<#
.SYNOPSIS
    Pops up a friendly "time to restart" reminder when the PC has been up longer than -Days.
.DESCRIPTION
    Works out how long Windows has been running from the last boot time. If that's under -Days it
    exits quietly. Otherwise it shows a small window with the uptime and two buttons: Later, which
    dismisses it, and Restart now, which asks for confirmation and then restarts with a short
    countdown (shutdown /a cancels it). With -RemindAgainMinutes, choosing Later brings it back after
    that many minutes instead of ending.
    Made to run as a scheduled task at logon, in the signed-in user's session. -WhatIf shows the
    reminder but only reports the restart instead of doing it. Returns an object describing what happened.
.PARAMETER Days
    Show the reminder when uptime is at least this many days. Default: 7.
.PARAMETER RemindAgainMinutes
    After Later, wait this long and ask again. 0 (the default) means Later ends it until next time.
.PARAMETER RestartDelaySeconds
    Countdown between confirming and the restart, so open apps get a moment. Default: 60.
.PARAMETER Title
    Window title. Default: Time for a restart.
.PARAMETER AlwaysShow
    Show the reminder whatever the uptime. Handy for testing how it looks.
.EXAMPLE
    .\Show-UptimeReminder.ps1 -Days 5
.EXAMPLE
    .\Show-UptimeReminder.ps1 -AlwaysShow -WhatIf
#>
[CmdletBinding(SupportsShouldProcess)]
param(
    [ValidateRange(1, 365)]
    [int]$Days = 7,

    [ValidateRange(0, 1440)]
    [int]$RemindAgainMinutes = 0,

    [ValidateRange(0, 3600)]
    [int]$RestartDelaySeconds = 60,

    [ValidateNotNullOrEmpty()]
    [string]$Title = 'Time for a restart',

    [switch]$AlwaysShow
)

$lastBoot = (Get-CimInstance -ClassName Win32_OperatingSystem -Property LastBootUpTime).LastBootUpTime
$uptime = (Get-Date) - $lastBoot
$result = [pscustomobject]@{
    ComputerName = $env:COMPUTERNAME
    LastBoot     = $lastBoot
    UptimeDays   = [math]::Round($uptime.TotalDays, 1)
    ThresholdDays = $Days
    Response     = 'NotNeeded'
}

if ($uptime.TotalDays -lt $Days -and -not $AlwaysShow) { return $result }

if ([Threading.Thread]::CurrentThread.GetApartmentState() -ne 'STA') {
    Write-Warning 'Windows Forms needs a single-threaded apartment. Run this with powershell.exe, or pwsh -STA.'
}

Add-Type -AssemblyName System.Windows.Forms, System.Drawing -ErrorAction Stop
[System.Windows.Forms.Application]::EnableVisualStyles()

function Show-Reminder {
    $upText = if ($uptime.TotalDays -ge 2) { '{0} days' -f [math]::Floor($uptime.TotalDays) } else { '{0} hours' -f [math]::Floor($uptime.TotalHours) }
    $font = [System.Drawing.Font]::new('Segoe UI', 10)

    $form = [System.Windows.Forms.Form]@{
        Text            = $Title
        ClientSize      = [System.Drawing.Size]::new(440, 170)
        StartPosition   = 'CenterScreen'
        FormBorderStyle = 'FixedDialog'
        MaximizeBox     = $false
        MinimizeBox     = $false
        TopMost         = $true
        ShowInTaskbar   = $true
        Font            = $font
    }

    $icon = [System.Windows.Forms.PictureBox]@{
        Image    = [System.Drawing.SystemIcons]::Information.ToBitmap()
        SizeMode = 'AutoSize'
        Location = [System.Drawing.Point]::new(20, 22)
    }
    $heading = [System.Windows.Forms.Label]@{
        Text     = "This PC has been running for $upText."
        Font     = [System.Drawing.Font]::new('Segoe UI', 11, [System.Drawing.FontStyle]::Bold)
        Location = [System.Drawing.Point]::new(64, 20)
        AutoSize = $true
    }
    $body = [System.Windows.Forms.Label]@{
        Text        = "A restart clears out memory leaks and finishes installing updates. Save your work and restart when it suits you. (Last started $($lastBoot.ToString('g')).)"
        Location    = [System.Drawing.Point]::new(64, 50)
        Size        = [System.Drawing.Size]::new(356, 60)
    }
    $later = [System.Windows.Forms.Button]@{
        Text         = 'Later'
        Size         = [System.Drawing.Size]::new(110, 32)
        Location     = [System.Drawing.Point]::new(190, 122)
        DialogResult = 'Cancel'
    }
    $restart = [System.Windows.Forms.Button]@{
        Text         = 'Restart now'
        Size         = [System.Drawing.Size]::new(110, 32)
        Location     = [System.Drawing.Point]::new(310, 122)
        DialogResult = 'OK'
    }

    $form.Controls.AddRange(@($icon, $heading, $body, $later, $restart))
    $form.AcceptButton = $later     # Enter shouldn't restart anyone by accident
    $form.CancelButton = $later     # Esc and the X both mean Later

    try { $form.ShowDialog() } finally { $form.Dispose(); $font.Dispose() }
}

while ($true) {
    $choice = Show-Reminder
    if ($choice -eq [System.Windows.Forms.DialogResult]::OK) {
        $confirm = [System.Windows.Forms.MessageBox]::Show(
            "Restart in $RestartDelaySeconds seconds? Anything unsaved will be lost.",
            $Title, 'YesNo', 'Warning', 'Button2')
        if ($confirm -eq [System.Windows.Forms.DialogResult]::Yes) {
            if ($PSCmdlet.ShouldProcess($env:COMPUTERNAME, "Restart in $RestartDelaySeconds seconds")) {
                try {
                    & "$env:SystemRoot\System32\shutdown.exe" /r /t $RestartDelaySeconds /c "Restarting in $RestartDelaySeconds seconds. Run 'shutdown /a' to cancel." /d p:0:0
                    if ($LASTEXITCODE -ne 0) { throw "shutdown.exe exited with code $LASTEXITCODE" }
                    $result.Response = 'Restart'
                }
                catch {
                    $result.Response = "RestartFailed: $($_.Exception.Message)"
                    Write-Warning $result.Response
                }
            }
            else { $result.Response = 'Restart (WhatIf)' }
            break
        }
        continue    # They said no to the confirmation; show the reminder again.
    }

    $result.Response = 'Later'
    if ($RemindAgainMinutes -le 0) { break }
    Start-Sleep -Seconds ($RemindAgainMinutes * 60)
    $uptime = (Get-Date) - $lastBoot
}

$result