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Fix newsletter week number calculation #35

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Merged
deepakjois merged 1 commit into from
Dec 29, 2025
Merged

Fix newsletter week number calculation #35

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42 changes: 33 additions & 9 deletions build_newsletter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,14 @@ type BuildNewsletterCmd struct {
Notify bool `help:"Send notification email after posting (RESEND_API_KEY must be set)"`
}

// NewsletterWeek holds the calculated week information for a newsletter.
type NewsletterWeek struct {
Start AppTimezone // Sunday (start of the newsletter period)
End AppTimezone // Saturday (end of the newsletter period)
Year int // ISO year from the Monday of the week
WeekNum int // ISO week number from the Monday of the week
}

// Validate ensures that --notify is only used with --post
func (cmd *BuildNewsletterCmd) Validate() error {
if cmd.Notify && !cmd.Post {
Expand All @@ -35,6 +43,25 @@ type ButtondownPayload struct {
Status string `json:"status"`
}

// calculateNewsletterWeek computes the newsletter week information for a given time.
// The newsletter covers Sunday to Saturday of the previous week.
// The week number is based on the Monday of that week (ISO week standard).
func calculateNewsletterWeek(t AppTimezone) NewsletterWeek {
sat := lastSaturday(t).Truncate(24 * time.Hour)
sun := sat.AddDate(0, 0, -6)
// Use Monday (sun + 1 day) to get the ISO week number
// This ensures the week number is consistent with the week the newsletter covers
mon := sun.AddDate(0, 0, 1)
year, weekNum := mon.ISOWeek()

return NewsletterWeek{
Start: sun,
End: sat,
Year: year,
WeekNum: weekNum,
}
}

// lastSaturday returns the most recent Saturday before the given time t.
// If t is Saturday, it returns the Saturday one week ago.
func lastSaturday(t AppTimezone) AppTimezone {
Expand All @@ -48,11 +75,9 @@ func lastSaturday(t AppTimezone) AppTimezone {
}

func (cmd *BuildNewsletterCmd) Run() error {
now := Now()
sat := lastSaturday(now).Truncate(24 * time.Hour)
sun := sat.AddDate(0, 0, -6)
week := calculateNewsletterWeek(Now())

files, err := collectFiles(sun, sat)
files, err := collectFiles(week.Start, week.End)
if err != nil {
return fmt.Errorf("failed to collect files: %w", err)
}
Expand All @@ -62,20 +87,19 @@ func (cmd *BuildNewsletterCmd) Run() error {
return fmt.Errorf("failed to process files: %w", err)
}

year, weekNum := sun.ISOWeek()
if cmd.Post {
fmt.Fprintf(os.Stderr, "posting weekly digest for Week %d, %d (%s to %s) to Buttondown\n", weekNum, year, sun.Format("2006-01-02"), sat.Format("2006-01-02"))
if err := postToButtondown(content, year, weekNum); err != nil {
fmt.Fprintf(os.Stderr, "posting weekly digest for Week %d, %d (%s to %s) to Buttondown\n", week.WeekNum, week.Year, week.Start.Format("2006-01-02"), week.End.Format("2006-01-02"))
if err := postToButtondown(content, week.Year, week.WeekNum); err != nil {
return fmt.Errorf("failed to post to ButtonDown: %w", err)
}

if cmd.Notify {
if err := sendNotificationEmail(year, weekNum); err != nil {
if err := sendNotificationEmail(week.Year, week.WeekNum); err != nil {
return fmt.Errorf("failed to send notification email: %w", err)
}
}
} else {
fmt.Fprintf(os.Stderr, "weekly digest for week %d %d (%s to %s)\n", weekNum, year, sun.Format("2006-01-02"), sat.Format("2006-01-02"))
fmt.Fprintf(os.Stderr, "weekly digest for week %d %d (%s to %s)\n", week.WeekNum, week.Year, week.Start.Format("2006-01-02"), week.End.Format("2006-01-02"))
fmt.Println(content)
}
return nil
Expand Down
207 changes: 207 additions & 0 deletions build_newsletter_test.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,207 @@
package main

