PsModelUI

1.1.1

PsModelUI.psm1

Add-Type -AssemblyName PresentationFramework, WindowsBase -ErrorAction Stop
# Use an object so we can hot swap the runspacepool on calls to Set-ViewModelPool on all ViewModels if needed.
$script:ViewModelThread = [System.Collections.Concurrent.ConcurrentDictionary[string, System.Management.Automation.Runspaces.RunspacePool]]::new()

# [NoRunspaceAffinity()]
class ViewModelBase : PSCustomObject, System.ComponentModel.INotifyPropertyChanged {
    # INotifyPropertyChanged Implementation
    [ComponentModel.PropertyChangedEventHandler]$PropertyChanged

    add_PropertyChanged([System.ComponentModel.PropertyChangedEventHandler]$handler) {
        $this.psobject.PropertyChanged = [Delegate]::Combine($this.psobject.PropertyChanged, $handler)
    }

    remove_PropertyChanged([System.ComponentModel.PropertyChangedEventHandler]$handler) {
        $this.psobject.PropertyChanged = [Delegate]::Remove($this.psobject.PropertyChanged, $handler)
    }

    RaisePropertyChanged([string]$propname) {
        if ($this.psobject.PropertyChanged) {
            $evargs = [System.ComponentModel.PropertyChangedEventArgs]::new($propname)
            $this.psobject.PropertyChanged.Invoke($this, $evargs)
        }
    }
    # End INotifyPropertyChanged Implementation

    ViewModelBase() {
        $this.psobject.UpdateWithDispatcherDelegate = $this.psobject.CreateDelegate($this.psobject.UpdateWithDispatcher)
        $this.psobject.AddPropertyChangedToProperties()
    }

    ViewModelBase([bool]$AddDefault) {
        $this.psobject.UpdateWithDispatcherDelegate = $this.psobject.CreateDelegate($this.psobject.UpdateWithDispatcher)
        if ($AddDefault) { $this.psobject.AddPropertyChangedToProperties() }
    }

    [void]AddPropertyChangedToProperties() {
        $this.psobject.AddPropertyChangedToProperties($null)
    }

    [void]AddPropertyChangedToProperties([string[]]$Exclude) {
        $PropertiesToExclude = 'PropertyChanged', 'Dispatcher', 'ViewModelThread', 'LastAction', 'UpdateWithDispatcherDelegate' + $Exclude
        $this.psobject.psobject.Members.Where({
                $_.MemberType -eq 'Property' -and
                $_.IsSettable -eq $true -and
                $_.IsGettable -eq $true -and
                $_.Name -notin $PropertiesToExclude
            }
        ).ForEach(
            {
                $Splat = @{
                    Name = $_.Name
                    MemberType = 'ScriptProperty'
                    Value = [scriptblock]::Create('return ,$this.psobject.{0}' -f $_.Name)
                    SecondValue = [scriptblock]::Create('param($value)
                        $this.psobject.{0} = $value
                        $this.psobject.RaisePropertyChanged("{0}")' -f $_.Name
                    )
                }
                $this | Add-Member @Splat
            }
        )
    }

    [Delegate]CreateDelegate([System.Management.Automation.PSMethod]$Method) {
        return $this.psobject.CreateDelegate($Method, $this)
    }

    [Delegate]CreateDelegate([System.Management.Automation.PSMethod]$Method, $Target) {
        $reflectionMethod = if ($Target.GetType().Name -eq 'PSCustomObject') {
            $Target.psobject.GetType().GetMethod($Method.Name)
        } else {
            $Target.GetType().GetMethod($Method.Name)
        }
        $parameterTypes = [System.Linq.Enumerable]::Select($reflectionMethod.GetParameters(), [func[object, object]] { $args[0].parametertype })
        $concatMethodTypes = $parameterTypes + $reflectionMethod.ReturnType
        $delegateType = [System.Linq.Expressions.Expression]::GetDelegateType($concatMethodTypes)
        $delegate = [delegate]::CreateDelegate($delegateType, $Target, $reflectionMethod.Name)
        return $delegate
    }

    [void]UpdateView([pscustomobject]$UpdateValue) {
        if ($null -eq $UpdateValue) { return }
        $this.psobject.InvokeDispatcher($UpdateValue)
    }

    hidden [void]UpdateWithDispatcher($UpdateValue) {
        $UpdateValue.psobject.Properties | ForEach-Object {
            try {
                $this.$($_.Name) = $_.Value
            } catch {
                Write-Warning ('Tried to update class property that does not exist: {0}' -f $_.Name)
            }
        }
    }

    hidden [void]InvokeDispatcher($UpdateValue) {
        $this.psobject.Dispatcher.BeginInvoke(9, $this.psobject.UpdateWithDispatcherDelegate, $UpdateValue)
    }

