/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.commons.configuration2;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.io.Reader;
  import java.io.Writer;
  import java.util.LinkedHashMap;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  import org.apache.commons.configuration2.convert.ListDelimiterHandler;
  import org.apache.commons.configuration2.ex.ConfigurationException;
  import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
  import org.apache.commons.configuration2.tree.ImmutableNode;
  import org.apache.commons.configuration2.tree.InMemoryNodeModel;
  import org.apache.commons.configuration2.tree.InMemoryNodeModelSupport;
  import org.apache.commons.configuration2.tree.NodeHandler;
  import org.apache.commons.configuration2.tree.NodeHandlerDecorator;
  import org.apache.commons.configuration2.tree.NodeSelector;
  import org.apache.commons.configuration2.tree.TrackedNodeModel;
  
  /**
   * <p>
   * A specialized hierarchical configuration implementation for parsing ini files.
   * </p>
   * <p>
   * An initialization or ini file is a configuration file typically found on Microsoft's Windows operating system and
   * contains data for Windows based applications.
   * </p>
   * <p>
   * Although popularized by Windows, ini files can be used on any system or platform due to the fact that they are merely
   * text files that can easily be parsed and modified by both humans and computers.
   * </p>
   * <p>
   * A typical ini file could look something like:
   * </p>
   *
   * <pre>
   * [section1]
   * ; this is a comment!
   * var1 = foo
   * var2 = bar
   *
   * [section2]
   * var1 = doo
   * </pre>
   * <p>
   * The format of ini files is fairly straight forward and is composed of three components:
   * </p>
   * <ul>
   * <li><b>Sections:</b> Ini files are split into sections, each section starting with a section declaration. A section
   * declaration starts with a '[' and ends with a ']'. Sections occur on one line only.</li>
   * <li><b>Parameters:</b> Items in a section are known as parameters. Parameters have a typical {@code key = value}
   * format.</li>
   * <li><b>Comments:</b> Lines starting with a ';' are assumed to be comments.</li>
   * </ul>
   * <p>
   * There are various implementations of the ini file format by various vendors which has caused a number of differences
   * to appear. As far as possible this configuration tries to be lenient and support most of the differences.
   * </p>
   * <p>
   * Some of the differences supported are as follows:
   * </p>
   * <ul>
   * <li><b>Comments:</b> The '#' character is also accepted as a comment signifier.</li>
   * <li><b>Key value separator:</b> The ':' character is also accepted in place of '=' to separate keys and values in
   * parameters, for example {@code var1 : foo}.</li>
   * <li><b>Duplicate sections:</b> Typically duplicate sections are not allowed, this configuration does however support
   * this feature. In the event of a duplicate section, the two section's values are merged so that there is only a single
   * section. <strong>Note</strong>: This also affects the internal data of the configuration. If it is saved, only a
   * single section is written!</li>
   * <li><b>Duplicate parameters:</b> Typically duplicate parameters are only allowed if they are in two different
   * sections, thus they are local to sections; this configuration simply merges duplicates; if a section has a duplicate
   * parameter the values are then added to the key as a list.</li>
   * </ul>
   * <p>
   * Global parameters are also allowed; any parameters declared before a section is declared are added to a global
   * section. It is important to note that this global section does not have a name.
   * </p>
  * <p>
  * In all instances, a parameter's key is prepended with its section name and a '.' (period). Thus a parameter named
  * "var1" in "section1" will have the key {@code section1.var1} in this configuration. (This is the default behavior.
  * Because this is a hierarchical configuration you can change this by setting a different
  * {@link org.apache.commons.configuration2.tree.ExpressionEngine}.)
  * </p>
  * <p>
  * <strong>Implementation Details:</strong> Consider the following ini file:
  * </p>
  * <pre>
  *  default = ok
  *
  *  [section1]
  *  var1 = foo
  *  var2 = doodle
  *
  *  [section2]
  *  ; a comment
  *  var1 = baz
  *  var2 = shoodle
  *  bad =
