util/regex/Matcher.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 *
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package java.util.regex;

import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * An engine that performs match operations on a {@linkplain
 * java.lang.CharSequence character sequence} by interpreting a {@link Pattern}.
 *
 * <p> A matcher is created from a pattern by invoking the pattern's {@link
 * Pattern#matcher matcher} method.  Once created, a matcher can be used to
 * perform three different kinds of match operations:
 *
 * <ul>
 *
 *   <li><p> The {@link #matches matches} method attempts to match the entire
 *   input sequence against the pattern.  </p></li>
 *
 *   <li><p> The {@link #lookingAt lookingAt} method attempts to match the
 *   input sequence, starting at the beginning, against the pattern.  </p></li>
 *
 *   <li><p> The {@link #find find} method scans the input sequence looking
 *   for the next subsequence that matches the pattern.  </p></li>
 *
 * </ul>
 *
 * <p> Each of these methods returns a boolean indicating success or failure.
 * More information about a successful match can be obtained by querying the
 * state of the matcher.
 *
 * <p> A matcher finds matches in a subset of its input called the
 * <i>region</i>. By default, the region contains all of the matcher's input.
 * The region can be modified via the {@link #region(int, int) region} method
 * and queried via the {@link #regionStart() regionStart} and {@link
 * #regionEnd() regionEnd} methods. The way that the region boundaries interact
 * with some pattern constructs can be changed. See {@link
 * #useAnchoringBounds(boolean) useAnchoringBounds} and {@link
 * #useTransparentBounds(boolean) useTransparentBounds} for more details.
 *
 * <p> This class also defines methods for replacing matched subsequences with
 * new strings whose contents can, if desired, be computed from the match
 * result.  The {@link #appendReplacement appendReplacement} and {@link
 * #appendTail appendTail} methods can be used in tandem in order to collect
 * the result into an existing string buffer or string builder. Alternatively,
 * the more convenient {@link #replaceAll replaceAll} method can be used to
 * create a string in which every matching subsequence in the input sequence
 * is replaced.
 *
 * <p> The explicit state of a matcher includes the start and end indices of
 * the most recent successful match.  It also includes the start and end
 * indices of the input subsequence captured by each <a
 * href="Pattern.html#cg">capturing group</a> in the pattern as well as a total
 * count of such subsequences.  As a convenience, methods are also provided for
 * returning these captured subsequences in string form.
 *
 * <p> The explicit state of a matcher is initially undefined; attempting to
 * query any part of it before a successful match will cause an {@link
 * IllegalStateException} to be thrown.  The explicit state of a matcher is
 * recomputed by every match operation.
 *
 * <p> The implicit state of a matcher includes the input character sequence as
 * well as the <i>append position</i>, which is initially zero and is updated
 * by the {@link #appendReplacement appendReplacement} method.
 *
 * <p> A matcher may be reset explicitly by invoking its {@link #reset()}
 * method or, if a new input sequence is desired, its {@link
 * #reset(java.lang.CharSequence) reset(CharSequence)} method.  Resetting a
 * matcher discards its explicit state information and sets the append position
 * to zero.
 *
 * <p> Instances of this class are not safe for use by multiple concurrent
 * threads. </p>
 *
 *
 * @author      Mike McCloskey
 * @author      Mark Reinhold
 * @author      JSR-51 Expert Group
 * @since       1.4
 * @spec        JSR-51
 */

public final class Matcher implements MatchResult {

    /**
     * The Pattern object that created this Matcher.
     */
    Pattern parentPattern;

    /**
     * The storage used by groups. They may contain invalid values if
     * a group was skipped during the matching.
     */
    int[] groups;

    /**
     * The range within the sequence that is to be matched. Anchors
     * will match at these "hard" boundaries. Changing the region
     * changes these values.
     */
    int from, to;

    /**
     * Lookbehind uses this value to ensure that the subexpression
     * match ends at the point where the lookbehind was encountered.
     */
    int lookbehindTo;

    /**
     * The original string being matched.
     */
    CharSequence text;

    /**
     * Matcher state used by the last node. NOANCHOR is used when a
     * match does not have to consume all of the input. ENDANCHOR is
     * the mode used for matching all the input.
     */
    static final int ENDANCHOR = 1;
    static final int NOANCHOR = 0;
    int acceptMode = NOANCHOR;

    /**
     * The range of string that last matched the pattern. If the last
     * match failed then first is -1; last initially holds 0 then it
     * holds the index of the end of the last match (which is where the
     * next search starts).
     */
    int first = -1, last = 0;

    /**
     * The end index of what matched in the last match operation.
     */
    int oldLast = -1;

    /**
     * The index of the last position appended in a substitution.
     */
    int lastAppendPosition = 0;

    /**
     * Storage used by nodes to tell what repetition they are on in
     * a pattern, and where groups begin. The nodes themselves are stateless,
     * so they rely on this field to hold state during a match.
     */
    int[] locals;

    /**
     * Storage used by top greedy Loop node to store a specific hash set to
     * keep the beginning index of the failed repetition match. The nodes
     * themselves are stateless, so they rely on this field to hold state
     * during a match.
     */
    IntHashSet[] localsPos;

    /**
     * Boolean indicating whether or not more input could change
     * the results of the last match.
     *
     * If hitEnd is true, and a match was found, then more input
     * might cause a different match to be found.
     * If hitEnd is true and a match was not found, then more
     * input could cause a match to be found.
     * If hitEnd is false and a match was found, then more input
     * will not change the match.
     * If hitEnd is false and a match was not found, then more
     * input will not cause a match to be found.
     */
    boolean hitEnd;

    /**
     * Boolean indicating whether or not more input could change
     * a positive match into a negative one.
     *
     * If requireEnd is true, and a match was found, then more
     * input could cause the match to be lost.
     * If requireEnd is false and a match was found, then more
     * input might change the match but the match won't be lost.
     * If a match was not found, then requireEnd has no meaning.
     */
    boolean requireEnd;

    /**
     * If transparentBounds is true then the boundaries of this
     * matcher's region are transparent to lookahead, lookbehind,
     * and boundary matching constructs that try to see beyond them.
     */
    boolean transparentBounds = false;

    /**
     * If anchoringBounds is true then the boundaries of this
     * matcher's region match anchors such as ^ and $.
     */
    boolean anchoringBounds = true;

    /**
     * Number of times this matcher's state has been modified
     */
    int modCount;

