every n weeks recurrer

Makefile

@@ -1,7 +1,7 @@
 test:
 	go test ./...
 
-deploy:
+deploy: test
 	go build -o gte-process-inbox ./cmd/process-inbox/main.go
 	go build -o gte-generate-recurring ./cmd/generate-recurring/main.go
 	scp gte-* zerocontent.org:bin/

internal/task/recur.go

@@ -2,6 +2,7 @@ package task
 
 import (
 	"fmt"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -33,6 +34,9 @@ func NewRecurrer(recurStr string) Recurrer {
 	if recur, ok := ParseBiweekly(start, terms); ok {
 		return recur
 	}
+	if recur, ok := ParseEveryNWeeks(start, terms); ok {
+		return recur
+	}
 
 	return nil
 }
@@ -179,3 +183,45 @@ func (b Biweekly) RecursOn(date Date) bool {
 func (b Biweekly) String() string {
 	return fmt.Sprintf("%s, biweekly, %s", b.Start.String(), strings.ToLower(b.Weekday.String()))
 }
+
+type EveryNWeeks struct {
+	Start Date
+	N     int
+}
+
+// yyyy-mm-dd, every 3 weeks
+func ParseEveryNWeeks(start Date, terms []string) (Recurrer, bool) {
+	if len(terms) < 1 || len(terms) > 1 {
+		return nil, false
+	}
+
+	terms = strings.Split(terms[0], " ")
+	if len(terms) != 3 || terms[0] != "every" || terms[2] != "weeks" {
+		return nil, false
+	}
+	n, err := strconv.Atoi(terms[1])
+	if err != nil || n < 1 {
+		return nil, false
+	}
+
+	return EveryNWeeks{
+		Start: start,
+		N:     n,
+	}, true
+}
+
+func (enw EveryNWeeks) RecursOn(date Date) bool {
+	if enw.Start.After(date) {
+		return false
+	}
+	if enw.Start.Equal(date) {
+		return true
+	}
+
+	intervalDays := enw.N * 7
+	return enw.Start.DaysBetween(date)%intervalDays == 0
+}
+
+func (enw EveryNWeeks) String() string {
+	return fmt.Sprintf("%s, every %d weeks", enw.Start.String(), enw.N)
+}

internal/task/recur_test.go

@@ -240,3 +240,63 @@ func TestBiweekly(t *testing.T) {
 		}
 	})
 }
+
+func TestEveryNWeeks(t *testing.T) {
+	everyNWeeks := task.EveryNWeeks{
+		Start: task.NewDate(2021, 2, 3),
+		N:     3,
+	}
+	everyNWeeksStr := "2021-02-03 (wednesday), every 3 weeks"
+
+	t.Run("parse", func(t *testing.T) {
+		test.Equals(t, everyNWeeks, task.NewRecurrer(everyNWeeksStr))
+	})
+
+	t.Run("string", func(t *testing.T) {
+		test.Equals(t, everyNWeeksStr, everyNWeeks.String())
+	})
+
+	t.Run("recurs on", func(t *testing.T) {
+		for _, tc := range []struct {
+			name string
+			date task.Date
+			exp  bool
+		}{
+			{
+				name: "before start",
+				date: task.NewDate(2021, 1, 27),
+			},
+			{
+				name: "on start",
+				date: task.NewDate(2021, 2, 3),
+				exp:  true,
+			},
+			{
+				name: "wrong day",
+				date: task.NewDate(2021, 2, 4),
+			},
+			{
+				name: "one week after",
+				date: task.NewDate(2021, 2, 10),
+			},
+			{
+				name: "first interval",
+				date: task.NewDate(2021, 2, 24),
+				exp:  true,
+			},
+			{
+				name: "second interval",
+				date: task.NewDate(2021, 3, 17),
+				exp:  true,
+			},
+			{
+				name: "second interval plus one week",
+				date: task.NewDate(2021, 3, 24),
+			},
+		} {
+			t.Run(tc.name, func(t *testing.T) {
+				test.Equals(t, tc.exp, everyNWeeks.RecursOn(tc.date))
+			})
+		}
+	})
+}