Update TCSSSelector for fluid chaining of methods

Modify TCSSSelector.AddProperty to reference to current TCSSSelector
instance to permit chaining the method to others that return aborts
TCSSSelector reference.

Add new TCSSSelector.AddPropertyIf fluid method to permit a choice of
two different properties to be added depending on the value of a Boolean
variable. This was created prevent chaining from being broken when a
conditional statement was encountered.

Closes #73

Author: delphidabbler

Src/UCSSBuilder.pas

@@ -3,7 +3,7 @@
  * v. 2.0. If a copy of the MPL was not distributed with this file, You can
  * obtain one at https://mozilla.org/MPL/2.0/
  *
- * Copyright (C) 2005-2021, Peter Johnson (gravatar.com/delphidabbler).
+ * Copyright (C) 2005-2022, Peter Johnson (gravatar.com/delphidabbler).
  *
  * Classes that help create and manage cascading style sheet code.
 }
@@ -46,12 +46,25 @@   TCSSSelector = class(TObject)
       {Checks whether the selector is empty, i.e. contains no code.
         @return True if selector is empty and false if not.
       }
-    procedure AddProperty(const CSSProp: string);
-      {Adds a new CSS property to the selector.
-        @param CSSProp [in] CSS property to be added.
-      }
+    ///  <summary>Adds a new CSS property to the selector.</summary>
+    ///  <param name="CSSProp">string [in] Property definition.</param>
+    ///  <returns>TCSSSelector. Class instance returned to enable the method to
+    ///  be chained.</returns>
+    function AddProperty(const CSSProp: string): TCSSSelector;
+    ///  <summary>Adds a new CSS property to the selector depending on a given
+    ///  condition.</summary>
+    ///  <param name="Condition">Boolean [in] Condition that determines which
+    ///  CSS property is added.</param>
+    ///  <param name="CSSPropTrue">string [in] CSS property that is added when
+    ///  Condition is True.</param>
+    ///  <param name="CSSPropFalse">string [in] CSS property that is added when
+    ///  Condition is False.</param>
+    ///  <returns>TCSSSelector. Class instance returned to enable the method to
+    ///  be chained.</returns>
+    function AddPropertyIf(const Condition: Boolean;
+      const CSSPropTrue: string; const CSSPropFalse: string = ''): TCSSSelector;
+    ///  <summary>Name of selector.</summary>
     property Selector: string read fSelector;
-      {Name of selector}
   end;
 
   {
@@ -112,12 +125,20 @@ implementation
 
 { TCSSSelector }
 
-procedure TCSSSelector.AddProperty(const CSSProp: string);
-  {Adds a new CSS property to the selector.
-    @param CSSProp [in] CSS property to be added.
-  }
+function TCSSSelector.AddProperty(const CSSProp: string): TCSSSelector;
 begin
   fProperties.Add(CSSProp);
+  Result := Self;
+end;
+
+function TCSSSelector.AddPropertyIf(const Condition: Boolean;
+  const CSSPropTrue: string; const CSSPropFalse: string): TCSSSelector;
+begin
+  if Condition then
+    AddProperty(CSSPropTrue)
+  else if CSSPropFalse <> '' then
+    AddProperty(CSSPropFalse);
+  Result := Self;
 end;
 
 function TCSSSelector.AsString: string;