feat: add content extension points for post and single page on theme-…

…side (halo-dev#4080)

#### What type of PR is this?
/kind feature
/milestone 2.7.x
/area core

#### What this PR does / why we need it:
为主题端的文章和自定义页面内容添加扩展点
插件可以通过实现扩展点来干预文章和自定义页面的内容显示，如修改内容的 html 结构，改变特定样式等

使用方式参考：[docs/extension-points/content.md](halo-dev@9b2b9f1)

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

Fixes halo-dev#4003

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

```release-note
为主题端的文章和自定义页面内容添加扩展点
```

api/src/main/java/run/halo/app/core/extension/Plugin.java

@@ -61,10 +61,11 @@ public static class PluginSpec {
          *
          * @see <a href="semver.org">semantic version</a>
          */
-        @Schema(requiredMode = REQUIRED, pattern = "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)\\.(0|[1-9]\\d*)(?:-("
-            + "(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\\."
-            + "(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\\+([0-9a-zA-Z-]+(?:\\"
-            + ".[0-9a-zA-Z-]+)*))?$")
+        @Schema(requiredMode = REQUIRED,
+            pattern = "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)\\.(0|[1-9]\\d*)(?:-("
+                + "(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\\."
+                + "(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\\+([0-9a-zA-Z-]+(?:\\"
+                + ".[0-9a-zA-Z-]+)*))?$")
         private String version;
 
         private PluginAuthor author;

api/src/main/java/run/halo/app/theme/ReactivePostContentHandler.java

@@ -0,0 +1,40 @@
+package run.halo.app.theme;
+
+import lombok.Builder;
+import lombok.Data;
+import org.pf4j.ExtensionPoint;
+import org.springframework.lang.NonNull;
+import reactor.core.publisher.Mono;
+import run.halo.app.core.extension.content.Post;
+
+/**
+ * <p>{@link ReactivePostContentHandler} provides a way to extend the content to be displayed in
+ * the theme.</p>
+ * Plugins can implement this interface to extend the content to be displayed in the theme,
+ * including but not limited to adding specific styles, JS libraries, inserting specific content,
+ * and intercepting content.
+ *
+ * @author guqing
+ * @since 2.7.0
+ */
+public interface ReactivePostContentHandler extends ExtensionPoint {
+
+    /**
+     * <p>Methods for handling {@link run.halo.app.core.extension.content.Post} content.</p>
+     * <p>For example, you can use this method to change the content for a better display in
+     * theme-side.</p>
+     *
+     * @param postContent content to be handled
+     * @return handled content
+     */
+    Mono<PostContentContext> handle(@NonNull PostContentContext postContent);
+
+    @Data
+    @Builder
+    class PostContentContext {
+        private Post post;
+        private String content;
+        private String raw;
+        private String rawType;
+    }
+}

api/src/main/java/run/halo/app/theme/ReactiveSinglePageContentHandler.java

@@ -0,0 +1,38 @@
+package run.halo.app.theme;
+
+import lombok.Builder;
+import lombok.Data;
+import org.pf4j.ExtensionPoint;
+import org.springframework.lang.NonNull;
+import reactor.core.publisher.Mono;
+import run.halo.app.core.extension.content.SinglePage;
+
+/**
+ * <p>{@link ReactiveSinglePageContentHandler} provides a way to extend the content to be
+ * displayed in the theme.</p>
+ *
+ * @author guqing
+ * @see ReactivePostContentHandler
+ * @since 2.7.0
+ */
+public interface ReactiveSinglePageContentHandler extends ExtensionPoint {
+
+    /**
+     * <p>Methods for handling {@link run.halo.app.core.extension.content.SinglePage} content.</p>
+     * <p>For example, you can use this method to change the content for a better display in
+     * theme-side.</p>
+     *
+     * @param singlePageContent content to be handled
+     * @return handled content
+     */
+    Mono<SinglePageContentContext> handle(@NonNull SinglePageContentContext singlePageContent);
+
+    @Data
+    @Builder
+    class SinglePageContentContext {
+        private SinglePage singlePage;
+        private String content;
+        private String raw;
+        private String rawType;
+    }
+}

