Provide ungrouped query param to filter ungrouped attachments (#2752)

#### What type of PR is this?

/kind feature
/area core
/milestone 2.0.0-rc.1

#### What this PR does / why we need it:

Provide `ungrouped` query param to filter ungrouped attachments. Please note that we will ignore `group` query param when `ungropued` is `true`.

```bash
curl -X 'GET' \
  'http://localhost:8090/apis/api.console.halo.run/v1alpha1/attachments?ungrouped=true' \
  -H 'accept: */*'
```

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/2451

#### Does this PR introduce a user-facing change?

```release-note
None
```

src/main/java/run/halo/app/core/extension/attachment/endpoint/AttachmentEndpoint.java

@@ -4,6 +4,7 @@ import static java.util.Comparator.comparing;
 import static org.springdoc.core.fn.builders.apiresponse.Builder.responseBuilder;
 import static org.springdoc.core.fn.builders.content.Builder.contentBuilder;
 import static org.springdoc.core.fn.builders.schema.Builder.schemaBuilder;
+import static org.springframework.boot.convert.ApplicationConversionService.getSharedInstance;
 import static org.springframework.web.reactive.function.BodyExtractors.toMultipartData;
 import static org.springframework.web.reactive.function.server.RequestPredicates.contentType;
 import static run.halo.app.extension.ListResult.generateGenericClass;
@@ -168,6 +169,10 @@ public class AttachmentEndpoint implements CustomEndpoint {
         @Schema(description = "Name of group")
         Optional<String> getGroup();
 
+        @Schema(description = "Filter attachments without group. This parameter will ignore group"
+            + " parameter.")
+        Optional<Boolean> getUngrouped();
+
         @Schema(description = "Name of user who uploaded the attachment")
         Optional<String> getUploadedBy();
 
@@ -209,6 +214,12 @@ public class AttachmentEndpoint implements CustomEndpoint {
                 .filter(StringUtils::hasText);
         }
 
+        @Override
+        public Optional<Boolean> getUngrouped() {
+            return Optional.ofNullable(queryParams.getFirst("ungrouped"))
+                .map(ungroupedStr -> getSharedInstance().convert(ungroupedStr, Boolean.class));
+        }
+
         @Override
         public Optional<String> getUploadedBy() {
             return Optional.ofNullable(queryParams.getFirst("uploadedBy"))
@@ -221,33 +232,49 @@ public class AttachmentEndpoint implements CustomEndpoint {
         }
 
         public Predicate<Attachment> toPredicate() {
-            var predicate = (Predicate<Attachment>) (attachment) -> getDisplayName()
+            Predicate<Attachment> displayNamePred = attachment -> getDisplayName()
                 .map(displayNameInParam -> {
                     String displayName = attachment.getSpec().getDisplayName();
                     return displayName.contains(displayNameInParam);
-                }).orElse(true)
+                }).orElse(true);
-                && getPolicy()
+
+            Predicate<Attachment> policyPred = attachment -> getPolicy()
                 .map(policy -> {
                     var policyRef = attachment.getSpec().getPolicyRef();
                     return policyRef != null && policy.equals(policyRef.getName());
-                }).orElse(true)
+                }).orElse(true);
-                && getGroup()
+
+            Predicate<Attachment> groupPred = attachment -> getGroup()
                 .map(group -> {
                     var groupRef = attachment.getSpec().getGroupRef();
                     return groupRef != null && group.equals(groupRef.getName());
                 })
-                .orElse(true)
+                .orElse(true);
-                && getUploadedBy()
+
+            Predicate<Attachment> ungroupedPred = attachment -> getUngrouped()
+                .filter(Boolean::booleanValue)
+                .map(ungrouped -> {
+                    var groupRef = attachment.getSpec().getGroupRef();
+                    return groupRef == null || !StringUtils.hasText(groupRef.getName());
+                })
+                .orElseGet(() -> groupPred.test(attachment));
+
+            Predicate<Attachment> uploadedByPred = attachment -> getUploadedBy()
                 .map(uploadedBy -> {
                     var uploadedByRef = attachment.getSpec().getUploadedBy();
                     return uploadedByRef != null && uploadedBy.equals(uploadedByRef.getName());
                 })
                 .orElse(true);
 
-            var selectorPredicate = labelAndFieldSelectorToPredicate(getLabelSelector(),
-                getFieldSelector());
 
-            return predicate.and(selectorPredicate);
+            var selectorPred =
+                labelAndFieldSelectorToPredicate(getLabelSelector(), getFieldSelector());
+
+            return displayNamePred
+                .and(policyPred)
+                .and(ungroupedPred)
+                .and(uploadedByPred)
+                .and(selectorPred);
         }
 
         public Comparator<Attachment> toComparator() {

src/test/java/run/halo/app/core/extension/attachment/endpoint/AttachmentEndpointTest.java

@@ -1,6 +1,10 @@
 package run.halo.app.core.extension.attachment.endpoint;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.same;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -18,13 +22,19 @@ import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 import org.springframework.http.MediaType;
 import org.springframework.http.client.MultipartBodyBuilder;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.reactive.function.server.MockServerRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.web.reactive.function.BodyInserters;
 import reactor.core.publisher.Mono;
 import run.halo.app.core.extension.attachment.Attachment;
+import run.halo.app.core.extension.attachment.Attachment.AttachmentSpec;
 import run.halo.app.core.extension.attachment.Policy;
 import run.halo.app.core.extension.attachment.Policy.PolicySpec;
+import run.halo.app.core.extension.attachment.endpoint.AttachmentEndpoint.SearchRequest;
 import run.halo.app.extension.ConfigMap;
+import run.halo.app.extension.ListResult;
 import run.halo.app.extension.Metadata;
 import run.halo.app.extension.ReactiveExtensionClient;
 import run.halo.app.extension.Ref;
@@ -149,4 +159,45 @@ class AttachmentEndpointTest {
         }
     }
 
+    @Nested
+    class SearchTest {
+
+        @Test
+        void shouldListUngroupedAttachments() {
+            when(client.list(same(Attachment.class), any(), any(), anyInt(), anyInt()))
+                .thenReturn(Mono.just(ListResult.emptyResult()));
+
+            webClient
+                .get()
+                .uri("/attachments")
+                .exchange()
+                .expectStatus().isOk()
+                .expectBody()
+                .jsonPath("items.length()").isEqualTo(0);
+        }
+
+        @Test
+        void shouldFilterWithUngrouped() {
+            var httpRequest = MockServerHttpRequest.get("/attachments")
+                .build();
+            var exchange = new MockServerWebExchange.Builder(httpRequest)
+                .build();
+            MockServerRequest request = MockServerRequest.builder()
+                .queryParam("ungrouped", "true")
+                .queryParam("group", "halo")
+                .exchange(exchange)
+                .build();
+            var searchRequest = new SearchRequest(request);
+            var pred = searchRequest.toPredicate();
+            var attachment = new Attachment();
+            var spec = new AttachmentSpec();
+            attachment.setSpec(spec);
+
+            assertTrue(pred.test(attachment));
+
+            spec.setGroupRef(Ref.of("halo"));
+            assertFalse(pred.test(attachment));
+        }
+    }
+
 }