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Core YAML 1.2 parser and emitter for Java
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/*
 * Copyright (c) 2018, SnakeYAML
 *
 * 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 org.snakeyaml.engine.v2.api.lowlevel;

import java.io.InputStream;
import java.io.Reader;
import java.io.StringReader;
import java.util.Iterator;
import java.util.Objects;
import java.util.Optional;
import org.snakeyaml.engine.v2.api.LoadSettings;
import org.snakeyaml.engine.v2.api.YamlUnicodeReader;
import org.snakeyaml.engine.v2.composer.Composer;
import org.snakeyaml.engine.v2.nodes.Node;
import org.snakeyaml.engine.v2.parser.ParserImpl;
import org.snakeyaml.engine.v2.scanner.StreamReader;

/**
 * Helper to compose input stream to Node
 */
public class Compose {

  private final LoadSettings settings;

  /**
   * Create instance with provided {@link LoadSettings}
   *
   * @param settings - configuration
   */
  public Compose(LoadSettings settings) {
    Objects.requireNonNull(settings, "LoadSettings cannot be null");
    this.settings = settings;
  }

  /**
   * Parse a YAML stream and produce {@link Node}
   *
   * @param yaml - YAML document(s). Since the encoding is already known the BOM must not be present
   *        (it will be parsed as content)
   * @return parsed {@link Node} if available
   * @see Processing Overview
   */
  public Optional composeReader(Reader yaml) {
    Objects.requireNonNull(yaml, "Reader cannot be null");
    return new Composer(settings, new ParserImpl(settings, new StreamReader(settings, yaml)))
        .getSingleNode();
  }

  /**
   * Parse a YAML stream and produce {@link Node}
   *
   * @param yaml - YAML document(s). Default encoding is UTF-8. The BOM must be present if the
   *        encoding is UTF-16 or UTF-32
   * @return parsed {@link Node} if available
   * @see Processing Overview
   */
  public Optional composeInputStream(InputStream yaml) {
    Objects.requireNonNull(yaml, "InputStream cannot be null");
    return new Composer(settings,
        new ParserImpl(settings, new StreamReader(settings, new YamlUnicodeReader(yaml))))
        .getSingleNode();
  }

  /**
   * Parse a YAML stream and produce {@link Node}
   *
   * @param yaml - YAML document(s).
   * @return parsed {@link Node} if available
   * @see Processing Overview
   */
  public Optional composeString(String yaml) {
    Objects.requireNonNull(yaml, "String cannot be null");
    return new Composer(settings,
        new ParserImpl(settings, new StreamReader(settings, new StringReader(yaml))))
        .getSingleNode();
  }

  // Compose all documents

  /**
   * Parse all YAML documents in a stream and produce corresponding representation trees.
   *
   * @param yaml stream of YAML documents
   * @return parsed root Nodes for all the specified YAML documents
   * @see Processing Overview
   */
  public Iterable composeAllFromReader(Reader yaml) {
    Objects.requireNonNull(yaml, "Reader cannot be null");
    return () -> new Composer(settings, new ParserImpl(settings, new StreamReader(settings, yaml)));
  }

  /**
   * Parse all YAML documents in a stream and produce corresponding representation trees.
   *
   * @param yaml - YAML document(s). Default encoding is UTF-8. The BOM must be present if the
   *        encoding is UTF-16 or UTF-32
   * @return parsed root Nodes for all the specified YAML documents
   * @see Processing Overview
   */
  public Iterable composeAllFromInputStream(InputStream yaml) {
    Objects.requireNonNull(yaml, "InputStream cannot be null");
    return () -> new Composer(settings,
        new ParserImpl(settings, new StreamReader(settings, new YamlUnicodeReader(yaml))));
  }

  /**
   * Parse all YAML documents in a stream and produce corresponding representation trees.
   *
   * @param yaml - YAML document(s).
   * @return parsed root Nodes for all the specified YAML documents
   * @see Processing Overview
   */
  public Iterable composeAllFromString(String yaml) {
    Objects.requireNonNull(yaml, "String cannot be null");
    // do not use lambda to keep Iterable and Iterator visible
    return new Iterable() {
      public Iterator iterator() {
        return new Composer(settings,
            new ParserImpl(settings, new StreamReader(settings, new StringReader(yaml))));
      }
    };
  }
}