chore: adding NameTransformer interface and default implementation (#30)

fixes: #29

Author: mnorbury

lib/src/main/java/io/cloudquery/transformers/NameTransformer.java

@@ -0,0 +1,32 @@
+package io.cloudquery.transformers;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.cloudquery.caser.Caser;
+
+import javax.xml.transform.TransformerException;
+import java.lang.reflect.Field;
+
+public interface NameTransformer {
+    class DefaultNameTransformer implements NameTransformer {
+        private final Caser caser = Caser.builder().build();
+
+        /**
+         * Transforms the field name to the name of the property in the JSON
+         * or use the {@link Caser#toSnake(String)} if no annotation.
+         *
+         * @param field Field to transform
+         * @return Transformed field name
+         * @throws TransformerException If the field name cannot be transformed
+         */
+        @Override
+        public String transform(Field field) throws TransformerException {
+            JsonProperty annotation = field.getAnnotation(JsonProperty.class);
+            if (annotation != null) {
+                return annotation.value();
+            }
+            return caser.toSnake(field.getName());
+        }
+    }
+
+    String transform(Field field) throws TransformerException;
+}

lib/src/test/java/io/cloudquery/transformers/DefaultNameTransformerTest.java

@@ -0,0 +1,44 @@
+package io.cloudquery.transformers;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.cloudquery.transformers.NameTransformer.DefaultNameTransformer;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import javax.xml.transform.TransformerException;
+import java.lang.reflect.Field;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class DefaultNameTransformerTest {
+
+    private DefaultNameTransformer transformer;
+
+    @SuppressWarnings("unused")
+    private static class SimpleClass {
+        // Simple fields with no custom property mapping
+        private String simpleField;
+        private String aLongerFieldName;
+
+        // Fields with custom property mapping
+        @JsonProperty("id")
+        private String userID;
+    }
+
+    @BeforeEach
+    void setUp() {
+        transformer = new DefaultNameTransformer();
+    }
+
+    @Test
+    public void shouldReturnSnakeCaseFieldNamesByDefault() throws TransformerException {
+        Field[] declaredFields = SimpleClass.class.getDeclaredFields();
+
+        // Simple fields with no custom property mapping
+        assertEquals("simple_field", transformer.transform(declaredFields[0]));
+        assertEquals("a_longer_field_name", transformer.transform(declaredFields[1]));
+
+        // Fields with custom property mapping
+        assertEquals("id", transformer.transform(declaredFields[2]));
+    }
+}