#requires -Version 3.0
Set-StrictMode -Version Latest

function Initialize-KBShortestScriptChallenge {
    <#
        .SYNOPSIS
        Initialize PowerShell environment for Shortest Script Challenge.
        .DESCRIPTION
        The Initialize-KBShortestScriptChallenge cmdlet removes all single character variables except those specified in ExcludeVariable parameter, switches off strict mode globally and clears all errors.
        .PARAMETER ExcludeVariable
        Specifies one or more single character variables that will be preserved.
        .EXAMPLE
        Initialize-KBShortestScriptChallenge -ExcludeVariable x, y, z

        This command initializes PowerShell environment for Shortest Script Challenge and removes all single character variables except x, y and z.
    #>
    [CmdletBinding()]
    param(
        [ValidateScript({$_.Length -eq 1})]
        [String[]]$ExcludeVariable = [String]::Empty
    )

    try {
        #Cache latest PowerShell build version
        if (-not (Get-Variable -Name KBLatestPowerShellBuildVersion -Scope Global -ErrorAction Ignore)) {
            Set-Variable -Name KBLatestPowerShellBuildVersion -Value $(Get-KBLatestPowerShellBuildVersion -ErrorAction Stop).Version -Scope Global -Option ReadOnly -Force
        }

        #Warn when initializing PowerShell environment for SSC on former version of PowerShell
        if ("v$($PSVersionTable.PSVersion)" -notmatch $Global:KBLatestPowerShellBuildVersion) {
            Write-Warning ("Initializing PowerShell environment for Shortest Script Challenge on former version of PowerShell ({0} < {1})" -f "v$($PSVersionTable.PSVersion)" , $Global:KBLatestPowerShellBuildVersion)
        }
    } catch {
        Write-Warning $_.Exception.Message
    } finally {
        #Extend HistoryInfo type data [/u/bis]
        Update-TypeData -TypeName 'Microsoft.PowerShell.Commands.HistoryInfo' -MemberType ScriptProperty -MemberName 'Duration' -Force -Value {
            $this.EndExecutionTime - $this.StartExecutionTime
        }
        Update-TypeData -TypeName 'Microsoft.PowerShell.Commands.HistoryInfo' -MemberType ScriptProperty -MemberName 'Length' -Force -Value {
            $this.CommandLine.Length
        }

        #Remove all single character variables except excluded
        foreach ($character in (65..90 | Where-Object {$_ -NotIn [int[]][char[]]$ExcludeVariable.ToUpper()})) {
            Remove-Variable ([char]$character) -Scope Global -Force -ErrorAction Ignore
        }

        #Switch off strict mode globally
        Set-PSDebug -Off

        #Clear any errors
        $Error.Clear()
    }
}