package org.gcube.common.scope.impl;

import java.util.Set;

import org.gcube.common.scope.api.DefaultScopeProvider;
import org.gcube.common.scope.api.ScopeProvider;
import org.reflections.Reflections;
import org.reflections.scanners.SubTypesScanner;
import org.reflections.util.ClasspathHelper;
import org.reflections.util.ConfigurationBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Scans the classpath for a {@link ScopeProvider} implementation.
 * <p>
 * Returns a shared {@link DefaultScopeProvider} by default.
 * 
 * @author Fabio Simeoni
 * @see ScopeProvider
 * @see ScopeProvider#instance
 */
public class ScopeProviderScanner {

	private static Logger log = LoggerFactory.getLogger(ScopeProviderScanner.class);
	
	/**
	 * Returns the configured provider. 
	 * @return the provider
	 */
	public static ScopeProvider provider() {
		try {

			// we include urls specified in manifest files, which is required
			// when we run tests in surefire's forked-mode
			ConfigurationBuilder builder = new ConfigurationBuilder().setUrls(
					ClasspathHelper.forManifest(Utils.urlsToScan())).setScanners(new SubTypesScanner());

			Reflections reflections = new Reflections(builder);

			 Set<Class<? extends ScopeProvider>> impls = 
		               reflections.getSubTypesOf(ScopeProvider.class);
			 
			 ScopeProvider defaultProvider = null;
			 
			 for (Class<? extends ScopeProvider> impl : impls)
				 if (impl.isAnnotationPresent(DefaultScopeProvider.class))
					if (defaultProvider==null) 
						defaultProvider = impl.newInstance();
					else
						throw new Exception("mis-configured environment: detected multiple deafult providers among "+impls);
			
			 if (defaultProvider==null) {
				 log.info("using default scope provider");
				 defaultProvider = new DefaultScopeProviderImpl();
			 }
			 
			 return defaultProvider;
			   
			
		} catch (Exception e) {
			throw new RuntimeException("could not configure scope provider", e);
		}
	}


	
}