feat: theme templates support global seo settings (#2801)

#### What type of PR is this?
/kind improvement
/area core
/milestone 2.0.0-rc.2

#### What this PR does / why we need it:
适配 SEO 系统设置，此功能之前遗漏

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

Fixes #2797

#### Special notes for your reviewer:
how to test it?
1. seo 设置禁用搜索引擎，会在所有页面的 head 添加 `<meta name="robots" content="noindex" />`
2. seo 设置填写`关键词`和`描述`会在所有页面的 head 标签填充 `<meta name="xxx> content="xxx" />` 

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

```release-note
支持 SEO 全局系统设置
```

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

@@ -2,6 +2,7 @@ package run.halo.app.theme.dialect;
 
 import java.util.List;
 import java.util.Map;
+import lombok.AllArgsConstructor;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.stereotype.Component;
 import org.thymeleaf.context.ITemplateContext;
@@ -11,34 +12,39 @@ 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.finders.SinglePageFinder;
 import run.halo.app.theme.router.strategy.ModelConst;
 
 /**
- * <p>The <code>head</code> html snippet injection processor for post template.</p>
+ * <p>The <code>head</code> html snippet injection processor for content template such as post
+ * and page.</p>
  *
  * @author guqing
  * @since 2.0.0
  */
 @Component
-public class PostTemplateHeadProcessor implements TemplateHeadProcessor {
+@AllArgsConstructor
+public class ContentTemplateHeadProcessor implements TemplateHeadProcessor {
     private static final String POST_NAME_VARIABLE = "name";
     private final PostFinder postFinder;
-
-
-    public PostTemplateHeadProcessor(PostFinder postFinder) {
-        this.postFinder = postFinder;
-    }
+    private final SinglePageFinder singlePageFinder;
 
     @Override
     public Mono<Void> process(ITemplateContext context, IModel model,
         IElementModelStructureHandler structureHandler) {
-        if (!isPostTemplate(context)) {
-            return Mono.empty();
+        Mono<String> nameMono = Mono.justOrEmpty((String) context.getVariable(POST_NAME_VARIABLE));
+
+        Mono<List<Map<String, String>>> htmlMetasMono = Mono.empty();
+        if (isPostTemplate(context)) {
+            htmlMetasMono = nameMono.flatMap(postFinder::getByName)
+                .map(post -> post.getSpec().getHtmlMetas());
+        } else if (isPageTemplate(context)) {
+            htmlMetasMono = nameMono.flatMap(singlePageFinder::getByName)
+                .map(page -> page.getSpec().getHtmlMetas());
         }
-        return Mono.justOrEmpty((String) context.getVariable(POST_NAME_VARIABLE))
-            .flatMap(postFinder::getByName)
-            .doOnNext(postVo -> {
-                List<Map<String, String>> htmlMetas = postVo.getSpec().getHtmlMetas();
+
+        return htmlMetasMono
+            .doOnNext(htmlMetas -> {
                 String metaHtml = headMetaBuilder(htmlMetas);
                 IModelFactory modelFactory = context.getModelFactory();
                 model.add(modelFactory.createText(metaHtml));
@@ -65,4 +71,9 @@ public class PostTemplateHeadProcessor implements TemplateHeadProcessor {
         return DefaultTemplateEnum.POST.getValue()
             .equals(context.getVariable(ModelConst.TEMPLATE_ID));
     }
+
+    private boolean isPageTemplate(ITemplateContext context) {
+        return DefaultTemplateEnum.SINGLE_PAGE.getValue()
+            .equals(context.getVariable(ModelConst.TEMPLATE_ID));
+    }
 }

