/**
 *
 * Copyright (c) 2006-2017, Speedment, Inc. All Rights Reserved.
 *
 * 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.speedment.plugins.json.internal;

import com.speedment.plugins.json.JsonCollector;

import java.util.*;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

import static java.util.Objects.requireNonNull;
import static java.util.stream.Collector.Characteristics.CONCURRENT;

/**
 *
 * @author  Emil Forslund
 * @since   1.0.0
 */
public final class JsonCollectorImpl<ENTITY> implements JsonCollector<ENTITY> {
    
    public static <ENTITY> JsonCollector<ENTITY> collect(Function<ENTITY, String> converter, Function<List<String>, String> merger) {
        return new JsonCollectorImpl<>(converter, merger);
    }
    
    @Override
    public Supplier<List<String>> supplier() {
        return () -> Collections.synchronizedList(new ArrayList<>());
    }

    @Override
    public BiConsumer<List<String>, ENTITY> accumulator() {
        return (l, t) -> {
            l.add(converter.apply(t));
        };
    }

    @Override
    public BinaryOperator<List<String>> combiner() {
        return (l1, l2) -> {
            l1.addAll(l2);
            return l1;
        };
    }

    @Override
    public Function<List<String>, String> finisher() {
        return merger::apply;
    }

    @Override
    public Set<Collector.Characteristics> characteristics() {
        return EnumSet.of(CONCURRENT);
    }
    
    private JsonCollectorImpl(Function<ENTITY, String> converter, Function<List<String>, String> merger) {
        this.converter = requireNonNull(converter);
        this.merger    = requireNonNull(merger);
    }
    
    private final Function<ENTITY, String> converter;
    private final Function<List<String>, String> merger;
}