refactor: fill in the name of the rendered template as the template id to the view model (#2626)

#### What type of PR is this?
/kind improvement
/area core
/milestone 2.0

#### What this PR does / why we need it:
渲染模板页面时将被渲染的模板名称填充到试图模型中作为 templateId
为什么需要它：
1. thymeleaf 渲染模板可以使用 fragment，此时在 thymeleaf 的 IElementTagProcessor 等处理器中获取到的 template name不一定是例如 post.html这样的名称
2. 比如渲染文章模板 post.html 而 #2569 计划将要在 theme.yaml 中通过配置允许用户选择文章所渲染的模板，因为无法确定渲染模板的标志，例如有些处理器想在文章页插入 head 这样的需求就需要知道哪个模板是文章页。see also [issuecomment-1215135195](https://github.com/halo-dev/halo/issues/2322#issuecomment-1215135195)
所以目前想到的是通过在 render 时填充一个 templateId 到 view model 中标识模板身份
#### Which issue(s) this PR fixes:

Fixes #2621

#### Special notes for your reviewer:
how to test it?
见 issue #2621

/cc @halo-dev/sig-halo 
#### Does this PR introduce a user-facing change?

```release-note
修复设置了文章的 htmlMetas 字段但没有在页面的 head 注入标签的问题
```

src/main/java/run/halo/app/theme/dialect/PostTemplateHeadProcessor.java

@@ -11,6 +11,7 @@ import org.thymeleaf.processor.element.IElementModelStructureHandler;
 import reactor.core.publisher.Mono;
 import run.halo.app.theme.DefaultTemplateEnum;
 import run.halo.app.theme.finders.PostFinder;
+import run.halo.app.theme.router.strategy.ModelConst;
 
 /**
  * <p>The <code>head</code> html snippet injection processor for post template.</p>
@@ -31,9 +32,10 @@ public class PostTemplateHeadProcessor implements TemplateHeadProcessor {
     @Override
     public Mono<Void> process(ITemplateContext context, IModel model,
         IElementModelStructureHandler structureHandler) {
-        return Mono.just(context.getTemplateData().getTemplate())
+        if (!isPostTemplate(context)) {
-            .filter(this::isPostTemplate)
+            return Mono.empty();
-            .map(template -> (String) context.getVariable(POST_NAME_VARIABLE))
+        }
+        return Mono.justOrEmpty((String) context.getVariable(POST_NAME_VARIABLE))
             .map(postFinder::getByName)
             .doOnNext(postVo -> {
                 List<Map<String, String>> htmlMetas = postVo.getSpec().getHtmlMetas();
@@ -59,7 +61,8 @@ public class PostTemplateHeadProcessor implements TemplateHeadProcessor {
         return sb.toString();
     }
 
-    private boolean isPostTemplate(String template) {
+    private boolean isPostTemplate(ITemplateContext context) {
-        return DefaultTemplateEnum.POST.getValue().equals(template);
+        return DefaultTemplateEnum.POST.getValue()
+            .equals(context.getVariable(ModelConst.TEMPLATE_ID));
     }
 }

src/main/java/run/halo/app/theme/dialect/TemplateGlobalHeadProcessor.java

@@ -10,6 +10,7 @@ import reactor.core.publisher.Mono;
 import run.halo.app.infra.SystemConfigurableEnvironmentFetcher;
 import run.halo.app.infra.SystemSetting;
 import run.halo.app.theme.DefaultTemplateEnum;
+import run.halo.app.theme.router.strategy.ModelConst;
 
 /**
  * <p>Global custom head snippet injection for theme global setting.</p>
@@ -39,8 +40,7 @@ public class TemplateGlobalHeadProcessor implements TemplateHeadProcessor {
 
                 // add content head to model
                 String contentHeader = codeInjection.getContentHead();
-                String template = context.getTemplateData().getTemplate();
+                if (StringUtils.isNotBlank(contentHeader) && isContentTemplate(context)) {
-                if (StringUtils.isNotBlank(contentHeader) && isContentTemplate(template)) {
                     model.add(modelFactory.createText(contentHeader + "\n"));
                 }
             })
@@ -51,8 +51,9 @@ public class TemplateGlobalHeadProcessor implements TemplateHeadProcessor {
         return fetcher.fetch(SystemSetting.CodeInjection.GROUP, SystemSetting.CodeInjection.class);
     }
 
-    private boolean isContentTemplate(String template) {
+    private boolean isContentTemplate(ITemplateContext context) {
-        // TODO includes custom page template
+        String templateId = (String) context.getVariable(ModelConst.TEMPLATE_ID);
-        return DefaultTemplateEnum.POST.getValue().equals(template);
+        return DefaultTemplateEnum.POST.getValue().equals(templateId)
+            || DefaultTemplateEnum.SINGLE_PAGE.getValue().equals(templateId);
     }
 }

src/main/java/run/halo/app/theme/router/strategy/CategoriesRouteStrategy.java

@@ -36,7 +36,8 @@ public class CategoriesRouteStrategy implements ListPageRouteHandlerStrategy {
     public HandlerFunction<ServerResponse> getHandler() {
         return request -> ServerResponse.ok()
             .render(DefaultTemplateEnum.CATEGORIES.getValue(),
-                Map.of("categories", categories()));
+                Map.of("categories", categories(),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.CATEGORIES.getValue()));
     }
 
