Automatically-added singletons

The registry can maintain a set of classes that contain annotated
singletons corresponding to the components.

TODO

@@ -3,7 +3,6 @@ To Do:
  * Registry tests
  * Registry doc
  * General usage documentation
- * Automatically-updated singletons
  * Document exceptions
 
 Other ideas (maybe later if needed):

src/main/java/info/ebenoit/ebul/cmp/ComponentRegistry.java

@@ -1,10 +1,13 @@
 package info.ebenoit.ebul.cmp;
 
 
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -34,20 +37,63 @@ public class ComponentRegistry
 
 	}
 
-	private ArrayList< ComponentState > components;
-	private HashMap< String , ComponentState > byName;
-	private HashMap< Class< ? > , ArrayList< ComponentState > > byType;
+	private final class SingletonClass
+	{
+		private final HashSet< Field > missingFields;
+		private final HashSet< Field > setFields;
+
+
+		private SingletonClass( Class< ? > klass )
+		{
+			this.missingFields = new HashSet< >( );
+			this.setFields = new HashSet< >( );
+
+			for ( Field fld : klass.getFields( ) ) {
+				if ( !fld.isAnnotationPresent( ComponentSingleton.class ) ) {
+					continue;
+				}
+				if ( ( fld.getModifiers( ) & Modifier.STATIC ) == 0 ) {
+					throw new ComponentManagementException( "singleton field " + fld.getName( ) + " in class "
+							+ klass.getCanonicalName( ) + " is not static" );
+				}
+				if ( ( fld.getModifiers( ) & Modifier.PUBLIC ) == 0 ) {
+					throw new ComponentManagementException( "singleton field " + fld.getName( ) + " in class "
+							+ klass.getCanonicalName( ) + " is not public" );
+				}
+				if ( ( fld.getModifiers( ) & Modifier.FINAL ) != 0 ) {
+					throw new ComponentManagementException( "singleton field " + fld.getName( ) + " in class "
+							+ klass.getCanonicalName( ) + " is final" );
+				}
+				missingFields.add( fld );
+			}
+		}
+	}
+
+	private final HashMap< Class< ? > , SingletonClass > singletonClasses = new HashMap< >( );
+
+	private ArrayList< ComponentState > components = new ArrayList< >( );
+	private HashMap< String , ComponentState > byName = new HashMap< >( );
+	private HashMap< Class< ? > , ArrayList< ComponentState > > byType = new HashMap< >( );
 
 	private boolean failed;
 	private boolean initialised;
 	private boolean active;
 
 
-	public ComponentRegistry( )
+	public void addSingletonClass( Class< ? > klass )
+			throws ComponentManagementException , AmbiguousComponentException
 	{
-		this.components = new ArrayList< >( );
-		this.byName = new HashMap< >( );
-		this.byType = new HashMap< >( );
+		if ( !this.singletonClasses.containsKey( klass ) ) {
+			SingletonClass info = new SingletonClass( klass );
+			this.fillSingletonFields( info );
+			this.singletonClasses.put( klass , info );
+		}
+	}
+
+
+	public void removeSingletonClass( Class< ? > klass )
+	{
+		this.singletonClasses.remove( klass );
 	}
 
 
@@ -227,6 +273,16 @@ public class ComponentRegistry
 		this.byName = byName;
 		this.byType = byType;
 
+		// Update singleton classes
+		for ( SingletonClass sc : this.singletonClasses.values( ) ) {
+			try {
+				this.fillSingletonFields( sc );
+			} catch ( ComponentManagementException e ) {
+				this.failed = true;
+				throw e;
+			}
+		}
+
 		// Initialise all new components if the registry has been initialised
 		if ( this.initialised ) {
 			for ( int i = nOld ; i < nOld + nAdd ; i++ ) {
@@ -320,6 +376,39 @@ public class ComponentRegistry
 	}
 
 
+	private void fillSingletonFields( SingletonClass info )
+			throws ComponentManagementException , AmbiguousComponentException
+	{
+		HashMap< Field , Object > matches = new HashMap< >( );
+		for ( Field fld : info.missingFields ) {
+			ComponentSingleton cs = fld.getAnnotation( ComponentSingleton.class );
+			ComponentState target;
+			if ( "".equals( cs.value( ) ) ) {
+				target = this.getState( fld.getType( ) );
+			} else {
+				target = this.getState( cs.value( ) );
+			}
+			if ( target != null ) {
+				matches.put( fld , target.getComponent( ) );
+			}
+		}
+
+		if ( matches.isEmpty( ) ) {
+			return;
+		}
+
+		for ( Map.Entry< Field , Object > entry : matches.entrySet( ) ) {
+			try {
+				entry.getKey( ).set( null , entry.getValue( ) );
+			} catch ( IllegalAccessException e ) {
+				throw new ComponentManagementException( "internal error while setting singleton" , e );
+			}
+		}
+		info.setFields.addAll( matches.keySet( ) );
+		info.missingFields.removeAll( matches.keySet( ) );
+	}
+
+
 	private static int resolveNewDependencies( ArrayList< TempBuildRec > adding ,
 			ArrayList< ComponentState > nComponents , HashMap< String , ComponentState > byName ,
 			HashMap< Class< ? > , ArrayList< ComponentState > > byType )

src/main/java/info/ebenoit/ebul/cmp/ComponentSingleton.java

@@ -0,0 +1,27 @@
+package info.ebenoit.ebul.cmp;
+
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+
+
+/**
+ * This annotation can be used to create automatically filled singleton fields that correspond to components. It can
+ * only be used on static, public fields.
+ * <p>
+ * If a string is given, it will be used as the component's name. Otherwise the component to fetch will be determined
+ * using the field's type.
+ *
+ * @author <a href="mailto:ebenoit@ebenoit.info">E. Benoît</a>
+ */
+@Retention( RetentionPolicy.RUNTIME )
+@Target( ElementType.METHOD )
+public @interface ComponentSingleton
+{
+
+	public String value( ) default "";
+
+}