  *  = worse
  *
  *  [section3]
  *  # another comment
  *  var1 : foo
  *  var2 : bar
  *  var5 : test1
  *
  *  [section3]
  *  var3 = foo
  *  var4 = bar
  *  var5 = test2
  *
  *  [sectionSeparators]
  *  passwd : abc=def
  *  a:b = "value"
  * </pre>
  * <p>
  * This ini file will be parsed without error. Note:
  * </p>
  * <ul>
  * <li>The parameter named "default" is added to the global section, it's value is accessed simply using
  * {@code getProperty("default")}.</li>
  * <li>Section 1's parameters can be accessed using {@code getProperty("section1.var1")}.</li>
  * <li>The parameter named "bad" simply adds the parameter with an empty value.</li>
  * <li>The empty key with value "= worse" is added using a key consisting of a single space character. This key is still
  * added to section 2 and the value can be accessed using {@code getProperty("section2. ")}, notice the period '.' and
  * the space following the section name.</li>
  * <li>Section three uses both '=' and ':' to separate keys and values.</li>
  * <li>Section 3 has a duplicate key named "var5". The value for this key is [test1, test2], and is represented as a
  * List.</li>
  * <li>The section called <em>sectionSeparators</em> demonstrates how the configuration deals with multiple occurrences
  * of separator characters. Per default the first separator character in a line is detected and used to split the key
  * from the value. Therefore the first property definition in this section has the key {@code passwd} and the value
  * {@code abc=def}. This default behavior can be changed by using quotes. If there is a separator character before the
  * first quote character (ignoring whitespace), this character is used as separator. Thus the second property definition
  * in the section has the key {@code a:b} and the value {@code value}.</li>
  * </ul>
  * <p>
  * Internally, this configuration maps the content of the represented ini file to its node structure in the following
  * way:
  * </p>
  * <ul>
  * <li>Sections are represented by direct child nodes of the root node.</li>
  * <li>For the content of a section, corresponding nodes are created as children of the section node.</li>
  * </ul>
  * <p>
  * This explains how the keys for the properties can be constructed. You can also use other methods of
  * {@link HierarchicalConfiguration} for querying or manipulating the hierarchy of configuration nodes, for instance the
  * {@code configurationAt()} method for obtaining the data of a specific section. However, be careful that the storage
  * scheme described above is not violated (e.g. by adding multiple levels of nodes or inserting duplicate section
  * nodes). Otherwise, the special methods for ini configurations may not work correctly!
  * </p>
  * <p>
  * The set of sections in this configuration can be retrieved using the {@code getSections()} method. For obtaining a
  * {@code SubnodeConfiguration} with the content of a specific section the {@code getSection()} method can be used.
  * </p>
  * <p>
  * Like other {@code Configuration} implementations, this class uses a {@code Synchronizer} object to control concurrent
  * access. By choosing a suitable implementation of the {@code Synchronizer} interface, an instance can be made
  * thread-safe or not. Note that access to most of the properties typically set through a builder is not protected by
  * the {@code Synchronizer}. The intended usage is that these properties are set once at construction time through the
  * builder and after that remain constant. If you wish to change such properties during life time of an instance, you
  * have to use the {@code lock()} and {@code unlock()} methods manually to ensure that other threads see your changes.
  * </p>
  * <p>
  * As this class extends {@link AbstractConfiguration}, all basic features like variable interpolation, list handling,
  * or data type conversions are available as well. This is described in the chapter
  * <a href="https://commons.apache.org/proper/commons-configuration/userguide/howto_basicfeatures.html"> Basic features
  * and AbstractConfiguration</a> of the user's guide.
  * </p>
  * <p>
  * Note that this configuration does not support properties with null values. Such properties are considered to be
  * section nodes.
  * </p>
  *
  * @since 1.6
  */
 public class INIConfiguration extends BaseHierarchicalConfiguration implements FileBasedConfiguration {
 