    [System.Threading.Tasks.Task]StartAsync($MethodToRunAsync, [ViewModelBase]$Target, $CommandParameter) {
        return $this.psobject.StartAsync($MethodToRunAsync, [ViewModelBase]$Target, $CommandParameter, $null)
    }

    [System.Threading.Tasks.Task]StartAsync($MethodToRunAsync, [ViewModelBase]$Target, $CommandParameter, $ActionCommand) {
        $Powershell = [powershell]::Create()
        $Powershell.RunspacePool = $Target.psobject.ViewModelThread['Pool'] # Will use a default runspace if ViewModelThread is $null

        $Delegate = if ($null -eq $CommandParameter -and $null -ne $ActionCommand) {
            {
                param($NoContextMethod, $ActionCommand)
                try {
                    $NoContextMethod.Invoke()
                    $null = $ActionCommand.psobject.Dispatcher.InvokeAsync($ActionCommand.psobject.RemoveWorkerDelegate)
                    # Pipeline output can be received in $LastAction.Result
                } catch { throw $_ }
            }
        } elseif ($null -eq $CommandParameter -and $null -eq $ActionCommand) {
            {
                param($NoContextMethod)
                try {
                    $NoContextMethod.Invoke()
                } catch { throw $_ }
            }
        } elseif ($null -ne $CommandParameter -and $null -eq $ActionCommand) {
            {
                param($NoContextMethod, $CommandParameter)
                try {
                    $NoContextMethod.Invoke($CommandParameter)
                } catch { throw $_ }
            }
        } else {
            {
                param($NoContextMethod, $ActionCommand, $CommandParameter)
                try {
                    $NoContextMethod.Invoke($CommandParameter)
                    $ActionCommand.psobject.Dispatcher.InvokeAsync($ActionCommand.psobject.RemoveWorkerDelegate)
                } catch { throw $_ }
            }
        }

        $NoContext = $Delegate.Ast.GetScriptBlock()

        $null = $Powershell.AddScript($NoContext)
        $null = $Powershell.AddParameter('NoContextMethod', $MethodToRunAsync)
        if ($null -ne $CommandParameter) { $null = $Powershell.AddParameter('CommandParameter', $CommandParameter) }
        if ($null -ne $ActionCommand) { $null = $Powershell.AddParameter('ActionCommand', $ActionCommand) }
        $Handle = $Powershell.BeginInvoke()

        $EndInvokeDelegate = $this.psobject.CreateDelegate($Powershell.EndInvoke, $Powershell) # Not needed with pwsh
        $Task = [System.Threading.Tasks.Task]::Factory.FromAsync($Handle, $EndInvokeDelegate)
        $this.psobject.LastAction = $Task

        return $Task
    }

    $Dispatcher #= [System.Windows.Threading.Dispatcher]::CurrentDispatcher # requires types to be loaded in ScriptsToProcess
    [System.Collections.Concurrent.ConcurrentDictionary[string, System.Management.Automation.Runspaces.RunspacePool]]$ViewModelThread
    [System.Threading.Tasks.Task]$LastAction
    $UpdateWithDispatcherDelegate
}

class ActionCommand : ViewModelBase, System.Windows.Input.ICommand {
    # ICommand Implementation
    [System.EventHandler]$InternalCanExecuteChanged
    add_CanExecuteChanged([EventHandler] $value) {
        $this.psobject.InternalCanExecuteChanged = [Delegate]::Combine($this.psobject.InternalCanExecuteChanged, $value)
    }

    remove_CanExecuteChanged([EventHandler] $value) {
        $this.psobject.InternalCanExecuteChanged = [Delegate]::Remove($this.psobject.InternalCanExecuteChanged, $value)
    }

    [bool]CanExecute([object]$CommandParameter) {
        if ($this.psobject.Throttle -gt 0) { return ($this.psobject.Workers -lt $this.psobject.Throttle) }
        if ($this.psobject.CanExecuteAction) { return $this.psobject.CanExecuteAction.Invoke() }
        return $true
    }

    [void]Execute([object]$CommandParameter) {
        if ($this.psobject.Throttle -gt 0) { $this.Workers++ }