application/src/main/java/run/halo/app/content/AbstractContentService.java

@@ -26,14 +26,14 @@ public abstract class AbstractContentService {
     private final ReactiveExtensionClient client;
 
     public Mono<ContentWrapper> getContent(String snapshotName, String baseSnapshotName) {
-        return client.fetch(Snapshot.class, baseSnapshotName)
+        return client.get(Snapshot.class, baseSnapshotName)
             .doOnNext(this::checkBaseSnapshot)
             .flatMap(baseSnapshot -> {
                 if (StringUtils.equals(snapshotName, baseSnapshotName)) {
                     var contentWrapper = ContentWrapper.patchSnapshot(baseSnapshot, baseSnapshot);
                     return Mono.just(contentWrapper);
                 }
-                return client.fetch(Snapshot.class, snapshotName)
+                return client.get(Snapshot.class, snapshotName)
                     .map(snapshot -> ContentWrapper.patchSnapshot(snapshot, baseSnapshot));
             });
     }
@@ -42,7 +42,7 @@ protected void checkBaseSnapshot(Snapshot snapshot) {
         Assert.notNull(snapshot, "The snapshot must not be null.");
         String keepRawAnno =
             MetadataUtil.nullSafeAnnotations(snapshot).get(Snapshot.KEEP_RAW_ANNO);
-        if (!org.thymeleaf.util.StringUtils.equals(Boolean.TRUE.toString(), keepRawAnno)) {
+        if (!StringUtils.equals(Boolean.TRUE.toString(), keepRawAnno)) {
             throw new IllegalArgumentException(
                 String.format("The snapshot [%s] is not a base snapshot.",
                     snapshot.getMetadata().getName()));

application/src/main/java/run/halo/app/theme/finders/PostPublicQueryService.java

@@ -7,7 +7,10 @@
 import reactor.core.publisher.Mono;
 import run.halo.app.core.extension.content.Post;
 import run.halo.app.extension.ListResult;
+import run.halo.app.theme.ReactivePostContentHandler;
+import run.halo.app.theme.finders.vo.ContentVo;
 import run.halo.app.theme.finders.vo.ListedPostVo;
+import run.halo.app.theme.finders.vo.PostVo;
 
 public interface PostPublicQueryService {
     Predicate<Post> FIXED_PREDICATE = post -> post.isPublished()
@@ -34,5 +37,27 @@ Mono<ListResult<ListedPostVo>> list(Integer page, Integer size,
      * @param post post must not be null
      * @return listed post vo
      */
-    Mono<ListedPostVo> convertToListedPostVo(@NonNull Post post);
+    Mono<ListedPostVo> convertToListedVo(@NonNull Post post);
+
+    /**
+     * Converts {@link Post} to post vo and populate post content by the given snapshot name.
+     * <p> This method will get post content by {@code snapshotName} and try to find
+     * {@link ReactivePostContentHandler}s to extend the content</p>
+     *
+     * @param post post must not be null
+     * @param snapshotName snapshot name must not be blank
+     * @return converted post vo
+     */
+    Mono<PostVo> convertToVo(Post post, String snapshotName);
+
+    /**
+     * Gets post content by post name.
+     * <p> This method will get post released content by post name and try to find
+     * {@link ReactivePostContentHandler}s to extend the content</p>
+     *
+     * @param postName post name must not be blank
+     * @return post content for theme-side
+     * @see ReactivePostContentHandler
+     */
+    Mono<ContentVo> getContent(String postName);
 }

application/src/main/java/run/halo/app/theme/finders/SinglePageConversionService.java

@@ -1,7 +1,10 @@
 package run.halo.app.theme.finders;
 
+import org.springframework.lang.NonNull;
 import reactor.core.publisher.Mono;
 import run.halo.app.core.extension.content.SinglePage;
+import run.halo.app.theme.ReactiveSinglePageContentHandler;
+import run.halo.app.theme.finders.vo.ContentVo;
 import run.halo.app.theme.finders.vo.ListedSinglePageVo;
 import run.halo.app.theme.finders.vo.SinglePageVo;
 
