1 files changed, 51 insertions, 0 deletions
diff --git a/internal/models/recurrence_test.go b/internal/models/recurrence_test.go
new file mode 100644
index 0000000..8d18996
--- /dev/null
+++ b/internal/models/recurrence_test.go
@@ -0,0 +1,51 @@
+package models
+
+import (
+	"testing"
+	"time"
+)
+
+func TestComputeNextOccurrence(t *testing.T) {
+	mustParse := func(t *testing.T, s string) time.Time {
+		t.Helper()
+		d, err := time.Parse("2006-01-02", s)
+		if err != nil {
+			t.Fatalf("bad fixture date %q: %v", s, err)
+		}
+		return d
+	}
+
+	tests := []struct {
+		name     string
+		due      string
+		freq     string
+		interval int
+		weekdays []int
+		want     string
+	}{
+		{"daily interval 1", "2026-07-13", "daily", 1, nil, "2026-07-14"},
+		{"daily interval 3", "2026-07-13", "daily", 3, nil, "2026-07-16"},
+		{"weekly no weekdays interval 1", "2026-07-13", "weekly", 1, nil, "2026-07-20"},
+		{"weekly no weekdays interval 2", "2026-07-13", "weekly", 2, nil, "2026-07-27"},
+		// 2026-07-13 is a Monday (weekday=1).
+		{"weekly with weekdays same week", "2026-07-13", "weekly", 1, []int{1, 3, 5}, "2026-07-15"},
+		{"weekly with weekdays wraps to next week", "2026-07-17", "weekly", 1, []int{1, 3, 5}, "2026-07-20"}, // due=Fri(5), wraps to Mon
+		{"weekly with weekdays interval 2 wraps", "2026-07-13", "weekly", 2, []int{1}, "2026-07-27"},          // due=Mon, only Mon active, skip a week
+		{"monthly interval 1", "2026-06-13", "monthly", 1, nil, "2026-07-13"},
+		{"monthly rollover", "2026-01-31", "monthly", 1, nil, "2026-03-03"},
+		{"monthly rollover locks in on the drifted day", "2026-03-03", "monthly", 1, nil, "2026-04-03"},
+		{"yearly interval 1", "2026-07-13", "yearly", 1, nil, "2027-07-13"},
+		{"unknown freq returns due unchanged", "2026-07-13", "bogus", 1, nil, "2026-07-13"},
+		{"interval below 1 is treated as 1", "2026-07-13", "daily", 0, nil, "2026-07-14"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := ComputeNextOccurrence(mustParse(t, tc.due), tc.freq, tc.interval, tc.weekdays)
+			want := mustParse(t, tc.want)
+			if !got.Equal(want) {
+				t.Errorf("ComputeNextOccurrence(%s, %s, %d, %v) = %s, want %s", tc.due, tc.freq, tc.interval, tc.weekdays, got.Format("2006-01-02"), tc.want)
+			}
+		})
+	}
+}