Imports System

Public Module PatronEstrategiaDemo

    Public Sub Main()

        Dim emp As New Empleado()

        emp.SueldoAnual = 500000

        Console.WriteLine("{0,12}: {1:C}", "Sueldo Anual", emp.SueldoAnual)

        Console.WriteLine("{0,12}: {1:C}", "Impuesto", emp.ImporteImpuesto)

        Console.WriteLine("{0,12}: {1:C}", "Isr", emp.Isr)

        Console.WriteLine("{0,12}: {1:C}", "Escala", emp.Escala)

    End Sub

End Module

​

​

Friend Class Empleado

​

    Private _sueldoAnual As Decimal

    Private _impuesto As Impuesto

​

    Public Property SueldoAnual As Decimal

        Get

            Return _sueldoAnual

        End Get

        Set

            If value < 0

                Throw New ArgumentOutOfRangeException("value","El sueldo anual no puede ser un número negativo")

            End If

            _sueldoAnual = value

            SetImpuesto()

        End Set

    End Property

​

    Private Sub SetImpuesto()

        _impuesto = Impuesto.ObtenerPara(Me)

    End Sub

​

    Public ReadOnly Property ImporteImpuesto As Decimal

        Get

            Return _impuesto.Importe

        End Get

    End Property

​

    Public ReadOnly Property Isr As Decimal

        Get

            Return _impuesto.Isr

        End Get

    End Property

​

    Public ReadOnly Property Escala As String

        Get

            Return _impuesto.Escala

        End Get

    End Property

​

End Class

​

Friend MustInherit Class Impuesto

​

    Public Shared ReadOnly MinimoPrimeraEscala As Decimal = 409281

    Public Shared ReadOnly MinimoSegundaEscala As Decimal = 613921

    Public Shared ReadOnly MinimoTerceraEscala As Decimal = 852667

​

    Protected ReadOnly Empleado As Empleado

    Protected Sub New(emp As Empleado)

        Empleado = emp

    End Sub

​

    Public MustOverride ReadOnly Property Importe As Decimal

    Public MustOverride ReadOnly Property Isr As Decimal

    Public MustOverride ReadOnly Property Escala As String

​

    Public Shared Function ObtenerPara(emp As Empleado) As Impuesto

        If emp Is Nothing

            Throw New ArgumentNullException("emp","El valor no puede ser nulo")

        End If

        Select Case emp.SueldoAnual

            Case Is <= MinimoPrimeraEscala

                Return New NoAplicaImpuesto(emp)

            Case Is <= MinimoSegundaEscala

                Return New PrimeraEscalaImpuesto(emp)

            Case Is <= MinimoTerceraEscala

                Return New SegundaEscalaImpuesto(emp)

            Case Else

                Return New TerceraEscalaImpuesto(emp)

        End Select

    End Function

​

End Class

Friend NotInheritable Class PrimeraEscalaImpuesto

    Inherits Impuesto

​

    Friend Sub New(emp As Empleado)

        MyBase.New(emp)

    End Sub

​

    Public Overrides ReadOnly Property Isr As Decimal

        Get

            Return Importe / 12

        End Get

    End Property

​

    Public Overrides ReadOnly Property Importe As Decimal

        Get

            Return (Empleado.SueldoAnual - MinimoPrimeraEscala) * 0.15D

        End Get

    End Property

​

    Public Overrides ReadOnly Property Escala As String

        Get

            Return "Primera"

        End Get

    End Property

​

End Class

Friend NotInheritable Class SegundaEscalaImpuesto

    Inherits Impuesto

​

    Friend Sub New(emp As Empleado)

        MyBase.New(emp)

    End Sub

​

    Public Overrides ReadOnly Property Isr As Decimal

        Get

            Return (Importe + 30696) / 12

        End Get

    End Property

​

    Public Overrides ReadOnly Property Importe As Decimal

        Get

            Return (Empleado.SueldoAnual - MinimoSegundaEscala) * 0.2D

        End Get

    End Property

​

    Public Overrides ReadOnly Property Escala As String

        Get

            Return "Segunda"

        End Get

    End Property

End Class

Friend NotInheritable Class TerceraEscalaImpuesto

    Inherits Impuesto

​

    Friend Sub New(emp As Empleado)

        MyBase.New(emp)

    End Sub

​

    Public Overrides ReadOnly Property Isr As Decimal

        Get

            Return (Importe + 78466) / 12

        End Get

    End Property

​

    Public Overrides ReadOnly Property Importe As Decimal

        Get

            Return (Empleado.SueldoAnual - MinimoTerceraEscala) * 0.25D

        End Get

    End Property

​

    Public Overrides ReadOnly Property Escala As String

        Get

            Return "Tercera"

        End Get

    End Property

​

End Class

Friend NotInheritable Class NoAplicaImpuesto

    Inherits Impuesto

​

    Friend Sub New(emp As Empleado)

        MyBase.New(emp)

    End Sub

​

    Public Overrides ReadOnly Property Isr As Decimal

        Get

            Return 0

        End Get

    End Property

​

    Public Overrides ReadOnly Property Importe As Decimal

        Get

            Return 0

        End Get

    End Property

​

    Public Overrides ReadOnly Property Escala As String

        Get

            Return "No Aplica"

        End Get

    End Property

​

End Class