BREAKING CHANGE: ScheduledTask: Allow better handling of multiple time zones

CHANGELOG.md

@@ -25,6 +25,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - BREAKING CHANGE: ScheduledTask
+  - Fixed SynchronizeAcrossTimeZone issue where Test always throws False when a date & time is used
+    where Daylight Savings Time is in operation. Fixes [Issue #374](https://github.com/dsccommunity/ComputerManagementDsc/issues/374).
+  - Fixed Test-DateStringContainsTimeZone to correctly process date strings behind UTC (-), as well
+    as UTC Zulu 'Z' strings.
   - Fixed User parameter to correctly return the user that triggers an AtLogon or OnSessionState
     Schedule Type, instead of the current value of ExecuteAsCredential. This parameter
     is only valid when using the AtLogon and OnSessionState Schedule Types.
@@ -41,8 +45,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - BREAKING CHANGE: ScheduledTask
+  - StartTime is now processed on the device, rather than at compile time. This makes it possible
+    to configure start times based on each device's timezone, rather than being fixed to the time zone
+    configured on the device where the Desired State Configuration compilation was run.
   - Allow StartTime to be used to set the 'Activate' setting when adding ScheduleType triggers
     other than 'Once', 'Daily' and 'Weekly'.
+  - Changed the default StartTime date from today to 1st January 1980 to prevent configuration flip flopping,
+    and added note to configuration README to advise always supplying a date, and not just a time.
+    Fixes [Issue #148](https://github.com/dsccommunity/ComputerManagementDsc/issues/148).
+    Fixes [Issue #411](https://github.com/dsccommunity/ComputerManagementDsc/issues/411).
+  - Added examples & note to configuration README to supply a timezone when using SynchronizeAcrossTimeZone.
+  - Allow SynchronizeAcrossTimeZone to be used when adding ScheduleType triggers other than 'Once',
+    'Daily' and 'Weekly'.
   - Updated Delay parameter to support ScheduleType AtLogon, AtStartup, AtCreation, OnSessionState.
     Fixes [Issue #345](https://github.com/dsccommunity/ComputerManagementDsc/issues/345).
   - Updated User parameter for use with ScheduleType OnSessionState in addition to AtLogon.

source/DSCResources/DSC_ScheduledTask/DSC_ScheduledTask.psm1

@@ -97,7 +97,8 @@ function Get-TargetResource
         How many units (minutes, hours, days) between each run of this task?
 
     .PARAMETER StartTime
-        The time of day this task should start at, or activate on - defaults to 12:00 AM.
+        The date and time of day this task should start at, or activate on, represented
+        as a string for local conversion to DateTime format - defaults to 1st January 1980 at 12:00 AM.
 
     .PARAMETER SynchronizeAcrossTimeZone
         Enable the scheduled task option to synchronize across time zones. This is enabled
@@ -301,8 +302,8 @@ function Set-TargetResource
         $RepeatInterval = '00:00:00',
 
         [Parameter()]
-        [System.DateTime]
-        $StartTime = [System.DateTime]::Today,
+        [System.String]
+        $StartTime = '1980-01-01T00:00:00',
 
         [Parameter()]
         [System.Boolean]
@@ -480,6 +481,9 @@ function Set-TargetResource
 
     Write-Verbose -Message ($script:localizedData.SetScheduledTaskMessage -f $TaskName, $TaskPath)
 
+    # Convert the strings containing dates & times to DateTime objects
+    [System.DateTime] $StartTime = [System.DateTime]::Parse($StartTime)
+
     # Convert the strings containing time spans to TimeSpan Objects
     [System.TimeSpan] $RepeatInterval = ConvertTo-TimeSpanFromTimeSpanString -TimeSpanString $RepeatInterval
     [System.TimeSpan] $RandomDelay = ConvertTo-TimeSpanFromTimeSpanString -TimeSpanString $RandomDelay
@@ -574,13 +578,6 @@ function Set-TargetResource
                 -ArgumentName ExecuteAsGMSA
         }
 
-        if ($SynchronizeAcrossTimeZone -and ($ScheduleType -notin @('Once', 'Daily', 'Weekly')))
-        {
-            New-InvalidArgumentException `
-                -Message ($script:localizedData.SynchronizeAcrossTimeZoneInvalidScheduleType) `
-                -ArgumentName SynchronizeAcrossTimeZone
-        }
-
         # Configure the action
         $actionParameters = @{
             Execute = $ActionExecutable
@@ -1038,8 +1035,11 @@ function Set-TargetResource
 
                 2018-09-27T18:45:08
 
-                The problem in New-ScheduledTaskTrigger is that it always writes the time the format that
-                includes the full timezone offset (W2016 behaviour, W2012R2 does it the other way around).
+                The problem in New-ScheduledTaskTrigger is that it always writes the time in the UTC format, which
+                includes the full timezone offset: (W2016+ behaviour, W2012R2 does it the other way around)
+
+                2018-09-27 16:45:08Z
+
                 Which means "Synchronize across time zones" is enabled by default on W2016 and disabled by
                 default on W2012R2. To prevent that, we are overwriting the StartBoundary here to insert
                 the time in the format we want it, so we can enable or disable "Synchronize across time zones".
@@ -1106,7 +1106,8 @@ function Set-TargetResource
         How many units (minutes, hours, days) between each run of this task?
 