     /**
      * The default characters that signal the start of a comment line.
      */
     protected static final String COMMENT_CHARS = "#;";
 
     /**
      * The default characters used to separate keys from values.
      */
     protected static final String SEPARATOR_CHARS = "=:";
 
     /**
      * Constant for the line separator.
      */
     private static final String LINE_SEPARATOR = System.lineSeparator();
 
     /**
      * The characters used for quoting values.
      */
     private static final String QUOTE_CHARACTERS = "\"'";
 
     /**
      * The line continuation character.
      */
     private static final String LINE_CONT = "\\";
 
     /**
      * The separator used when writing an INI file.
      */
     private String separatorUsedInOutput = " = ";
 
     /**
      * The separator used when reading an INI file.
      */
     private String separatorUsedInInput = SEPARATOR_CHARS;
 
     /**
      * The characters used to separate keys from values when reading an INI file.
      */
     private String commentCharsUsedInInput = COMMENT_CHARS;
 
     /**
      * The flag for decision, whether inline comments on the section line are allowed.
      */
     private boolean sectionInLineCommentsAllowed;
 
     /**
      * Create a new empty INI Configuration.
      */
     public INIConfiguration() {
     }
 
     /**
      * Creates a new instance of {@code INIConfiguration} with the content of the specified
      * {@code HierarchicalConfiguration}.
      *
      * @param c the configuration to be copied
      * @since 2.0
      */
     public INIConfiguration(final HierarchicalConfiguration<ImmutableNode> c) {
         super(c);
     }
 
     /**
      * Create a new empty INI Configuration with option to allow inline comments on the section line.
      *
      * @param sectionInLineCommentsAllowed when true inline comments on the section line are allowed
      */
     private INIConfiguration(final boolean sectionInLineCommentsAllowed) {
         this.sectionInLineCommentsAllowed = sectionInLineCommentsAllowed;
     }
 
     /**
      * Creates a new builder.
      *
      * @return a new builder.
      * @since 2.9.0
      */
     public static Builder builder() {
         return new Builder();
     }
 
     /**
      * Builds instances of INIConfiguration.
      *
      * @since 2.9.0
      */
     public static class Builder {
 
         /**
          * The flag for decision, whether inline comments on the section line are allowed.
          */
         private boolean sectionInLineCommentsAllowed;
 
         public Builder setSectionInLineCommentsAllowed(final boolean sectionInLineCommentsAllowed) {
             this.sectionInLineCommentsAllowed = sectionInLineCommentsAllowed;
             return this;
         }
 
         public INIConfiguration build() {
             return new INIConfiguration(sectionInLineCommentsAllowed);
         }
 
     }
 
     /**
      * Gets separator used in INI output. see {@code setSeparatorUsedInOutput} for further explanation
      *
      * @return the current separator for writing the INI output
      * @since 2.2
      */
     public String getSeparatorUsedInOutput() {
         beginRead(false);
         try {
             return separatorUsedInOutput;
         } finally {
             endRead();
         }
     }
 
     /**
      * Allows setting the key and value separator which is used for the creation of the resulting INI output
      *
      * @param separator String of the new separator for INI output
      * @since 2.2
      */
     public void setSeparatorUsedInOutput(final String separator) {
         beginWrite(false);
         try {
             this.separatorUsedInOutput = separator;
         } finally {
             endWrite();
         }
     }
 
     /**
      * Gets separator used in INI reading. see {@code setSeparatorUsedInInput} for further explanation
      *
      * @return the current separator for reading the INI input
      * @since 2.5
      */
     public String getSeparatorUsedInInput() {
         beginRead(false);
         try {
             return separatorUsedInInput;
         } finally {
             endRead();
         }
     }
 
     /**
      * Allows setting the key and value separator which is used in reading an INI file
      *
      * @param separator String of the new separator for INI reading
      * @since 2.5
      */
     public void setSeparatorUsedInInput(final String separator) {
         beginRead(false);
         try {
             this.separatorUsedInInput = separator;
         } finally {
             endRead();
         }
     }
 
