refactor: the value structure of ConfigMap for Setting custom extension (#2243)

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#### What type of PR is this?
/kind improvement
/area core
/milestone 2.0
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#### What this PR does / why we need it:
由于 Setting 自定义模型关联表单值的存储结构改变，对应修改 SettingFetcher 的取值方式
https://github.com/halo-dev/rfcs/pull/18
#### Which issue(s) this PR fixes:

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#### Special notes for your reviewer:
/cc @halo-dev/sig-halo 
#### Does this PR introduce a user-facing change?

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src/main/java/run/halo/app/core/extension/endpoint/UserEndpoint.java

@@ -135,7 +135,7 @@ public class UserEndpoint implements CustomEndpoint {
                     .parameter(parameterBuilder().in(ParameterIn.PATH).name("name")
                         .description("User name")
                         .required(true))
-                    .response(responseBuilder().implementation(Set.class)))
+                    .response(responseBuilder().implementation(UserPermission.class)))
             .build();
     }
 

src/main/java/run/halo/app/plugin/SettingFetcher.java

@@ -3,8 +3,11 @@ package run.halo.app.plugin;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import java.util.Collection;
+import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.stream.Collectors;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
@@ -25,9 +28,7 @@ import run.halo.app.infra.utils.JsonUtils;
  */
 public class SettingFetcher {
 
-    private static final String PLUGIN_SETTING_VALUE = "setting";
-
-    private final AtomicReference<JsonNode> valueRef = new AtomicReference<>(null);
+    private final AtomicReference<Map<String, JsonNode>> valueRef = new AtomicReference<>(null);
 
     private final ExtensionClient extensionClient;
 
@@ -49,9 +50,16 @@ public class SettingFetcher {
         return getInternal(group);
     }
 
+    /**
+     * Get values from {@link ConfigMap}.
+     *
+     * @return a unmodifiable map of values(non-null).
+     */
     @NonNull
-    public JsonNode getValues() {
-        return valueRef.updateAndGet(m -> m != null ? m : getValuesInternal());
+    public Map<String, JsonNode> getValues() {
+        Map<String, JsonNode> values =
+            valueRef.updateAndGet(m -> m != null ? m : getValuesInternal());
+        return Map.copyOf(values);
     }
 
     private JsonNode getInternal(String group) {
@@ -59,13 +67,14 @@ public class SettingFetcher {
             .orElse(JsonNodeFactory.instance.missingNode());
     }
 
-    private JsonNode getValuesInternal() {
+    private Map<String, JsonNode> getValuesInternal() {
         return configMap(pluginName)
-            .filter(configMap -> configMap.getData() != null
-                && configMap.getData().containsKey(PLUGIN_SETTING_VALUE))
-            .map(configMap -> configMap.getData().get(PLUGIN_SETTING_VALUE))
-            .map(this::readTree)
-            .orElse(JsonNodeFactory.instance.missingNode());
+            .filter(configMap -> configMap.getData() != null)
+            .map(ConfigMap::getData)
+            .map(Map::entrySet)
+            .stream()
+            .flatMap(Collection::stream)
+            .collect(Collectors.toMap(Map.Entry::getKey, entry -> readTree(entry.getValue())));
     }
 
     private Optional<ConfigMap> configMap(String pluginName) {
@@ -80,6 +89,9 @@ public class SettingFetcher {
     }
 
     private JsonNode readTree(String json) {
+        if (StringUtils.isBlank(json)) {
+            return JsonNodeFactory.instance.missingNode();
+        }
         try {
             return JsonUtils.DEFAULT_JSON_MAPPER.readTree(json);
         } catch (JsonProcessingException e) {

src/test/java/run/halo/app/plugin/SettingFetcherTest.java

@@ -54,7 +54,7 @@ class SettingFetcherTest {
 
     @Test
     void getValues() throws JSONException {
-        JsonNode values = settingFetcher.getValues();
+        Map<String, JsonNode> values = settingFetcher.getValues();
 
         verify(extensionClient, times(1)).fetch(eq(ConfigMap.class), any());
 
@@ -62,7 +62,7 @@ class SettingFetcherTest {
         JSONAssert.assertEquals(getSns(), JsonUtils.objectToJson(values.get("sns")), true);
 
         // The extensionClient will only be called once
-        JsonNode callAgain = settingFetcher.getValues();
+        Map<String, JsonNode> callAgain = settingFetcher.getValues();
         assertThat(callAgain).isNotNull();
         verify(extensionClient, times(1)).fetch(eq(ConfigMap.class), any());
     }
@@ -98,15 +98,14 @@ class SettingFetcherTest {
         configMap.setMetadata(metadata);
         configMap.setKind("ConfigMap");
         configMap.setApiVersion("v1alpha1");
-        configMap.setData(Map.of("setting", String.format("""
-            {
-                 "sns": %s,
-                 "basic": {
+        configMap.setData(Map.of("sns", getSns(),
+            "basic", """
+                {
                      "color": "red",
                      "width": "100"
                  }
-            }
-            """, getSns())));
+                """)
+        );
         return configMap;
     }