    /**
     * No default constructor.
     */
    Matcher() {
    }

    /**
     * All matchers have the state used by Pattern during a match.
     */
    Matcher(Pattern parent, CharSequence text) {
        this.parentPattern = parent;
        this.text = text;

        // Allocate state storage
        int parentGroupCount = Math.max(parent.capturingGroupCount, 10);
        groups = new int[parentGroupCount * 2];
        locals = new int[parent.localCount];
        localsPos = new IntHashSet[parent.localTCNCount];

        // Put fields into initial states
        reset();
    }

    /**
     * Returns the pattern that is interpreted by this matcher.
     *
     * @return  The pattern for which this matcher was created
     */
    public Pattern pattern() {
        return parentPattern;
    }

    /**
     * Returns the match state of this matcher as a {@link MatchResult}.
     * The result is unaffected by subsequent operations performed upon this
     * matcher.
     *
     * @return  a {@code MatchResult} with the state of this matcher
     * @since 1.5
     */
    public MatchResult toMatchResult() {
        return toMatchResult(text.toString());
    }

    private MatchResult toMatchResult(String text) {
        return new ImmutableMatchResult(this.first,
                                        this.last,
                                        groupCount(),
                                        this.groups.clone(),
                                        text);
    }

    private static class ImmutableMatchResult implements MatchResult {
        private final int first;
        private final int last;
        private final int[] groups;
        private final int groupCount;
        private final String text;

        ImmutableMatchResult(int first, int last, int groupCount,
                             int groups[], String text)
        {
            this.first = first;
            this.last = last;
            this.groupCount = groupCount;
            this.groups = groups;
            this.text = text;
        }

        @Override
        public int start() {
            checkMatch();
            return first;
        }

        @Override
        public int start(int group) {
            checkMatch();
            if (group < 0 || group > groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            return groups[group * 2];
        }

        @Override
        public int end() {
            checkMatch();
            return last;
        }

        @Override
        public int end(int group) {
            checkMatch();
            if (group < 0 || group > groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            return groups[group * 2 + 1];
        }

        @Override
        public int groupCount() {
            return groupCount;
        }

        @Override
        public String group() {
            checkMatch();
            return group(0);
        }

        @Override
        public String group(int group) {
            checkMatch();
            if (group < 0 || group > groupCount)
                throw new IndexOutOfBoundsException("No group " + group);
            if ((groups[group*2] == -1) || (groups[group*2+1] == -1))
                return null;
            return text.subSequence(groups[group * 2], groups[group * 2 + 1]).toString();
        }

        private void checkMatch() {
            if (first < 0)
                throw new IllegalStateException("No match found");

        }
    }

    /**
     * Changes the {@code Pattern} that this {@code Matcher} uses to
     * find matches with.
     *
     * <p> This method causes this matcher to lose information
     * about the groups of the last match that occurred. The
     * matcher's position in the input is maintained and its
     * last append position is unaffected.</p>
     *
     * @param  newPattern
     *         The new pattern used by this matcher
     * @return  This matcher
     * @throws  IllegalArgumentException
     *          If newPattern is {@code null}
     * @since 1.5
     */
    public Matcher usePattern(Pattern newPattern) {
        if (newPattern == null)
            throw new IllegalArgumentException("Pattern cannot be null");
        parentPattern = newPattern;

        // Reallocate state storage
        int parentGroupCount = Math.max(newPattern.capturingGroupCount, 10);
        groups = new int[parentGroupCount * 2];
        locals = new int[newPattern.localCount];
        for (int i = 0; i < groups.length; i++)
            groups[i] = -1;
        for (int i = 0; i < locals.length; i++)
            locals[i] = -1;
        localsPos = new IntHashSet[parentPattern.localTCNCount];
        modCount++;
        return this;
    }

    /**
     * Resets this matcher.
     *
     * <p> Resetting a matcher discards all of its explicit state information
     * and sets its append position to zero. The matcher's region is set to the
     * default region, which is its entire character sequence. The anchoring
     * and transparency of this matcher's region boundaries are unaffected.
     *
     * @return  This matcher
     */
    public Matcher reset() {
        first = -1;
        last = 0;
        oldLast = -1;
        for(int i=0; i<groups.length; i++)
            groups[i] = -1;
        for(int i=0; i<locals.length; i++)
            locals[i] = -1;
        for (int i = 0; i < localsPos.length; i++) {
            if (localsPos[i] != null)
                localsPos[i].clear();
        }
        lastAppendPosition = 0;
        from = 0;
        to = getTextLength();
        modCount++;
        return this;
    }

    /**
     * Resets this matcher with a new input sequence.
     *
     * <p> Resetting a matcher discards all of its explicit state information
     * and sets its append position to zero.  The matcher's region is set to
     * the default region, which is its entire character sequence.  The
     * anchoring and transparency of this matcher's region boundaries are
     * unaffected.
     *
     * @param  input
     *         The new input character sequence
     *
     * @return  This matcher
     */
    public Matcher reset(CharSequence input) {
        text = input;
        return reset();
    }

    /**
     * Returns the start index of the previous match.
     *
     * @return  The index of the first character matched
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public int start() {
        if (first < 0)
            throw new IllegalStateException("No match available");
        return first;
    }

    /**
     * Returns the start index of the subsequence captured by the given group
     * during the previous match operation.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code start(0)} is equivalent to
     * <i>m.</i>{@code start()}.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The index of the first character captured by the group,
     *          or {@code -1} if the match was successful but the group
     *          itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public int start(int group) {
        if (first < 0)
            throw new IllegalStateException("No match available");
        if (group < 0 || group > groupCount())
            throw new IndexOutOfBoundsException("No group " + group);
        return groups[group * 2];
    }

    /**
     * Returns the start index of the subsequence captured by the given
     * <a href="Pattern.html#groupname">named-capturing group</a> during the
     * previous match operation.
     *
     * @param  name
     *         The name of a named-capturing group in this matcher's pattern
     *
     * @return  The index of the first character captured by the group,
     *          or {@code -1} if the match was successful but the group
     *          itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IllegalArgumentException
     *          If there is no capturing group in the pattern
     *          with the given name
     * @since 1.8
     */
    public int start(String name) {
        return groups[getMatchedGroupIndex(name) * 2];
    }

    /**
     * Returns the offset after the last character matched.
     *
     * @return  The offset after the last character matched
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public int end() {
        if (first < 0)
            throw new IllegalStateException("No match available");
        return last;
    }

