Adding Define (Fixes #299)

Author: James Brundage

Transpilers/Define.psx.ps1

@@ -0,0 +1,135 @@
+<#
+.SYNOPSIS
+    defines a variable
+.DESCRIPTION
+    Defines a variable using a value provided during a build
+.EXAMPLE
+    {
+        [Define(Value={Get-Random})]$RandomNumber
+    }.Transpile()
+.EXAMPLE
+    {
+        [Define(Value={$global:ThisValueExistsAtBuildTime})]$MyVariable
+    }.Transpile()
+#>
+param(
+# The value to define.
+# When this value is provided within an attribute as a ScriptBlock, the ScriptBlock will be run at build time.
+[Parameter(Mandatory)]
+[AllowNull()]
+[PSObject]
+$Value,
+
+# The variable the definition will be applied to.
+[Parameter(Mandatory,ParameterSetName='VariableAST', ValueFromPipeline)]
+[Management.Automation.Language.VariableExpressionast]
+$VariableAst,
+
+# A scriptblock the definition will be applied to
+[Parameter(Mandatory,ParameterSetName='ScriptBlock', ValueFromPipeline)]
+[scriptblock]
+$ScriptBlock = {},
+
+# The name of the variable.  If define is applied as an attribute of a variable, this does not need to be provided.
+[Alias('Name')]
+[string]
+$VariableName
+)
+
+begin {
+    function EmbedString {
+        param($str) {
+            if ($val.Contains('$')) {
+                if ($val -match '[\r\n]') {
+                    '"@' + [Environment]::NewLine + $val.Replace('"', '`"') + [Environment]::NewLine + '@"'
+                } else {
+                    '"' + $val.Replace('"', '`"') + '"'
+                }
+            } else {
+                if ($val -match '[\r\n]') {
+                    "'@" + [Environment]::NewLine + $val.Replace("'", "''") + [Environment]::NewLine + "@'"
+                } else {
+                    "'" + $val.Replace("'", "''") + "'"
+                }
+            }        
+        }
+    }
+}
+
+process {
+    # Get the value we want to define
+    $definedValue = 
+        # A null will become 
+        if ($value -eq $null) {
+            '$null' # $null
+        }
+        # a string
+        elseif ($value -is [string]) {
+            EmbedString $value # will be embedded
+        }
+        # a boolean        
+        elseif ($value -is [bool]) {
+            if ($value) {
+                '$true' # will become $true
+            }
+            else {
+                '$false' # or $false
+            }
+        }
+        # a primitive
+        elseif ($value.GetType().IsPrimitive) {
+            # will be embedded and typecast
+            "[$($value.GetType().Name)]$value"
+        }
+        # a [ScriptBlock]
+        elseif ($value -is [ScriptBlock]) {
+            "{$value}" # will be embedded within {}
+        }
+        # a [timespan]
+        elseif ($value -is [Timespan]) {
+            # can be cast from it's stringified value
+            "[Timespan]'$value'"
+        }
+        # a [DateTime]
+        elseif ($value -is [DateTime]) {
+            # can be cast from a standardized string value
+            "[DateTime]'$($value.ToString('o'))'"
+        }
+        # Otherwise,
+        else {
+            # embed the variable as JSON
+            "@'
+$($value | ConvertTo-Json -Depth 100)
+'@ | ConvertFrom-Json"
+        }
+
+    if ($PSCmdlet.ParameterSetName -eq 'ScriptBlock') {
+        if (-not $VariableName) {
+            Write-Error "Must provide a -VariableName"
+            return
+        }
+    }
+
+
+    if ($PSCmdlet.ParameterSetName -eq 'VariableAst') {
+        [ScriptBlock]::Create('$' + $VariableAst.VariablePath.ToString() + ' = ' + $definedValue)
+    }
+    elseif ($PSCmdlet.ParameterSetName -eq 'ScriptBlock') {
+        $blockName  =
+            if ($ScriptBlock.Ast.DynamicParamBlock) {
+                "dynamicParam"
+            } elseif ($scriptblock.Ast.beignBlock.Statements) {
+                "begin"
+            } elseif ($scriptBlock.Ast.processblock.Statements) {
+                "process"
+            } else {
+                ""   
+            }
+        if ($blockName) {
+            [ScriptBlock]::Create("$blockName {'$' + $VariableName + ' = ' + $definedValue}"), $ScriptBlock | Join-PipeScript
+        }
+        else {
+            [ScriptBlock]::Create('$' + $VariableName + ' = ' + $definedValue), $ScriptBlock | Join-PipeScript
+        }        
+    }
+}