     @Override

src/main/java/run/halo/app/theme/router/strategy/CategoryRouteStrategy.java

@@ -65,7 +65,8 @@ public class CategoryRouteStrategy implements DetailsPageRouteHandlerStrategy {
             .render(DefaultTemplateEnum.CATEGORY.getValue(),
                 Map.of("name", name,
                     "posts", postListByCategoryName(name, request),
-                    "category", categoryByName(name)));
+                    "category", categoryByName(name),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.CATEGORY.getValue()));
     }
 
     @Override

src/main/java/run/halo/app/theme/router/strategy/IndexRouteStrategy.java

@@ -48,7 +48,8 @@ public class IndexRouteStrategy implements ListPageRouteHandlerStrategy {
     public HandlerFunction<ServerResponse> getHandler() {
         return request -> ServerResponse.ok()
             .render(DefaultTemplateEnum.INDEX.getValue(),
-                Map.of("posts", postList(request)));
+                Map.of("posts", postList(request),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.INDEX.getValue()));
     }
 
     @Override

src/main/java/run/halo/app/theme/router/strategy/ModelConst.java

@@ -0,0 +1,12 @@
+package run.halo.app.theme.router.strategy;
+
+/**
+ * Static variable keys for view model.
+ *
+ * @author guqing
+ * @since 2.0.0
+ */
+public enum ModelConst {
+    ;
+    public static final String TEMPLATE_ID = "_templateId";
+}

src/main/java/run/halo/app/theme/router/strategy/PermalinkPredicates.java

@@ -1,17 +0,0 @@
-package run.halo.app.theme.router.strategy;
-
-import static java.nio.charset.StandardCharsets.UTF_8;
-import static org.springframework.web.reactive.function.server.RequestPredicates.method;
-import static org.springframework.web.reactive.function.server.RequestPredicates.path;
-
-import org.springframework.http.HttpMethod;
-import org.springframework.web.reactive.function.server.RequestPredicate;
-import org.springframework.web.util.UriUtils;
-
-public enum PermalinkPredicates {
-    ;
-
-    public static RequestPredicate get(String permalink) {
-        return method(HttpMethod.GET).and(path(UriUtils.decode(permalink, UTF_8)));
-    }
-}

src/main/java/run/halo/app/theme/router/strategy/PostRouteStrategy.java

@@ -50,8 +50,12 @@ public class PostRouteStrategy implements DetailsPageRouteHandlerStrategy {
                 model.putAll(pathMatchInfo.getUriVariables());
             }
             model.put("post", postByName(name));
+            // used by HaloTrackerProcessor
             model.put("groupVersionKind", groupVersionKind);
             model.put("plural", gvk.plural());
+            // used by TemplateGlobalHeadProcessor and PostTemplateHeadProcessor
+            model.put(ModelConst.TEMPLATE_ID, DefaultTemplateEnum.POST.getValue());
+
             return ServerResponse.ok()
                 .render(DefaultTemplateEnum.POST.getValue(), model);
         };

src/main/java/run/halo/app/theme/router/strategy/SinglePageRouteStrategy.java

@@ -48,7 +48,10 @@ public class SinglePageRouteStrategy implements DetailsPageRouteHandlerStrategy
                 Map.of("name", name,
                     "groupVersionKind", gvk,
                     "plural", getPlural(),
-                    "singlePage", singlePageByName(name)));
+                    "singlePage", singlePageByName(name),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.SINGLE_PAGE.getValue()
+                )
+            );
     }
 
     @Override

src/main/java/run/halo/app/theme/router/strategy/TagRouteStrategy.java

@@ -65,7 +65,9 @@ public class TagRouteStrategy implements DetailsPageRouteHandlerStrategy {
             .render(DefaultTemplateEnum.TAG.getValue(),
                 Map.of("name", name,
                     "posts", postList(request, name),
-                    "tag", tagByName(name))
+                    "tag", tagByName(name),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.TAG.getValue()
+                )
             );
     }
 

src/main/java/run/halo/app/theme/router/strategy/TagsRouteStrategy.java

@@ -37,7 +37,10 @@ public class TagsRouteStrategy implements ListPageRouteHandlerStrategy {
     public HandlerFunction<ServerResponse> getHandler() {
         return request -> ServerResponse.ok()
             .render(DefaultTemplateEnum.TAGS.getValue(),
-                Map.of("tags", tags()));
+                Map.of("tags", tags(),
+                    ModelConst.TEMPLATE_ID, DefaultTemplateEnum.TAGS.getValue()
+                )
+            );
     }
 
     @Override

src/test/java/run/halo/app/theme/dialect/HaloProcessorDialectTest.java

@@ -34,6 +34,7 @@ import run.halo.app.plugin.ExtensionComponentsFinder;
 import run.halo.app.theme.DefaultTemplateEnum;
 import run.halo.app.theme.finders.PostFinder;
 import run.halo.app.theme.finders.vo.PostVo;
+import run.halo.app.theme.router.strategy.ModelConst;
 
 /**
  * Tests for {@link HaloProcessorDialect}.
@@ -128,6 +129,8 @@ class HaloProcessorDialectTest {
     void contentHeadAndFooterAndPostProcessors() {
         Context context = getContext();
         context.setVariable("name", "fake-post");
+        // template id flag is used by TemplateGlobalHeadProcessor
+        context.setVariable(ModelConst.TEMPLATE_ID, DefaultTemplateEnum.POST.getValue());
 
         List<Map<String, String>> htmlMetas = new ArrayList<>();
         htmlMetas.add(ImmutableSortedMap.of("name", "post-meta-V1", "content", "post-meta-V1"));