    /**
     * Returns the offset after the last character of the subsequence
     * captured by the given group during the previous match operation.
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression <i>m.</i>{@code end(0)} is equivalent to
     * <i>m.</i>{@code end()}.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The offset after the last character captured by the group,
     *          or {@code -1} if the match was successful
     *          but the group itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public int end(int group) {
        if (first < 0)
            throw new IllegalStateException("No match available");
        if (group < 0 || group > groupCount())
            throw new IndexOutOfBoundsException("No group " + group);
        return groups[group * 2 + 1];
    }

    /**
     * Returns the offset after the last character of the subsequence
     * captured by the given <a href="Pattern.html#groupname">named-capturing
     * group</a> during the previous match operation.
     *
     * @param  name
     *         The name of a named-capturing group in this matcher's pattern
     *
     * @return  The offset after the last character captured by the group,
     *          or {@code -1} if the match was successful
     *          but the group itself did not match anything
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IllegalArgumentException
     *          If there is no capturing group in the pattern
     *          with the given name
     * @since 1.8
     */
    public int end(String name) {
        return groups[getMatchedGroupIndex(name) * 2 + 1];
    }

    /**
     * Returns the input subsequence matched by the previous match.
     *
     * <p> For a matcher <i>m</i> with input sequence <i>s</i>,
     * the expressions <i>m.</i>{@code group()} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(),}&nbsp;<i>m.</i>
     * {@code end())} are equivalent.  </p>
     *
     * <p> Note that some patterns, for example {@code a*}, match the empty
     * string.  This method will return the empty string when the pattern
     * successfully matches the empty string in the input.  </p>
     *
     * @return The (possibly empty) subsequence matched by the previous match,
     *         in string form
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     */
    public String group() {
        return group(0);
    }

    /**
     * Returns the input subsequence captured by the given group during the
     * previous match operation.
     *
     * <p> For a matcher <i>m</i>, input sequence <i>s</i>, and group index
     * <i>g</i>, the expressions <i>m.</i>{@code group(}<i>g</i>{@code )} and
     * <i>s.</i>{@code substring(}<i>m.</i>{@code start(}<i>g</i>{@code
     * ),}&nbsp;<i>m.</i>{@code end(}<i>g</i>{@code ))}
     * are equivalent.  </p>
     *
     * <p> <a href="Pattern.html#cg">Capturing groups</a> are indexed from left
     * to right, starting at one.  Group zero denotes the entire pattern, so
     * the expression {@code m.group(0)} is equivalent to {@code m.group()}.
     * </p>
     *
     * <p> If the match was successful but the group specified failed to match
     * any part of the input sequence, then {@code null} is returned. Note
     * that some groups, for example {@code (a*)}, match the empty string.
     * This method will return the empty string when such a group successfully
     * matches the empty string in the input.  </p>
     *
     * @param  group
     *         The index of a capturing group in this matcher's pattern
     *
     * @return  The (possibly empty) subsequence captured by the group
     *          during the previous match, or {@code null} if the group
     *          failed to match part of the input
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IndexOutOfBoundsException
     *          If there is no capturing group in the pattern
     *          with the given index
     */
    public String group(int group) {
        if (first < 0)
            throw new IllegalStateException("No match found");
        if (group < 0 || group > groupCount())
            throw new IndexOutOfBoundsException("No group " + group);
        if ((groups[group*2] == -1) || (groups[group*2+1] == -1))
            return null;
        return getSubSequence(groups[group * 2], groups[group * 2 + 1]).toString();
    }

    /**
     * Returns the input subsequence captured by the given
     * <a href="Pattern.html#groupname">named-capturing group</a> during the
     * previous match operation.
     *
     * <p> If the match was successful but the group specified failed to match
     * any part of the input sequence, then {@code null} is returned. Note
     * that some groups, for example {@code (a*)}, match the empty string.
     * This method will return the empty string when such a group successfully
     * matches the empty string in the input.  </p>
     *
     * @param  name
     *         The name of a named-capturing group in this matcher's pattern
     *
     * @return  The (possibly empty) subsequence captured by the named group
     *          during the previous match, or {@code null} if the group
     *          failed to match part of the input
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IllegalArgumentException
     *          If there is no capturing group in the pattern
     *          with the given name
     * @since 1.7
     */
    public String group(String name) {
        int group = getMatchedGroupIndex(name);
        if ((groups[group*2] == -1) || (groups[group*2+1] == -1))
            return null;
        return getSubSequence(groups[group * 2], groups[group * 2 + 1]).toString();
    }

    /**
     * Returns the number of capturing groups in this matcher's pattern.
     *
     * <p> Group zero denotes the entire pattern by convention. It is not
     * included in this count.
     *
     * <p> Any non-negative integer smaller than or equal to the value
     * returned by this method is guaranteed to be a valid group index for
     * this matcher.  </p>
     *
     * @return The number of capturing groups in this matcher's pattern
     */
    public int groupCount() {
        return parentPattern.capturingGroupCount - 1;
    }

    /**
     * Attempts to match the entire region against the pattern.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return  {@code true} if, and only if, the entire region sequence
     *          matches this matcher's pattern
     */
    public boolean matches() {
        return match(from, ENDANCHOR);
    }

    /**
     * Attempts to find the next subsequence of the input sequence that matches
     * the pattern.
     *
     * <p> This method starts at the beginning of this matcher's region, or, if
     * a previous invocation of the method was successful and the matcher has
     * not since been reset, at the first character not matched by the previous
     * match.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return  {@code true} if, and only if, a subsequence of the input
     *          sequence matches this matcher's pattern
     */
    public boolean find() {
        int nextSearchIndex = last;
        if (nextSearchIndex == first)
            nextSearchIndex++;

        // If next search starts before region, start it at region
        if (nextSearchIndex < from)
            nextSearchIndex = from;

        // If next search starts beyond region then it fails
        if (nextSearchIndex > to) {
            for (int i = 0; i < groups.length; i++)
                groups[i] = -1;
            return false;
        }
        return search(nextSearchIndex);
    }

    /**
     * Resets this matcher and then attempts to find the next subsequence of
     * the input sequence that matches the pattern, starting at the specified
     * index.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods, and subsequent
     * invocations of the {@link #find()} method will start at the first
     * character not matched by this match.  </p>
     *
     * @param start the index to start searching for a match
     * @throws  IndexOutOfBoundsException
     *          If start is less than zero or if start is greater than the
     *          length of the input sequence.
     *
     * @return  {@code true} if, and only if, a subsequence of the input
     *          sequence starting at the given index matches this matcher's
     *          pattern
     */
    public boolean find(int start) {
        int limit = getTextLength();
        if ((start < 0) || (start > limit))
            throw new IndexOutOfBoundsException("Illegal start index");
        reset();
        return search(start);
    }

