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Gluon - Core micro services implementation.
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/**
 * Copyright 2017 Zaradai
 * 
 * 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.zaradai.gluon.server;

import com.zaradai.gluon.MicroService;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executor;
import java.util.concurrent.ForkJoinPool;
import java.util.function.Function;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.zaradai.gluon.util.Validations.checkString;

public final class MicroServiceFactory {
    public static  MicroService fixed(String serviceName, Rep reply) {
        return new MicroServiceFactory.FixedMicroService<>(serviceName, CompletableFuture.completedFuture(reply));
    }

    public static  MicroService failing(String serviceName, Throwable throwable) {
        CompletableFuture completableFuture = new CompletableFuture<>();
        completableFuture.completeExceptionally(throwable);

        return new MicroServiceFactory.FixedMicroService<>(serviceName, completableFuture);
    }

    public static  MicroService create(String serviceName, Function function) {
        return new MicroServiceFactory.MicroServiceImpl<>(serviceName, function, false);
    }

    public static  MicroService createAsync(String serviceName, Function function) {
        return new MicroServiceFactory.MicroServiceImpl<>(serviceName, function, true);
    }

    public static  MicroService createAsync(String serviceName, Function function, Executor executor) {
        return new MicroServiceFactory.MicroServiceImpl<>(serviceName, function, true, executor);
    }

    private static abstract class AbstractMicroService implements MicroService {
        private final String name;

        protected AbstractMicroService(String name) {
            this.name = checkString(name, "Service name cannot be null or empty");
        }

        @Override
        public Status getStatus() {
            return Status.OPEN;
        }

        @Override
        public String name() {
            return name;
        }
    }

    private static class FixedMicroService extends MicroServiceFactory.AbstractMicroService {
        private final CompletableFuture rep;

        public FixedMicroService(String name, CompletableFuture rep) {
            super(name);
            this.rep = rep;
        }

        @Override
        public CompletableFuture apply(Req req) {
            return rep;
        }
    }

    private static class MicroServiceImpl extends MicroServiceFactory.AbstractMicroService {
        private final Function function;
        private final Executor executor;
        private final boolean async;

        private MicroServiceImpl(String name, Function function, boolean async) {
            this(name, function, async, ForkJoinPool.commonPool());
        }

        private MicroServiceImpl(String name, Function function, boolean async, Executor executor) {
            super(name);
            this.function = checkNotNull(function, "Function cannot be null");
            this.executor = checkNotNull(executor, "Supplied executor is invalid.");
            this.async = async;
        }

        @Override
        public CompletableFuture apply(Req req) {
            if (async) {
                return CompletableFuture.supplyAsync(() -> function.apply(req), executor);
            } else {
                return CompletableFuture.completedFuture(function.apply(req));
            }
        }
    }
}