<#
.SYNOPSIS
    Switches a Windows device to a built-in power plan, creating it first if it's hidden.
.DESCRIPTION
    Works with the plans by GUID rather than by name, so it behaves the same on every
    language of Windows. If the plan you ask for isn't on the machine (Ultimate Performance
    is hidden by default, and some OEM images drop High Performance), -CreateIfMissing
    copies it from the built-in template under a fixed GUID, so running the script twice
    doesn't leave you with two copies.
.PARAMETER Plan
    Balanced, HighPerformance, UltimatePerformance or PowerSaver.
.PARAMETER CreateIfMissing
    Restore the plan from its built-in template if it isn't listed.
.PARAMETER StandbyTimeoutAC
    Optional. Minutes before sleep when plugged in, applied to the chosen plan. 0 means never.
.EXAMPLE
    .\Set-PowerPlan.ps1 -Plan HighPerformance -WhatIf
.EXAMPLE
    .\Set-PowerPlan.ps1 -Plan UltimatePerformance -CreateIfMissing -StandbyTimeoutAC 0
#>
[CmdletBinding(SupportsShouldProcess)]
param(
    [Parameter(Mandatory)]
    [ValidateSet('Balanced', 'HighPerformance', 'UltimatePerformance', 'PowerSaver')]
    [string]$Plan,
    [switch]$CreateIfMissing,
    [ValidateRange(0, 600)]
    [int]$StandbyTimeoutAC = -1
)

# Built-in template GUIDs, plus the fixed GUID we use if we have to restore a copy.
$plans = @{
    Balanced            = @{ Template = '381b4222-f694-41f0-9685-ff5bb260df2e'; Copy = '0d8f2a6c-4e1b-4c79-a3d5-8b6e2f9c1a07' }
    HighPerformance     = @{ Template = '8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c'; Copy = '3f1c8b2e-7a64-4d0f-9b3e-6c2a1d8e5f47' }
    UltimatePerformance = @{ Template = 'e9a42b02-d5df-448d-aa00-03f14749eb61'; Copy = '5b1a7c3e-9d42-4f6e-8a1b-2c7d9e0f4a61' }
    PowerSaver          = @{ Template = 'a1841308-3541-4fab-bc81-f71556f20b4a'; Copy = 'c7e4a9d1-2b58-4e3a-8f06-1d9b7c3a2e84' }
}
$guidPattern = '[0-9a-fA-F]{8}-(?:[0-9a-fA-F]{4}-){3}[0-9a-fA-F]{12}'

function Get-PowerSchemes {
    foreach ($line in @(powercfg /list)) {
        if ($line -match "($guidPattern)\s+\((.+?)\)") {
            [pscustomobject]@{ Guid = $Matches[1].ToLower(); Name = $Matches[2]; Active = $line.TrimEnd().EndsWith('*') }
        }
    }
}

$schemes  = @(Get-PowerSchemes)
$previous = $schemes | Where-Object Active | Select-Object -First 1
$wanted   = $plans[$Plan]
$target   = $schemes | Where-Object { $_.Guid -in $wanted.Template, $wanted.Copy } | Select-Object -First 1
$action   = 'NoChange'

if (-not $target) {
    if (-not $CreateIfMissing) {
        Write-Error "The $Plan plan isn't available on this device. Run again with -CreateIfMissing to restore it."
        exit 1
    }
    if ($PSCmdlet.ShouldProcess($env:COMPUTERNAME, "Restore $Plan plan as $($wanted.Copy)")) {
        $null = powercfg /duplicatescheme $wanted.Template $wanted.Copy
        if ($LASTEXITCODE -ne 0) { Write-Error "powercfg couldn't restore the $Plan plan (exit $LASTEXITCODE)."; exit 1 }
        $target = [pscustomobject]@{ Guid = $wanted.Copy; Name = $Plan; Active = $false }
        $action = 'Created'
    }
    else { $target = [pscustomobject]@{ Guid = $wanted.Copy; Name = $Plan; Active = $false }; $action = 'WhatIf' }
}

if (-not $target.Active -and $action -ne 'WhatIf') {
    if ($PSCmdlet.ShouldProcess($env:COMPUTERNAME, "Activate $($target.Name) ($($target.Guid))")) {
        powercfg /setactive $target.Guid
        if ($LASTEXITCODE -ne 0) { Write-Error "powercfg /setactive failed (exit $LASTEXITCODE)."; exit 1 }
        $action = if ($action -eq 'Created') { 'CreatedAndActivated' } else { 'Activated' }
    }
    else { $action = 'WhatIf' }
}

if ($StandbyTimeoutAC -ge 0 -and $action -ne 'WhatIf') {
    # SUB_SLEEP / STANDBYIDLE takes seconds; set it on the target plan, not whatever happens to be active.
    if ($PSCmdlet.ShouldProcess($target.Name, "Set AC sleep timeout to $StandbyTimeoutAC minute(s)")) {
        powercfg /setacvalueindex $target.Guid SUB_SLEEP STANDBYIDLE ($StandbyTimeoutAC * 60)
        powercfg /setactive $target.Guid
    }
}

$active = Get-PowerSchemes | Where-Object Active | Select-Object -First 1
[pscustomobject]@{
    ComputerName = $env:COMPUTERNAME
    Requested    = $Plan
    Previous     = if ($previous) { $previous.Name } else { $null }
    Active       = if ($active) { $active.Name } else { $null }
    ActiveGuid   = if ($active) { $active.Guid } else { $null }
    Action       = $action
}