    /**
     * Attempts to match the input sequence, starting at the beginning of the
     * region, against the pattern.
     *
     * <p> Like the {@link #matches matches} method, this method always starts
     * at the beginning of the region; unlike that method, it does not
     * require that the entire region be matched.
     *
     * <p> If the match succeeds then more information can be obtained via the
     * {@code start}, {@code end}, and {@code group} methods.  </p>
     *
     * @return  {@code true} if, and only if, a prefix of the input
     *          sequence matches this matcher's pattern
     */
    public boolean lookingAt() {
        return match(from, NOANCHOR);
    }

    /**
     * Returns a literal replacement {@code String} for the specified
     * {@code String}.
     *
     * This method produces a {@code String} that will work
     * as a literal replacement {@code s} in the
     * {@code appendReplacement} method of the {@link Matcher} class.
     * The {@code String} produced will match the sequence of characters
     * in {@code s} treated as a literal sequence. Slashes ('\') and
     * dollar signs ('$') will be given no special meaning.
     *
     * @param  s The string to be literalized
     * @return  A literal string replacement
     * @since 1.5
     */
    public static String quoteReplacement(String s) {
        if ((s.indexOf('\\') == -1) && (s.indexOf('$') == -1))
            return s;
        StringBuilder sb = new StringBuilder();
        for (int i=0; i<s.length(); i++) {
            char c = s.charAt(i);
            if (c == '\\' || c == '$') {
                sb.append('\\');
            }
            sb.append(c);
        }
        return sb.toString();
    }

    /**
     * Implements a non-terminal append-and-replace step.
     *
     * <p> This method performs the following actions: </p>
     *
     * <ol>
     *
     *   <li><p> It reads characters from the input sequence, starting at the
     *   append position, and appends them to the given string buffer.  It
     *   stops after reading the last character preceding the previous match,
     *   that is, the character at index {@link
     *   #start()}&nbsp;{@code -}&nbsp;{@code 1}.  </p></li>
     *
     *   <li><p> It appends the given replacement string to the string buffer.
     *   </p></li>
     *
     *   <li><p> It sets the append position of this matcher to the index of
     *   the last character matched, plus one, that is, to {@link #end()}.
     *   </p></li>
     *
     * </ol>
     *
     * <p> The replacement string may contain references to subsequences
     * captured during the previous match: Each occurrence of
     * <code>${</code><i>name</i><code>}</code> or {@code $}<i>g</i>
     * will be replaced by the result of evaluating the corresponding
     * {@link #group(String) group(name)} or {@link #group(int) group(g)}
     * respectively. For {@code $}<i>g</i>,
     * the first number after the {@code $} is always treated as part of
     * the group reference. Subsequent numbers are incorporated into g if
     * they would form a legal group reference. Only the numerals '0'
     * through '9' are considered as potential components of the group
     * reference. If the second group matched the string {@code "foo"}, for
     * example, then passing the replacement string {@code "$2bar"} would
     * cause {@code "foobar"} to be appended to the string buffer. A dollar
     * sign ({@code $}) may be included as a literal in the replacement
     * string by preceding it with a backslash ({@code \$}).
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> This method is intended to be used in a loop together with the
     * {@link #appendTail(StringBuffer) appendTail} and {@link #find() find}
     * methods.  The following code, for example, writes {@code one dog two dogs
     * in the yard} to the standard-output stream: </p>
     *
     * <blockquote><pre>
     * Pattern p = Pattern.compile("cat");
     * Matcher m = p.matcher("one cat two cats in the yard");
     * StringBuffer sb = new StringBuffer();
     * while (m.find()) {
     *     m.appendReplacement(sb, "dog");
     * }
     * m.appendTail(sb);
     * System.out.println(sb.toString());</pre></blockquote>
     *
     * @param  sb
     *         The target string buffer
     *
     * @param  replacement
     *         The replacement string
     *
     * @return  This matcher
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     *
     * @throws  IllegalArgumentException
     *          If the replacement string refers to a named-capturing
     *          group that does not exist in the pattern
     *
     * @throws  IndexOutOfBoundsException
     *          If the replacement string refers to a capturing group
     *          that does not exist in the pattern
     */
    public Matcher appendReplacement(StringBuffer sb, String replacement) {
        // If no match, return error
        if (first < 0)
            throw new IllegalStateException("No match available");
        StringBuilder result = new StringBuilder();
        appendExpandedReplacement(replacement, result);
        // Append the intervening text
        sb.append(text, lastAppendPosition, first);
        // Append the match substitution
        sb.append(result);
        lastAppendPosition = last;
        modCount++;
        return this;
    }

    /**
     * Implements a non-terminal append-and-replace step.
     *
     * <p> This method performs the following actions: </p>
     *
     * <ol>
     *
     *   <li><p> It reads characters from the input sequence, starting at the
     *   append position, and appends them to the given string builder.  It
     *   stops after reading the last character preceding the previous match,
     *   that is, the character at index {@link
     *   #start()}&nbsp;{@code -}&nbsp;{@code 1}.  </p></li>
     *
     *   <li><p> It appends the given replacement string to the string builder.
     *   </p></li>
     *
     *   <li><p> It sets the append position of this matcher to the index of
     *   the last character matched, plus one, that is, to {@link #end()}.
     *   </p></li>
     *
     * </ol>
     *
     * <p> The replacement string may contain references to subsequences
     * captured during the previous match: Each occurrence of
     * {@code $}<i>g</i> will be replaced by the result of
     * evaluating {@link #group(int) group}{@code (}<i>g</i>{@code )}.
     * The first number after the {@code $} is always treated as part of
     * the group reference. Subsequent numbers are incorporated into g if
     * they would form a legal group reference. Only the numerals '0'
     * through '9' are considered as potential components of the group
     * reference. If the second group matched the string {@code "foo"}, for
     * example, then passing the replacement string {@code "$2bar"} would
     * cause {@code "foobar"} to be appended to the string builder. A dollar
     * sign ({@code $}) may be included as a literal in the replacement
     * string by preceding it with a backslash ({@code \$}).
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> This method is intended to be used in a loop together with the
     * {@link #appendTail(StringBuilder) appendTail} and
     * {@link #find() find} methods. The following code, for example, writes
     * {@code one dog two dogs in the yard} to the standard-output stream: </p>
     *
     * <blockquote><pre>
     * Pattern p = Pattern.compile("cat");
     * Matcher m = p.matcher("one cat two cats in the yard");
     * StringBuilder sb = new StringBuilder();
     * while (m.find()) {
     *     m.appendReplacement(sb, "dog");
     * }
     * m.appendTail(sb);
     * System.out.println(sb.toString());</pre></blockquote>
     *
     * @param  sb
     *         The target string builder
     * @param  replacement
     *         The replacement string
     * @return  This matcher
     *
     * @throws  IllegalStateException
     *          If no match has yet been attempted,
     *          or if the previous match operation failed
     * @throws  IllegalArgumentException
     *          If the replacement string refers to a named-capturing
     *          group that does not exist in the pattern
     * @throws  IndexOutOfBoundsException
     *          If the replacement string refers to a capturing group
     *          that does not exist in the pattern
     * @since 9
     */
    public Matcher appendReplacement(StringBuilder sb, String replacement) {
        // If no match, return error
        if (first < 0)
            throw new IllegalStateException("No match available");
        StringBuilder result = new StringBuilder();
        appendExpandedReplacement(replacement, result);
        // Append the intervening text
        sb.append(text, lastAppendPosition, first);
        // Append the match substitution
        sb.append(result);
        lastAppendPosition = last;
        modCount++;
        return this;
    }

