add a tool to generate a properties file from configuration (#1691)

commafeed-server/pom.xml

@@ -115,6 +115,34 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.codehaus.mojo</groupId>
+				<artifactId>exec-maven-plugin</artifactId>
+				<version>3.5.0</version>
+				<dependencies>
+					<dependency>
+						<groupId>io.quarkus</groupId>
+						<artifactId>quarkus-extension-processor</artifactId>
+						<version>${quarkus.version}</version>
+					</dependency>
+				</dependencies>
+				<configuration>
+					<includePluginDependencies>true</includePluginDependencies>
+					<mainClass>com.commafeed.tools.CommaFeedPropertiesGenerator</mainClass>
+					<arguments>
+						<argument>${project.build.directory}</argument>
+					</arguments>
+				</configuration>
+				<executions>
+					<execution>
+						<phase>process-test-resources</phase>
+						<goals>
+							<goal>java</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
+
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-assembly-plugin</artifactId>

commafeed-server/src/main/java/com/commafeed/tools/CommaFeedPropertiesGenerator.java

@@ -0,0 +1,80 @@
+package com.commafeed.tools;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import com.commafeed.CommaFeedConfiguration;
+
+import io.quarkus.annotation.processor.Outputs;
+import io.quarkus.annotation.processor.documentation.config.model.AbstractConfigItem;
+import io.quarkus.annotation.processor.documentation.config.model.ConfigProperty;
+import io.quarkus.annotation.processor.documentation.config.model.ConfigRoot;
+import io.quarkus.annotation.processor.documentation.config.model.ConfigSection;
+import io.quarkus.annotation.processor.documentation.config.model.JavadocElements;
+import io.quarkus.annotation.processor.documentation.config.model.ResolvedModel;
+import io.quarkus.annotation.processor.documentation.config.util.JacksonMappers;
+
+/**
+ * This class generates an application.properties file with all the properties from {@link CommaFeedConfiguration}.
+ *
+ * This is useful for people who want to be able to configure CommaFeed without having to look at the code or the documentation, or for
+ * distribution packages that want to provide a default configuration file.
+ *
+ **/
+public class CommaFeedPropertiesGenerator {
+
+	private final List<String> lines = new ArrayList<>();
+
+	public static void main(String[] args) throws Exception {
+		new CommaFeedPropertiesGenerator().generate(args);
+	}
+
+	private void generate(String[] args) throws IOException {
+		Path targetPath = Paths.get(args[0]);
+
+		ResolvedModel resolvedModel = JacksonMappers.yamlObjectReader()
+				.readValue(targetPath.resolve(Outputs.QUARKUS_CONFIG_DOC_MODEL).toFile(), ResolvedModel.class);
+		JavadocElements javadocElements = JacksonMappers.yamlObjectReader()
+				.readValue(targetPath.resolve(Outputs.QUARKUS_CONFIG_DOC_JAVADOC).toFile(), JavadocElements.class);
+
+		for (ConfigRoot configRoot : resolvedModel.getConfigRoots()) {
+			for (AbstractConfigItem item : configRoot.getItems()) {
+				handleAbstractConfigItem(item, javadocElements);
+			}
+		}
+
+		Files.writeString(targetPath.resolve("quarkus-generated-doc").resolve("application.properties"), String.join("\n", lines));
+	}
+
+	private void handleAbstractConfigItem(AbstractConfigItem item, JavadocElements javadocElements) {
+		if (item.isSection()) {
+			handleSection((ConfigSection) item, javadocElements);
+		} else {
+			handleProperty((ConfigProperty) item, javadocElements);
+		}
+	}
+
+	private void handleSection(ConfigSection section, JavadocElements javadocElements) {
+		for (AbstractConfigItem item : section.getItems()) {
+			handleAbstractConfigItem(item, javadocElements);
+		}
+	}
+
+	private void handleProperty(ConfigProperty property, JavadocElements javadocElements) {
+		String key = property.getPath().property();
+		String description = javadocElements.elements()
+				.get(property.getSourceType() + "." + property.getSourceElementName())
+				.description()
+				.replace("\n", "\n# ");
+		String defaultValue = Optional.ofNullable(property.getDefaultValue()).orElse("").toLowerCase();
+
+		lines.add("# " + description);
+		lines.add(key + "=" + defaultValue);
+		lines.add("");
+	}
+}