import (
"testing"
"time"
)

func TestLastSaturday(t *testing.T) {
tests := []struct {
name string
input AppTimezone
expected string // YYYY-MM-DD format
}{
{
name: "from Sunday returns previous Saturday",
input: DateInAppTimezone(2024, time.December, 29, 12, 0, 0, 0), // Sunday
expected: "2024-12-28",
},
{
name: "from Monday returns previous Saturday",
input: DateInAppTimezone(2024, time.December, 30, 12, 0, 0, 0), // Monday
expected: "2024-12-28",
},
{
name: "from Saturday returns Saturday one week ago",
input: DateInAppTimezone(2024, time.December, 28, 12, 0, 0, 0), // Saturday
expected: "2024-12-21",
},
{
name: "from Friday returns previous Saturday",
input: DateInAppTimezone(2024, time.December, 27, 12, 0, 0, 0), // Friday
expected: "2024-12-21",
},
{
name: "crossing year boundary from January",
input: DateInAppTimezone(2025, time.January, 2, 12, 0, 0, 0), // Thursday
expected: "2024-12-28",
},
}

for _, tc := range tests {
t.Run(tc.name, func(t *testing.T) {
result := lastSaturday(tc.input)
got := result.Format("2006-01-02")
if got != tc.expected {
t.Errorf("lastSaturday(%s) = %s, want %s", tc.input.Format("2006-01-02"), got, tc.expected)
}
// Verify it's actually a Saturday
if result.Weekday() != time.Saturday {
t.Errorf("lastSaturday returned %s which is %s, not Saturday", got, result.Weekday())
}
})
}
}

func TestCalculateNewsletterWeek(t *testing.T) {
tests := []struct {
name string
input AppTimezone
expectedStart string // Sunday YYYY-MM-DD
expectedEnd string // Saturday YYYY-MM-DD
expectedYear int
expectedWeekNum int
}{
{
name: "regular week in middle of year",
input: DateInAppTimezone(2024, time.June, 17, 12, 0, 0, 0), // Monday June 17
expectedStart: "2024-06-09", // Sunday
expectedEnd: "2024-06-15", // Saturday
expectedYear: 2024,
expectedWeekNum: 24, // Week 24 (Monday June 10 is in ISO week 24)
},
{
name: "called on Sunday gets previous week",
input: DateInAppTimezone(2024, time.June, 16, 12, 0, 0, 0), // Sunday June 16
expectedStart: "2024-06-09", // Sunday
expectedEnd: "2024-06-15", // Saturday
expectedYear: 2024,
expectedWeekNum: 24,
},
{
name: "called on Saturday gets week before last",
input: DateInAppTimezone(2024, time.June, 15, 12, 0, 0, 0), // Saturday June 15
expectedStart: "2024-06-02", // Sunday
expectedEnd: "2024-06-08", // Saturday
expectedYear: 2024,
expectedWeekNum: 23, // Week 23 (Monday June 3 is in ISO week 23)
},
// Year transition edge cases
{
name: "year transition: called on Jan 1 2025 (Wednesday)",
input: DateInAppTimezone(2025, time.January, 1, 12, 0, 0, 0),
expectedStart: "2024-12-22", // Sunday
expectedEnd: "2024-12-28", // Saturday
expectedYear: 2024,
expectedWeekNum: 52, // Monday Dec 23 is in ISO week 52 of 2024
},
{
name: "year transition: called on Jan 5 2025 (Sunday)",
input: DateInAppTimezone(2025, time.January, 5, 12, 0, 0, 0),
expectedStart: "2024-12-29", // Sunday
expectedEnd: "2025-01-04", // Saturday (crosses year boundary)
expectedYear: 2025,
expectedWeekNum: 1, // Monday Dec 30 is in ISO week 1 of 2025
},
{
name: "year transition: called on Jan 6 2025 (Monday)",
input: DateInAppTimezone(2025, time.January, 6, 12, 0, 0, 0),
expectedStart: "2024-12-29", // Sunday
expectedEnd: "2025-01-04", // Saturday
expectedYear: 2025,
expectedWeekNum: 1,
},
{
name: "ISO week 1 starts in previous year (2020)",
input: DateInAppTimezone(2020, time.January, 5, 12, 0, 0, 0), // Sunday
expectedStart: "2019-12-29", // Sunday
expectedEnd: "2020-01-04", // Saturday
expectedYear: 2020,
expectedWeekNum: 1, // Monday Dec 30 2019 is ISO week 1 of 2020
},
{
name: "week 53 edge case (2020 has 53 weeks)",
input: DateInAppTimezone(2021, time.January, 3, 12, 0, 0, 0), // Sunday
expectedStart: "2020-12-27", // Sunday
expectedEnd: "2021-01-02", // Saturday
expectedYear: 2020,
expectedWeekNum: 53, // Monday Dec 28 2020 is ISO week 53 of 2020
},
{
name: "week 53 to week 1 transition (2021)",
input: DateInAppTimezone(2021, time.January, 10, 12, 0, 0, 0), // Sunday
expectedStart: "2021-01-03", // Sunday
expectedEnd: "2021-01-09", // Saturday
expectedYear: 2021,
expectedWeekNum: 1, // Monday Jan 4 2021 is ISO week 1 of 2021
},
}

