package cz.cuni.amis.utils.configuration;
   
   import java.util.Collections;
   import java.util.HashSet;
   import java.util.LinkedList;
   import java.util.List;
   import java.util.ServiceLoader;
   import java.util.Set;
   import java.util.logging.Handler;
  import java.util.logging.Level;
  import java.util.logging.LogRecord;
  import java.util.logging.Logger;
  
  import cz.cuni.amis.utils.exception.PogamutException;
  import cz.cuni.amis.utils.logging.DefaultLogFormatter;
  
  /**
   * Root object for obtaining property values. Properties are obtained from a chain
   * of PropertyProviders. PropertyProviders are loaded through SPI.
   * @author ik
   */
  public class PropertiesManager {
  
      Logger log = Logger.getLogger("PropertiesManager");
      private List<PropertyProvider> providers = null;
      
      public PropertiesManager() {
      	log.addHandler(new Handler() {
      		
      		DefaultLogFormatter logFormatter = new DefaultLogFormatter("Platform", false);
  
  			@Override
  			public void close() throws SecurityException {
  			}
  
  			@Override
  			public void flush() {
  			}
  
  			@Override
  			public void publish(LogRecord record) {
  				System.out.println(logFormatter.format(record));
  			}
      		
      	});
      	log.setLevel(Level.INFO);
      	log.info("Instantiated");
      }
  
      protected List<PropertyProvider> getProvidersList() {
          try {
          	if (providers == null) {
  	            providers = new LinkedList<PropertyProvider>();
  	            ServiceLoader<PropertyProvider> loader = ServiceLoader.load(PropertyProvider.class);
  	            Set<Class> loaded = new HashSet<Class>();
  	            for (PropertyProvider provider : loader) {
  	            	if (loaded.contains(provider.getClass())) {
  	            		if (log.isLoggable(Level.WARNING)) log.warning("Attempt to register PropertyProvider of class " + provider.getClass() + " twice, ignoring.");
  	            	} else {
  	            		providers.add(provider);
  	            		loaded.add(provider.getClass());
  	            	}
  	            }
  	            Collections.sort(providers);
  	            
  	            logProvidersOrder();
  	        }
          } catch (Exception e) {
          	throw new PogamutException("Could not initialize PropertiesManager: " + e.getMessage(), e, log, this);
          }
          return providers;
      }
  
      protected void logProvidersOrder() {
          if (log.isLoggable(Level.INFO)) log.info("Property providers order:");
          if (getProvidersList() != null && getProvidersList().size() != 0) {
  	        for (PropertyProvider provider : getProvidersList()) {
  	            String str = "[" + provider.getPriority() + "] \t " + provider.toString();
  	            if (log.isLoggable(Level.INFO)) log.info(str);
  	        }
          } else {
          	if (log.isLoggable(Level.WARNING)) log.warning("There are no PropertyProvider(s) registered inside PropertiesManager! No properties will be available!");
          }
      }
  
      /**
       * Returns property for given key.
       * Asks property providers ordered by their priority. When first of them
       * returns a value then it will be returned and later providers wont be asked.
       * @param key
       * @return null if the property value wasn't found
       */
      public String getProperty(String key) {
          for (PropertyProvider provider : getProvidersList()) {
              String val = provider.getProperty(key);
              if (val != null) {
                  if (log.isLoggable(Level.FINEST)) log.finest("Property " + key + " was loaded from " + provider.toString() + ".");
                  return val;
              }
         }
         return null;
     }
 }