     /**
      * Gets comment leading separator used in INI reading. see {@code setCommentLeadingCharsUsedInInput} for further
      * explanation
      *
      * @return the current separator for reading the INI input
      * @since 2.5
      */
     public String getCommentLeadingCharsUsedInInput() {
         beginRead(false);
         try {
             return commentCharsUsedInInput;
         } finally {
             endRead();
         }
     }
 
     /**
      * Allows setting the leading comment separator which is used in reading an INI file
      *
      * @param separator String of the new separator for INI reading
      * @since 2.5
      */
     public void setCommentLeadingCharsUsedInInput(final String separator) {
         beginRead(false);
         try {
             this.commentCharsUsedInInput = separator;
         } finally {
             endRead();
         }
     }
 
     /**
      * Save the configuration to the specified writer.
      *
      * @param writer - The writer to save the configuration to.
      * @throws ConfigurationException If an error occurs while writing the configuration
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public void write(final Writer writer) throws ConfigurationException, IOException {
         final PrintWriter out = new PrintWriter(writer);
         boolean first = true;
         final String separator = getSeparatorUsedInOutput();
 
         beginRead(false);
         try {
             for (final ImmutableNode node : getModel().getNodeHandler().getRootNode().getChildren()) {
                 if (isSectionNode(node)) {
                     if (!first) {
                         out.println();
                     }
                     out.print("[");
                     out.print(node.getNodeName());
                     out.print("]");
                     out.println();
 
                     node.forEach(child -> writeProperty(out, child.getNodeName(), child.getValue(), separator));
                 } else {
                     writeProperty(out, node.getNodeName(), node.getValue(), separator);
                 }
                 first = false;
             }
             out.println();
             out.flush();
         } finally {
             endRead();
         }
     }
 
     /**
      * Load the configuration from the given reader. Note that the {@code clear()} method is not called so the configuration
      * read in will be merged with the current configuration.
      *
      * @param in the reader to read the configuration from.
      * @throws ConfigurationException If an error occurs while reading the configuration
      * @throws IOException if an I/O error occurs.
      */
     @Override
     public void read(final Reader in) throws ConfigurationException, IOException {
         final BufferedReader bufferedReader = new BufferedReader(in);
         final Map<String, ImmutableNode.Builder> sectionBuilders = new LinkedHashMap<>();
         final ImmutableNode.Builder rootBuilder = new ImmutableNode.Builder();
 
         createNodeBuilders(bufferedReader, rootBuilder, sectionBuilders);
         final ImmutableNode rootNode = createNewRootNode(rootBuilder, sectionBuilders);
         addNodes(null, rootNode.getChildren());
     }
 
     /**
      * Creates a new root node from the builders constructed while reading the configuration file.
      *
      * @param rootBuilder the builder for the top-level section
      * @param sectionBuilders a map storing the section builders
      * @return the root node of the newly created hierarchy
      */
     private static ImmutableNode createNewRootNode(final ImmutableNode.Builder rootBuilder, final Map<String, ImmutableNode.Builder> sectionBuilders) {
         sectionBuilders.forEach((k, v) -> rootBuilder.addChild(v.name(k).create()));
         return rootBuilder.create();
     }
 
