FunctionFactory.java

/*
 * Copyright 2016 The original authors.
 *
 *    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 io.sundr;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

public class FunctionFactory<X,Y> implements Function<X,Y> {

    private final Map<X,Y> cache;
    private final Function<X,Y> function;
    private final Function<X,Y> fallback;
    private final Function<X, Boolean> fallbackPredicate;
    private final int maximumRecursionLevel;
    private final int maximumNestingDepth;


    private final Stack<X> ownStack;
    private static final Stack globalStack = new Stack();

    public FunctionFactory(Map<X, Y> cache, Function<X, Y> function, Function<X, Y> fallback, Function<X, Boolean> fallbackPredicate, int maximumRecursionLevel, int maximumNestingDepth, Stack<X> ownStack) {
        this.cache = cache;
        this.function = function;
        this.fallback = fallback;
        this.fallbackPredicate = fallbackPredicate;
        this.maximumRecursionLevel = maximumRecursionLevel;
        this.maximumNestingDepth = maximumNestingDepth;
        this.ownStack = ownStack;
    }


    public Y apply(X item) {
        Y result;
        synchronized (function) {
            ownStack.push(item);
            globalStack.push(item);
            try {
                result = cache != null ? cache.get(item) : null;
                if (result == null) {
                    int recursionLevel = ownStack != null ? Collections.frequency(ownStack, item) : 0;
                    int nestingDepth = globalStack.size();
                    boolean recursionLevelExceeded = recursionLevel > maximumRecursionLevel && maximumRecursionLevel > 0;
                    boolean nestringDeptExceeded =nestingDepth > maximumNestingDepth && maximumNestingDepth > 0;
                    boolean predicateMatched = fallbackPredicate != null && fallbackPredicate.apply(item);
                    if ((recursionLevelExceeded || nestringDeptExceeded || predicateMatched) && fallback != null) {
                        result = fallback.apply(item);
                    }  else {
                        result = function.apply(item);
                        cacheIfEnabled(item, result);
                    }
                }
            } finally {
                ownStack.pop();
                globalStack.pop();
            }
            return result;
        }
    }

    private void cacheIfEnabled(X item, Y result) {
        if (cache != null) {
            cache.put(item, result);
        }
    }


    public static <X, Y> FunctionFactory<X, Y> cache(Function<X, Y> function) {
        return new FunctionFactory<X, Y>(new HashMap<X, Y>(), function, null, null, 0, 0, new Stack<X>());
    }

    public static <X, Y> FunctionFactory<X, Y> wrap(Function<X, Y> function) {
        return new FunctionFactory<X, Y>(null, function, null, null, 0, 0, new Stack<X>());
    }

    public FunctionFactory<X,Y> withFallback(Function<X,Y> fallback) {
        return new FunctionFactory<X, Y>(cache, function, fallback, fallbackPredicate, maximumRecursionLevel, maximumNestingDepth, ownStack);
    }

    public FunctionFactory<X,Y> withMaximumRecursionLevel(int maximumRecursionLevel) {
        return new FunctionFactory<X, Y>(cache, function, fallback, fallbackPredicate, maximumRecursionLevel, maximumNestingDepth, ownStack);
    }

    public FunctionFactory<X,Y> withMaximumNestingDepth(int maximumNestingDepth) {
        return new FunctionFactory<X, Y>(cache, function, fallback, fallbackPredicate, maximumRecursionLevel, maximumNestingDepth, ownStack);
    }

    public FunctionFactory<X,Y> withFallbackPredicate(Function<X,Boolean> fallbackPredicate) {
        return new FunctionFactory<X, Y>(cache, function, fallback, fallbackPredicate, maximumRecursionLevel, maximumNestingDepth, ownStack);
    }
}