        $Delegate = if ($this.psobject.Action) { $this.psobject.Action } else { $this.psobject.ActionObject }

        if ($this.psobject.IsAsync) {
            if ($this.psobject.Throttle -gt 0) {
                $null = $this.psobject.StartAsync($Delegate, $this.psobject.Target, $null, $this)
            } else {
                $null = $this.psobject.StartAsync($Delegate, $this.psobject.Target, $null)
            }
        } else {
            $Delegate.Invoke()
            if ($this.psobject.Throttle -gt 0) { $this.psobject.RemoveWorker() }
        }
    }
    # End ICommand Implementation

    ActionCommand([System.Management.Automation.PSMethod]$Action) : Base($false) {
        $this.psobject.Init($Action, $false, $null, 0)
    }

    ActionCommand([System.Management.Automation.PSMethod]$Action, [bool]$IsAsync, [ViewModelBase]$Target, [int]$Throttle) : Base($false) {
        $this.psobject.Init($Action, $IsAsync, $Target, $Throttle)
    }

    hidden Init([System.Management.Automation.PSMethod]$Action, [bool]$IsAsync, [ViewModelBase]$Target, [int]$Throttle) {
        $Delegate = $this.psobject.CreateDelegate($Action, $Target)

        $this.psobject.Action = $Delegate
        $this.psobject.IsAsync = $IsAsync
        $this.psobject.Target = $Target
        $this.psobject.Throttle = $Throttle

        $this.psobject.RaiseCanExecuteChangedDelegate = $this.psobject.CreateDelegate($this.psobject.RaiseCanExecuteChanged)
        $this.psobject.RemoveWorkerDelegate = $this.psobject.CreateDelegate($this.psobject.RemoveWorker)

        @('Workers').ForEach(
            {
                $Splat = @{
                    Name = $_
                    MemberType = 'ScriptProperty'
                    Value = [scriptblock]::Create('return ,$this.psobject.{0}' -f $_)
                    SecondValue = [scriptblock]::Create('param($value)
                        $this.psobject.{0} = $value
                        $this.psobject.RaisePropertyChanged("{0}")
                        if ($this.psobject.Dispatcher) {{
                            $this.psobject.RaiseCanExecuteChanged()
                        }} elseif ([System.Windows.Threading.Dispatcher]::CurrentDispatcher.CheckAccess()) {{
                            $this.psobject.RaiseCanExecuteChanged()
                            $this.psobject.Dispatcher = [System.Windows.Threading.Dispatcher]::CurrentDispatcher
                        }} else {{
                            [System.Windows.Threading.Dispatcher]::CurrentDispatcher.InvokeAsync($this.psobject.RaiseCanExecuteChangedDelegate)
                        }}' -f $_
                    )
                }
                $this | Add-Member @Splat
            }
        )
    }

    [void]RaiseCanExecuteChanged() {
        $eCanExecuteChanged = $this.psobject.InternalCanExecuteChanged
        if ($eCanExecuteChanged) {
            $eCanExecuteChanged.Invoke($this, [System.EventArgs]::Empty)
        }
    }

    [void]RemoveWorker() {
        $this.Workers--
    }

    [ViewModelBase]$Target
    [bool]$IsAsync = $false
    $Action
    $ActionObject
    $CanExecuteAction
    $Workers = 0
    $Throttle = 1
    $RaiseCanExecuteChangedDelegate
    $RemoveWorkerDelegate
}

$script:Powershell = $null

function New-UnboundClassInstance ([type] $type, [object[]] $arguments = $null, [scriptblock]$definition) {
    if ($null -eq $script:Powershell) {
        $script:Powershell = [powershell]::Create()
        $script:Powershell.AddScript({
                function New-UnboundClassInstance ([type] $type, [object[]] $arguments, [scriptblock]$definition) {
                    if ($definition) { $definition.Invoke() }
                    [activator]::CreateInstance($type, $arguments)
                }
            }.Ast.GetScriptBlock()
        ).Invoke()
        $script:Powershell.Commands.Clear()
    }

    try {
        if ($null -eq $arguments) { $arguments = @() }
        $result = $script:Powershell.AddCommand('New-UnboundClassInstance').
        AddParameter('type', $type).
        AddParameter('arguments', $arguments).
        AddParameter('definition', $definition).
        Invoke()
        return $result
    } finally {
        $script:Powershell.Commands.Clear()
    }
}

function New-ActionCommand {
    <#
        .SYNOPSIS
        Creates an [ActionCommand] object with the provided method in $Target.

