package liquibase.precondition;

 import liquibase.exception.UnexpectedLiquibaseException;

 import liquibase.servicelocator.ServiceLocator;

 import java.util.HashMap;

 import java.util.Map;

 public class PreconditionFactory {

     @SuppressWarnings("unchecked")

     private final Map<String, Class<? extends Precondition>> preconditions;

     private static PreconditionFactory instance;

     @SuppressWarnings("unchecked")

     private PreconditionFactory() {

         preconditions = new HashMap<String, Class<? extends Precondition>>();

         Class[] classes;

         try {

             classes = ServiceLocator.getInstance().findClasses(Precondition.class);

             for (Class<? extends Precondition> clazz : classes) {

                 register(clazz);

             }

         } catch (Exception e) {

             throw new UnexpectedLiquibaseException(e);

         }

     }

     public static PreconditionFactory getInstance() {

         if (instance == null) {

             instance = new PreconditionFactory();

         }

         return instance;

     }

     public static void reset() {

         instance = new PreconditionFactory();

     }

     public Map<String, Class<? extends Precondition>> getPreconditions() {

         return preconditions;

     }

     public void register(Class<? extends Precondition> clazz) {

         try {

             preconditions.put(clazz.newInstance().getName(), clazz);

         } catch (Exception e) {

             throw new UnexpectedLiquibaseException(e);

         }

     }

     public void unregister(String name) {

         preconditions.remove(name);

     }

     /**

      * Create a new Precondition subclass based on the given tag name.

      */

     public Precondition create(String tagName) {

         Class<?> aClass = preconditions.get(tagName);

         if (aClass == null) {

             throw new UnexpectedLiquibaseException("Unknown tag: " + tagName);

         }

         try {

             return (Precondition) aClass.newInstance();

         } catch (Exception e) {

             throw new RuntimeException(e);

         }

     }

 }