feat: restructure RSS generation to support extension by other plugins (#39)

### What this PR does?
重写 RSS 生成并支持被其他插件扩展

```release-note
重写 RSS 生成并支持被其他插件扩展
```

Author: guqing

.github/workflows/cd.yaml

@@ -16,3 +16,4 @@ jobs:
     with:
       app-id: app-KhIVw
       skip-node-setup: true
+      artifacts-path: 'app/build/libs'

.github/workflows/ci.yaml

@@ -13,3 +13,4 @@ jobs:
     uses: halo-sigs/reusable-workflows/.github/workflows/plugin-ci.yaml@v1
     with:
       skip-node-setup: true
+      artifacts-path: 'app/build/libs'

.gitignore

@@ -72,3 +72,4 @@ application-local.properties
 
 /admin-frontend/node_modules/
 /workplace/
+*/workplace/

README.md

@@ -2,6 +2,92 @@
 
 Halo 2.0 的 RSS 订阅链接生成插件
 
+## 如何扩展 RSS 源
+
+> 从 feed 插件 v1.4.0 版本开始，支持扩展 RSS 功能。
+
+`feed` 插件提供了扩展点，允许其他插件扩展 RSS 源。
+
+### 步骤 1：在插件中引入 feed 依赖
+
+在你的插件项目中添加 `feed` 插件的依赖：
+
+```groovy
+dependencies {
+    // ...
+    compileOnly "run.halo.feed:api:{version}"
+}
+```
+
+将 `{version}` 替换为实际的 `feed` 插件版本号。
+
+### 步骤 2：实现 `RssRouteItem` 扩展点接口
+
+创建一个类实现 `run.halo.feed.RssRouteItem` 接口，提供自定义的 RSS 数据源。例如：
+
+```java
+public class MomentRssProvider implements RssRouteItem {
+    // 实现具体的 RSS 提供逻辑
+}
+```
+
+你可以参考 [PostRssProvider](./app/src/main/java/run/halo/feed/provider/PostRssProvider.java) 示例。
+
+### 步骤 3：声明扩展点
+
+在 `src/main/resources/extensions`
+目录下，声明你的扩展。你可以参考 [ext-definition.yaml](app/src/main/resources/extensions/ext-definition.yaml) 文件来完成此步骤。
+
+### 步骤 4：定义配置类并清理 RSS 缓存
+
+在插件中定义一个配置类，使用 `@ConditionalOnClass` 注解确保只有在 `run.halo.feed.RssRouteItem` 类存在时才会创建对应的
+Bean。同时，定义事件监听器来清理缓存。
+
+`@ConditionalOnClass` 注解只能使用 name 属性来指定类全限定名，不支持使用 value 属性。
+
+示例代码：
+
+```java
+
+@Configuration
+@ConditionalOnClass(name = "run.halo.feed.RssRouteItem")
+@RequiredArgsConstructor
+public class RssAutoConfiguration {
+    private final ApplicationEventPublisher eventPublisher;
+
+    @Bean
+    public MomentRssProvider momentRssProvider() {
+        return new MomentRssProvider();
+    }
+
+    @Async
+    @EventListener({MomentUpdatedEvent.class, MomentDeletedEvent.class, ContextClosedEvent.class})
+    public void onMomentUpdatedOrDeleted() {
+        var rule = CacheClearRule.forExact("/feed/moments/rss.xml");
+        var event = RssCacheClearRequested.forRule(this, rule);
+        eventPublisher.publishEvent(event);
+    }
+}
+```
+
+此配置确保了当 `RssRouteItem` 接口存在时，插件才会自动创建 `MomentRssProvider` 并监听相关事件来清理缓存。
+
+### 步骤 5：声明插件依赖
+
+在 `plugin.yaml` 文件中声明 `feed` 插件为可选依赖，确保当 `feed` 插件存在并启用时，插件能够自动注册 RSS 源。
+
+```yaml
+apiVersion: plugin.halo.run/v1alpha1
+kind: Plugin
+metadata:
+    name: moment
+spec:
+    pluginDependencies:
+        "PluginFeed?": ">=1.4.0"
+```
+
+这样，当 `feed` 插件可用时，插件会自动注册自定义的 RSS 源。
+
 ## 开发环境
 
 ```bash
@@ -28,15 +114,15 @@ cd path/to/plugin-feed
 
