add email validation

Author: Piiit

src/main/java/it/aboutbits/springboot/testing/validation/rule/EmailRule.java

@@ -0,0 +1,24 @@
+package it.aboutbits.springboot.testing.validation.rule;
+
+import com.google.errorprone.annotations.CheckReturnValue;
+import it.aboutbits.springboot.testing.validation.core.BaseRuleBuilder;
+import it.aboutbits.springboot.testing.validation.core.Rule;
+import it.aboutbits.springboot.testing.validation.core.ValidationRulesData;
+import it.aboutbits.springboot.testing.validation.source.InvalidEmailValueSource;
+import org.jspecify.annotations.NullMarked;
+
+@SuppressWarnings("unchecked")
+@NullMarked
+public interface EmailRule<V extends BaseRuleBuilder<?>> extends ValidationRulesData {
+    /**
+     * Bean validation considers `null` and blank values to be valid e-mail addresses.
+     * Combine this rule with `notNull` or `notBlank` if the property must be present.
+     */
+    @CheckReturnValue
+    default V email(String property) {
+        addRule(
+                new Rule(property, InvalidEmailValueSource.class)
+        );
+        return (V) this;
+    }
+}

src/main/java/it/aboutbits/springboot/testing/validation/source/InvalidEmailValueSource.java

@@ -0,0 +1,47 @@
+package it.aboutbits.springboot.testing.validation.source;
+
+import it.aboutbits.springboot.testing.validation.core.ValueSource;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+@NullMarked
+public class InvalidEmailValueSource implements ValueSource {
+    private static final Map<Class<?>, Function<Object[], Stream<?>>> TYPE_SOURCES = new HashMap<>();
+
+    static {
+        TYPE_SOURCES.put(
+                String.class,
+                (Object[] args) -> Stream.of(
+                        "plainaddress",
+                        "@example.com",
+                        "someone@",
+                        "someone@@example.com",
+                        "some one@example.com",
+                        "someone@exam ple.com",
+                        "someone@example..com",
+                        "someone@.example.com"
+                )
+        );
+    }
+
+    @SuppressWarnings("unused")
+    public static void registerType(Class<?> type, Function<Object[], Stream<?>> source) {
+        TYPE_SOURCES.put(type, source);
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public <T> Stream<@Nullable T> values(Class<T> propertyClass, Object... args) {
+        var sourceFunction = TYPE_SOURCES.get(propertyClass);
+        if (sourceFunction != null) {
+            return (Stream<@Nullable T>) sourceFunction.apply(args);
+        }
+
+        throw new IllegalArgumentException("Property class not supported!");
+    }
+}