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There is a newer version: 2021.12.006
package com.devonfw.cobigen.impl.extension;

import java.util.Collections;
import java.util.Map;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.devonfw.cobigen.api.annotation.Name;
import com.devonfw.cobigen.api.exception.CobiGenRuntimeException;
import com.devonfw.cobigen.api.extension.TextTemplateEngine;
import com.devonfw.cobigen.impl.aop.ProxyFactory;
import com.google.common.collect.Maps;

/**
 * Registry for {@link TextTemplateEngine template engines}.
 */
public class TemplateEngineRegistry {

  /** Logger instance. */
  private static final Logger LOG = LoggerFactory.getLogger(TemplateEngineRegistry.class);

  /**
   * Currently registered {@link TextTemplateEngine}s mapped by their type
   */
  private static Map registeredEngines = Collections
      .synchronizedMap(Maps. newHashMap());

  /**
   * Registers a new {@link TextTemplateEngine template engine}
   *
   * @param  type of the {@link TextTemplateEngine template engine} to be registered
   * @param templateEngine {@link TextTemplateEngine template engine} to be registered
   * @param name of the template engine
   */
  public static  void register(Class templateEngine, String name) {

    try {
      TextTemplateEngine engine = templateEngine.newInstance();
      LOG.info("Register template engine '{}'.", templateEngine.getCanonicalName());

      if (StringUtils.isNotBlank(name)) {
        if (registeredEngines.containsKey(name)) {
          throw new CobiGenRuntimeException("An template engine with name " + name + " has already been registered.");
        }
        registeredEngines.put(name, engine);
      } else {
        throw new CobiGenRuntimeException("Cannot register a template engine without a type.");
      }

    } catch (InstantiationException | IllegalAccessException e) {
      throw new CobiGenRuntimeException("Could not intantiate TemplateEngine '" + templateEngine.getCanonicalName(), e);
    }
  }

  /**
   * Returns a {@link TextTemplateEngine template engine} based on its name.
   *
   * @param name of the {@link TextTemplateEngine template engine}
   * @return the {@link TextTemplateEngine template engine} or {@code null} if no template engine has been registered
   *         with the name.
   */
  public static TextTemplateEngine getEngine(String name) {

    TextTemplateEngine templateEngine = registeredEngines.get(name);
    if (templateEngine == null) {
      for (Class engine : ClassServiceLoader.getTemplateEngineClasses()) {
        if (engine.isAnnotationPresent(Name.class)) {
          Name engineNameAnnotation = engine.getAnnotation(Name.class);
          String engineName = engineNameAnnotation.value();
          if (name.equals(engineName)) {
            register(engine, engineName);
            break;
          }
        } else {
          LOG.warn("Template engine '{}' should have a name specified by @Name annotation.",
              engine.getClass().getCanonicalName());
        }
      }
    }

    templateEngine = registeredEngines.get(name);
    if (templateEngine == null) {
      throw new CobiGenRuntimeException("No template engine with name '" + name + "' registered.");
    }

    return ProxyFactory.getProxy(templateEngine);
  }
}