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

@@ -0,0 +1,59 @@
+package run.halo.app.theme.dialect;
+
+import lombok.AllArgsConstructor;
+import org.apache.commons.lang3.BooleanUtils;
+import org.apache.commons.lang3.StringUtils;
+import org.springframework.core.annotation.Order;
+import org.springframework.stereotype.Component;
+import org.thymeleaf.context.ITemplateContext;
+import org.thymeleaf.model.IModel;
+import org.thymeleaf.model.IModelFactory;
+import org.thymeleaf.processor.element.IElementModelStructureHandler;
+import reactor.core.publisher.Mono;
+import run.halo.app.infra.SystemConfigurableEnvironmentFetcher;
+import run.halo.app.infra.SystemSetting;
+
+/**
+ * Inject code to the template head tag according to the global seo settings.
+ *
+ * @author guqing
+ * @see SystemSetting.Seo
+ * @since 2.0.0
+ */
+@Order
+@Component
+@AllArgsConstructor
+public class GlobalSeoProcessor implements TemplateHeadProcessor {
+
+    private final SystemConfigurableEnvironmentFetcher environmentFetcher;
+
+    @Override
+    public Mono<Void> process(ITemplateContext context, IModel model,
+        IElementModelStructureHandler structureHandler) {
+        return environmentFetcher.fetch(SystemSetting.Seo.GROUP, SystemSetting.Seo.class)
+            .map(seo -> {
+                boolean blockSpiders = BooleanUtils.isTrue(seo.getBlockSpiders());
+                IModelFactory modelFactory = context.getModelFactory();
+                if (blockSpiders) {
+                    String noIndexMeta = "<meta name=\"robots\" content=\"noindex\" />\n";
+                    model.add(modelFactory.createText(noIndexMeta));
+                    return model;
+                }
+
+                String keywords = seo.getKeywords();
+                if (StringUtils.isNotBlank(keywords)) {
+                    String keywordsMeta =
+                        "<meta name=\"keywords\" content=\"" + keywords + "\" />\n";
+                    model.add(modelFactory.createText(keywordsMeta));
+                }
+
+                if (StringUtils.isNotBlank(seo.getDescription())) {
+                    String descriptionMeta =
+                        "<meta name=\"description\" content=\"" + seo.getDescription() + "\" />\n";
+                    model.add(modelFactory.createText(descriptionMeta));
+                }
+                return model;
+            })
+            .then();
+    }
+}

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

@@ -33,6 +33,7 @@ import run.halo.app.infra.SystemSetting;
 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.SinglePageFinder;
 import run.halo.app.theme.finders.vo.PostVo;
 import run.halo.app.theme.router.strategy.ModelConst;
 
@@ -42,7 +43,7 @@ import run.halo.app.theme.router.strategy.ModelConst;
  * @author guqing
  * @see HaloProcessorDialect
  * @see GlobalHeadInjectionProcessor
- * @see PostTemplateHeadProcessor
+ * @see ContentTemplateHeadProcessor
  * @see TemplateHeadProcessor
  * @see TemplateGlobalHeadProcessor
  * @see TemplateFooterElementTagProcessor
@@ -56,6 +57,9 @@ class HaloProcessorDialectTest {
     @Mock
     private PostFinder postFinder;
 
+    @Mock
+    private SinglePageFinder singlePageFinder;
+
     @Mock
     private SystemConfigurableEnvironmentFetcher fetcher;
 
@@ -72,9 +76,11 @@ class HaloProcessorDialectTest {
         templateEngine.addTemplateResolver(new TestTemplateResolver());
 
         Map<String, TemplateHeadProcessor> map = new HashMap<>();
-        map.put("postTemplateHeadProcessor", new PostTemplateHeadProcessor(postFinder));
+        map.put("postTemplateHeadProcessor",
+            new ContentTemplateHeadProcessor(postFinder, singlePageFinder));
         map.put("templateGlobalHeadProcessor", new TemplateGlobalHeadProcessor(fetcher));
         map.put("faviconHeadProcessor", new DefaultFaviconHeadProcessor(fetcher));
+        map.put("globalSeoProcessor", new GlobalSeoProcessor(fetcher));
         lenient().when(applicationContext.getBeansOfType(eq(TemplateHeadProcessor.class)))
             .thenReturn(map);
 
@@ -85,8 +91,10 @@ class HaloProcessorDialectTest {
         when(fetcher.fetch(eq(SystemSetting.CodeInjection.GROUP),
             eq(SystemSetting.CodeInjection.class))).thenReturn(Mono.just(codeInjection));
 