        .PARAMETER MethodName
        Name of the method in $Target.

        .PARAMETER IsAsync
        This signals the equivalent command to be invoked in another runspace if $true or on the console thread.

        .PARAMETER Target
        The class object of the method.

        .PARAMETER Throttle
        The max number of times the equivalent method command can be running at a given time.
    #>
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [string]$MethodName,
        [bool]$IsAsync = $true,
        [object]$Target,
        [int]$Throttle = 1
    )

    $Method = if ($Target.GetType().Name -eq 'PSCustomObject') {
        $Target.psobject.$MethodName
    } else {
        $Target.$MethodName
    }

    [ActionCommand]::new($Method, $IsAsync, $Target, $Throttle)
}

function New-Class {
    <#
        .SYNOPSIS
        Dynamically creates a class object that inherits ViewModeBase.
        Properties preceeed by `$this` used in Methods that aren't defined in PropertyDeclaration will automatically be defined as a property of the class.
        Method overloads are not supported.

        Allows for classes of the same type name with different properties and methods but allows for hot reloading of classes.

        .EXAMPLE
        $A = New-ViewModel -ClassName 'ClassType' -PropertyDeclaration 'One'
        $B = New-ViewModel -ClassName 'ClassType' -PropertyInitialization ([pscustomobject]@{
            Name = 'NewProperty'
            Type = ([string])
            Initialization = 'Hello World'
        })
        $C = New-ViewModel -ClassName 'ClassType' -Methods ([pscustomobject]@{
            Name = 'ClassMethod'
            Body = {return 'Hello World'}
        })

        .PARAMETER ClassName
        The name of the class
        'MyClass'

        Creates:
        class MyClass : ViewModeBase {
            MyClass() {}
        }

        .PARAMETER Inherits
        The name of the class to inherit and interface names.
        Follows powershell interitance so only ONE class can be inherited and any dotnet interfaces can be added.

        'Foo', 'System.IDisposable', System.ComponentModel.INotifyPropertyChanged

        class Foo {
            $Property = 1
        }

        class Bar : Foo, System.IDisposable, System.ComponentModel.INotifyPropertyChanged {
            $NewProperty = 2
            Dispose(){}
            $PropertyChanged
            add_PropertyChanged([System.ComponentModel.PropertyChangedEventHandler]$handler) {}
            remove_PropertyChanged([System.ComponentModel.PropertyChangedEventHandler]$handler) {}
        }

        .PARAMETER PropertyDeclaration
        Takes an array of strings.
        @('property1', 'PropertY2')

        Creates:

        class ViewModel : ViewModelBase {
            $property1
            $PropertY2
        }

        .PARAMETER Methods
        Will also create class properties for methods that call $this.propertyname that isn't in $PropertyDeclaration
        Requires a hashtable of name and it's Body as a scriptblock
        @(
            DoMethod = {return 'hello world'}
            OtherMethod = {$this.Property = 'foo'} # if '$Property' is not defined in PropertyDeclaration, it will be added automatically.
        )

        Creates:

        class ViewModel : ViewModelBase {
            $Property
            [object]DoMethod() {
                return "hello world"
            }
            [void]OtherMethod() {
                $this.Property = 'foo'
            }
        }

        .PARAMETER Unbound
        Creates the class with no runspace affinity if $true. Otherwise class methods cannot be called when the UI is running.

        .PARAMETER AsString
        Returns the full class definition as a string instead of the object.
    #>
    [CmdletBinding(DefaultParameterSetName = 'AsObject')]
    param (
        [Parameter(Mandatory)]
        [string]$ClassName,
        [string[]]$Inherits,
        [Parameter(ParameterSetName = 'AsObject')]
        [string[]]$PropertyDeclaration,
        [Parameter(ParameterSetName = 'AsTypeWithDefinition')]
        [pscustomobject[]]$PropertyInitialization,
        [pscustomobject[]]$Methods,
        [bool]$Unbound = $true,
        [switch]$AsString
    )

    $StringBuilder = [System.Text.StringBuilder]::new()

    # start class line
    $null = $StringBuilder.Append("class $ClassName")
    if ($Inherits) {
        $null = $StringBuilder.Append(' : ')
        $null = $StringBuilder.Append(($Inherits -join ','))
    }
    $null = $StringBuilder.AppendLine(' {')

