/* 
 * Copyright (c) 2008 Stiftung Deutsches Elektronen-Synchrotron, 
 * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY.
 *
 * THIS SOFTWARE IS PROVIDED UNDER THIS LICENSE ON AN "../AS IS" BASIS. 
 * WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND 
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE 
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. SHOULD THE SOFTWARE PROVE DEFECTIVE 
 * IN ANY RESPECT, THE USER ASSUMES THE COST OF ANY NECESSARY SERVICING, REPAIR OR 
 * CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. 
 * NO USE OF ANY SOFTWARE IS AUTHORIZED HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
 * DESY HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, 
 * OR MODIFICATIONS.
 * THE FULL LICENSE SPECIFYING FOR THE SOFTWARE THE REDISTRIBUTION, MODIFICATION, 
 * USAGE AND OTHER RIGHTS AND OBLIGATIONS IS INCLUDED WITH THE DISTRIBUTION OF THIS 
 * PROJECT IN THE FILE LICENSE.HTML. IF THE LICENSE IS NOT INCLUDED YOU MAY FIND A COPY 
 * AT HTTP://WWW.DESY.DE/LEGAL/LICENSE.HTM
 */
package org.csstudio.platform.simpledal;

import java.util.List;

import org.csstudio.platform.model.pvs.IProcessVariableAddress;
import org.csstudio.platform.model.pvs.ProcessVariableAdressFactory;
import org.csstudio.platform.model.pvs.ValueType;

/**
 * A service which can be used for easy access to control system channels.
 * 
 * A control system channel is addressed via a {@link IProcessVariableAddress}.
 * Please use {@link ProcessVariableAdressFactory} to create these addresses.
 * 
 * The service is designed to save system resources and share physical channels
 * whenever possible.
 * 
 * The same physical connection (in case of EPICs, TINE, TANGO) is reused in the
 * following cases:
 * <li>for all connections to the same process variable with the same value
 * type</li>
 * <li>for all connections to characteristics of the same process variable</li>
 * 
 * You may use the {@link ProcessVariableConnectionServiceFactory} to create
 * instances of this service.
 * 
 * @author Sven Wende, Matthias Zeimer
 */
public interface IProcessVariableConnectionService {

	/**
	 * Asynchronously writes the specified value to the channel addressed by the
	 * the given process variable address.
	 * 
	 * @param processVariableAddress
	 *            the address
	 * @param value
	 *            the value
	 * @param listener TODO
	 * 
	 * @return true, if the value was set successful, false otherwise
	 */
	void writeValueAsynchronously(IProcessVariableAddress processVariableAddress, Object value,
			ValueType expectedValueType, IProcessVariableWriteListener listener);

	/**
	 * Synchronously writes the specified value to the channel addressed by the
	 * the given process variable address.
	 * 
	 * @param processVariableAddress
	 *            the address
	 * 
	 * @param value
	 *            the value
	 * 
	 * @return true, if the value was set successful, false otherwise
	 */
	boolean writeValueSynchronously(IProcessVariableAddress processVariableAddress, Object value,
			ValueType expectedValueType) throws ConnectionException;
	
	/**
	 * Asynchronously reads a value from the channel addressed by the the given
	 * process variable address. When the value was received, the
	 * {@link IProcessVariableValueListener#valueChanged(Object)} method will be
	 * called on the given listener.
	 * 
	 * @param processVariableAddress
	 *            the process variable address
	 * @param valueType
	 *            the expected value type
	 * @param listener
	 *            the call-back listener
	 */
	void readValueAsynchronously(IProcessVariableAddress processVariableAddress,
			ValueType valueType, IProcessVariableValueListener listener);

	/**
	 * Synchronously reads a value from the channel addressed by the given
	 * process variable address.
	 * 
	 * @param processVariableAddress
	 *            the process variable address
	 * 
	 * @return the current value
	 */
	<E> E readValueSynchronously(
			IProcessVariableAddress processVariableAddress, ValueType valueType)
			throws ConnectionException;

	/**
	 * Starts listening permanently on the channel addressed by the specified
	 * process variable address. The corresponding channel will be open as long
	 * as any permanent listener is alive. For convenience this service
	 * references the specified listener only weakly which means that it will be
	 * garbage collected when its no longer referenced outside this service. If
	 * you want to stop listening explicitly please use the
	 * {@link #unregister(IProcessVariableValueListener)} method.
	 * 
	 * To stop listening just
	 * 
	 * Use the {@link #unregister(IProcessVariableValueListener)}
	 * 
	 * @param listener
	 *            the listener that will receive the value change notifications
	 * @param pv
	 *            the process variable address
	 * 
	 * @param valueType
	 *            the expected value type
	 */
	void register(IProcessVariableValueListener listener,
			IProcessVariableAddress pv, ValueType valueType);

	/**
	 * Stops the specified permanent listener.
	 * 
	 * @param listener
	 *            the listener
	 */
	void unregister(IProcessVariableValueListener listener);

	/**
	 * Checks whether the current user is allowed to write values to
	 * the specified channel.
	 * 
	 * @param pv
	 *            the process variable address
	 * 
	 * @return one of {@link SettableState#values()}
	 */
	SettableState checkWriteAccessSynchronously(IProcessVariableAddress pv);

	/**
	 * Returns all living connector.
	 * 
	 * @return all living connectors
	 */
	List<IConnector> getConnectors();
	
	int getNumberOfActiveConnectors();
}