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/*
 * Copyright 2016 Goldman Sachs.
 *
 * 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.gs.dmn.feel.interpreter;

import org.apache.commons.lang3.ClassUtils;

abstract class MemberUtils {
    /**
     * Array of primitive number types ordered by "promotability"
     */
    private static final Class[] ORDERED_PRIMITIVE_TYPES = {Byte.TYPE, Short.TYPE,
            Character.TYPE, Integer.TYPE, Long.TYPE, Float.TYPE, Double.TYPE};

    /**
     * Compares the relative fitness of two sets of parameter types in terms of
     * matching a third set of runtime parameter types, such that a list ordered
     * by the results of the comparison would return the best match first
     * (least).
     *
     * @param left   the "left" parameter set
     * @param right  the "right" parameter set
     * @param actual the runtime parameter types to match against
     *               {@code left}/{@code right}
     * @return int consistent with {@code compare} semantics
     */
    static int compareParameterTypes(final Class[] left, final Class[] right, final Class[] actual) {
        final float leftCost = getTotalTransformationCost(actual, left);
        final float rightCost = getTotalTransformationCost(actual, right);
        return Float.compare(leftCost, rightCost);
    }

    /**
     * Returns the sum of the object transformation cost for each class in the
     * source argument list.
     *
     * @param srcArgs  The source arguments
     * @param destArgs The destination arguments
     * @return The total transformation cost
     */
    private static float getTotalTransformationCost(final Class[] srcArgs, final Class[] destArgs) {
        float totalCost = 0.0f;
        for (int i = 0; i < srcArgs.length; i++) {
            Class srcClass = srcArgs[i];
            Class destClass = destArgs[i];
            totalCost += getObjectTransformationCost(srcClass, destClass);
        }
        return totalCost;
    }

    /**
     * Gets the number of steps required needed to turn the source class into
     * the destination class. This represents the number of steps in the object
     * hierarchy graph.
     *
     * @param srcClass  The source class
     * @param destClass The destination class
     * @return The cost of transforming an object
     */
    private static float getObjectTransformationCost(Class srcClass, final Class destClass) {
        if (destClass.isPrimitive()) {
            return getPrimitivePromotionCost(srcClass, destClass);
        }
        float cost = 0.0f;
        while (srcClass != null && !destClass.equals(srcClass)) {
            if (destClass.isInterface() && ClassUtils.isAssignable(srcClass, destClass)) {
                // slight penalty for interface match.
                // we still want an exact match to override an interface match,
                // but
                // an interface match should override anything where we have to
                // get a superclass.
                cost += 0.25f;
                break;
            }
            cost++;
            srcClass = srcClass.getSuperclass();
        }
        /*
         * If the destination class is null, we've travelled all the way up to
         * an Object match. We'll penalize this by adding 1.5 to the cost.
         */
        if (srcClass == null) {
            cost += 1.5f;
        }
        return cost;
    }

    /**
     * Gets the number of steps required to promote a primitive number to another
     * type.
     *
     * @param srcClass  the (primitive) source class
     * @param destClass the (primitive) destination class
     * @return The cost of promoting the primitive
     */
    private static float getPrimitivePromotionCost(final Class srcClass, final Class destClass) {
        float cost = 0.0f;
        Class cls = srcClass;
        if (!cls.isPrimitive()) {
            // slight unwrapping penalty
            cost += 0.1f;
            cls = ClassUtils.wrapperToPrimitive(cls);
        }
        for (int i = 0; cls != destClass && i < ORDERED_PRIMITIVE_TYPES.length; i++) {
            if (cls == ORDERED_PRIMITIVE_TYPES[i]) {
                cost += 0.1f;
                if (i < ORDERED_PRIMITIVE_TYPES.length - 1) {
                    cls = ORDERED_PRIMITIVE_TYPES[i + 1];
                }
            }
        }
        return cost;
    }

}