    # class properties
    foreach ($Name in $PropertyDeclaration) {
        if ($Name -notmatch '^\w+$') { throw 'property name can only contain letters and numbers' }
        $null = $StringBuilder.AppendLine(('${0}' -f $Name))
    }

    foreach ($ClassProperty in $PropertyInitialization) {
        if ($ClassProperty.Name -notmatch '^\w+$') { throw 'property name can only contain letters and numbers' }
        $null = $StringBuilder.AppendLine(('[{0}]${1}' -f $ClassProperty.Type, $ClassProperty.Name))
    }

    # base constructor
    $null = $StringBuilder.AppendLine(('{0}(){{' -f $ClassName))

    foreach ($ClassProperty in $PropertyInitialization) {
        if ($null -eq $ClassProperty.Initialization -or $ClassProperty.Initialization.Ast.EndBlock.Statements.Count -eq 0) { continue }
        $RawText = @"
`$this.$($ClassProperty.Name) = [scriptblock]::Create(
@'
,($($ClassProperty.Initialization.ToString()))
'@
).InvokeReturnAsIs()
"@
        $null = $StringBuilder.AppendLine($RawText)
    }

    $null = $StringBuilder.AppendLine(('}}' -f $ClassName))


    # methods
    foreach ($PSMethod in $Methods) {
        if (($PSMethod.Body.Ast.EndBlock.Statements.Where({ $null -ne $_.Pipeline })).Count -eq 0) {
            $null = $StringBuilder.AppendLine(('[void]{0}({1}) {{' -f $PSMethod.Name, $PSMethod.MethodParameterNames))
        } else {
            $null = $StringBuilder.AppendLine(('[object]{0}({1}) {{' -f $PSMethod.Name, $PSMethod.MethodParameterNames))
        }
        $null = $StringBuilder.AppendLine($($PSMethod.Body.ToString().Trim()))
        $null = $StringBuilder.AppendLine('}')
    }

    # end class definition
    $null = $StringBuilder.AppendLine('}')

    # find all $this references from preliminary definition
    $DefinitionBeforeVariables = ([scriptblock]::Create($StringBuilder.ToString()))
    $ClassProperties = $DefinitionBeforeVariables.Ast.FindAll({ $args[0] -is [System.Management.Automation.Language.VariableExpressionAst] }, $true) | Where-Object { $_.VariablePath.UserPath -eq 'this' }

    # remove the newline and closing brace to add $this variables as properties from methods.
    $null = $StringBuilder.Remove($StringBuilder.Length - 3, 3)

    # get all unique $this properties and add them as $property if not added in $PropertyDeclaration
    $UniqueProperties = [System.Collections.Generic.HashSet[string]]::new()
    foreach ($Property in $ClassProperties.Parent.Member.Extent.Text) {
        if ([string]::IsNullOrWhiteSpace($Property)) { continue }
        if ($PropertyDeclaration -contains $Property) { continue }
        if ($PropertyInitialization.Name -contains $Property) { continue }
        $null = $UniqueProperties.Add($Property)
    }

    foreach ($Property in $UniqueProperties.GetEnumerator()) {
        $null = $StringBuilder.AppendLine('${0}' -f $Property)
    }

    # finish class definition
    $null = $StringBuilder.AppendLine('}')

    if ($AsString) {
        return $StringBuilder.ToString()
    }

    $Definition = ([scriptblock]::Create($StringBuilder.ToString()))
    . $Definition

    $DynamicClass = if ($Unbound) {
        New-UnboundClassInstance $ClassName
    } else {
        [activator]::CreateInstance($ClassName)
    }

    if (!$script:ViewModelThread['Pool'] -or $script:ViewModelThread['Pool'].IsDisposed) { Set-ViewModelPool }
    $DynamicClass.psobject.ViewModelThread = $script:ViewModelThread

    $DynamicClass
}

function New-ClassProperty {
    <#
        .SYNOPSIS
        Creates a pscustomobject to be consumed by New-ViewModel to create a class property with initial value.

        .PARAMETER PropertyName
        Name of the property

        .PARAMETER Type
        Type of the property
        'string'
        ([string])
        'object'
        'int'
        ([System.Collections.Generic.List[object]])

        .PARAMETER Initialization
        A scriptblock containing the initial value or object to create.
        Similar to list initialization in C++. Same braces!

