #   nth period after the FROM date
       #
       # @example
       #   Cycle.for("V1E18MF2020-01-09").final_date
-      #   # => #<Date: 2021-06-30>
+      #   # => #<Date: 2021-07-31>
       def final_date(_ = nil)
         return nil if parser.dormant? || from_date.nil?
         time_span
-          .end_date(start_date - 1.send(period))
+          .end_date(start_date)
           .end_of_month
       end
 
@@ -86,7 +86,7 @@ def dormant_to_s
       end
 
       def subsequent_ordinal
-        ActiveSupport::Inflector.ordinalize(period_count - 1)
+        ActiveSupport::Inflector.ordinalize(period_count)
       end
     end
   end

spec/sof/cycles/dormant_spec.rb

@@ -58,7 +58,7 @@ module SOF
 
       context "with a dormant EndOf cycle" do
         it "returns the cycle string representation with (dormant) suffix" do
-          expect(end_of_cycle.to_s).to eq "2x by the last day of the 17th subsequent month (dormant)"
+          expect(end_of_cycle.to_s).to eq "2x by the last day of the 18th subsequent month (dormant)"
         end
       end
     end

spec/sof/cycles/end_of_spec.rb

@@ -10,7 +10,7 @@ module SOF
     let(:notation) { "V2E18MF#{from_date}" }
     let(:anchor) { nil }
 
-    let(:end_date) { (from_date + 17.months).end_of_month }
+    let(:end_date) { (from_date + 18.months).end_of_month }
     let(:from_date) { "2020-01-01".to_date }
 
     let(:completed_dates) { [] }
@@ -24,21 +24,21 @@ module SOF
       end
     end
 
-    @end_date = ("2020-01-01".to_date + 17.months).end_of_month
+    @end_date = ("2020-01-01".to_date + 18.months).end_of_month
     it_behaves_like "#to_s returns",
       "2x by #{@end_date.to_fs(:american)}"
 
     context "when the cycle is dormant" do
       before { allow(cycle.parser).to receive(:dormant?).and_return(true) }
 
       it_behaves_like "#to_s returns",
-        "2x by the last day of the 17th subsequent month"
+        "2x by the last day of the 18th subsequent month"
     end
     it_behaves_like "#volume returns the volume"
     it_behaves_like "#notation returns the notation"
     it_behaves_like "#as_json returns the notation"
     it_behaves_like "it computes #final_date(given)",
-      given: nil, returns: ("2020-01-01".to_date + 17.months).end_of_month
+      given: nil, returns: ("2020-01-01".to_date + 18.months).end_of_month
     it_behaves_like "it cannot be extended"
 
     describe "#last_completed" do
@@ -66,7 +66,7 @@ module SOF
           too_late_date
         ]
       end
-      let(:recent_date) { from_date + 17.months }
+      let(:recent_date) { from_date + 18.months }
       let(:middle_date) { from_date + 2.months }
       let(:early_date) { from_date + 1.month }
       let(:too_early_date) { from_date - 1.day }
@@ -85,23 +85,23 @@ module SOF
 
     describe "#satisfied_by?(anchor:)" do
       context "when the anchor date is < the final date" do
-        let(:anchor) { "2021-06-29".to_date }
+        let(:anchor) { "2021-07-30".to_date }
 
         it "returns true" do
           expect(cycle).to be_satisfied_by(anchor:)
         end
       end
 
       context "when the anchor date is = the final date" do
-        let(:anchor) { "2021-06-30".to_date }
+        let(:anchor) { "2021-07-31".to_date }
 
         it "returns true" do
           expect(cycle).to be_satisfied_by(anchor:)
         end
       end
 
       context "when the anchor date is > the final date" do
-        let(:anchor) { "2021-07-01".to_date }
+        let(:anchor) { "2021-08-01".to_date }
 
         it "returns false" do
           expect(cycle).not_to be_satisfied_by(completed_dates, anchor:)
@@ -111,26 +111,26 @@ module SOF
 
     describe "#expiration_of(completion_dates)" do
       context "when the anchor date is < the final date" do
-        let(:anchor) { "2021-06-29".to_date }
+        let(:anchor) { "2021-07-30".to_date }
 
         it "returns the final date" do
-          expect(cycle.expiration_of(anchor:)).to eq "2021-06-30".to_date
+          expect(cycle.expiration_of(anchor:)).to eq "2021-07-31".to_date
         end
       end
 
       context "when the anchor date = the final date" do
-        let(:anchor) { "2021-06-30".to_date }
+        let(:anchor) { "2021-07-31".to_date }
 
         it "returns the final date" do
-          expect(cycle.expiration_of(anchor:)).to eq "2021-06-30".to_date
+          expect(cycle.expiration_of(anchor:)).to eq "2021-07-31".to_date
         end
       end
 
       context "when the anchor date > the final date" do
-        let(:anchor) { "2021-07-31".to_date }
+        let(:anchor) { "2021-08-31".to_date }
 
         it "returns the final date" do
-          expect(cycle.expiration_of(anchor:)).to eq "2021-06-30".to_date
+          expect(cycle.expiration_of(anchor:)).to eq "2021-07-31".to_date
         end
       end
     end