Add Locale scalar - partial fix for #4

Author: Eugen Stan

.gitignore

@@ -1,4 +1,6 @@
 .idea
 .gradle
 out
-*.iml
+*.iml
+
+build

src/main/java/graphql/scalars/ExtendedScalars.java

@@ -17,6 +17,7 @@
 import graphql.scalars.object.ObjectScalar;
 import graphql.scalars.regex.RegexScalar;
 import graphql.scalars.url.UrlScalar;
+import graphql.scalars.locale.LocaleScalar;
 import graphql.schema.GraphQLScalarType;
 
 /**
@@ -111,6 +112,12 @@ public class ExtendedScalars {
      */
     public static GraphQLScalarType Url = new UrlScalar();
 
+    /**
+     * A Locale scalar that accepts a IETF BCP 47 language tag string and produces {@link
+     * java.util.Locale} objects at runtime.
+     */
+    public static GraphQLScalarType Locale = new LocaleScalar();
+
     /**
      * An `Int` scalar that MUST be greater than zero
      *

src/main/java/graphql/scalars/locale/LocaleScalar.java

@@ -0,0 +1,67 @@
+package graphql.scalars.locale;
+
+import static graphql.scalars.util.Kit.typeName;
+
+import graphql.Internal;
+import graphql.language.StringValue;
+import graphql.schema.Coercing;
+import graphql.schema.CoercingParseLiteralException;
+import graphql.schema.CoercingParseValueException;
+import graphql.schema.CoercingSerializeException;
+import graphql.schema.GraphQLScalarType;
+import java.util.Locale;
+
+/**
+ * Access this via {@link graphql.scalars.ExtendedScalars#Locale}
+ */
+@Internal
+public class LocaleScalar extends GraphQLScalarType {
+
+  public LocaleScalar() {
+    super("Locale", "A IETF BCP 47 language tag", new Coercing<Locale, String>() {
+
+      @Override
+      public String serialize(Object input) throws CoercingSerializeException {
+        if (input instanceof String) {
+          try {
+            return Locale.forLanguageTag((String) input).toLanguageTag();
+          } catch (Exception e) {
+            throw new CoercingSerializeException(
+                "Expected a valid language tag string but was but was " + typeName(input));
+          }
+        }
+        if (input instanceof Locale) {
+          return ((Locale) input).toLanguageTag();
+        } else {
+          throw new CoercingSerializeException(
+              "Expected a 'java.util.Locale' object but was " + typeName(input));
+        }
+      }
+
+      @Override
+      public Locale parseValue(Object input) throws CoercingParseValueException {
+        if (input instanceof String) {
+          try {
+            return Locale.forLanguageTag(input.toString());
+          } catch (Exception e) {
+            throw new CoercingParseValueException(
+                "Unable to parse value to 'java.util.Locale' because of: " + e.getMessage());
+          }
+        } else {
+          throw new CoercingParseValueException(
+              "Expected a 'java.lang.String' object but was " + typeName(input));
+        }
+      }
+
+      @Override
+      public Locale parseLiteral(Object input) throws CoercingParseLiteralException {
+        if (input instanceof StringValue) {
+          return Locale.forLanguageTag(((StringValue) input).getValue());
+        } else {
+          throw new CoercingParseLiteralException(
+              "Expected a 'java.lang.String' object but was " + typeName(input));
+        }
+      }
+    });
+  }
+}

src/test/groovy/graphql/scalars/locale/LocaleScalarTest.groovy

@@ -0,0 +1,56 @@
+package graphql.scalars.locale
+
+import graphql.language.StringValue
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static graphql.scalars.util.TestKit.mkLocalDate
+import static graphql.scalars.util.TestKit.mkLocalDate
+import static graphql.scalars.util.TestKit.mkLocalDate
+import static graphql.scalars.util.TestKit.mkLocale
+import static graphql.scalars.util.TestKit.mkOffsetDT
+import static graphql.scalars.util.TestKit.mkZonedDT
+
+class LocaleScalarTest extends Specification {
+
+    def coercing = new LocaleScalar().getCoercing()
+
+    @Unroll
+    def "full locale parseValue"() {
+
+        when:
+        def result = coercing.parseValue(input)
+        then:
+        result == expectedValue
+        where:
+        input                           | expectedValue
+        "en"                            | mkLocale("en")
+        "ro-RO"                         | mkLocale("ro-RO")
+        "zh-hakka"                      | mkLocale("zh-hakka")
+    }
+
+    @Unroll
+    def "full Locale parseLiteral"() {
+        when:
+        def result = coercing.parseLiteral(input)
+        then:
+        result == expectedValue
+        where:
+        input                           | expectedValue
+        new StringValue("ro-RO")        | mkLocale("ro-RO")
+    }
+
+    @Unroll
+    def "full Locale serialization"() {
+        when:
+        def result = coercing.serialize(input)
+        then:
+        result == expectedValue
+        where:
+        input                           | expectedValue
+        "ro-RO"                         | "ro-RO"
+        mkLocale("ro-RO")               | "ro-RO"
+        mkLocale("en")                  | "en"
+    }
+
+}

src/test/groovy/graphql/scalars/util/TestKit.groovy

@@ -12,6 +12,11 @@ import java.time.ZoneOffset
 import java.time.ZonedDateTime
 
 class TestKit {
+
+    static Locale mkLocale(String s) {
+        Locale.forLanguageTag(s)
+    }
+
     static LocalDate mkLocalDate(String s) {
         LocalDate.parse(s)
     }