     .PARAMETER StartTime
-        The time of day this task should start at, or activate on - defaults to 12:00 AM.
+        The date and time of day this task should start at, or activate on, represented
+        as a string for local conversion to DateTime format - defaults to 1st January 1980 at 12:00 AM.
 
     .PARAMETER SynchronizeAcrossTimeZone
         Enable the scheduled task option to synchronize across time zones. This is enabled
@@ -1311,8 +1312,8 @@ function Test-TargetResource
         $RepeatInterval = '00:00:00',
 
         [Parameter()]
-        [System.DateTime]
-        $StartTime = [System.DateTime]::Today,
+        [System.String]
+        $StartTime = '1980-01-01T00:00:00',
 
         [Parameter()]
         [System.Boolean]
@@ -1492,6 +1493,12 @@ function Test-TargetResource
 
     $currentValues = Get-CurrentResource -TaskName $TaskName -TaskPath $TaskPath
 
+    # Convert the strings containing dates & times to DateTime objects
+    if ($PSBoundParameters.ContainsKey('StartTime'))
+    {
+        $PSBoundParameters['StartTime'] = [System.DateTime]::Parse($StartTime)
+    }
+
     # Convert the strings containing time spans to TimeSpan Objects
     if ($PSBoundParameters.ContainsKey('RepeatInterval'))
     {
@@ -1569,7 +1576,7 @@ function Test-TargetResource
         $PSBoundParameters['StartTime'] = Get-DateTimeString -Date $StartTime -SynchronizeAcrossTimeZone $SynchronizeAcrossTimeZone
         <#
             If the current StartTime is null then we need to set it to
-            the desired StartTime (which defaults to Today if not passed)
+            the desired StartTime (which defaults to 1st January 1980 at 12:00 AM if not passed)
             so that the test does not fail.
         #>
         if ($currentValues['StartTime'])
@@ -1877,7 +1884,7 @@ function Disable-ScheduledTaskEx
         The date to format.
 
     .PARAMETER SynchronizeAcrossTimeZone
-        Boolean to specifiy if the returned string is formatted in synchronize
+        Boolean to specify if the returned string is formatted in synchronize
         across time zone format.
 #>
 function Get-DateTimeString
@@ -1894,14 +1901,14 @@ function Get-DateTimeString
         $SynchronizeAcrossTimeZone
     )
 
-    $format = (Get-Culture).DateTimeFormat.SortableDateTimePattern
-
     if ($SynchronizeAcrossTimeZone)
     {
-        $returnDate = (Get-Date -Date $Date -Format $format) + (Get-Date -Format 'zzz')
+        $format = (Get-Culture).DateTimeFormat.SortableDateTimePattern + 'zzz'
+        $returnDate = Get-Date -Date $Date.ToLocalTime() -Format $format
     }
     else
     {
+        $format = (Get-Culture).DateTimeFormat.SortableDateTimePattern
         $returnDate = Get-Date -Date $Date -Format $format
     }
 
@@ -2040,7 +2047,7 @@ function Get-CurrentResource
         if ($startAt)
         {
             $synchronizeAcrossTimeZone = Test-DateStringContainsTimeZone -DateString $startAt
-            $startTime = [System.DateTime] $startAt
+            $startTime = $startAt
         }
         else
         {
@@ -2228,7 +2235,9 @@ function Test-DateStringContainsTimeZone
         $DateString
     )
 
-    return $DateString.Contains('+')
+    # When parsing a DateTime, Kind will be 'Unspecified' unless parsed string includes time zone information
+    # See https://learn.microsoft.com/en-us/dotnet/api/system.datetime.parse?view=netframework-4.5#the-return-value-and-datetimekind
+    return [DateTime]::Parse($DateString).Kind -ne 'Unspecified'
 }
 
