Mocking static property getter using Harmony

Mocking static property getter

$harmony = "$PSScriptRoot/0Harmony.dll"
Import-Module $harmony

$Script:Patches = @()


function Set-StaticPropertyGetter {
    param (
        [Parameter(Mandatory)]
        [Type] $Type,
        [Parameter(Mandatory)]
        [string] $PropertyName,
        [Parameter(Mandatory)]
        $Value
    )

    $property = $Type.GetProperty($PropertyName, [System.Reflection.BindingFlags]"Public, Static")
    $get = $property.GetAccessors() | where { $_.Name -like "get_*" }

    $fullTypeName = $Type.FullName

    if (-not $get) {
        throw "No public get accessor is defined for $fullTypeName.$PropertyName"
    }

    $dll = [IO.Path]::ChangeExtension([IO.Path]::GetTempPath(), ".dll"); 
    $fakeTypeName = "Fake_$($fullTypeName -replace "\.","_")"

    $code = @"
    using HarmonyLib;
    using System.Reflection;
    using System.Linq;

    public static class $fakeTypeName
    {
        private static Harmony _harmony;
        public static $fullTypeName Return { get; set; }
        public static MethodInfo Getter { get; set; }
        public static bool Action (ref $fullTypeName __result)
        {
            __result = Return;
            return false;  
        } 

        public static void Patch()
        {
            var prefix = typeof($fakeTypeName).GetMethod("Action", BindingFlags.Static | BindingFlags.Public);

            _harmony = new Harmony("$fullTypeName.$PropertyName");
            _harmony.Patch(Getter, new HarmonyMethod(prefix));
        }

        public static void Unpatch() {
            _harmony.UnpatchAll();
        }
    }
"@

    $d = Add-Type -TypeDefinition $code -ReferencedAssemblies $harmony -PassThru -ErrorAction Stop
    $t = [Type]$fakeTypeName
    $t::Getter = $get
    $t::Return = [DateTime]::MaxValue
    $t::Patch()
    $script:Patches += $t
}

if ([datetime]::Now -eq [DateTime]::MaxValue) {
    throw "already patched"
}

try {
    Set-StaticPropertyGetter -Type ([datetime]) -PropertyName "Now" -Value [DateTime]::MaxValue
    $now = [datetime]::now
    if ($now -ne [datetime]::MaxValue) {
        throw "Faking did not work. DateTime.Now did not return Max value, it returned '$now' instead."
    }
    else { 
        Write-Host -ForegroundColor Green "Success [DateTime]::Now returned '$now'!"
    }
}
finally { 
    foreach ($p in $script:Patches) {
        $p::Unpatch()
    }
}

The same but with a killswitch to disable the mocking when we need to run our own code:

$harmony = "$PSScriptRoot/0Harmony.dll"
Import-Module $harmony

$Script:Patches = @()


function Set-StaticPropertyGetter {
    param (
        [Parameter(Mandatory)]
        [Type] $Type,
        [Parameter(Mandatory)]
        [string] $PropertyName,
        [Parameter(Mandatory)]
        $Value
    )

    $property = $Type.GetProperty($PropertyName, [System.Reflection.BindingFlags]"Public, Static")
    $get = $property.GetAccessors() | where { $_.Name -like "get_*" }

    $fullTypeName = $Type.FullName

    if (-not $get) {
        throw "No public get accessor is defined for $fullTypeName.$PropertyName"
    }

    $dll = [IO.Path]::ChangeExtension([IO.Path]::GetTempPath(), ".dll"); 
    $fakeTypeName = "Fake_$($fullTypeName -replace "\.","_")"

    $code = @"
    using HarmonyLib;
    using System.Reflection;
    using System.Linq;

    public static class $fakeTypeName
    {
        private static Harmony _harmony;
        public static $fullTypeName Return { get; set; }
        public static MethodInfo Getter { get; set; }
        public static bool Disable { get; set; }
        public static bool Action (ref $fullTypeName __result)
        {
            if (!Disable) {
                __result = Return;
                return false;  
            }
            else {
                __result = default($fullTypeName);
                return true;
            }
        } 

        public static void Patch()
        {
            var prefix = typeof($fakeTypeName).GetMethod("Action", BindingFlags.Static | BindingFlags.Public);

            _harmony = new Harmony("$fullTypeName.$PropertyName");
            _harmony.Patch(Getter, new HarmonyMethod(prefix));
        }

        public static void Unpatch() {
            _harmony.UnpatchAll();
        }
    }
"@

    $d = Add-Type -TypeDefinition $code -ReferencedAssemblies $harmony -PassThru -ErrorAction Stop
    $t = [Type]$fakeTypeName
    $t::Getter = $get
    $t::Return = [DateTime]::MaxValue
    $t::Patch()
    $script:Patches += $t
}

if ([datetime]::Now -eq [DateTime]::MaxValue) {
    throw "already patched"
}

try {


    Set-StaticPropertyGetter -Type ([datetime]) -PropertyName "Now" -Value [DateTime]::MaxValue
    foreach ($f in $patches) { 
        $f::Disable = $false
    }
    $now = [datetime]::now
    if ($now -ne [datetime]::MaxValue) {
        throw "Faking did not work. DateTime.Now did not return Max value, it returned '$now' instead."
    }
    else { 
        Write-Host -ForegroundColor Green "Success [DateTime]::Now returned '$now'!"
    }

    foreach ($f in $patches) { 
        $f::Disable = $true
    }

    $now = [datetime]::now
    if ($now -eq [datetime]::MaxValue) {
        throw "Disabling faking did not work. DateTime.Now returned Max value."
    }
    else { 
        Write-Host -ForegroundColor Green "Success [DateTime]::Now returned '$now'!"
    }
}
finally { 
    foreach ($p in $script:Patches) {
        $p::Unpatch()
    }
}

few bugs in the above code, I am not passing $Value, and the return type should not the the same as the source type.