    /**
     * Processes replacement string to replace group references with
     * groups.
     */
    private StringBuilder appendExpandedReplacement(
        String replacement, StringBuilder result) {
        int cursor = 0;
        while (cursor < replacement.length()) {
            char nextChar = replacement.charAt(cursor);
            if (nextChar == '\\') {
                cursor++;
                if (cursor == replacement.length())
                    throw new IllegalArgumentException(
                        "character to be escaped is missing");
                nextChar = replacement.charAt(cursor);
                result.append(nextChar);
                cursor++;
            } else if (nextChar == '$') {
                // Skip past $
                cursor++;
                // Throw IAE if this "$" is the last character in replacement
                if (cursor == replacement.length())
                   throw new IllegalArgumentException(
                        "Illegal group reference: group index is missing");
                nextChar = replacement.charAt(cursor);
                int refNum = -1;
                if (nextChar == '{') {
                    cursor++;
                    StringBuilder gsb = new StringBuilder();
                    while (cursor < replacement.length()) {
                        nextChar = replacement.charAt(cursor);
                        if (ASCII.isLower(nextChar) ||
                            ASCII.isUpper(nextChar) ||
                            ASCII.isDigit(nextChar)) {
                            gsb.append(nextChar);
                            cursor++;
                        } else {
                            break;
                        }
                    }
                    if (gsb.length() == 0)
                        throw new IllegalArgumentException(
                            "named capturing group has 0 length name");
                    if (nextChar != '}')
                        throw new IllegalArgumentException(
                            "named capturing group is missing trailing '}'");
                    String gname = gsb.toString();
                    if (ASCII.isDigit(gname.charAt(0)))
                        throw new IllegalArgumentException(
                            "capturing group name {" + gname +
                            "} starts with digit character");
                    if (!parentPattern.namedGroups().containsKey(gname))
                        throw new IllegalArgumentException(
                            "No group with name {" + gname + "}");
                    refNum = parentPattern.namedGroups().get(gname);
                    cursor++;
                } else {
                    // The first number is always a group
                    refNum = nextChar - '0';
                    if ((refNum < 0) || (refNum > 9))
                        throw new IllegalArgumentException(
                            "Illegal group reference");
                    cursor++;
                    // Capture the largest legal group string
                    boolean done = false;
                    while (!done) {
                        if (cursor >= replacement.length()) {
                            break;
                        }
                        int nextDigit = replacement.charAt(cursor) - '0';
                        if ((nextDigit < 0) || (nextDigit > 9)) { // not a number
                            break;
                        }
                        int newRefNum = (refNum * 10) + nextDigit;
                        if (groupCount() < newRefNum) {
                            done = true;
                        } else {
                            refNum = newRefNum;
                            cursor++;
                        }
                    }
                }
                // Append group
                if (start(refNum) != -1 && end(refNum) != -1)
                    result.append(text, start(refNum), end(refNum));
            } else {
                result.append(nextChar);
                cursor++;
            }
        }
        return result;
    }

    /**
     * Implements a terminal append-and-replace step.
     *
     * <p> This method reads characters from the input sequence, starting at
     * the append position, and appends them to the given string buffer.  It is
     * intended to be invoked after one or more invocations of the {@link
     * #appendReplacement(StringBuffer, String) appendReplacement} method in
     * order to copy the remainder of the input sequence.  </p>
     *
     * @param  sb
     *         The target string buffer
     *
     * @return  The target string buffer
     */
    public StringBuffer appendTail(StringBuffer sb) {
        sb.append(text, lastAppendPosition, getTextLength());
        return sb;
    }

    /**
     * Implements a terminal append-and-replace step.
     *
     * <p> This method reads characters from the input sequence, starting at
     * the append position, and appends them to the given string builder.  It is
     * intended to be invoked after one or more invocations of the {@link
     * #appendReplacement(StringBuilder, String)
     * appendReplacement} method in order to copy the remainder of the input
     * sequence.  </p>
     *
     * @param  sb
     *         The target string builder
     *
     * @return  The target string builder
     *
     * @since 9
     */
    public StringBuilder appendTail(StringBuilder sb) {
        sb.append(text, lastAppendPosition, getTextLength());
        return sb;
    }

    /**
     * Replaces every subsequence of the input sequence that matches the
     * pattern with the given replacement string.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for matches of the pattern.  Characters that are not
     * part of any match are appended directly to the result string; each match
     * is replaced in the result by the replacement string.  The replacement
     * string may contain references to captured subsequences as in the {@link
     * #appendReplacement appendReplacement} method.
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code a*b}, the input
     * {@code "aabfooaabfooabfoob"}, and the replacement string
     * {@code "-"}, an invocation of this method on a matcher for that
     * expression would yield the string {@code "-foo-foo-foo-"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * @param  replacement
     *         The replacement string
     *
     * @return  The string constructed by replacing each matching subsequence
     *          by the replacement string, substituting captured subsequences
     *          as needed
     */
    public String replaceAll(String replacement) {
        reset();
        boolean result = find();
        if (result) {
            StringBuilder sb = new StringBuilder();
            do {
                appendReplacement(sb, replacement);
                result = find();
            } while (result);
            appendTail(sb);
            return sb.toString();
        }
        return text.toString();
    }