 ```yaml
 halo:
-  plugin:
-    runtime-mode: development
-    classes-directories:
-      - "build/classes"
-      - "build/resources"
-    lib-directories:
-      - "libs"
-    fixedPluginPath:
-      - "/path/to/plugin-feed"
+    plugin:
+        runtime-mode: development
+        classes-directories:
+            - "build/classes"
+            - "build/resources"
+        lib-directories:
+            - "libs"
+        fixedPluginPath:
+            - "/path/to/plugin-feed"
 ```
 
 ## 使用方式

api/build.gradle

@@ -0,0 +1,76 @@
+plugins {
+    id 'java-library'
+    id 'maven-publish'
+    id "io.freefair.lombok" version "8.0.0-rc2"
+}
+
+group = 'run.halo.feed'
+version = rootProject.version
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+    withSourcesJar()
+}
+
+compileJava.options.encoding = "UTF-8"
+compileTestJava.options.encoding = "UTF-8"
+javadoc.options.encoding = "UTF-8"
+
+dependencies {
+    api platform('run.halo.tools.platform:plugin:2.20.11')
+    compileOnly 'run.halo.app:api'
+}
+
+test {
+    useJUnitPlatform()
+}
+
+publishing {
+    publications {
+        mavenJava(MavenPublication) {
+            from components.java
+            artifact tasks.sourcesJar
+
+            artifactId = 'api'
+            version = project.hasProperty('version') ? project.property('version') : 'unspecified'
+
+            pom {
+                name = 'RSS'
+                description = '为站点生成 RSS 订阅链接'
+                url = 'https://www.halo.run/store/apps/app-KhIVw'
+
+                licenses {
+                    license {
+                        name = 'GPL-3.0'
+                        url = 'https://github.com/halo-dev/plugin-feed/blob/main/LICENSE'
+                    }
+                }
+
+                developers {
+                    developer {
+                        id = 'guqing'
+                        name = 'guqing'
+                        email = '[email protected]'
+                    }
+                }
+
+                scm {
+                    connection = 'scm:git:[email protected]:halo-dev/plugin-feed.git'
+                    developerConnection = 'scm:git:[email protected]:halo-dev/plugin-feed.git'
+                    url = 'https://github.com/halo-dev/plugin-feed'
+                }
+            }
+        }
+    }
+    repositories {
+        maven {
+            url = version.endsWith('-SNAPSHOT') ? 'https://s01.oss.sonatype.org/content/repositories/snapshots/' :
+                    'https://s01.oss.sonatype.org/content/repositories/releases/'
+            credentials {
+                username = project.findProperty("ossr.user") ?: System.getenv("OSSR_USERNAME")
+                password = project.findProperty("ossr.password") ?: System.getenv("OSSR_PASSWORD")
+            }
+        }
+    }
+}

api/src/main/java/run/halo/feed/CacheClearRule.java

@@ -0,0 +1,40 @@
+package run.halo.feed;
+
+import org.springframework.util.Assert;
+
+public record CacheClearRule(Type type, String value) {
+    public CacheClearRule {
+        Assert.notNull(type, "Type cannot be null");
+        Assert.notNull(value, "Value cannot be null");
+        if (type == Type.EXACT && !value.startsWith("/")) {
+            throw new IllegalArgumentException("Exact value must start with /");
+        }
+    }
+
+    public static CacheClearRule forPrefix(String prefix) {
+        return new CacheClearRule(Type.PREFIX, prefix);
+    }
+
+    public static CacheClearRule forExact(String exact) {
+        return new CacheClearRule(Type.EXACT, exact);
+    }
+
+    public static CacheClearRule forContains(String contains) {
+        return new CacheClearRule(Type.CONTAINS, contains);
+    }
+
+    @Override
+    public String toString() {
+        return "CacheClearRule{" +
+            "type=" + type +
+            ", value='" + value + '\'' +
+            '}';
+    }
+
+    public enum Type {
+        PREFIX,
+        EXACT,
+        CONTAINS
+    }
+}
+