     /**
      * Reads the content of an INI file from the passed in reader and creates a structure of builders for constructing the
      * {@code ImmutableNode} objects representing the data.
      *
      * @param in the reader
      * @param rootBuilder the builder for the top-level section
      * @param sectionBuilders a map storing the section builders
      * @throws IOException if an I/O error occurs.
      */
     private void createNodeBuilders(final BufferedReader in, final ImmutableNode.Builder rootBuilder, final Map<String, ImmutableNode.Builder> sectionBuilders)
         throws IOException {
         ImmutableNode.Builder sectionBuilder = rootBuilder;
         String line = in.readLine();
         while (line != null) {
             line = line.trim();
             if (!isCommentLine(line)) {
                 if (isSectionLine(line)) {
                     final int length = sectionInLineCommentsAllowed ? line.indexOf("]") : line.length() - 1;
                     final String section = line.substring(1, length);
                     sectionBuilder = sectionBuilders.computeIfAbsent(section, k -> new ImmutableNode.Builder());
                 } else {
                     String key;
                     String value = "";
                     final int index = findSeparator(line);
                     if (index >= 0) {
                         key = line.substring(0, index);
                         value = parseValue(line.substring(index + 1), in);
                     } else {
                         key = line;
                     }
                     key = key.trim();
                     if (key.isEmpty()) {
                         // use space for properties with no key
                         key = " ";
                     }
                     createValueNodes(sectionBuilder, key, value);
                 }
             }
 
             line = in.readLine();
         }
     }
 
     /**
      * Creates the node(s) for the given key value-pair. If delimiter parsing is enabled, the value string is split if
      * possible, and for each single value a node is created. Otherwise only a single node is added to the section.
      *
      * @param sectionBuilder the section builder for adding new nodes
      * @param key the key
      * @param value the value string
      */
     private void createValueNodes(final ImmutableNode.Builder sectionBuilder, final String key, final String value) {
         getListDelimiterHandler().split(value, false).forEach(v -> sectionBuilder.addChild(new ImmutableNode.Builder().name(key).value(v).create()));
     }
 
     /**
      * Writes data about a property into the given stream.
      *
      * @param out the output stream
      * @param key the key
      * @param value the value
      */
     private void writeProperty(final PrintWriter out, final String key, final Object value, final String separator) {
         out.print(key);
         out.print(separator);
         out.print(escapeValue(value.toString()));
         out.println();
     }
 
     /**
      * Parse the value to remove the quotes and ignoring the comment. Example:
      *
      * <pre>
      * &quot;value&quot; ; comment -&gt; value
      * </pre>
      *
      * <pre>
      * 'value' ; comment -&gt; value
      * </pre>
      *
      * Note that a comment character is only recognized if there is at least one whitespace character before it. So it can
      * appear in the property value, e.g.:
      *
      * <pre>
      * C:\\Windows;C:\\Windows\\system32
      * </pre>
      *
      * @param val the value to be parsed
      * @param reader the reader (needed if multiple lines have to be read)
      * @throws IOException if an IO error occurs
      */
     private String parseValue(final String val, final BufferedReader reader) throws IOException {
         final StringBuilder propertyValue = new StringBuilder();
         boolean lineContinues;
         String value = val.trim();
 
         do {
             final boolean quoted = value.startsWith("\"") || value.startsWith("'");
             boolean stop = false;
             boolean escape = false;
 
             final char quote = quoted ? value.charAt(0) : 0;
 
             int i = quoted ? 1 : 0;
 
             final StringBuilder result = new StringBuilder();
             char lastChar = 0;
             while (i < value.length() && !stop) {
                 final char c = value.charAt(i);
 
                 if (quoted) {
                     if ('\\' == c && !escape) {
                         escape = true;
                     } else if (!escape && quote == c) {
                         stop = true;
                     } else {
                         if (escape && quote == c) {
                             escape = false;
                         } else if (escape) {
                             escape = false;
                             result.append('\\');
                         }
                         result.append(c);
                     }
                 } else if (isCommentChar(c) && Character.isWhitespace(lastChar)) {
                     stop = true;
                 } else {
                     result.append(c);
                 }
 
                 i++;
                 lastChar = c;
             }
 
             String v = result.toString();
             if (!quoted) {
                 v = v.trim();
                 lineContinues = lineContinues(v);
                 if (lineContinues) {
                     // remove trailing "\"
                     v = v.substring(0, v.length() - 1).trim();
                 }
             } else {
                 lineContinues = lineContinues(value, i);
             }
             propertyValue.append(v);
 
             if (lineContinues) {
                 propertyValue.append(LINE_SEPARATOR);
                 value = reader.readLine();
             }
         } while (lineContinues && value != null);
 
         return propertyValue.toString();
     }
 
     /**
      * Tests whether the specified string contains a line continuation marker.
      *
      * @param line the string to check
      * @return a flag whether this line continues
      */
     private static boolean lineContinues(final String line) {
         final String s = line.trim();
         return s.equals(LINE_CONT) || s.length() > 2 && s.endsWith(LINE_CONT) && Character.isWhitespace(s.charAt(s.length() - 2));
     }
 
