Generate UUIDv5 values in PowerShell

New-Uuid5.ps1

# Copyright: (c) 2023, Jordan Borean (@jborean93) <jborean93@gmail.com>
# MIT License (see LICENSE or https://opensource.org/licenses/MIT)

class EncodingTransformAttribute : System.Management.Automation.ArgumentTransformationAttribute {
    [object] Transform([System.Management.Automation.EngineIntrinsics]$engineIntrinsics, [object]$InputData) {
        $result = switch ($InputData) {
            { $_ -is [System.Text.Encoding] } { $_ }

            { $_ -is [string] } {
                switch ($_) {
                    ASCII { [System.Text.ASCIIEncoding]::new() }
                    BigEndianUnicode { [System.Text.UnicodeEncoding]::new($true, $true) }
                    BigEndianUTF32 { [System.Text.UTF32Encoding]::new($true, $true) }
                    ANSI {
                        # I don't like using the term ANSI here but it's better than Default used in Windows
                        # PowerShell and it's more relevant to the terms that Windows uses. This is the "ANSI"
                        # system codepage set
                        [System.Text.Encoding]::GetEncoding([System.Globalization.CultureInfo]::CurrentCulture.TextInfo.ANSICodePage)
                    }
                    OEM { [System.Console]::OutputEncoding }
                    Unicode { [System.Text.UnicodeEncoding]::new() }
                    UTF8 { [System.Text.UTF8Encoding]::new($false) }
                    UTF8BOM { [System.Text.UTF8Encoding]::new($true) }
                    UTF8NoBOM { [System.Text.UTF8Encoding]::new($false) }
                    UTF32 { [System.Text.UTF32Encoding]::new() }
                    default { [System.Text.Encoding]::GetEncoding($_) }
                }
            }

            { $_ -is [int] } { [System.Text.Encoding]::GetEncoding($_) }

            default {
                throw [Management.Automation.ArgumentTransformationMetadataException]::new(
                    "Could not convert input '$_' to a valid Encoding object."
                )
            }
        }

        return $result
    }
}

Function New-Uuid5 {
    [OutputType([Guid])]
    [CmdletBinding()]
    param (
        [Parameter(Mandatory, Position = 0)]
        [Guid]
        $Namespace,

        [Parameter(Mandatory, Position = 1)]
        [object]
        $Value,

        [Parameter()]
        [EncodingTransformAttribute()]
        [System.Text.Encoding]
        $Encoding = 'UTF8'
    )
    <#
    .SYNOPSIS
    Generates a UUID5 value from a namespace and value.

    .EXAMPLE
    Create a UUID5 value for a Windows Terminal Profile
    $terminalNamespace = '2bde4a90-d05f-401c-9492-e40884ead1d8'
    New-Uuid5 $terminalNamespace 'Ubuntu' -Encoding Unicode

    .PARAMETER Namespace
    A known UUID to use as the namespace when generating the UUID5 value.

    .PARAMETER Value
    The value to use alongside the namespace to generate the final UUID5 value.
    Can be a byte array to use as is, otherwise the value will be casted to a
    string and converted to a byte array using the -Encoding value.

    .PARAMETER Encoding
    The encoding to use when convert the -Value to bytes.
    Defaults to UTF8 but can be any other encoding that is needed.
    #>
    # Thanks to the following answer
    # https://stackoverflow.com/questions/10867405/generating-v5-uuid-what-is-name-and-namespace

    if ($Value -is [System.Collections.Generic.IEnumerable[byte]]) {
        $valueBytes = [System.Linq.Enumerable]::ToArray($Value)
    }
    else {
        $valueBytes = $Encoding.GetBytes([string]$Value)
    }

    # Guid.ToByteArray() is in the little endian order for time_low, time_mid,
    # and time_hi_version. The hashing operation must use the big endian
    # ordered GUID.
    $namespaceBytes = $Namespace.ToByteArray()
    [System.Array]::Reverse($namespaceBytes, 0, 4)
    [System.Array]::Reverse($namespaceBytes, 4, 2)
    [System.Array]::Reverse($namespaceBytes, 6, 2)

    $buffer = [byte[]]::new($namespaceBytes.Length + $valueBytes.Length)
    [System.Buffer]::BlockCopy($namespaceBytes, 0, $buffer, 0, $namespaceBytes.Length)
    [System.Buffer]::BlockCopy($valueBytes, 0, $buffer, $namespaceBytes.Length, $valueBytes.Length)

    $sha1 = [System.Security.Cryptography.SHA1]::Create()
    $hash = $sha1.ComputeHash($buffer)

    $guidBytes = [byte[]]::new(16)
    [System.Buffer]::BlockCopy($hash, 0, $guidBytes, 0, $guidBytes.Length)
    # Set high-nibble to 5 to indicate type 5
    $guidBytes[6] = $guidBytes[6] -band 0x0F
    $guidBytes[6] = $guidBytes[6] -bor 0x50

    # Set upper two bits to 0b10
    $guidBytes[8] = $guidBytes[8] -band 0x3F
    $guidBytes[8] = $guidBytes[8] -bor 0x80

    # Need to convert back to the little endian for dotnet
    [System.Array]::Reverse($guidBytes, 0, 4)
    [System.Array]::Reverse($guidBytes, 4, 2)
    [System.Array]::Reverse($guidBytes, 6, 2)

    [Guid]::new($guidBytes)
}