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/*
 * Copyright 2019 the original author or authors.
 *
 * Licensed under the Apache, 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.gnu.org/licenses/lgpl-3.0.html
 *
 * 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 net.sf.json.util;

import net.sf.json.JSONArray;
import net.sf.json.JSONException;
import net.sf.json.JSONObject;

/**
 * Base class for cycle detection in a hierarchy.

 * The JSON spec forbides cycles in a hierarchy and most parsers will raise and
 * error when a cycle is detected. This class defines a contract for handling
 * those cycles and two base implementations:
 * 
 * STRICT - will throw a JSONException if a cycle is found.
 * LENIENT - will return an empty array or null object if a cycle is found.
 * 
 *
 * @author Andres Almiray 
 */
public abstract class CycleDetectionStrategy {
    public static final JSONArray IGNORE_PROPERTY_ARR = new JSONArray();
    public static final JSONObject IGNORE_PROPERTY_OBJ = new JSONObject();

    /**
     * Returns empty array and null object
     */
    public static final CycleDetectionStrategy LENIENT = new LenientCycleDetectionStrategy();
    /**
     * Returns a special object (IGNORE_PROPERTY_OBJ) that indicates the entire
     * property should be ignored
     */
    public static final CycleDetectionStrategy NOPROP = new LenientNoRefCycleDetectionStrategy();
    /**
     * Throws a JSONException
     */
    public static final CycleDetectionStrategy STRICT = new StrictCycleDetectionStrategy();

    /**
     * Handle a repeated reference

     * Must return a valid JSONArray or null.
     *
     * @param reference the repeated reference.
     */
    public abstract JSONArray handleRepeatedReferenceAsArray(Object reference);

    /**
     * Handle a repeated reference

     * Must return a valid JSONObject or null.
     *
     * @param reference the repeated reference.
     */
    public abstract JSONObject handleRepeatedReferenceAsObject(Object reference);

    private static final class LenientCycleDetectionStrategy extends CycleDetectionStrategy {
        @Override
        public JSONArray handleRepeatedReferenceAsArray(Object reference) {
            return new JSONArray();
        }

        @Override
        public JSONObject handleRepeatedReferenceAsObject(Object reference) {
            return new JSONObject(true);
        }
    }

    /**
     * A cycle detection strategy that prevents any mention of the possible
     * conflict from appearing.
     *
     * @author small
     */
    private static final class LenientNoRefCycleDetectionStrategy extends CycleDetectionStrategy {
        @Override
        public JSONArray handleRepeatedReferenceAsArray(Object reference) {
            return IGNORE_PROPERTY_ARR;
        }

        @Override
        public JSONObject handleRepeatedReferenceAsObject(Object reference) {
            return IGNORE_PROPERTY_OBJ;
        }
    }

    private static final class StrictCycleDetectionStrategy extends CycleDetectionStrategy {
        @Override
        public JSONArray handleRepeatedReferenceAsArray(Object reference) {
            throw new JSONException("There is a cycle in the hierarchy!");
        }

        @Override
        public JSONObject handleRepeatedReferenceAsObject(Object reference) {
            throw new JSONException("There is a cycle in the hierarchy!");
        }
    }
}