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YAML Parser implementation.
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/*
 * Copyright (c) 2020, 2023 Oracle and/or its affiliates.
 *
 * 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.helidon.config.yaml;

import java.io.InputStreamReader;
import java.io.Reader;
import java.util.List;
import java.util.Map;
import java.util.Set;

import io.helidon.common.Weight;
import io.helidon.common.Weighted;
import io.helidon.common.media.type.MediaType;
import io.helidon.common.media.type.MediaTypes;
import io.helidon.config.ConfigException;
import io.helidon.config.spi.ConfigNode.ListNode;
import io.helidon.config.spi.ConfigNode.ObjectNode;
import io.helidon.config.spi.ConfigParser;
import io.helidon.config.spi.ConfigParserException;

import org.yaml.snakeyaml.LoaderOptions;
import org.yaml.snakeyaml.Yaml;
import org.yaml.snakeyaml.constructor.SafeConstructor;

/**
 * YAML {@link ConfigParser} implementation that supports {@link io.helidon.common.media.type.MediaTypes#APPLICATION_YAML}.
 * 
 * The parser implementation supports {@link java.util.ServiceLoader}, i.e. {@link io.helidon.config.Config.Builder}
 * can automatically load and register {@code YamlConfigParser} instance,
 * if not {@link io.helidon.config.Config.Builder#disableParserServices() disabled}.
 * And of course it can be {@link io.helidon.config.Config.Builder#addParser(ConfigParser) registered programmatically}.
 * 
 * Weight of the {@code YamlConfigParser} to be used by {@link io.helidon.config.Config.Builder},
 * if loaded automatically as a {@link java.util.ServiceLoader service}, is {@value WEIGHT}.
 *
 * @see io.helidon.config.Config.Builder#addParser(ConfigParser)
 * @see io.helidon.config.Config.Builder#disableParserServices()
 */
@Weight(YamlConfigParser.WEIGHT)
public class YamlConfigParser implements ConfigParser {

    /**
     * Priority of the parser used if registered by {@link io.helidon.config.Config.Builder} automatically.
     */
    public static final double WEIGHT = Weighted.DEFAULT_WEIGHT - 10;

    private static final Set SUPPORTED_MEDIA_TYPES = Set.of(MediaTypes.APPLICATION_YAML,
                                                                       MediaTypes.APPLICATION_X_YAML);
    private static final List SUPPORTED_SUFFIXES = List.of("yml", "yaml");

    /**
     * Default constructor needed by Java Service loader.
     * @deprecated This method should not be directly used, use {@link #create()}
     */
    @SuppressWarnings("DeprecatedIsStillUsed")
    @Deprecated
    public YamlConfigParser() {
        // fix for NPE in Yaml parser when running in Graal
        // cannot be in static block, as that gets ignored
        if (System.getProperty("java.runtime.name") == null) {
            System.setProperty("java.runtime.name", "unknown");
        }
    }

    /**
     * Create a new YAML Config Parser.
     *
     * @return a new instance of parser for YAML
     */
    public static YamlConfigParser create() {
        return new YamlConfigParser();
    }

    @Override
    public Set supportedMediaTypes() {
        return SUPPORTED_MEDIA_TYPES;
    }

    @Override
    public List supportedSuffixes() {
        return SUPPORTED_SUFFIXES;
    }

    @Override
    public ObjectNode parse(Content content) throws ConfigParserException {
        try (InputStreamReader reader = new InputStreamReader(content.data(), content.charset())) {
            Map yamlMap = toMap(reader);
            if (yamlMap == null) { // empty source
                return ObjectNode.empty();
            }

            return fromMap(yamlMap);
        } catch (ConfigException e) {
            throw e;
        } catch (Exception e) {
            throw new ConfigParserException("Cannot read from source: " + e.getLocalizedMessage(), e);
        }
    }

    static Map toMap(Reader reader) {
        // the default of Snake YAML is a Map, safe constructor makes sure we never deserialize into anything
        // harmful
        Yaml yaml = new Yaml(new SafeConstructor(new LoaderOptions()));
        return (Map) yaml.loadAs(reader, Object.class);
    }

    private static ObjectNode fromMap(Map map) {
        ObjectNode.Builder builder = ObjectNode.builder();
        if (map != null) {
            map.forEach((k, v) -> {
                String strKey = k.toString();
                if (v instanceof List) {
                    builder.addList(strKey, fromList((List) v));
                } else if (v instanceof Map) {
                    builder.addObject(strKey, fromMap((Map) v));
                } else {
                    String strValue = v == null ? "" : v.toString();
                    builder.addValue(strKey, strValue);
                }
            });
        }
        return builder.build();
    }

    private static ListNode fromList(List list) {
        ListNode.Builder builder = ListNode.builder();
        list.forEach(value -> {
            if (value instanceof List) {
                builder.addList(fromList((List) value));
            } else if (value instanceof Map) {
                builder.addObject(fromMap((Map) value));
            } else {
                String strValue = value == null ? "" : value.toString();
                builder.addValue(strValue);
            }
        });
        return builder.build();
    }
}