feature: create clean architecture package structure

src/main/java/tk/antoine/roux/domain/UseCases.java

@@ -0,0 +1,12 @@
+package tk.antoine.roux.domain;
+
+public interface UseCases<R, T> {
+
+    /**
+     * Every use cases should have one and only one method named execute
+     * Every use cases should take one argument
+     * Every use cases should return a value
+     */
+    R execute(T arg);
+
+}

src/main/java/tk/antoine/roux/domain/model/Either.java

@@ -0,0 +1,36 @@
+package tk.antoine.roux.domain.model;
+
+public final class Either<T> {
+    private final Exception error;
+    private final T success;
+
+    private Either(Exception error, T success) {
+        this.error = error;
+        this.success = success;
+    }
+
+    public Exception left() {
+        return error;
+    }
+
+    public T right() {
+        return success;
+    }
+
+    public static <T> Either<T> right(T success) {
+        return new Either<>(null, success);
+    }
+
+    public static <T> Either<T> left(Exception error) {
+        return new Either<>(error, null);
+    }
+
+    public boolean isLeft() {
+        return success == null;
+    }
+
+    public boolean isRight() {
+        return error == null;
+    }
+
+}

src/main/java/tk/antoine/roux/infrastructure/Manager.java

@@ -0,0 +1,27 @@
+package tk.antoine.roux.infrastructure;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ProblemDetail;
+import org.springframework.http.ResponseEntity;
+import tk.antoine.roux.domain.model.Either;
+
+public interface Manager {
+
+    static <T> ResponseEntity<T> eitherToResponseEntity(Either<T> either, String errorMessage) {
+        ResponseEntity<T> response;
+        if (either.isLeft()) {
+            ProblemDetail problemDetail = exceptionToProblemDetail(either, errorMessage);
+            response = ResponseEntity.of(problemDetail).build();
+        } else {
+            response = ResponseEntity.ok(either.right());
+        }
+        return response;
+    }
+
+    private static ProblemDetail exceptionToProblemDetail(Either<?> either, String errorMessage) {
+        ProblemDetail problemDetail = ProblemDetail
+            .forStatusAndDetail(HttpStatus.BAD_REQUEST, either.left().getMessage());
+        problemDetail.setTitle(errorMessage);
+        return problemDetail;
+    }
+}