codegen/core/src/main/java/org/jclouds/codegen/util/CodeGenerator.java

/**
 *
 * Copyright (C) 2009 Cloud Conscious, LLC. <info@cloudconscious.com>
 *
 * ====================================================================
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * ====================================================================
 */
package org.jclouds.codegen.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.HashMap;
import java.util.Map;

import org.jclouds.codegen.model.API;
import org.jclouds.codegen.model.Command;
import org.jclouds.codegen.model.DomainType;
import org.jclouds.codegen.model.Package;
import org.jclouds.codegen.model.Type;

import com.google.gson.Gson;
import com.google.gson.JsonParseException;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;

/**
 * Converts object models representing AWS API beans into Java classes.
 * <p>
 * This implementation is designed to perform the following steps:
 * <ul>
 * <li>Parse the JSON object representation produced by the <tt>parse_ec2.pl</tt> perl script</li>
 * <li>Convert the JSON into Java object models (@see org.jclouds.aws.codegen.models)</li>
 * <li>Iterate through the Command objects generated above and with each one:
 * <ul>
 * <li>Load the <a href="http://freemarker.org/">FreeMarker</a>template file for the given object</li>
 * <li>Create a package directory to receive the Java file, if necessary</li>
 * <li>Process the object through the template, producing a Java implementation of the object</li>
 * <ul></li>
 * 
 * @author James Murty
 */
public class CodeGenerator {
   public final static String COMMAND_TEMPLATE_FILENAME = "Command.ftl";
   public final static String BEAN_TEMPLATE_FILENAME = "Bean.ftl";
   public final static String OPTIONS_TEMPLATE_FILENAME = "Options.ftl";
   public final static String VALUE_TEMPLATE_FILENAME = "Value.ftl";
   public final static String RESPONSE_TEMPLATE_FILENAME = "Response.ftl";

   private final File targetDirectory;
   private final String rootPackageName;
   private final Configuration config;

   public CodeGenerator(String rootPackageName, File targetDirectory) throws IOException {
      this.rootPackageName = rootPackageName;
      this.targetDirectory = targetDirectory;

      config = new Configuration();
      config.setClassForTemplateLoading(this.getClass(), "/templates");
   }

   /**
    * Parse a JSON object model file (as generated by <tt>aws/src/main/bin/parse_ec2.pl</tt>) and
    * convert it into a Java object graph.
    * 
    * @param objectModelFile
    * @return
    * @throws JsonParseException
    * @throws FileNotFoundException
    */
   public API parseModelFromJSON(File objectModelFile) throws JsonParseException,
            FileNotFoundException {
      Gson gson = new Gson();
      return gson.fromJson(new FileReader(objectModelFile), API.class);
   }

   /**
    * Parse a JSON object model file and iterate over the resulting objects generating Java code
    * files.
    * 
    * @param objectModelFile
    * @throws JsonParseException
    * @throws IOException
    * @throws TemplateException
    */
   public void generateCode(File objectModelFile) throws JsonParseException, IOException,
            TemplateException {
      API model = parseModelFromJSON(objectModelFile);

      for (Package pkg : model.getPackages()) {
         for (Command command : pkg.getCommands()) {
            generateClassFile(command, COMMAND_TEMPLATE_FILENAME);

            if (command.getHandler() != null) {
               generateClassFile(command.getHandler(), BEAN_TEMPLATE_FILENAME);
            }
            if (command.getOptions() != null
                     && command.getOptions().getJavaName().indexOf(
                              "BaseEC2RequestOptions<EC2RequestOptions>") == -1) {
               generateClassFile(command.getOptions(), OPTIONS_TEMPLATE_FILENAME);
            }
            if (command.getResponse() != null
                     && !command.getResponse().getJavaName().equals("Boolean")) {
               generateClassFile(command.getResponse(), RESPONSE_TEMPLATE_FILENAME);
            }
         }
      }
      for (DomainType value : model.getDomain().values()) {
         generateClassFile(value, VALUE_TEMPLATE_FILENAME);
      }

   }

   /**
    * Generate a Java code file for the given object model bean, using the given template name as
    * the basis for the Java class.
    * 
    * @param bean
    * @param templateFileName
    * @throws IOException
    * @throws TemplateException
    */
   public void generateClassFile(Type bean, String templateFileName) throws IOException,
            TemplateException {
      String shortClassName = bean.getJavaName().substring(
               bean.getJavaName().lastIndexOf('.') + 1);

      Map<String, Object> objectMap = new HashMap<String, Object>();
      objectMap.put("bean", bean);
      objectMap.put("rootPackageName", this.rootPackageName);
      objectMap.put("shortClassName", shortClassName);

      File packageDir = new File(this.targetDirectory, bean.getPackageName().replace('.', '/'));

      if (packageDir.exists() || packageDir.mkdirs()) {
         File javaFile = new File(packageDir, shortClassName + ".java");
         FileWriter fw = new FileWriter(javaFile);
         System.out.println("Generated " + javaFile);
         applyTemplate(templateFileName, objectMap, fw);
      } else {
         throw new IllegalStateException("Unable to create target package directory: " + packageDir);
      }
   }

   /**
    * Apply the given template to the given object, and output the results into the given writer.
    * 
    * @param templateFileName
    * @param objectMap
    * @param writer
    * @throws IOException
    * @throws TemplateException
    */
   public void applyTemplate(String templateFileName, Map<String, Object> objectMap, Writer writer)
            throws IOException, TemplateException {
      Template template = this.config.getTemplate(templateFileName, "UTF-8");
      template.process(objectMap, writer);
   }

   public static void main(String[] args) throws Exception {
      if (args.length != 3) {
         System.out.println("Usage: CodeGenerator objectModelFile rootPackage targetDir");
         System.out.println("  E.g: CodeGenerator ec2.json org.jclouds.aws.ec2 aws/ec2/api/src");
         System.exit(1);
      }
      File objectModelFile = new File(args[0]);

      String rootPackage = args[1];

      File targetDir = new File(args[2]);

      new CodeGenerator(rootPackage, targetDir).generateCode(objectModelFile);
   }

}