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A Java Bitcoin library
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/*
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.bitcoinj.protocols.channels;

import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;

import java.util.Locale;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * A class representing a state machine, with limited transitions between states.
 * @param  An enum of states to use
 */
public class StateMachine> {
    private State currentState;

    private final Multimap transitions;

    public StateMachine(State startState, Multimap transitions) {
        currentState = checkNotNull(startState);
        this.transitions = checkNotNull(transitions);
    }

    /**
     * Checks that the machine is in the given state. Throws if it isn't.
     * @param requiredState
     */
    public synchronized void checkState(State requiredState) throws IllegalStateException {
        if (requiredState != currentState) {
            throw new IllegalStateException(String.format(Locale.US,
                    "Expected state %s, but in state %s", requiredState, currentState));
        }
    }

    /**
     * Checks that the machine is in one of the given states. Throws if it isn't.
     * @param requiredStates
     */
    public synchronized void checkState(State... requiredStates) throws IllegalStateException {
        for (State requiredState : requiredStates) {
            if (requiredState.equals(currentState)) {
                return;
            }
        }
        throw new IllegalStateException(String.format(Locale.US,
                "Expected states %s, but in state %s", Lists.newArrayList(requiredStates), currentState));
    }

    /**
     * Transitions to a new state, provided that the required transition exists
     * @param newState
     * @throws IllegalStateException If no state transition exists from oldState to newState
     */
    public synchronized void transition(State newState) throws IllegalStateException {
        if (transitions.containsEntry(currentState, newState)) {
            currentState = newState;
        } else {
            throw new IllegalStateException(String.format(Locale.US,
                    "Attempted invalid transition from %s to %s", currentState, newState));
        }
    }

    public synchronized State getState() {
        return currentState;
    }

    @Override
    public String toString() {
        return new StringBuilder().append('[').append(getState()).append(']').toString();
    }
}