    /**
     * Replaces every subsequence of the input sequence that matches the
     * pattern with the result of applying the given replacer function to the
     * match result of this matcher corresponding to that subsequence.
     * Exceptions thrown by the function are relayed to the caller.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for matches of the pattern.  Characters that are not
     * part of any match are appended directly to the result string; each match
     * is replaced in the result by the applying the replacer function that
     * returns a replacement string.  Each replacement string may contain
     * references to captured subsequences as in the {@link #appendReplacement
     * appendReplacement} method.
     *
     * <p> Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * a replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the function
     * {@code mr -> mr.group().toUpperCase()}, an invocation of this method on
     * a matcher for that expression would yield the string
     * {@code "zzzDOGzzzDOGzzz"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * <p> The replacer function should not modify this matcher's state during
     * replacement.  This method will, on a best-effort basis, throw a
     * {@link java.util.ConcurrentModificationException} if such modification is
     * detected.
     *
     * <p> The state of each match result passed to the replacer function is
     * guaranteed to be constant only for the duration of the replacer function
     * call and only if the replacer function does not modify this matcher's
     * state.
     *
     * @implNote
     * This implementation applies the replacer function to this matcher, which
     * is an instance of {@code MatchResult}.
     *
     * @param  replacer
     *         The function to be applied to the match result of this matcher
     *         that returns a replacement string.
     * @return  The string constructed by replacing each matching subsequence
     *          with the result of applying the replacer function to that
     *          matched subsequence, substituting captured subsequences as
     *          needed.
     * @throws NullPointerException if the replacer function is null
     * @throws ConcurrentModificationException if it is detected, on a
     *         best-effort basis, that the replacer function modified this
     *         matcher's state
     * @since 9
     */
    public String replaceAll(Function<MatchResult, String> replacer) {
        Objects.requireNonNull(replacer);
        reset();
        boolean result = find();
        if (result) {
            StringBuilder sb = new StringBuilder();
            do {
                int ec = modCount;
                String replacement =  replacer.apply(this);
                if (ec != modCount)
                    throw new ConcurrentModificationException();
                appendReplacement(sb, replacement);
                result = find();
            } while (result);
            appendTail(sb);
            return sb.toString();
        }
        return text.toString();
    }

    /**
     * Returns a stream of match results for each subsequence of the input
     * sequence that matches the pattern.  The match results occur in the
     * same order as the matching subsequences in the input sequence.
     *
     * <p> Each match result is produced as if by {@link #toMatchResult()}.
     *
     * <p> This method does not reset this matcher.  Matching starts on
     * initiation of the terminal stream operation either at the beginning of
     * this matcher's region, or, if the matcher has not since been reset, at
     * the first character not matched by a previous match.
     *
     * <p> If the matcher is to be used for further matching operations after
     * the terminal stream operation completes then it should be first reset.
     *
     * <p> This matcher's state should not be modified during execution of the
     * returned stream's pipeline.  The returned stream's source
     * {@code Spliterator} is <em>fail-fast</em> and will, on a best-effort
     * basis, throw a {@link java.util.ConcurrentModificationException} if such
     * modification is detected.
     *
     * @return a sequential stream of match results.
     * @since 9
     */
    public Stream<MatchResult> results() {
        class MatchResultIterator implements Iterator<MatchResult> {
            // -ve for call to find, 0 for not found, 1 for found
            int state = -1;
            // State for concurrent modification checking
            // -1 for uninitialized
            int expectedCount = -1;
            // The input sequence as a string, set once only after first find
            // Avoids repeated conversion from CharSequence for each match
            String textAsString;

            @Override
            public MatchResult next() {
                if (expectedCount >= 0 && expectedCount != modCount)
                    throw new ConcurrentModificationException();

                if (!hasNext())
                    throw new NoSuchElementException();

                state = -1;
                return toMatchResult(textAsString);
            }

            @Override
            public boolean hasNext() {
                if (state >= 0)
                    return state == 1;

                // Defer throwing ConcurrentModificationException to when next
                // or forEachRemaining is called.  The is consistent with other
                // fail-fast implementations.
                if (expectedCount >= 0 && expectedCount != modCount)
                    return true;

                boolean found = find();
                // Capture the input sequence as a string on first find
                if (found && state < 0)
                    textAsString = text.toString();
                state = found ? 1 : 0;
                expectedCount = modCount;
                return found;
            }

            @Override
            public void forEachRemaining(Consumer<? super MatchResult> action) {
                if (expectedCount >= 0 && expectedCount != modCount)
                    throw new ConcurrentModificationException();

                int s = state;
                if (s == 0)
                    return;

                // Set state to report no more elements on further operations
                state = 0;
                expectedCount = -1;

                // Perform a first find if required
                if (s < 0 && !find())
                    return;

                // Capture the input sequence as a string on first find
                textAsString = text.toString();

                do {
                    int ec = modCount;
                    action.accept(toMatchResult(textAsString));
                    if (ec != modCount)
                        throw new ConcurrentModificationException();
                } while (find());
            }
        }
        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
                new MatchResultIterator(), Spliterator.ORDERED | Spliterator.NONNULL), false);
    }

    /**
     * Replaces the first subsequence of the input sequence that matches the
     * pattern with the given replacement string.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for a match of the pattern.  Characters that are not
     * part of the match are appended directly to the result string; the match
     * is replaced in the result by the replacement string.  The replacement
     * string may contain references to captured subsequences as in the {@link
     * #appendReplacement appendReplacement} method.
     *
     * <p>Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the replacement string
     * {@code "cat"}, an invocation of this method on a matcher for that
     * expression would yield the string {@code "zzzcatzzzdogzzz"}.  </p>
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.  </p>
     *
     * @param  replacement
     *         The replacement string
     * @return  The string constructed by replacing the first matching
     *          subsequence by the replacement string, substituting captured
     *          subsequences as needed
     */
    public String replaceFirst(String replacement) {
        if (replacement == null)
            throw new NullPointerException("replacement");
        reset();
        if (!find())
            return text.toString();
        StringBuilder sb = new StringBuilder();
        appendReplacement(sb, replacement);
        appendTail(sb);
        return sb.toString();
    }