@@ -13,9 +16,40 @@
  */
 public interface SinglePageConversionService {
 
+    /**
+     * Converts the given {@link SinglePage} to {@link SinglePageVo} and populate content by
+     * given snapshot name.
+     *
+     * @param singlePage the single page must not be null
+     * @param snapshotName the snapshot name to get content must not be blank
+     * @return the converted single page vo
+     * @see #convertToVo(SinglePage)
+     */
     Mono<SinglePageVo> convertToVo(SinglePage singlePage, String snapshotName);
 
-    Mono<SinglePageVo> convertToVo(SinglePage singlePage);
+    /**
+     * Converts the given {@link SinglePage} to {@link SinglePageVo}.
+     * <p>This method will query the additional information of the {@link SinglePageVo} needed to
+     * populate.</p>
+     * <p>This method will try to find {@link ReactiveSinglePageContentHandler}s to extend the
+     * content.</p>
+     *
+     * @param singlePage the single page must not be null
+     * @return the converted single page vo
+     * @see #getContent(String)
+     */
+    Mono<SinglePageVo> convertToVo(@NonNull SinglePage singlePage);
+
+    /**
+     * Gets content by given page name.
+     * <p>This method will get released content by page name and try to find
+     * {@link ReactiveSinglePageContentHandler}s to extend the content.</p>
+     *
+     * @param pageName page name must not be blank
+     * @return content of the specified page
+     * @since 2.7.0
+     */
+    Mono<ContentVo> getContent(String pageName);
 
     Mono<ListedSinglePageVo> convertToListedVo(SinglePage singlePage);
 }

application/src/main/java/run/halo/app/theme/finders/impl/PostFinderImpl.java

@@ -18,7 +18,6 @@
 import org.springframework.util.comparator.Comparators;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
-import run.halo.app.content.PostService;
 import run.halo.app.core.extension.content.Post;
 import run.halo.app.extension.ListResult;
 import run.halo.app.extension.ReactiveExtensionClient;
@@ -47,27 +46,20 @@ public class PostFinderImpl implements PostFinder {
 
     private final ReactiveExtensionClient client;
 
-    private final PostService postService;
-
     private final PostPublicQueryService postPublicQueryService;
 
     @Override
     public Mono<PostVo> getByName(String postName) {
         return client.get(Post.class, postName)
             .filter(FIXED_PREDICATE)
-            .flatMap(postPublicQueryService::convertToListedPostVo)
-            .map(PostVo::from)
-            .flatMap(postVo -> content(postName)
-                .doOnNext(postVo::setContent)
-                .thenReturn(postVo)
+            .flatMap(post -> postPublicQueryService.convertToVo(post,
+                post.getSpec().getReleaseSnapshot())
             );
     }
 
     @Override
     public Mono<ContentVo> content(String postName) {
-        return postService.getReleaseContent(postName)
-            .map(wrapper -> ContentVo.builder().content(wrapper.getContent())
-                .raw(wrapper.getRaw()).build());
+        return postPublicQueryService.getContent(postName);
     }
 
     @Override
@@ -107,7 +99,7 @@ private Mono<PostVo> fetchByName(String name) {
     @Override
     public Flux<ListedPostVo> listAll() {
         return client.list(Post.class, FIXED_PREDICATE, defaultComparator())
-            .concatMap(postPublicQueryService::convertToListedPostVo);
+            .concatMap(postPublicQueryService::convertToListedVo);
     }
 
     static Pair<String, String> postPreviousNextPair(List<String> postNames,

application/src/main/java/run/halo/app/theme/finders/impl/PostPublicQueryServiceImpl.java

@@ -2,6 +2,7 @@
 
 import java.util.Comparator;
 import java.util.List;
+import java.util.function.Function;
 import java.util.function.Predicate;
 import lombok.RequiredArgsConstructor;
 import org.apache.commons.lang3.ObjectUtils;
@@ -11,16 +12,22 @@
 import org.springframework.util.CollectionUtils;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import run.halo.app.content.ContentWrapper;
+import run.halo.app.content.PostService;
 import run.halo.app.core.extension.content.Post;
 import run.halo.app.extension.ListResult;
 import run.halo.app.extension.ReactiveExtensionClient;
 import run.halo.app.metrics.CounterService;
 import run.halo.app.metrics.MeterUtils;
+import run.halo.app.plugin.extensionpoint.ExtensionGetter;
+import run.halo.app.theme.ReactivePostContentHandler;
 import run.halo.app.theme.finders.CategoryFinder;
 import run.halo.app.theme.finders.ContributorFinder;
 import run.halo.app.theme.finders.PostPublicQueryService;
 import run.halo.app.theme.finders.TagFinder;
+import run.halo.app.theme.finders.vo.ContentVo;
 import run.halo.app.theme.finders.vo.ListedPostVo;
+import run.halo.app.theme.finders.vo.PostVo;
 import run.halo.app.theme.finders.vo.StatsVo;
 