     /**
      * Tests whether the specified string contains a line continuation marker after the specified position. This method
      * parses the string to remove a comment that might be present. Then it checks whether a line continuation marker can be
      * found at the end.
      *
      * @param line the line to check
      * @param pos the start position
      * @return a flag whether this line continues
      */
     private boolean lineContinues(final String line, final int pos) {
         final String s;
 
         if (pos >= line.length()) {
             s = line;
         } else {
             int end = pos;
             while (end < line.length() && !isCommentChar(line.charAt(end))) {
                 end++;
             }
             s = line.substring(pos, end);
         }
 
         return lineContinues(s);
     }
 
     /**
      * Tests whether the specified character is a comment character.
      *
      * @param c the character
      * @return a flag whether this character starts a comment
      */
     private boolean isCommentChar(final char c) {
         return getCommentLeadingCharsUsedInInput().indexOf(c) >= 0;
     }
 
     /**
      * Tries to find the index of the separator character in the given string. This method checks for the presence of
      * separator characters in the given string. If multiple characters are found, the first one is assumed to be the
      * correct separator. If there are quoting characters, they are taken into account, too.
      *
      * @param line the line to be checked
      * @return the index of the separator character or -1 if none is found
      */
     private int findSeparator(final String line) {
         int index = findSeparatorBeforeQuote(line, findFirstOccurrence(line, QUOTE_CHARACTERS));
         if (index < 0) {
             index = findFirstOccurrence(line, getSeparatorUsedInInput());
         }
         return index;
     }
 
     /**
      * Checks for the occurrence of the specified separators in the given line. The index of the first separator is
      * returned.
      *
      * @param line the line to be investigated
      * @param separators a string with the separator characters to look for
      * @return the lowest index of a separator character or -1 if no separator is found
      */
     private static int findFirstOccurrence(final String line, final String separators) {
         int index = -1;
 
         for (int i = 0; i < separators.length(); i++) {
             final char sep = separators.charAt(i);
             final int pos = line.indexOf(sep);
             if (pos >= 0 && (index < 0 || pos < index)) {
                 index = pos;
             }
         }
 
         return index;
     }
 
     /**
      * Searches for a separator character directly before a quoting character. If the first non-whitespace character before
      * a quote character is a separator, it is considered the "real" separator in this line - even if there are other
      * separators before.
      *
      * @param line the line to be investigated
      * @param quoteIndex the index of the quote character
      * @return the index of the separator before the quote or &lt; 0 if there is none
      */
     private static int findSeparatorBeforeQuote(final String line, final int quoteIndex) {
         int index = quoteIndex - 1;
         while (index >= 0 && Character.isWhitespace(line.charAt(index))) {
             index--;
         }
 
         if (index >= 0 && SEPARATOR_CHARS.indexOf(line.charAt(index)) < 0) {
             index = -1;
         }
 
         return index;
     }
 
     /**
      * Escapes the given property value before it is written. This method add quotes around the specified value if it
      * contains a comment character and handles list delimiter characters.
      *
      * @param value the string to be escaped
      */
     private String escapeValue(final String value) {
         return String.valueOf(getListDelimiterHandler().escape(escapeComments(value), ListDelimiterHandler.NOOP_TRANSFORMER));
     }
 
