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/**
 * Copyright (c) 2016-2020, Mihai Emil Andronache
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 * Redistributions of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *  Redistributions in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 * Neither the name of the copyright holder nor the names of its
 *  contributors may be used to endorse or promote products derived from
 *  this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
package com.amihaiemil.eoyaml.extensions;

import com.amihaiemil.eoyaml.*;

import java.util.Collection;
import java.util.Set;
import java.util.function.Supplier;

/**
 * Merge two YAML Mappings into a single one. Very useful in implementing
 * Updating of an existing YamlMapping. Use it like this:
 *  *     final YamlMapping original = ...;
 *     final YamlMapping changed = ...;
 *     final YamlMapping merged = new MergedYamlMapping(
 *         original, changed, true|false
 *     );
 *     //or, via the Supplier constructor:
 *     final YamlMapping merged = new MergedYamlMapping(
 *         original,
 *         () -> {
 *             //create the changed version on-the-fly, right here.
 *         },
 *         true|false
 *     );
 * 
 * @author Mihai Andronache ([email protected])
 * @version $Id: 9ac485880d3472c78d9559d2576b02e2576f60ba $
 * @since 4.1.0
 */
public final class MergedYamlMapping extends BaseYamlMapping {

    /**
     * The merged YamlMapping.
     */
    private YamlMapping merged;

    /**
     * Constructor. By default, conflicting keys will not be overriden.
     * @param original YamlMapping in which the changes will be merged.
     * @param changed YamlMapping containing the differences.
     */
    public MergedYamlMapping(
        final YamlMapping original,
        final YamlMapping changed
    ) {
        this(original, changed, false);
    }

    /**
     * Constructor. By default, conflicting keys will not be overriden.
     * @param original YamlMapping in which the changes will be merged.
     * @param changed Supplier of YamlMapping containing the differences.
     */
    public MergedYamlMapping(
        final YamlMapping original,
        final Supplier changed
    ) {
        this(original, changed, false);
    }

    /**
     * Constructor. You can choose whether conflicting keys will be
     * overriden or not.
     * @param original YamlMapping in which the changes will be merged.
     * @param changed YamlMapping containing the differences.
     * @param overrideConflicts Override key conflicts or not?
     */
    public MergedYamlMapping(
        final YamlMapping original,
        final Supplier changed,
        final boolean overrideConflicts
    ) {
        this(original, changed.get(), overrideConflicts);
    }

    /**
     * Constructor. You can choose whether conflicting keys will be
     * overriden or not.
     * @param original YamlMapping in which the changes will be merged.
     * @param changed YamlMapping containing the differences.
     * @param overrideConflicts Override key conflicts or not?
     */
    public MergedYamlMapping(
        final YamlMapping original,
        final YamlMapping changed,
        final boolean overrideConflicts
    ) {
        if(original == null && changed == null) {
            throw new IllegalArgumentException(
                "Both mappings cannot be null!"
            );
        } else {
            this.merged = merge(original, changed, overrideConflicts);
        }
    }

    @Override
    public Set keys() {
        return this.merged.keys();
    }

    @Override
    public Collection values() {
        return this.merged.values();
    }

    @Override
    public YamlNode value(final YamlNode key) {
        return this.merged.value(key);
    }

    @Override
    public Comment comment() {
        return this.merged.comment();
    }

    @Override
    public YamlMapping yamlMapping(final YamlNode key) {
        return this.merged.yamlMapping(key);
    }

    @Override
    public YamlSequence yamlSequence(final YamlNode key) {
        return this.merged.yamlSequence(key);
    }

    @Override
    public String string(final YamlNode key) {
        return this.merged.string(key);
    }

    @Override
    public String foldedBlockScalar(final YamlNode key) {
        return this.merged.foldedBlockScalar(key);
    }

    @Override
    public Collection literalBlockScalar(final YamlNode key) {
        return this.merged.literalBlockScalar(key);
    }

    /**
     * Merge the two mappings.
     * @param original Original mapping.
     * @param changed Changed mapping.
     * @param overrideConflicts Should conflicting keys be overriden or not?
     * @return Merged mapping.
     */
    private static YamlMapping merge(
        final YamlMapping original,
        final YamlMapping changed,
        final boolean overrideConflicts
    ) {
        final YamlMapping merged;
        if(original == null || original.keys().isEmpty()) {
            merged = changed;
        } else if (changed == null || changed.keys().isEmpty()) {
            merged = original;
        } else {
            YamlMappingBuilder builder = Yaml.createYamlMappingBuilder();
            final Set changedKeys = changed.keys();
            for (final YamlNode key : original.keys()) {
                if(changedKeys.contains(key)) {
                    if(overrideConflicts) {
                        builder = builder.add(key, changed.value(key));
                    } else {
                        builder = builder.add(key, original.value(key));
                    }
                    changedKeys.remove(key);
                } else {
                    builder = builder.add(key, original.value(key));
                }
            }
            for(final YamlNode key : changedKeys) {
                builder = builder.add(key, changed.value(key));
            }
            merged = builder.build(original.comment().value());
        }
        return merged;
    }

}