        { 123 }
        { [System.Collections.Generic.List[object]]::new() }

        .EXAMPLE
        New-ViewModelProperty -PropertyName 'a' -Type int -Initialization {1+1}
        The above will be consumed in New-ViewModel to generate:

        class Sample {
            [int]$a
            Sample() {
                $this.a = {1+1}.InvokeReturnAsIs()
            }
        }
    #>
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [string]$Name,
        [type]$Type,
        [scriptblock]$Initialization
    )

    [pscustomobject]@{
        Name = $Name
        Type = if ($Type) { $Type } else { [object] }
        Initialization = if ($Initialization.Ast.EndBlock.Statements.Count -gt 0) { $Initialization } else { $null }
    }
}

function New-ViewModel {
    <#
        .SYNOPSIS
        Dynamically creates a class object that inherits ViewModeBase.
        Properties preceeed by `$this` used in Methods that aren't defined in PropertyDeclaration will automatically be defined as a property of the class.
        Method overloads are not supported.

        Allows for classes of the same type name with different properties and methods but allows for hot reloading of classes.

        .EXAMPLE
        $A = New-ViewModel -ClassName 'ClassType' -PropertyDeclaration 'One'
        $B = New-ViewModel -ClassName 'ClassType' -PropertyInitialization ([pscustomobject]@{
            Name = 'NewProperty'
            Type = ([string])
            Initialization = 'Hello World'
        })
        $C = New-ViewModel -ClassName 'ClassType' -Methods ([pscustomobject]@{
            Name = 'ClassMethod'
            Body = {return 'Hello World'}
        })

        .PARAMETER ClassName
        The name of the class
        'MyClass'

        Creates:
        class MyClass : ViewModeBase {
            MyClass() {}
        }

        .PARAMETER PropertyDeclaration
        Takes an array of strings.
        @('property1', 'PropertY2')

        Creates:

        class ViewModel : ViewModelBase {
            $property1
            $PropertY2
        }

        .PARAMETER Methods
        Will also create class properties for methods that call $this.propertyname that isn't in $PropertyDeclaration
        Requires a hashtable of name and it's Body as a scriptblock
        @(
            DoMethod = {return 'hello world'}
            OtherMethod = {$this.Property = 'foo'} # if '$Property' is not defined in PropertyDeclaration, it will be added automatically.
        )

        Creates:

        class ViewModel : ViewModelBase {
            $Property
            [object]DoMethod() {
                return "hello world"
            }
            [void]OtherMethod() {
                $this.Property = 'foo'
            }
        }

        .PARAMETER Unbound
        Creates the class with no runspace affinity if $true. Otherwise class methods cannot be called when the UI is running.

        .PARAMETER CreateMethodCommand
        Creates a Command object for each method in $Methods that is populated with an [ActionCommand]
        Overloads are not supported.

        class ViewModel : ViewModelBase {
            $DoMethodCommand
            [object]DoMethod() {
                return "hello world"
            }
        }

        .PARAMETER AsString
        Returns the full class definition as a string instead of the object.
    #>
    [CmdletBinding(DefaultParameterSetName = 'AsObject')]
    param (
        [Parameter(Mandatory)]
        [string]$ClassName,
        [Parameter(ParameterSetName = 'AsObject')]
        [string[]]$PropertyDeclaration,
        [Parameter(ParameterSetName = 'AsTypeWithDefinition')]
        [pscustomobject[]]$PropertyInitialization,
        [pscustomobject[]]$Methods,
        [bool]$Unbound = $true,
        [bool]$CreateMethodCommand = $true,
        [switch]$AsString
    )

    $StringBuilder = [System.Text.StringBuilder]::new()

    # start class line
    $null = $StringBuilder.Append("class $ClassName")
    $null = $StringBuilder.Append(' : ViewModelBase')
    $null = $StringBuilder.AppendLine(' {')

    # class properties
    foreach ($Name in $PropertyDeclaration) {
        if ($Name -notmatch '^\w+$') { throw 'property name can only contain letters and numbers' }
        $null = $StringBuilder.AppendLine(('${0}' -f $Name))
    }

    foreach ($ClassProperty in $PropertyInitialization) {
        if ($ClassProperty.Name -notmatch '^\w+$') { throw 'property name can only contain letters and numbers' }
        $null = $StringBuilder.AppendLine(('[{0}]${1}' -f $ClassProperty.Type, $ClassProperty.Name))
    }

    # base constructor
    $null = $StringBuilder.AppendLine(('{0}(){{' -f $ClassName))

    foreach ($ClassProperty in $PropertyInitialization) {
        if ($null -eq $ClassProperty.Initialization -or $ClassProperty.Initialization.Ast.EndBlock.Statements.Count -eq 0) { continue }
        $RawText = @"
`$this.$($ClassProperty.Name) = [scriptblock]::Create(
@'
,($($ClassProperty.Initialization.ToString()))
'@
).InvokeReturnAsIs()
"@
        $null = $StringBuilder.AppendLine($RawText)
    }