    /**
     * Replaces the first subsequence of the input sequence that matches the
     * pattern with the result of applying the given replacer function to the
     * match result of this matcher corresponding to that subsequence.
     * Exceptions thrown by the replace function are relayed to the caller.
     *
     * <p> This method first resets this matcher.  It then scans the input
     * sequence looking for a match of the pattern.  Characters that are not
     * part of the match are appended directly to the result string; the match
     * is replaced in the result by the applying the replacer function that
     * returns a replacement string.  The replacement string may contain
     * references to captured subsequences as in the {@link #appendReplacement
     * appendReplacement} method.
     *
     * <p>Note that backslashes ({@code \}) and dollar signs ({@code $}) in
     * the replacement string may cause the results to be different than if it
     * were being treated as a literal replacement string. Dollar signs may be
     * treated as references to captured subsequences as described above, and
     * backslashes are used to escape literal characters in the replacement
     * string.
     *
     * <p> Given the regular expression {@code dog}, the input
     * {@code "zzzdogzzzdogzzz"}, and the function
     * {@code mr -> mr.group().toUpperCase()}, an invocation of this method on
     * a matcher for that expression would yield the string
     * {@code "zzzDOGzzzdogzzz"}.
     *
     * <p> Invoking this method changes this matcher's state.  If the matcher
     * is to be used in further matching operations then it should first be
     * reset.
     *
     * <p> The replacer function should not modify this matcher's state during
     * replacement.  This method will, on a best-effort basis, throw a
     * {@link java.util.ConcurrentModificationException} if such modification is
     * detected.
     *
     * <p> The state of the match result passed to the replacer function is
     * guaranteed to be constant only for the duration of the replacer function
     * call and only if the replacer function does not modify this matcher's
     * state.
     *
     * @implNote
     * This implementation applies the replacer function to this matcher, which
     * is an instance of {@code MatchResult}.
     *
     * @param  replacer
     *         The function to be applied to the match result of this matcher
     *         that returns a replacement string.
     * @return  The string constructed by replacing the first matching
     *          subsequence with the result of applying the replacer function to
     *          the matched subsequence, substituting captured subsequences as
     *          needed.
     * @throws NullPointerException if the replacer function is null
     * @throws ConcurrentModificationException if it is detected, on a
     *         best-effort basis, that the replacer function modified this
     *         matcher's state
     * @since 9
     */
    public String replaceFirst(Function<MatchResult, String> replacer) {
        Objects.requireNonNull(replacer);
        reset();
        if (!find())
            return text.toString();
        StringBuilder sb = new StringBuilder();
        int ec = modCount;
        String replacement = replacer.apply(this);
        if (ec != modCount)
            throw new ConcurrentModificationException();
        appendReplacement(sb, replacement);
        appendTail(sb);
        return sb.toString();
    }

    /**
     * Sets the limits of this matcher's region. The region is the part of the
     * input sequence that will be searched to find a match. Invoking this
     * method resets the matcher, and then sets the region to start at the
     * index specified by the {@code start} parameter and end at the
     * index specified by the {@code end} parameter.
     *
     * <p>Depending on the transparency and anchoring being used (see
     * {@link #useTransparentBounds(boolean) useTransparentBounds} and
     * {@link #useAnchoringBounds(boolean) useAnchoringBounds}), certain
     * constructs such as anchors may behave differently at or around the
     * boundaries of the region.
     *
     * @param  start
     *         The index to start searching at (inclusive)
     * @param  end
     *         The index to end searching at (exclusive)
     * @throws  IndexOutOfBoundsException
     *          If start or end is less than zero, if
     *          start is greater than the length of the input sequence, if
     *          end is greater than the length of the input sequence, or if
     *          start is greater than end.
     * @return  this matcher
     * @since 1.5
     */
    public Matcher region(int start, int end) {
        if ((start < 0) || (start > getTextLength()))
            throw new IndexOutOfBoundsException("start");
        if ((end < 0) || (end > getTextLength()))
            throw new IndexOutOfBoundsException("end");
        if (start > end)
            throw new IndexOutOfBoundsException("start > end");
        reset();
        from = start;
        to = end;
        return this;
    }

    /**
     * Reports the start index of this matcher's region. The
     * searches this matcher conducts are limited to finding matches
     * within {@link #regionStart() regionStart} (inclusive) and
     * {@link #regionEnd() regionEnd} (exclusive).
     *
     * @return  The starting point of this matcher's region
     * @since 1.5
     */
    public int regionStart() {
        return from;
    }

    /**
     * Reports the end index (exclusive) of this matcher's region.
     * The searches this matcher conducts are limited to finding matches
     * within {@link #regionStart() regionStart} (inclusive) and
     * {@link #regionEnd() regionEnd} (exclusive).
     *
     * @return  the ending point of this matcher's region
     * @since 1.5
     */
    public int regionEnd() {
        return to;
    }

    /**
     * Queries the transparency of region bounds for this matcher.
     *
     * <p> This method returns {@code true} if this matcher uses
     * <i>transparent</i> bounds, {@code false} if it uses <i>opaque</i>
     * bounds.
     *
     * <p> See {@link #useTransparentBounds(boolean) useTransparentBounds} for a
     * description of transparent and opaque bounds.
     *
     * <p> By default, a matcher uses opaque region boundaries.
     *
     * @return {@code true} iff this matcher is using transparent bounds,
     *         {@code false} otherwise.
     * @see java.util.regex.Matcher#useTransparentBounds(boolean)
     * @since 1.5
     */
    public boolean hasTransparentBounds() {
        return transparentBounds;
    }

    /**
     * Sets the transparency of region bounds for this matcher.
     *
     * <p> Invoking this method with an argument of {@code true} will set this
     * matcher to use <i>transparent</i> bounds. If the boolean
     * argument is {@code false}, then <i>opaque</i> bounds will be used.
     *
     * <p> Using transparent bounds, the boundaries of this
     * matcher's region are transparent to lookahead, lookbehind,
     * and boundary matching constructs. Those constructs can see beyond the
     * boundaries of the region to see if a match is appropriate.
     *
     * <p> Using opaque bounds, the boundaries of this matcher's
     * region are opaque to lookahead, lookbehind, and boundary matching
     * constructs that may try to see beyond them. Those constructs cannot
     * look past the boundaries so they will fail to match anything outside
     * of the region.
     *
     * <p> By default, a matcher uses opaque bounds.
     *
     * @param  b a boolean indicating whether to use opaque or transparent
     *         regions
     * @return this matcher
     * @see java.util.regex.Matcher#hasTransparentBounds
     * @since 1.5
     */
    public Matcher useTransparentBounds(boolean b) {
        transparentBounds = b;
        return this;
    }