     /**
      * Escapes comment characters in the given value.
      *
      * @param value the value to be escaped
      * @return the value with comment characters escaped
      */
     private String escapeComments(final String value) {
         final String commentChars = getCommentLeadingCharsUsedInInput();
         boolean quoted = false;
 
         for (int i = 0; i < commentChars.length(); i++) {
             final char c = commentChars.charAt(i);
             if (value.indexOf(c) != -1) {
                 quoted = true;
                 break;
             }
         }
 
         if (quoted) {
             return '"' + value.replace("\"", "\\\"") + '"';
         }
         return value;
     }
 
     /**
      * Determine if the given line is a comment line.
      *
      * @param line The line to check.
      * @return true if the line is empty or starts with one of the comment characters
      */
     protected boolean isCommentLine(final String line) {
         if (line == null) {
             return false;
         }
         // blank lines are also treated as comment lines
         return line.isEmpty() || getCommentLeadingCharsUsedInInput().indexOf(line.charAt(0)) >= 0;
     }
 
     /**
      * Determine if the given line is a section.
      *
      * @param line The line to check.
      * @return true if the line contains a section
      */
     protected boolean isSectionLine(final String line) {
         if (line == null) {
             return false;
         }
         return sectionInLineCommentsAllowed ? isNonStrictSection(line) : isStrictSection(line);
     }
 
     /**
      * Determine if the entire given line is a section - inline comments are not allowed.
      *
      * @param line The line to check.
      * @return true if the entire line is a section
      */
     private static boolean isStrictSection(final String line) {
         return line.startsWith("[") && line.endsWith("]");
     }
 
     /**
      * Determine if the given line contains a section - inline comments are allowed.
      *
      * @param line The line to check.
      * @return true if the line contains a section
      */
     private static boolean isNonStrictSection(final String line) {
         return line.startsWith("[") && line.contains("]");
     }
 
     /**
      * Gets a set containing the sections in this ini configuration. Note that changes to this set do not affect the
      * configuration.
      *
      * @return a set containing the sections.
      */
     public Set<String> getSections() {
         final Set<String> sections = new LinkedHashSet<>();
         boolean globalSection = false;
         boolean inSection = false;
 
         beginRead(false);
         try {
             for (final ImmutableNode node : getModel().getNodeHandler().getRootNode().getChildren()) {
                 if (isSectionNode(node)) {
                     inSection = true;
                     sections.add(node.getNodeName());
                 } else if (!inSection && !globalSection) {
                     globalSection = true;
                     sections.add(null);
                 }
             }
         } finally {
             endRead();
         }
 
         return sections;
     }
 
     /**
      * Gets a configuration with the content of the specified section. This provides an easy way of working with a single
      * section only. The way this configuration is structured internally, this method is very similar to calling
      * {@link HierarchicalConfiguration#configurationAt(String)} with the name of the section in question. There are the
      * following differences however:
      * <ul>
      * <li>This method never throws an exception. If the section does not exist, it is created now. The configuration
      * returned in this case is empty.</li>
      * <li>If section is contained multiple times in the configuration, the configuration returned by this method is
      * initialized with the first occurrence of the section. (This can only happen if {@code addProperty()} has been used in
      * a way that does not conform to the storage scheme used by {@code INIConfiguration}. If used correctly, there will not
      * be duplicate sections.)</li>
      * <li>There is special support for the global section: Passing in <b>null</b> as section name returns a configuration
      * with the content of the global section (which may also be empty).</li>
      * </ul>
      *
      * @param name the name of the section in question; <b>null</b> represents the global section
      * @return a configuration containing only the properties of the specified section
      */
     public SubnodeConfiguration getSection(final String name) {
         if (name == null) {
             return getGlobalSection();
         }
         try {
             return (SubnodeConfiguration) configurationAt(name, true);
         } catch (final ConfigurationRuntimeException iex) {
             // the passed in key does not map to exactly one node
             // obtain the node for the section, create it on demand
             final InMemoryNodeModel parentModel = getSubConfigurationParentModel();
             final NodeSelector selector = parentModel.trackChildNodeWithCreation(null, name, this);
             return createSubConfigurationForTrackedNode(selector, this);
         }
     }
 
