feat: provide builder-wrapper

Author: Nylle

src/main/java/com/github/nylle/javafixture/Builder.java

@@ -0,0 +1,59 @@
+package com.github.nylle.javafixture;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collectors.toList;
+
+public class Builder<T> {
+
+    private final Method buildMethod;
+    private final Method builderMethod;
+
+    private Builder(Method builderMethod, Method buildMethod) {
+        this.builderMethod = builderMethod;
+        this.buildMethod = buildMethod;
+    }
+
+    public static <T> Builder<T> create(Method builderMethodCandidate, SpecimenType<T> targetType) {
+        return findBuildMethod(builderMethodCandidate.getReturnType(), targetType.asClass())
+                .map(x -> new Builder<T>(builderMethodCandidate, x))
+                .orElse(null);
+    }
+
+    public T invoke(SpecimenFactory specimenFactory, CustomizationContext customizationContext) {
+        try {
+            var builder = builderMethod.invoke(null, new Object[]{});
+
+            for (var method : findSetMethods()) {
+                method.invoke(builder, new Object[]{specimenFactory.build(SpecimenType.fromClass(method.getGenericParameterTypes()[0])).create(customizationContext, new Annotation[0])});
+            }
+
+            return (T) buildMethod.invoke(builder, new Object[]{});
+        } catch (InvocationTargetException | IllegalAccessException ex) {
+            return null;
+        }
+    }
+
+    private List<Method> findSetMethods() {
+        return Stream.of(builderMethod.getReturnType().getDeclaredMethods())
+                .filter(x -> !Modifier.isStatic(x.getModifiers()))
+                .filter(x -> Modifier.isPublic(x.getModifiers()))
+                .filter(x -> x.getParameterCount() == 1)
+                .collect(toList());
+    }
+
+    private static <T> Optional<Method> findBuildMethod(Class<?> builderClass, Class<T> targetType) {
+        return Stream.of(builderClass.getDeclaredMethods())
+                .filter(x -> !Modifier.isStatic(x.getModifiers()))
+                .filter(x -> Modifier.isPublic(x.getModifiers()))
+                .filter(x -> x.getReturnType().equals(targetType))
+                .filter(x -> x.getParameterCount() == 0)
+                .findFirst();
+    }
+}

src/test/java/com/github/nylle/javafixture/BuilderTest.java

@@ -0,0 +1,24 @@
+package com.github.nylle.javafixture;
+
+import com.github.nylle.javafixture.testobjects.ClassWithBuilder;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class BuilderTest {
+
+    @Test
+    void invokeReturnsBuiltObjectWithAllMethodsCalled() throws NoSuchMethodException {
+        var sut = Builder.create(ClassWithBuilder.class.getMethod("builder"), SpecimenType.fromClass(ClassWithBuilder.class));
+
+        var result = sut.invoke(new SpecimenFactory(new Context(new Configuration())), CustomizationContext.noContext());
+
+        assertThat(result).isInstanceOf(ClassWithBuilder.class);
+
+        var actual = (ClassWithBuilder) result;
+
+        assertThat(actual.getNumber()).isNotNull();
+        assertThat(actual.getString()).isNotNull();
+    }
+
+}

src/test/java/com/github/nylle/javafixture/testobjects/ClassWithBuilder.java

@@ -0,0 +1,42 @@
+package com.github.nylle.javafixture.testobjects;
+
+public class ClassWithBuilder {
+    private final String string;
+    private final Integer number;
+
+    private ClassWithBuilder(String string, Integer number) {
+        this.string = string;
+        this.number = number;
+    }
+
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    public String getString() {
+        return string;
+    }
+
+    public Integer getNumber() {
+        return number;
+    }
+
+    public static class Builder {
+        private String string;
+        private Integer number;
+
+        public Builder string(String string) {
+            this.string = string;
+            return this;
+        }
+
+        public Builder number(Integer number) {
+            this.number = number;
+            return this;
+        }
+
+        public ClassWithBuilder build() {
+            return new ClassWithBuilder(string, number);
+        }
+    }
+}