for _, tc := range tests {
t.Run(tc.name, func(t *testing.T) {
result := calculateNewsletterWeek(tc.input)

gotStart := result.Start.Format("2006-01-02")
if gotStart != tc.expectedStart {
t.Errorf("Start = %s, want %s", gotStart, tc.expectedStart)
}

gotEnd := result.End.Format("2006-01-02")
if gotEnd != tc.expectedEnd {
t.Errorf("End = %s, want %s", gotEnd, tc.expectedEnd)
}

if result.Year != tc.expectedYear {
t.Errorf("Year = %d, want %d", result.Year, tc.expectedYear)
}

if result.WeekNum != tc.expectedWeekNum {
t.Errorf("WeekNum = %d, want %d", result.WeekNum, tc.expectedWeekNum)
}

// Verify Start is a Sunday
if result.Start.Weekday() != time.Sunday {
t.Errorf("Start (%s) is %s, want Sunday", gotStart, result.Start.Weekday())
}

// Verify End is a Saturday
if result.End.Weekday() != time.Saturday {
t.Errorf("End (%s) is %s, want Saturday", gotEnd, result.End.Weekday())
}

// Verify the period is exactly 6 days (Sunday to Saturday)
diff := result.End.Sub(result.Start)
expectedDiff := 6 * 24 * time.Hour
if diff != expectedDiff {
t.Errorf("Period duration = %v, want %v", diff, expectedDiff)
}
})
}
}

func TestCalculateNewsletterWeek_WeekNumberFromMondayNotSunday(t *testing.T) {
// This test specifically verifies that the week number is based on Monday,
// not Sunday. This is important because the newsletter runs Sunday-Saturday,
// and ISO weeks change on Monday.

// Dec 29, 2024 is a Sunday - it's in ISO week 52 of 2024
// Dec 30, 2024 is a Monday - it's in ISO week 1 of 2025
// So a newsletter covering Dec 29 - Jan 4 should use week 1 of 2025 (from Monday)

input := DateInAppTimezone(2025, time.January, 5, 12, 0, 0, 0) // Sunday Jan 5
result := calculateNewsletterWeek(input)

// The newsletter covers Dec 29 (Sun) to Jan 4 (Sat)
if result.Start.Format("2006-01-02") != "2024-12-29" {
t.Errorf("Start = %s, want 2024-12-29", result.Start.Format("2006-01-02"))
}

// Using Monday (Dec 30) for week number should give us week 1 of 2025
// If we used Sunday (Dec 29), we'd get week 52 of 2024 - which would be wrong
if result.Year != 2025 {
t.Errorf("Year = %d, want 2025 (should use Monday's year, not Sunday's)", result.Year)
}
if result.WeekNum != 1 {
t.Errorf("WeekNum = %d, want 1 (should use Monday's week number, not Sunday's)", result.WeekNum)
}
}