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/*
  Copyright (C) 2013-2018 Expedia 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 com.hotels.styx.api.service.spi;

import com.google.common.collect.ImmutableMap;
import com.hotels.styx.api.HttpHandler;

import java.util.Map;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Function;

import static com.hotels.styx.api.HttpHeaderNames.CONTENT_TYPE;
import static com.hotels.styx.api.HttpHeaderValues.APPLICATION_JSON;
import static com.hotels.styx.api.messages.FullHttpResponse.response;
import static com.hotels.styx.api.messages.HttpResponseStatus.OK;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.CREATED;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.FAILED;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.RUNNING;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.STARTING;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.STOPPED;
import static com.hotels.styx.api.service.spi.StyxServiceStatus.STOPPING;
import static java.lang.String.format;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.util.concurrent.CompletableFuture.completedFuture;
import static rx.Observable.just;

/**
 * A helper class for implementing StyxService interface.
 *
 * AbstractStyxService provides service state management facilities
 * for implementing a StyxSerive interface.
 */
public abstract class AbstractStyxService implements StyxService {
    private final String name;
    private final AtomicReference status = new AtomicReference<>(CREATED);

    public AbstractStyxService(String name) {
        this.name = name;
    }

    public StyxServiceStatus status() {
        return status.get();
    }

    protected CompletableFuture startService() {
        return completedFuture(null);
    }

    protected CompletableFuture stopService() {
        return completedFuture(null);
    }

    @Override
    public CompletableFuture start() {
        boolean changed = status.compareAndSet(CREATED, STARTING);

        if (changed) {
            return startService()
                    .exceptionally(failWithMessage("Service failed to start."))
                    .thenAccept(na -> status.compareAndSet(STARTING, RUNNING));
        } else {
            throw new IllegalStateException(format("Start called in %s state", status.get()));
        }
    }

    @Override
    public CompletableFuture stop() {
        boolean changed = status.compareAndSet(RUNNING, STOPPING);

        if (changed) {
            return stopService()
                    .exceptionally(failWithMessage("Service failed to stop."))
                    .thenAccept(na -> status.compareAndSet(STOPPING, STOPPED));
        } else {
            throw new IllegalStateException(format("Stop called in %s state", status.get()));
        }
    }

    private Function failWithMessage(String message) {
        return cause -> {
            status.set(FAILED);
            throw new ServiceFailureException(message, cause);
        };
    }

    @Override
    public Map adminInterfaceHandlers() {
        return ImmutableMap.of("status", request -> just(
                response(OK)
                        .addHeader(CONTENT_TYPE, APPLICATION_JSON)
                        .body(format("{ name: \"%s\" status: \"%s\" }", name, status), UTF_8)
                        .build()
                        .toStreamingResponse()));
    }

    public String serviceName() {
        return name;
    }
}