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rxjava-core developed by Netflix
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/**
 * Copyright 2014 Netflix, 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 rx.operators;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

import rx.Observable;
import rx.functions.Func1;
import rx.functions.Func2;

/**
 * Returns the minimum element in an observable sequence.
 */
public class OperationMinMax {

    public static > Observable min(
            Observable source) {
        return minMax(source, -1L);
    }

    public static  Observable min(Observable source,
            final Comparator comparator) {
        return minMax(source, comparator, -1L);
    }

    public static > Observable> minBy(
            Observable source, final Func1 selector) {
        return minMaxBy(source, selector, -1L);
    }

    public static  Observable> minBy(Observable source,
            final Func1 selector, final Comparator comparator) {
        return minMaxBy(source, selector, comparator, -1L);
    }

    public static > Observable max(
            Observable source) {
        return minMax(source, 1L);
    }

    public static  Observable max(Observable source,
            final Comparator comparator) {
        return minMax(source, comparator, 1L);
    }

    public static > Observable> maxBy(
            Observable source, final Func1 selector) {
        return minMaxBy(source, selector, 1L);
    }

    public static  Observable> maxBy(Observable source,
            final Func1 selector, final Comparator comparator) {
        return minMaxBy(source, selector, comparator, 1L);
    }

    private static > Observable minMax(
            Observable source, final long flag) {
        return source.reduce(new Func2() {
            @Override
            public T call(T acc, T value) {
                if (flag * acc.compareTo(value) > 0) {
                    return acc;
                }
                return value;
            }
        });
    }

    private static  Observable minMax(Observable source,
            final Comparator comparator, final long flag) {
        return source.reduce(new Func2() {
            @Override
            public T call(T acc, T value) {
                if (flag * comparator.compare(acc, value) > 0) {
                    return acc;
                }
                return value;
            }
        });
    }

    private static > Observable> minMaxBy(
            Observable source, final Func1 selector, final long flag) {
        return source.reduce(new ArrayList(),
                new Func2, T, List>() {

                    @Override
                    public List call(List acc, T value) {
                        if (acc.isEmpty()) {
                            acc.add(value);
                        } else {
                            int compareResult = selector.call(acc.get(0))
                                    .compareTo(selector.call(value));
                            if (compareResult == 0) {
                                acc.add(value);
                            } else if (flag * compareResult < 0) {
                                acc.clear();
                                acc.add(value);
                            }
                        }
                        return acc;
                    }
                });
    }

    private static  Observable> minMaxBy(Observable source,
            final Func1 selector, final Comparator comparator,
            final long flag) {
        return source.reduce(new ArrayList(),
                new Func2, T, List>() {

                    @Override
                    public List call(List acc, T value) {
                        if (acc.isEmpty()) {
                            acc.add(value);
                        } else {
                            int compareResult = comparator.compare(
                                    selector.call(acc.get(0)),
                                    selector.call(value));
                            if (compareResult == 0) {
                                acc.add(value);
                            } else if (flag * compareResult < 0) {
                                acc.clear();
                                acc.add(value);
                            }
                        }
                        return acc;
                    }
                });
    }

}