[cmdletbinding(SupportsShouldProcess=$True,DefaultParameterSetName="Time")]

Param (
[Parameter(Position=0,ValueFromPipelineByPropertyName=$True)]
[ValidateNotNullorEmpty()]
[string]$Command="Notepad",
[Parameter(Position=1,ValueFromPipelineByPropertyName=$True,ParameterSetName="Time")]
[ValidateNotNullorEmpty()]
[Alias("time")]
[datetime]$Alarm=(Get-Date).AddMinutes(5),
[Parameter(ValueFromPipelineByPropertyName=$True,ParameterSetName="Seconds")]
[int]$Seconds,
[Parameter(ValueFromPipelineByPropertyName=$True,ParameterSetName="Minutes")]
[int]$Minutes,
[Parameter(ValueFromPipelineByPropertyName=$True,ParameterSetName="Hours")]
[int]$Hours,
[Parameter(ValueFromPipelineByPropertyName=$True)]
[Alias("init","is")]
[string]$InitializationScript
)

Process {

if ($seconds) {$Alarm=(Get-Date).AddSeconds($seconds)}
if ($minutes) {$Alarm=(Get-Date).AddMinutes($minutes)}
if ($Hours) {$Alarm=(Get-Date).AddHours($hours)}

Write-Verbose ("{0} Creating an alarm for {1} to execute {2}" -f (Get-Date),$Alarm,$Command)

#define a scriptblock that takes parameters. Parameters are validated in the
#function so we don't need to do it here.
$sbText=@"
Param ([string]`$Command,[datetime]`$Alarm,[string]`$Init)

#define a boolean flag
`$Done=`$False

#loop until the time is greater or equal to the alarm time
#sleeping every 10 seconds
do {
if ((get-date) -ge `$Alarm) {
#run the command
`$ActualTime=Get-Date
Invoke-Expression `$Command
#set the flag to True
`$Done=`$True
}
else {
sleep -Seconds 10
}
} while (-Not `$Done)

#write an alarm summary object which can be retrieved with Receive-Job
New-Object -TypeName PSObject -Property @{
ScheduledTime=`$Alarm
ActualTime=`$ActualTime
Command=`$Command
Initialization=`$Init
}
"@

#append metadata to the scriptblock text so they can be parsed out with Get-Alarm
#to discover information for currently running alarm jobs

$meta=@"

#Alarm Command::$Command
#Alarm Time::$Alarm
#Alarm Init::$InitializationScript
#Alarm Created::$(Get-Date)

"@

#add meta data to scriptblock text
$sbText+=$meta

Write-Debug "Scriptblock text:"
Write-Debug $sbText
Write-Debug "Creating the scriptblock"

#create a scriptblock to use with Start-Job
$sb=$ExecutionContext.InvokeCommand.NewScriptBlock($sbText)

Try {
If ($InitializationScript) {
#turn $initializationscript into a script block
$initsb=$ExecutionContext.InvokeCommand.NewScriptBlock($initializationscript)
Write-Verbose ("{0} Using an initialization script: {1}" -f (Get-Date),$InitializationScript)
}
else {
#no initialization command so create an empty scriptblock
$initsb={}
}

#WhatIf
if ($pscmdlet.ShouldProcess("$command at $Alarm")) {
#create a background job
Start-job -ScriptBlock $sb -ArgumentList @($Command,$Alarm,$InitializationScript) -ErrorAction "Stop" -InitializationScript $Initsb
Write-Verbose ("{0} Alarm Created" -f (Get-Date))
}
}

Catch {
$msg="{0} Exception creating the alarm job. {1}" -f (Get-Date),$_.Exception.Message
Write-Warning $msg
}
} #Process

#define a boolean flag
`$Done=`$False

#loop until the time is greater or equal to the alarm time
#sleeping every 10 seconds
do {
if ((get-date) -ge `$Alarm) {
#run the command
`$ActualTime=Get-Date
Invoke-Expression `$Command
#set the flag to True
`$Done=`$True
}
else {
sleep -Seconds 10
}
} while (-Not `$Done)

$meta=@"

#Alarm Command::$Command
#Alarm Time::$Alarm
#Alarm Init::$InitializationScript
#Alarm Created::$(Get-Date)

"@

#add meta data to scriptblock text
$sbText+=$meta

Write-Debug "Scriptblock text:"
Write-Debug $sbText
Write-Debug "Creating the scriptblock"