#359 Added HasDirection() capability to RDFPlainLiteral

Author: Marco De Salvo

RDFSharp.Test/Model/RDFPlainLiteralTest.cs

@@ -37,6 +37,7 @@ public void ShouldCreatePlainLiteral(string value)
 
             Assert.IsNotNull(pl);
             Assert.IsFalse(pl.HasLanguage());
+            Assert.IsFalse(pl.HasDirection());
             Assert.IsTrue(pl.ToString().Equals(value ?? ""));
         }
 
@@ -65,6 +66,7 @@ public void ShouldCreatePlainLiteralWithEmptyLanguage(string value, string langu
 
             Assert.IsNotNull(pl);
             Assert.IsFalse(pl.HasLanguage());
+            Assert.IsFalse(pl.HasDirection());
             Assert.IsTrue(pl.ToString().Equals(value ?? ""));
         }
 
@@ -82,6 +84,7 @@ public void ShouldCreatePlainLiteralWithLanguage(string value, string language)
 
             Assert.IsNotNull(pl);
             Assert.IsTrue(pl.HasLanguage());
+            Assert.IsFalse(pl.HasDirection());
             Assert.IsTrue(pl.ToString().Equals(string.Concat(value, "@", language.ToUpperInvariant())));
         }
 
@@ -93,14 +96,15 @@ public void ShouldCreatePlainLiteralWithLanguage(string value, string language)
         [DataRow("donal duck@en-US", "en-US--rtl")]
         [DataRow("donal duck@", "en--rtl")]
         [DataRow("donal duck@", "en--rTL")]
-        [DataRow("", "en")]
-        [DataRow(null, "en")]
+        [DataRow("", "en--ltr")]
+        [DataRow(null, "en--rtl")]
         public void ShouldCreatePlainLiteralWithLanguageDirection(string value, string language)
         {
             RDFPlainLiteral pl = new RDFPlainLiteral(value, language);
 
             Assert.IsNotNull(pl);
             Assert.IsTrue(pl.HasLanguage());
+            Assert.IsTrue(pl.HasDirection());
             Assert.IsTrue(pl.ToString().Equals(string.Concat(value, "@", language.ToUpperInvariant())));
         }
         #endregion

RDFSharp/Model/RDFPlainLiteral.cs

@@ -76,6 +76,14 @@ public override string ToString()
         /// </summary>
         public bool HasLanguage()
             => !string.IsNullOrEmpty(Language);
+
+        /// <summary>
+        /// Checks if the plain literal has a language tag with base direction
+        /// </summary>
+        public bool HasDirection()
+            => HasLanguage() 
+                && (Language.EndsWith("--ltr", System.StringComparison.OrdinalIgnoreCase)
+                    || Language.EndsWith("--rtl", System.StringComparison.OrdinalIgnoreCase));
         #endregion
     }
 }

RDFSharp/Query/Mirella/Algebra/Expressions/RDFLangDirExpression.cs

@@ -87,10 +87,8 @@ internal override RDFPatternMember ApplyExpression(DataRow row)
                 #region Calculate Result
                 if (leftArgumentPMember is RDFPlainLiteral leftArgumentPMemberPLiteral)
                 {
-                    if (leftArgumentPMemberPLiteral.Language.EndsWith("--ltr", System.StringComparison.OrdinalIgnoreCase))
-                        expressionResult = new RDFPlainLiteral("ltr");
-                    else if (leftArgumentPMemberPLiteral.Language.EndsWith("--rtl", System.StringComparison.OrdinalIgnoreCase))
-                        expressionResult = new RDFPlainLiteral("rtl");
+                    if (leftArgumentPMemberPLiteral.HasDirection())
+                        expressionResult = new RDFPlainLiteral(leftArgumentPMemberPLiteral.Language.Substring(leftArgumentPMemberPLiteral.Language.Length-3).ToLower()); //ltr / rtl
                     else
                         expressionResult = RDFPlainLiteral.Empty;
                 }