 @Component
@@ -37,6 +44,10 @@ public class PostPublicQueryServiceImpl implements PostPublicQueryService {
 
     private final CounterService counterService;
 
+    private final PostService postService;
+
+    private final ExtensionGetter extensionGetter;
+
     @Override
     public Mono<ListResult<ListedPostVo>> list(Integer page, Integer size,
         Predicate<Post> postPredicate, Comparator<Post> comparator) {
@@ -45,7 +56,7 @@ public Mono<ListResult<ListedPostVo>> list(Integer page, Integer size,
         return client.list(Post.class, predicate,
                 comparator, pageNullSafe(page), sizeNullSafe(size))
             .flatMap(list -> Flux.fromStream(list.get())
-                .concatMap(post -> convertToListedPostVo(post)
+                .concatMap(post -> convertToListedVo(post)
                     .flatMap(postVo -> populateStats(postVo)
                         .doOnNext(postVo::setStats).thenReturn(postVo)
                     )
@@ -59,7 +70,7 @@ comparator, pageNullSafe(page), sizeNullSafe(size))
     }
 
     @Override
-    public Mono<ListedPostVo> convertToListedPostVo(@NonNull Post post) {
+    public Mono<ListedPostVo> convertToListedVo(@NonNull Post post) {
         Assert.notNull(post, "Post must not be null");
         ListedPostVo postVo = ListedPostVo.from(post);
         postVo.setCategories(List.of());
@@ -105,6 +116,53 @@ public Mono<ListedPostVo> convertToListedPostVo(@NonNull Post post) {
             .defaultIfEmpty(postVo);
     }
 
+    @Override
+    public Mono<PostVo> convertToVo(Post post, String snapshotName) {
+        final String postName = post.getMetadata().getName();
+        final String baseSnapshotName = post.getSpec().getBaseSnapshot();
+        return convertToListedVo(post)
+            .map(PostVo::from)
+            .flatMap(postVo -> postService.getContent(snapshotName, baseSnapshotName)
+                .flatMap(wrapper -> extendPostContent(post, wrapper))
+                .doOnNext(postVo::setContent)
+                .thenReturn(postVo)
+            );
+    }
+
+    @Override
+    public Mono<ContentVo> getContent(String postName) {
+        return client.get(Post.class, postName)
+            .filter(FIXED_PREDICATE)
+            .flatMap(post -> {
+                String releaseSnapshot = post.getSpec().getReleaseSnapshot();
+                return postService.getContent(releaseSnapshot, post.getSpec().getBaseSnapshot())
+                    .flatMap(wrapper -> extendPostContent(post, wrapper));
+            });
+    }
+
+    @NonNull
+    protected Mono<ContentVo> extendPostContent(Post post,
+        ContentWrapper wrapper) {
+        Assert.notNull(post, "Post name must not be null");
+        Assert.notNull(wrapper, "Post content must not be null");
+        return extensionGetter.getEnabledExtensionByDefinition(ReactivePostContentHandler.class)
+            .reduce(Mono.fromSupplier(() -> ReactivePostContentHandler.PostContentContext.builder()
+                    .post(post)
+                    .content(wrapper.getContent())
+                    .raw(wrapper.getRaw())
+                    .rawType(wrapper.getRawType())
+                    .build()
+                ),
+                (contentMono, handler) -> contentMono.flatMap(handler::handle)
+            )
+            .flatMap(Function.identity())
+            .map(postContent -> ContentVo.builder()
+                .content(postContent.getContent())
+                .raw(postContent.getRaw())
+                .build()
+            );
+    }
+
     private <T extends ListedPostVo> Mono<StatsVo> populateStats(T postVo) {
         return counterService.getByName(MeterUtils.nameOf(Post.class, postVo.getMetadata()
                 .getName())