    /**
     * Queries the anchoring of region bounds for this matcher.
     *
     * <p> This method returns {@code true} if this matcher uses
     * <i>anchoring</i> bounds, {@code false} otherwise.
     *
     * <p> See {@link #useAnchoringBounds(boolean) useAnchoringBounds} for a
     * description of anchoring bounds.
     *
     * <p> By default, a matcher uses anchoring region boundaries.
     *
     * @return {@code true} iff this matcher is using anchoring bounds,
     *         {@code false} otherwise.
     * @see java.util.regex.Matcher#useAnchoringBounds(boolean)
     * @since 1.5
     */
    public boolean hasAnchoringBounds() {
        return anchoringBounds;
    }

    /**
     * Sets the anchoring of region bounds for this matcher.
     *
     * <p> Invoking this method with an argument of {@code true} will set this
     * matcher to use <i>anchoring</i> bounds. If the boolean
     * argument is {@code false}, then <i>non-anchoring</i> bounds will be
     * used.
     *
     * <p> Using anchoring bounds, the boundaries of this
     * matcher's region match anchors such as ^ and $.
     *
     * <p> Without anchoring bounds, the boundaries of this
     * matcher's region will not match anchors such as ^ and $.
     *
     * <p> By default, a matcher uses anchoring region boundaries.
     *
     * @param  b a boolean indicating whether or not to use anchoring bounds.
     * @return this matcher
     * @see java.util.regex.Matcher#hasAnchoringBounds
     * @since 1.5
     */
    public Matcher useAnchoringBounds(boolean b) {
        anchoringBounds = b;
        return this;
    }

    /**
     * <p>Returns the string representation of this matcher. The
     * string representation of a {@code Matcher} contains information
     * that may be useful for debugging. The exact format is unspecified.
     *
     * @return  The string representation of this matcher
     * @since 1.5
     */
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("java.util.regex.Matcher")
                .append("[pattern=").append(pattern())
                .append(" region=")
                .append(regionStart()).append(',').append(regionEnd())
                .append(" lastmatch=");
        if ((first >= 0) && (group() != null)) {
            sb.append(group());
        }
        sb.append(']');
        return sb.toString();
    }

    /**
     * <p>Returns true if the end of input was hit by the search engine in
     * the last match operation performed by this matcher.
     *
     * <p>When this method returns true, then it is possible that more input
     * would have changed the result of the last search.
     *
     * @return  true iff the end of input was hit in the last match; false
     *          otherwise
     * @since 1.5
     */
    public boolean hitEnd() {
        return hitEnd;
    }

    /**
     * <p>Returns true if more input could change a positive match into a
     * negative one.
     *
     * <p>If this method returns true, and a match was found, then more
     * input could cause the match to be lost. If this method returns false
     * and a match was found, then more input might change the match but the
     * match won't be lost. If a match was not found, then requireEnd has no
     * meaning.
     *
     * @return  true iff more input could change a positive match into a
     *          negative one.
     * @since 1.5
     */
    public boolean requireEnd() {
        return requireEnd;
    }

    /**
     * Initiates a search to find a Pattern within the given bounds.
     * The groups are filled with default values and the match of the root
     * of the state machine is called. The state machine will hold the state
     * of the match as it proceeds in this matcher.
     *
     * Matcher.from is not set here, because it is the "hard" boundary
     * of the start of the search which anchors will set to. The from param
     * is the "soft" boundary of the start of the search, meaning that the
     * regex tries to match at that index but ^ won't match there. Subsequent
     * calls to the search methods start at a new "soft" boundary which is
     * the end of the previous match.
     */
    boolean search(int from) {
        this.hitEnd = false;
        this.requireEnd = false;
        from        = from < 0 ? 0 : from;
        this.first  = from;
        this.oldLast = oldLast < 0 ? from : oldLast;
        for (int i = 0; i < groups.length; i++)
            groups[i] = -1;
        for (int i = 0; i < localsPos.length; i++) {
            if (localsPos[i] != null)
                localsPos[i].clear();
        }
        acceptMode = NOANCHOR;
        boolean result = parentPattern.root.match(this, from, text);
        if (!result)
            this.first = -1;
        this.oldLast = this.last;
        this.modCount++;
        return result;
    }

    /**
     * Initiates a search for an anchored match to a Pattern within the given
     * bounds. The groups are filled with default values and the match of the
     * root of the state machine is called. The state machine will hold the
     * state of the match as it proceeds in this matcher.
     */
    boolean match(int from, int anchor) {
        this.hitEnd = false;
        this.requireEnd = false;
        from        = from < 0 ? 0 : from;
        this.first  = from;
        this.oldLast = oldLast < 0 ? from : oldLast;
        for (int i = 0; i < groups.length; i++)
            groups[i] = -1;
        for (int i = 0; i < localsPos.length; i++) {
            if (localsPos[i] != null)
                localsPos[i].clear();
        }
        acceptMode = anchor;
        boolean result = parentPattern.matchRoot.match(this, from, text);
        if (!result)
            this.first = -1;
        this.oldLast = this.last;
        this.modCount++;
        return result;
    }

    /**
     * Returns the end index of the text.
     *
     * @return the index after the last character in the text
     */
    int getTextLength() {
        return text.length();
    }

    /**
     * Generates a String from this matcher's input in the specified range.
     *
     * @param  beginIndex   the beginning index, inclusive
     * @param  endIndex     the ending index, exclusive
     * @return A String generated from this matcher's input
     */
    CharSequence getSubSequence(int beginIndex, int endIndex) {
        return text.subSequence(beginIndex, endIndex);
    }

    /**
     * Returns this matcher's input character at index i.
     *
     * @return A char from the specified index
     */
    char charAt(int i) {
        return text.charAt(i);
    }

    /**
     * Returns the group index of the matched capturing group.
     *
     * @return the index of the named-capturing group
     */
    int getMatchedGroupIndex(String name) {
        Objects.requireNonNull(name, "Group name");
        if (first < 0)
            throw new IllegalStateException("No match found");
        if (!parentPattern.namedGroups().containsKey(name))
            throw new IllegalArgumentException("No group with name <" + name + ">");
        return parentPattern.namedGroups().get(name);
    }
}