feat: Add different examples router implementation

src/main/java/edu/kit/provideq/toolbox/api/ExamplesRouter.java

@@ -0,0 +1,119 @@
+package edu.kit.provideq.toolbox.api;
+
+import static org.springdoc.core.fn.builders.apiresponse.Builder.responseBuilder;
+import static org.springdoc.core.fn.builders.arrayschema.Builder.arraySchemaBuilder;
+import static org.springdoc.core.fn.builders.content.Builder.contentBuilder;
+import static org.springdoc.core.fn.builders.schema.Builder.schemaBuilder;
+import static org.springdoc.webflux.core.fn.SpringdocRouteBuilder.route;
+import static org.springframework.http.MediaType.APPLICATION_JSON_VALUE;
+import static org.springframework.web.reactive.function.server.ServerResponse.ok;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import edu.kit.provideq.toolbox.meta.Problem;
+import edu.kit.provideq.toolbox.meta.ProblemManager;
+import edu.kit.provideq.toolbox.meta.ProblemManagerProvider;
+import edu.kit.provideq.toolbox.meta.ProblemType;
+import java.util.List;
+import java.util.Optional;
+import java.util.logging.Logger;
+import org.springdoc.core.fn.builders.operation.Builder;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.json.JsonParseException;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.reactive.config.EnableWebFlux;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.ServerResponse;
+import reactor.core.publisher.Mono;
+
+/**
+ * This router provides example problems for each problem type.
+ */
+@Configuration
+@EnableWebFlux
+public class ExamplesRouter {
+  private ProblemManagerProvider problemManagerProvider;
+  private static final Logger logger = Logger.getLogger(ExamplesRouter.class.getName());
+
+  @Bean
+  RouterFunction<ServerResponse> getExamplesRoutes() {
+    return problemManagerProvider.getProblemManagers().stream()
+        .map(this::defineExamplesRouteForManager)
+        .reduce(RouterFunction::and)
+        .orElseThrow();
+  }
+
+  private RouterFunction<ServerResponse> defineExamplesRouteForManager(
+      ProblemManager<?, ?> manager) {
+    var problemType = manager.getType();
+    return route().GET(
+        getExamplesRouteForProblemType(problemType),
+        req -> handleExamplesRouteForManager(manager),
+        ops -> handleExamplesRouteDocumentation(ops, manager)
+    ).build();
+  }
+
+  private Mono<ServerResponse> handleExamplesRouteForManager(ProblemManager<?, ?> manager) {
+    logger.warning("Handling read for manager: " + manager.getType().getId());
+    var exampleProblems = List.of("example1", "example2", "example3");
+    logger.warning("Example problems: " + exampleProblems);
+
+    return ok().body(Mono.just(exampleProblems), new ParameterizedTypeReference<>() {})
+        .doOnError(error -> logger.severe("Error handling read: " + error.getMessage()));
+  }
+
+  private void handleExamplesRouteDocumentation(Builder ops, ProblemManager<?, ?> manager) {
+    ops
+        .operationId(getExamplesRouteForProblemType(manager.getType()))
+        .tag(manager.getType().getId())
+        .description("This endpoint can be used to view example problems for '"
+            + manager.getType().getId() + "'.")
+        .response(responseBuilder()
+            .responseCode(String.valueOf(HttpStatus.OK.value()))
+            .content(getOkResponseContent(manager))
+        );
+  }
+
+  private static <InputT, ResultT> List<InputT> getExampleInput(
+      ProblemManager<InputT, ResultT> manager
+  ) {
+    return manager.getExampleInstances()
+        .stream()
+        .map(Problem::getInput)
+        .filter(Optional::isPresent)
+        .map(Optional::get)
+        .toList();
+  }
+
+  private static org.springdoc.core.fn.builders.content.Builder getOkResponseContent(
+      ProblemManager<?, ?> manager) {
+    var allExamples = getExampleInput(manager);
+    String example;
+    try {
+      example = new ObjectMapper().writeValueAsString(allExamples);
+    } catch (JsonProcessingException e) {
+      throw new JsonParseException(e);
+    }
+
+    return contentBuilder()
+        .mediaType(APPLICATION_JSON_VALUE)
+        .example(org.springdoc.core.fn.builders.exampleobject.Builder.exampleOjectBuilder()
+            .name(manager.getType().getId())
+            .value(example))
+        .array(arraySchemaBuilder()
+            .schema(schemaBuilder()
+                .implementation(String.class)));
+  }
+
+  private String getExamplesRouteForProblemType(ProblemType<?, ?> type) {
+    return "/examples/" + type.getId();
+  }
+
+  @Autowired
+  public void setProblemManagerProvider(ProblemManagerProvider problemManagerProvider) {
+    this.problemManagerProvider = problemManagerProvider;
+  }
+}