-        when(applicationContext.getBean(eq(SystemConfigurableEnvironmentFetcher.class)))
+        lenient().when(applicationContext.getBean(eq(SystemConfigurableEnvironmentFetcher.class)))
             .thenReturn(fetcher);
+        lenient().when(fetcher.fetch(eq(SystemSetting.Seo.GROUP),
+            eq(SystemSetting.Seo.class))).thenReturn(Mono.empty());
 
         when(applicationContext.getBean(eq(ExtensionComponentsFinder.class)))
             .thenReturn(extensionComponentsFinder);
@@ -172,6 +180,68 @@ class HaloProcessorDialectTest {
             """);
     }
 
+    @Test
+    void blockSeo() {
+        final Context context = getContext();
+        SystemSetting.Seo seo = new SystemSetting.Seo();
+        seo.setBlockSpiders(true);
+        when(fetcher.fetch(eq(SystemSetting.Seo.GROUP),
+            eq(SystemSetting.Seo.class))).thenReturn(Mono.just(seo));
+        SystemSetting.Basic basic = new SystemSetting.Basic();
+        basic.setFavicon("favicon.ico");
+        when(fetcher.fetch(eq(SystemSetting.Basic.GROUP),
+            eq(SystemSetting.Basic.class))).thenReturn(Mono.just(basic));
+
+        String result = templateEngine.process("seo", context);
+        assertThat(result).isEqualTo("""
+            <!DOCTYPE html>
+            <html lang="en">
+              <head>
+                <meta charset="UTF-8" />
+                <title>Seo Test</title>
+              <meta name="global-head-test" content="test" />
+            <link rel="icon" href="favicon.ico" />
+            <meta name="robots" content="noindex" />
+            </head>
+              <body>
+                seo setting test.
+              </body>
+            </html>
+            """);
+    }
+
+    @Test
+    void seoWithKeywordsAndDescription() {
+        final Context context = getContext();
+        SystemSetting.Seo seo = new SystemSetting.Seo();
+        seo.setKeywords("K1, K2, K3");
+        seo.setDescription("This is a description.");
+        when(fetcher.fetch(eq(SystemSetting.Seo.GROUP),
+            eq(SystemSetting.Seo.class))).thenReturn(Mono.just(seo));
+        SystemSetting.Basic basic = new SystemSetting.Basic();
+        basic.setFavicon("favicon.ico");
+        when(fetcher.fetch(eq(SystemSetting.Basic.GROUP),
+            eq(SystemSetting.Basic.class))).thenReturn(Mono.just(basic));
+
+        String result = templateEngine.process("seo", context);
+        assertThat(result).isEqualTo("""
+            <!DOCTYPE html>
+            <html lang="en">
+              <head>
+                <meta charset="UTF-8" />
+                <title>Seo Test</title>
+              <meta name="global-head-test" content="test" />
+            <link rel="icon" href="favicon.ico" />
+            <meta name="keywords" content="K1, K2, K3" />
+            <meta name="description" content="This is a description." />
+            </head>
+              <body>
+                seo setting test.
+              </body>
+            </html>
+            """);
+    }
+
     private Context getContext() {
         Context context = new Context();
         context.setVariable(
@@ -192,6 +262,10 @@ class HaloProcessorDialectTest {
             if (template.equals(DefaultTemplateEnum.POST.getValue())) {
                 return new StringTemplateResource(postTemplate());
             }
+
+            if (template.equals("seo")) {
+                return new StringTemplateResource(seoTemplate());
+            }
             return null;
         }
 
@@ -227,5 +301,20 @@ class HaloProcessorDialectTest {
                 </html>
                 """;
         }
+
+        private String seoTemplate() {
+            return """
+                <!DOCTYPE html>
+                <html lang="en" xmlns:th="http://www.thymeleaf.org">
+                  <head>
+                    <meta charset="UTF-8" />
+                    <title>Seo Test</title>
+                  </head>
+                  <body>
+                    seo setting test.
+                  </body>
+                </html>
+                """;
+        }
     }
 }