Preserve civil daypart clocks across DST

2026-08-13 00:39:46 +00:00
parent 8bb7307f22
commit 8fafacf921
4 changed files with 116 additions and 4 deletions
--- a/internal/timeutil/periods_test.go
+++ b/internal/timeutil/periods_test.go
@@ -33,3 +33,72 @@ func TestClockWindowHandlesOvernight(t *testing.T) {
 		t.Fatalf("End = %s, want 2026-05-30T06:00", got)
 	}
 }
+
+func TestClockWindowUsesCivilTimeAcrossDSTTransitions(t *testing.T) {
+	location, err := LoadLocation("America/Chicago")
+	if err != nil {
+		t.Fatalf("LoadLocation() error = %v", err)
+	}
+	tests := []struct {
+		name      string
+		date      time.Time
+		start     string
+		end       string
+		wantStart string
+		wantEnd   string
+	}{
+		{
+			name:      "spring-forward daytime",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "00:00",
+			end:       "06:00",
+			wantStart: "2026-03-08T00:00:00-06:00",
+			wantEnd:   "2026-03-08T06:00:00-05:00",
+		},
+		{
+			name:      "fall-back daytime",
+			date:      time.Date(2026, time.November, 1, 12, 0, 0, 0, location),
+			start:     "00:00",
+			end:       "06:00",
+			wantStart: "2026-11-01T00:00:00-05:00",
+			wantEnd:   "2026-11-01T06:00:00-06:00",
+		},
+		{
+			name:      "spring-forward overnight",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "22:00",
+			end:       "06:00",
+			wantStart: "2026-03-08T22:00:00-05:00",
+			wantEnd:   "2026-03-09T06:00:00-05:00",
+		},
+		{
+			name:      "spring-forward end of day",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "18:00",
+			end:       "24:00",
+			wantStart: "2026-03-08T18:00:00-05:00",
+			wantEnd:   "2026-03-09T00:00:00-05:00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			start, err := ParseClock(tt.start)
+			if err != nil {
+				t.Fatalf("ParseClock(%q) error = %v", tt.start, err)
+			}
+			end, err := ParseClock(tt.end)
+			if err != nil {
+				t.Fatalf("ParseClock(%q) error = %v", tt.end, err)
+			}
+
+			window := ClockWindow(tt.date, location, start, end)
+			if got := window.Start.Format(time.RFC3339); got != tt.wantStart {
+				t.Fatalf("Start = %s, want %s", got, tt.wantStart)
+			}
+			if got := window.End.Format(time.RFC3339); got != tt.wantEnd {
+				t.Fatalf("End = %s, want %s", got, tt.wantEnd)
+			}
+		})
+	}
+}