/*

 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package jdk.jshell.execution;

import java.io.PrintWriter;

import java.io.StringWriter;

import java.util.HashMap;

import java.util.Map;

import java.util.logging.Level;

import java.util.logging.Logger;

import jdk.jshell.spi.ExecutionControl;

import jdk.jshell.spi.ExecutionControlProvider;

import jdk.jshell.spi.ExecutionEnv;

/**

 * Tries other providers in sequence until one works.

 *

 * @since 9

 */

public class FailOverExecutionControlProvider  implements ExecutionControlProvider{

    private Logger logger = null;

    /**

     * Create an instance. The instance can be used to start and return an

     * {@link ExecutionControl} instance by attempting to start a series of

     * {@code ExecutionControl} specs, until one is successful.

     *

     * @see #generate(jdk.jshell.spi.ExecutionEnv, java.util.Map)

     */

    public FailOverExecutionControlProvider() {

    }

    /**

     * The unique name of this {@code ExecutionControlProvider}.

     *

     * @return "failover"

     */

    @Override

    public String name() {

        return "failover";

    }

    /**

     * Create and return the default parameter map for this

     * {@code ExecutionControlProvider}. There are ten parameters, "0" through

     * "9", their values are {@code ExecutionControlProvider} specification

     * strings, or empty string.

     *

     * @return a default parameter map

     */

    @Override

    public Map<String, String> defaultParameters() {

        Map<String, String> dp = new HashMap<>();

        dp.put("0", "jdi");

        for (int i = 1; i <= 9; ++i) {

            dp.put("" + i, "");

        }

        return dp;

    }

    /**

     * Create and return a locally executing {@code ExecutionControl} instance.

     * At least one parameter should have a spec.

     *

     * @param env the execution environment, provided by JShell

     * @param parameters the modified parameter map.

     * @return the execution engine

     * @throws Throwable if all the given providers fail, the exception that

     * occurred on the first attempt to create the execution engine.

     */

    @Override

    public ExecutionControl generate(ExecutionEnv env, Map<String, String> parameters)

            throws Throwable {

        Throwable thrown = null;

        for (int i = 0; i <= 9; ++i) {

            String param = parameters.get("" + i);

            if (param != null && !param.isEmpty()) {

                try {

                    ExecutionControl ec =  ExecutionControl.generate(env, param);

                    logger().finest(

                            String.format("FailOverExecutionControlProvider: Success %s -- %d = %s\n",

                                    name(), i, param));

                    return ec;

                } catch (Throwable ex) {

                    logger().warning(

                            String.format("FailOverExecutionControlProvider: Failure %s -- %d = %s -- %s\n",

                                    name(), i, param, ex.toString()));

                    StringWriter writer = new StringWriter();

                    PrintWriter log = new PrintWriter(writer);

                    log.println("FailOverExecutionControlProvider:");

                    ex.printStackTrace(log);

                    log.flush();

                    logger().fine(writer.toString());

                    // only care about the first, and only if they all fail

                    if (thrown == null) {

                        thrown = ex;

                    }

                }

            }

        }

        logger().severe("FailOverExecutionControlProvider: Terminating, failovers exhausted");

        if (thrown == null) {

            throw new IllegalArgumentException("All least one parameter must be set to a provider.");

        }

        throw thrown;

    }

    private Logger logger() {

        if (logger == null) {

            logger = Logger.getLogger("jdk.jshell.execution");

            if (logger.getLevel() == null) {

                // Logging has not been specifically requested, turn it off

                logger.setLevel(Level.OFF);

            }

        }

        return logger;

    }

}