 <#

source/DSCResources/DSC_ScheduledTask/DSC_ScheduledTask.schema.mof

@@ -9,7 +9,7 @@ class DSC_ScheduledTask : OMI_BaseResource
     [Write, Description("The working path to specify for the executable.")] string ActionWorkingPath;
     [Write, Description("When should the task be executed."), ValueMap{"Once", "Daily", "Weekly", "AtStartup", "AtLogon", "OnIdle", "OnEvent", "AtCreation", "OnSessionState"}, Values{"Once", "Daily", "Weekly", "AtStartup", "AtLogon", "OnIdle", "OnEvent", "AtCreation", "OnSessionState"}] string ScheduleType;
     [Write, Description("How many units (minutes, hours, days) between each run of this task?")] String RepeatInterval;
-    [Write, Description("The time of day this task should start at, or activate on - defaults to 12:00 AM.")] DateTime StartTime;
+    [Write, Description("The date and time of day this task should start at, or activate on, represented as a string for local conversion to DateTime format - defaults to 1st January 1980 at 12:00 AM.")] String StartTime;
     [Write, Description("Enable the scheduled task option to synchronize across time zones. This is enabled by including the timezone offset in the scheduled task trigger. Defaults to false which does not include the timezone offset.")] boolean SynchronizeAcrossTimeZone;
     [Write, Description("Present if the task should exist, Absent if it should be removed."), ValueMap{"Present","Absent"}, Values{"Present","Absent"}] string Ensure;
     [Write, Description("True if the task should be enabled, false if it should be disabled.")] boolean Enable;

source/DSCResources/DSC_ScheduledTask/README.md

@@ -6,6 +6,14 @@ scheduled tasks.
 
 ## Known Issues
 
+When creating a scheduled task with a StartTime, you should always specify both
+a date and a time, with the SortableDateTimePattern format (e.g. 1980-01-01T00:00:00).
+Not providing a date may result in 'flip flopping' if the remote server enters daylight
+savings time. The date and time specified will be set based on the time zone that has been
+configured on the device. If you want to synchronize a scheduled task across timezones,
+use the SynchronizeAcrossTimeZone parameter, and specify the timezone offset that is needed
+(e.g. 1980-01-01T00:00:00-08:00).
+
 One of the values needed for the `MultipleInstances` parameter is missing from the
 `Microsoft.PowerShell.Cmdletization.GeneratedTypes.ScheduledTask.MultipleInstancesEnum`
 enumerator. There are four valid values defined for the `MultipleInstances` property of the

source/DSCResources/DSC_ScheduledTask/en-US/DSC_ScheduledTask.strings.psd1

@@ -13,7 +13,6 @@ ConvertFrom-StringData @'
     OnEventSubscriptionError = No (valid) XML Event Subscription was provided. This is required when the scheduletype is OnEvent.
     OnSessionStateChangeError = No kind of session state change was provided. This is required when the scheduletype is OnSessionState.
     gMSAandCredentialError = Both ExecuteAsGMSA and (ExecuteAsCredential or BuiltInAccount) parameters have been specified. A task can run as a gMSA (Group Managed Service Account), a builtin service account or as a custom credential. Please modify your configuration to include just one of the three options.
-    SynchronizeAcrossTimeZoneInvalidScheduleType = Setting SynchronizeAcrossTimeZone to true when the ScheduleType is not Once, Daily or Weekly is not a valid configuration. Please keep the default value of false when using other schedule types.
     TriggerCreationError = Error creating new scheduled task trigger.
     ConfigureTriggerRepetitionMessage = Configuring trigger repetition.
     RepetitionIntervalError = Repetition interval is set to '{0}' but repetition duration is '{1}'.

source/Examples/Resources/ScheduledTask/15-ScheduledTask_CreateScheduledTaskOnceSynchronizeAcrossTimeZoneEnabled_Config.ps1

@@ -20,8 +20,8 @@
 <#
     .DESCRIPTION
         This example creates a scheduled task called 'Test task sync across time zone enabled'
-        in the folder 'MyTasks' that starts a new powershell process once at 2018-10-01 01:00.
-        The task will have the option Synchronize across time zone enabled.
+        in the folder 'MyTasks' that starts a new powershell process once at 2018-10-01 01:00
+        in the -08:00 timezone. The task will have the option Synchronize across time zone enabled.
 #>
 Configuration ScheduledTask_CreateScheduledTaskOnceSynchronizeAcrossTimeZoneEnabled_Config
 {
@@ -35,7 +35,7 @@ Configuration ScheduledTask_CreateScheduledTaskOnceSynchronizeAcrossTimeZoneEnab
             TaskPath                  = '\MyTasks\'
             ActionExecutable          = 'C:\windows\system32\WindowsPowerShell\v1.0\powershell.exe'
             ScheduleType              = 'Once'
-            StartTime                 = '2018-10-01T01:00:00'
+            StartTime                 = '2018-10-01T01:00:00-08:00'
             SynchronizeAcrossTimeZone = $true
             ActionWorkingPath         = (Get-Location).Path
             Enable                    = $true