    $null = $StringBuilder.AppendLine(('}}' -f $ClassName))


    # methods
    foreach ($PSMethod in $Methods) {
        # Create a command property for the method and append 'Command' to the end.
        if ($CreateMethodCommand) {
            if ([string]::IsNullOrWhiteSpace($PSMethod.CommandName)) {
                $null = $StringBuilder.AppendLine(('${0}Command' -f $PSMethod.Name))
            } else {
                $null = $StringBuilder.AppendLine(('${0}' -f $PSMethod.CommandName))
            }
        }

        if (($PSMethod.Body.Ast.EndBlock.Statements.Where({ $null -ne $_.Pipeline })).Count -eq 0) {
            $null = $StringBuilder.AppendLine(('[void]{0}({1}) {{' -f $PSMethod.Name, $PSMethod.MethodParameterNames))
        } else {
            $null = $StringBuilder.AppendLine(('[object]{0}({1}) {{' -f $PSMethod.Name, $PSMethod.MethodParameterNames))
        }
        $null = $StringBuilder.AppendLine($($PSMethod.Body.ToString().Trim()))
        $null = $StringBuilder.AppendLine('}')
    }

    # end class definition
    $null = $StringBuilder.AppendLine('}')

    # find all $this references from preliminary definition
    $DefinitionBeforeVariables = ([scriptblock]::Create($StringBuilder.ToString()))
    $ClassProperties = $DefinitionBeforeVariables.Ast.FindAll({ $args[0] -is [System.Management.Automation.Language.VariableExpressionAst] }, $true) | Where-Object { $_.VariablePath.UserPath -eq 'this' }

    # remove the newline and closing brace to add $this variables as properties from methods.
    $null = $StringBuilder.Remove($StringBuilder.Length - 3, 3)

    # get all unique $this properties and add them as $property if not added in $PropertyDeclaration
    $UniqueProperties = [System.Collections.Generic.HashSet[string]]::new()
    foreach ($Property in $ClassProperties.Parent.Member.Extent.Text) {
        if ([string]::IsNullOrWhiteSpace($Property)) { continue }
        if ($PropertyDeclaration -contains $Property) { continue }
        if ($PropertyInitialization.Name -contains $Property) { continue }
        $null = $UniqueProperties.Add($Property)
    }

    foreach ($Property in $UniqueProperties.GetEnumerator()) {
        $null = $StringBuilder.AppendLine('${0}' -f $Property)
    }

    # finish class definition
    $null = $StringBuilder.AppendLine('}')

    if ($AsString) {
        return $StringBuilder.ToString()
    }

    $Definition = ([scriptblock]::Create($StringBuilder.ToString()))
    . $Definition

    $DynamicClass = if ($Unbound) {
        New-UnboundClassInstance $ClassName
    } else {
        [activator]::CreateInstance($ClassName)
    }

    # add a command property for each method
    if ($CreateMethodCommand) {
        foreach ($PSMethod in $Methods) {
            $CommandName = if ([string]::IsNullOrWhiteSpace($PSMethod.CommandName)) { "$($PSMethod.Name)Command" } else { $PSMethod.CommandName }
            $DynamicClass."$CommandName" = New-ActionCommand -MethodName $PSMethod.Name -Target $DynamicClass -Throttle $PSMethod.Throttle -IsAsync $PSMethod.IsAsync
        }
    }

    if (!$script:ViewModelThread['Pool'] -or $script:ViewModelThread['Pool'].IsDisposed) { Set-ViewModelPool }
    $DynamicClass.psobject.ViewModelThread = $script:ViewModelThread

    $DynamicClass
}

function New-ViewModelMethod {
    <#
        .SYNOPSIS
        Creates a pscustomobject to be consumed by New-ViewModel to create a class method.
        Overloads are not supported.

        .PARAMETER Name
        Name of the method to be defined in the class by New-ViewModel.

        .PARAMETER Body
        Body of the method to be defined in the class by New-ViewModel.
        All `$this` references will be of the class. Otherwise it is invalid if invoked as is.

        .PARAMETER MethodParameterNames
        Parameter names for the method.

        .PARAMETER Throttle
        The max number of times the equivalent method command can be running at a given time.

