From 03252488cf54db84341ed30d8bb488cb9847eff0 Mon Sep 17 00:00:00 2001
From: Erik Winter <erik@publicsonar.com>
Date: Mon, 6 Jun 2022 11:17:49 +0200
Subject: [PATCH] every n days recurrer

---
 internal/task/recur.go      | 71 +++++++++++++++++++++++++++++--------
 internal/task/recur_test.go | 47 ++++++++++++++++++++++++
 2 files changed, 104 insertions(+), 14 deletions(-)

diff --git a/internal/task/recur.go b/internal/task/recur.go
index c5a2447..2407dbd 100644
--- a/internal/task/recur.go
+++ b/internal/task/recur.go
@@ -25,20 +25,13 @@ func NewRecurrer(recurStr string) Recurrer {
 
 	terms = terms[1:]
 
-	if recur, ok := ParseDaily(start, terms); ok {
-		return recur
-	}
-	if recur, ok := ParseWeekly(start, terms); ok {
-		return recur
-	}
-	if recur, ok := ParseBiweekly(start, terms); ok {
-		return recur
-	}
-	if recur, ok := ParseEveryNWeeks(start, terms); ok {
-		return recur
-	}
-	if recur, ok := ParseEveryNMonths(start, terms); ok {
-		return recur
+	for _, parseFunc := range []func(Date, []string) (Recurrer, bool){
+		ParseDaily, ParseEveryNDays, ParseWeekly, ParseBiweekly,
+		ParseEveryNWeeks, ParseEveryNMonths,
+	} {
+		if recur, ok := parseFunc(start, terms); ok {
+			return recur
+		}
 	}
 
 	return nil
@@ -48,6 +41,7 @@ type Daily struct {
 	Start Date
 }
 
+// yyyy-mm-dd, daily
 func ParseDaily(start Date, terms []string) (Recurrer, bool) {
 	if len(terms) < 1 {
 		return nil, false
@@ -70,6 +64,55 @@ func (d Daily) String() string {
 	return fmt.Sprintf("%s, daily", d.Start.String())
 }
 
+type EveryNDays struct {
+	Start Date
+	N     int
+}
+
+// yyyy-mm-dd, every 3 days
+func ParseEveryNDays(start Date, terms []string) (Recurrer, bool) {
+	if len(terms) != 1 {
+		return EveryNDays{}, false
+	}
+
+	terms = strings.Split(terms[0], " ")
+	if len(terms) != 3 || terms[0] != "every" || terms[2] != "days" {
+		return EveryNDays{}, false
+	}
+
+	n, err := strconv.Atoi(terms[1])
+	if err != nil {
+		return EveryNDays{}, false
+	}
+
+	return EveryNDays{
+		Start: start,
+		N:     n,
+	}, true
+}
+
+func (nd EveryNDays) RecursOn(date Date) bool {
+	if nd.Start.After(date) {
+		return false
+	}
+
+	testDate := nd.Start
+	for {
+		switch {
+		case testDate.Equal(date):
+			return true
+		case testDate.After(date):
+			return false
+		default:
+			testDate = testDate.Add(nd.N)
+		}
+	}
+}
+
+func (nd EveryNDays) String() string {
+	return fmt.Sprintf("%s, every %d days", nd.Start.String(), nd.N)
+}
+
 type Weekly struct {
 	Start    Date
 	Weekdays Weekdays
diff --git a/internal/task/recur_test.go b/internal/task/recur_test.go
index 7e905e6..d183b8c 100644
--- a/internal/task/recur_test.go
+++ b/internal/task/recur_test.go
@@ -50,6 +50,53 @@ func TestDaily(t *testing.T) {
 	})
 }
 
+func TestEveryNDays(t *testing.T) {
+	every := task.EveryNDays{
+		Start: task.NewDate(2022, 6, 8),
+		N:     5,
+	}
+	everyStr := "2022-06-08 (wednesday), every 5 days"
+
+	t.Run("parse", func(t *testing.T) {
+		test.Equals(t, every, task.NewRecurrer(everyStr))
+	})
+
+	t.Run("string", func(t *testing.T) {
+		test.Equals(t, everyStr, every.String())
+	})
+
+	t.Run("recurs on", func(t *testing.T) {
+		for _, tc := range []struct {
+			name string
+			date task.Date
+			exp  bool
+		}{
+			{
+				name: "before",
+				date: task.NewDate(2022, 1, 1),
+			},
+			{
+				name: "start",
+				date: every.Start,
+				exp:  true,
+			},
+			{
+				name: "after true",
+				date: every.Start.Add(15),
+				exp:  true,
+			},
+			{
+				name: "after false",
+				date: every.Start.Add(16),
+			},
+		} {
+			t.Run(tc.name, func(t *testing.T) {
+				test.Equals(t, tc.exp, every.RecursOn(tc.date))
+			})
+		}
+	})
+}
+
 func TestParseWeekly(t *testing.T) {
 	start := task.NewDate(2021, 2, 7)
 	for _, tc := range []struct {