/* 
 * Copyright (c) 2006 Stiftung Deutsches Elektronen-Synchroton, 
 * 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.sds.ui.scripting;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.csstudio.sds.internal.rules.LogicException;
import org.csstudio.sds.model.IScript;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.ContextAction;
import org.mozilla.javascript.Function;
import org.mozilla.javascript.ImporterTopLevel;
import org.mozilla.javascript.Scriptable;

/**
 * This calls describes a script, which can be executed by a Timer-widget.
 * @author Kai Meyer
 *
 */
public final class RunnableScript implements IScript {
	
	/**
	 * The name of the script function that will be executed.
	 */
	private static final String SCRIPT_LOGIC_FUNCTION_NAME = "execute"; //$NON-NLS-1$
	/**
	 * The name of the script field that contains the textual description of the
	 * script.
	 */
	private static final String SCRIPT_DESCRIPTION = "description"; //$NON-NLS-1$
	/**
	 * A textual description of this rule.
	 */
	private String _description;
	/**
	 * The script function that will be executed.
	 */
	private Function _scriptFunction;
	/**
	 * The scripting scope.
	 */
	private Scriptable _scriptScope;

	/**
	 * Constructor.
	 * @param name The name of the script.
	 * @param scriptFileInputStream The {@link InputStream} for the script
	 * @throws LogicException Thrown if an error occurs during parsing the script
	 */
	public RunnableScript(final String name, final InputStream scriptFileInputStream)
		throws LogicException {
		_description = null;

		try {
			Context scriptContext = Context.enter();
			scriptContext.setApplicationClassLoader(RunnableScript.class.getClassLoader());
			
			_scriptScope = new ImporterTopLevel(scriptContext);

			_scriptFunction = parseScriptFile(scriptFileInputStream,
					scriptContext);
		} catch (Exception e) {
			throw new LogicException(
					"Script " + name + ": Error parsing script", e); //$NON-NLS-1$ //$NON-NLS-2$
		} finally {
			Context.exit();
		}

		if (_scriptFunction == null) {
			throw new LogicException(
					"Script " + name + ": " + SCRIPT_LOGIC_FUNCTION_NAME + " is undefined!"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
		}
		if (_description == null) {
			throw new LogicException("Script " + name //$NON-NLS-1$
					+ ": No textual description was defined!"); //$NON-NLS-1$
		}
	}
	
	/**
	 * Parse the given script file and try to allocate the "doLogic" function.
	 * 
	 * @param scriptFileInputStream
	 *            The input stream that contains the script
	 * @param scriptContext
	 *            The script context that is used to initially parse the script
	 *            file.
	 * @return The "doLogic" function or null if it is not defined within the
	 *         given script.
	 * @throws IOException
	 *             If an IO error occurs while the script file is parsed.
	 */
	private Function parseScriptFile(final InputStream scriptFileInputStream,
			final Context scriptContext) throws IOException {
		Function result = null;

		String scriptString = ""; //$NON-NLS-1$

		BufferedReader reader = new BufferedReader(new InputStreamReader(
				scriptFileInputStream));

		while (reader.ready()) {
			scriptString += reader.readLine();
		}

		reader.close();

		// Evaluate the script string. Ignore the result. This is needed to
		// allocate the proper function object.
		scriptContext.evaluateString(_scriptScope, scriptString,
				"script file", 1, null); //$NON-NLS-1$

		_description = fetchTextualDescription();

		// Try to allocate the function object.
		Object functionObject = _scriptScope.get(SCRIPT_LOGIC_FUNCTION_NAME,
				_scriptScope);

		if (functionObject instanceof Function) {
			result = (Function) functionObject;
		}

		return result;
	}
	
	/**
	 * Try to fetch the textual description from the script.
	 * @return The textual description for the script
	 */
	private String fetchTextualDescription() {
		String result = "";
		Object descriptionObject = _scriptScope.get(SCRIPT_DESCRIPTION,
				_scriptScope);

		if (descriptionObject != Scriptable.NOT_FOUND) {
			result = Context.toString(descriptionObject);
		}
		
		return result;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void execute() {
		Context.call(new ContextAction() {
			/**
			 * {@inheritDoc}
			 */
			@Override
			public Object run(final Context cx) {
				_scriptFunction.call(cx, _scriptScope,
						_scriptScope, new Object[] {});
				return null;
			}
		});
	}

}