        .PARAMETER IsAsync
        This signals the equivalent command to be invoked in another runspace if $true or on the console thread.
    #>
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [string]$Name,
        [Parameter(Mandatory)]
        [scriptblock]$Body,
        [string[]]$MethodParameterNames,
        [string]$CommandName,
        [int]$Throttle = 1,
        [bool]$IsAsync = $true
    )

    $Parameters = foreach ($ParameterName in $MethodParameterNames) {
        if ($ParameterName -notmatch '^\w+$') { throw ('parameter name can only contain letters and numbers: "{0}"' -f $ParameterName) }
        '${0}' -f $ParameterName
    }
    $JoinedParameters = $Parameters -join ','

    [pscustomobject]@{
        Name = $Name
        Body = $Body.Ast.GetScriptBlock()
        MethodParameterNames = $JoinedParameters
        CommandName = $CommandName
        Throttle = $Throttle
        IsAsync = $IsAsync
    }
}

function New-WpfObject {
    <#
        .SYNOPSIS
        Creates a WPF object with given Xaml from a string or file
        Uses the dedicated wpf xaml reader rather than the xmlreader.

        .PARAMETER Xaml
        The xaml string for to be parsed.

        .PARAMETER Path
        The full name to the xaml file to be parsed.

        .PARAMETER DataContext
        The ViewModel class object that the WpfObject will use.

        .EXAMPLE
        $Window = New-WpfObject -Xaml $Xaml -DataContext $ViewModel
        $ResourceDictionary = New-WpfObject -Path $Path
    #>
    [CmdletBinding(DefaultParameterSetName = 'Path')]
    param (
        [Parameter(Mandatory, ValueFromPipeline, Position = 0, ParameterSetName = 'HereString')]
        [string[]]$Xaml,
        [Parameter(Mandatory, ValueFromPipeline, ValueFromPipelineByPropertyName, Position = 0, ParameterSetName = 'Path')]
        [ValidateScript({ Test-Path $_ })]
        [string[]]$Path,
        [string]$BaseUri,
        [ViewModelBase]$DataContext
    )

    process {
        $Xml = [xml]::new()
        $RawXaml = if ($PSBoundParameters.ContainsKey('Path')) {
            $Xml.Load($Path)
            $Xml.InnerXml
        } else {
            $Xml.LoadXml($Xaml)
            $Xml.InnerXml
        }

        $WpfObject = [System.Windows.Markup.XamlReader]::Parse($RawXaml)

        if ($DataContext) {
            # because $DataContext can be created unbound, it may not have the same dispatcher as $WpfObject so it is set here.
            $DataContext.psobject.Dispatcher = $WpfObject.Dispatcher
            $WpfObject.DataContext = $DataContext
        }

        $WpfObject
    }
}

function Set-ViewModelPool {
    <#
        .SYNOPSIS
        Creates and opens the global runspacepool to be used by each viewmodel created by New-ViewModel.

        .DESCRIPTION
        Runspacepool is stored in module script scope: $script:ViewModelThread as a concurrent dictionary.
        It is added to each ViewModel created by New-ViewModel.
        Will be disposed and recreated on each call.

        .PARAMETER MaxRunspaces
        Max number of runspaces in the pool to be available for use.

        .PARAMETER Functions
        Name of the function defined inline to be available in the runspacepool.

        .PARAMETER StartupScripts
        Full paths of the scripts to run in the new runspace created by the runspacepool.
    #>
    [CmdletBinding()]
    param (
        [int]$MaxRunspaces = $([int]$env:NUMBER_OF_PROCESSORS + 1),
        [string[]]$Functions,
        [string[]]$StartupScripts
    )

    $State = [System.Management.Automation.Runspaces.InitialSessionState]::CreateDefault()
    $State.ThrowOnRunspaceOpenError = $true

    foreach ($Name in $Functions) {
        $FunctionDefinition = Get-Content "Function:\$Name" -ErrorAction Stop
        $State.Commands.Add([System.Management.Automation.Runspaces.SessionStateFunctionEntry]::new($Name, $FunctionDefinition))
    }

    foreach ($ScriptPath in $StartupScripts) {
        $null = $State.StartupScripts.Add($ScriptPath)
    }

    if ($script:ViewModelThread['Pool']) {
        $script:ViewModelThread['Pool'].Dispose()
    }

    $script:ViewModelThread['Pool'] = [RunspaceFactory]::CreateRunspacePool(1, $MaxRunspaces, $State, (Get-Host))
    $script:ViewModelThread['Pool'].CleanupInterval = [timespan]::FromMinutes(5)
    $script:ViewModelThread['Pool'].Open()
}