     /**
      * Creates a sub configuration for the global section of the represented INI configuration.
      *
      * @return the sub configuration for the global section
      */
     private SubnodeConfiguration getGlobalSection() {
         final InMemoryNodeModel parentModel = getSubConfigurationParentModel();
         final NodeSelector selector = new NodeSelector(null); // selects parent
         parentModel.trackNode(selector, this);
         final GlobalSectionNodeModel model = new GlobalSectionNodeModel(this, selector);
         final SubnodeConfiguration sub = new SubnodeConfiguration(this, model);
         initSubConfigurationForThisParent(sub);
         return sub;
     }
 
     /**
      * Checks whether the specified configuration node represents a section.
      *
      * @param node the node in question
      * @return a flag whether this node represents a section
      */
     private static boolean isSectionNode(final ImmutableNode node) {
         return node.getValue() == null;
     }
 
     /**
      * A specialized node model implementation for the sub configuration representing the global section of the INI file.
      * This is a regular {@code TrackedNodeModel} with one exception: The {@code NodeHandler} used by this model applies a
      * filter on the children of the root node so that only nodes are visible that are no sub sections.
      */
     private static final class GlobalSectionNodeModel extends TrackedNodeModel {
         /**
          * Creates a new instance of {@code GlobalSectionNodeModel} and initializes it with the given underlying model.
          *
          * @param modelSupport the underlying {@code InMemoryNodeModel}
          * @param selector the {@code NodeSelector}
          */
         public GlobalSectionNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector selector) {
             super(modelSupport, selector, true);
         }
 
         @Override
         public NodeHandler<ImmutableNode> getNodeHandler() {
             return new NodeHandlerDecorator<ImmutableNode>() {
                 @Override
                 public List<ImmutableNode> getChildren(final ImmutableNode node) {
                     final List<ImmutableNode> children = super.getChildren(node);
                     return filterChildrenOfGlobalSection(node, children);
                 }
 
                 @Override
                 public List<ImmutableNode> getChildren(final ImmutableNode node, final String name) {
                     final List<ImmutableNode> children = super.getChildren(node, name);
                     return filterChildrenOfGlobalSection(node, children);
                 }
 
                 @Override
                 public int getChildrenCount(final ImmutableNode node, final String name) {
                     final List<ImmutableNode> children = name != null ? super.getChildren(node, name) : super.getChildren(node);
                     return filterChildrenOfGlobalSection(node, children).size();
                 }
 
                 @Override
                 public ImmutableNode getChild(final ImmutableNode node, final int index) {
                     final List<ImmutableNode> children = super.getChildren(node);
                     return filterChildrenOfGlobalSection(node, children).get(index);
                 }
 
                 @Override
                 public int indexOfChild(final ImmutableNode parent, final ImmutableNode child) {
                     final List<ImmutableNode> children = super.getChildren(parent);
                     return filterChildrenOfGlobalSection(parent, children).indexOf(child);
                 }
 
                 @Override
                 protected NodeHandler<ImmutableNode> getDecoratedNodeHandler() {
                     return GlobalSectionNodeModel.super.getNodeHandler();
                 }
 
                 /**
                  * Filters the child nodes of the global section. This method checks whether the passed in node is the root node of the
                  * configuration. If so, from the list of children all nodes are filtered which are section nodes.
                  *
                  * @param node the node in question
                  * @param children the children of this node
                  * @return a list with the filtered children
                  */
                 private List<ImmutableNode> filterChildrenOfGlobalSection(final ImmutableNode node, final List<ImmutableNode> children) {
                     final List<ImmutableNode> filteredList;
                     if (node == getRootNode()) {
                         filteredList = children.stream().filter(child -> !isSectionNode(child)).collect(Collectors.toList());
                     } else {
                         filteredList = children;
                     }
 
                     return filteredList;
                 }
             };
         }
     }
 }