fix: Fix daily frequency compensating for DST (#96)

The date transitioning from Standard Time to DST "has" 25 hours in the day. This fixes genNextDay to use `date-fns` so the correct day is returned instead of naively adding 24 hours to the date.

Fixes #95

lib/utils.js

@@ -2,7 +2,7 @@
 
 const { readdir, stat, unlink, symlink, lstat, readlink } = require('fs/promises')
 const { dirname, join } = require('path')
-const { format } = require('date-fns')
+const { format, addDays, addHours } = require('date-fns')
 
 function parseSize (size) {
   let multiplier = 1024 ** 2
@@ -53,11 +53,11 @@ function validateLimitOptions (limit) {
 }
 
 function getNextDay (start) {
-  return new Date(start + 24 * 60 * 60 * 1000).setHours(0, 0, 0, 0)
+  return addDays(new Date(start), 1).setHours(0, 0, 0, 0)
 }
 
 function getNextHour (start) {
-  return new Date(start + 60 * 60 * 1000).setMinutes(0, 0, 0)
+  return addHours(new Date(start), 1).setMinutes(0, 0, 0)
 }
 
 function getNextCustom (frequency) {

package.json

@@ -28,6 +28,7 @@
   },
   "devDependencies": {
     "husky": "^9.0.11",
+    "mockdate": "^3.0.5",
     "pino": "^9.2.0",
     "snazzy": "^9.0.0",
     "standard": "^17.0.0-2",

test/lib/utils.test.js

@@ -5,6 +5,7 @@ const { writeFile, rm, stat, readlink, symlink } = require('fs/promises')
 const { join } = require('path')
 const { test } = require('tap')
 const { format } = require('date-fns')
+const MockDate = require('mockdate')
 
 const {
   buildFileName,
@@ -69,6 +70,66 @@ test('getNext()', async ({ same }) => {
   same(getNext(custom), Date.now() + custom, 'supports custom frequency and does not return start')
 })
 
+test('getNext() on dates transitioning from DST to Standard Time', async ({ same }) => {
+  // on these days the time rolls back 1 hour so there "are" 25 hours in the day
+  // genNext() should account for variable number of hours in the day
+
+  // test two different timezones
+  const data = [
+    {
+      tz: 'Europe/Berlin',
+      mockDate: '27 Oct 2024 00:00:00 GMT+0100'
+    },
+    {
+      tz: 'America/New_York',
+      mockDate: '03 Nov 2024 00:00:00 GMT-0500'
+    }
+  ]
+
+  for (const d of data) {
+    MockDate.set(d.mockDate)
+    process.env.TZ = d.tz
+    const today = new Date()
+
+    same(getNext('daily'), startOfDay(addDays(today, 1)).getTime(), 'supports daily frequency')
+    same(getNext('hourly'), startOfHour(addHours(today, 1)).getTime(), 'supports hourly frequency')
+    const custom = 3000
+    same(getNext(custom), Date.now() + custom, 'supports custom frequency and does not return start')
+    MockDate.reset()
+    process.env.TZ = undefined
+  }
+})
+
+test('getNext() on dates transitioning from Standard Time to DST', async ({ same }) => {
+  // on these days the time rolls forward 1 hour so there "are" 23 hours in the day
+  // genNext() should account for variable number of hours in the day
+
+  // test two different timezones
+  const data = [
+    {
+      tz: 'Europe/Berlin',
+      mockDate: '31 March 2024 01:00:00 GMT+0100'
+    },
+    {
+      tz: 'America/New_York',
+      mockDate: '10 Nov 2024 01:00:00 GMT-0500'
+    }
+  ]
+
+  for (const d of data) {
+    MockDate.set(d.mockDate)
+    process.env.TZ = d.tz
+    const today = new Date()
+
+    same(getNext('daily'), startOfDay(addDays(today, 1)).getTime(), 'supports daily frequency')
+    same(getNext('hourly'), startOfHour(addHours(today, 1)).getTime(), 'supports hourly frequency')
+    const custom = 3000
+    same(getNext(custom), Date.now() + custom, 'supports custom frequency and does not return start')
+    MockDate.reset()
+    process.env.TZ = undefined
+  }
+})
+
 test('getFileName()', async ({ equal, throws }) => {
   const strFunc = () => 'my-func'
   throws(getFileName, 'throws on empty input')