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/*******************************************************************************
* Copyright (c) 2019 Paul Pazderski, Thomas Wolf, and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* Paul Pazderski; Thomas Wolf - initial API and implementation
*******************************************************************************/
package org.eclipse.jface.text;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.stream.Collectors;
/**
* Fast matcher to find the occurrences of any of a fixed set of constant strings. Supports finding
* all (possibly overlapping) matches, or only the leftmost longest match.
*
* @since 3.9
*/
public class MultiStringMatcher {
// An implementation of the Aho-Corasick algorithm (without the DFA construction from section 6 of the
// paper; just the failure and output links).
//
// See Aho, Alfred V.; Corasick, Margaret J.: "Efficient String Matching: An Aid to Bibliographic Search",
// CACM 18(6), 1975.
//
// The algorithm has been modified to support reporting either all matches or only leftmost longest matches.
/**
* Describes a match result of {@link MultiStringMatcher#indexOf(CharSequence, int)}, giving
* access to the matched string and the offset in the text it was matched at.
*/
public static interface Match {
/**
* Obtains the matched string.
*
* @return the text matched
*/
String getText();
/**
* Obtains the offset the {@link #getText() text} was matched at.
*
* @return the offset
*/
int getOffset();
}
/** A Builder for creating a {@link MultiStringMatcher}. */
public static interface Builder {
/**
* Adds search strings to be looked for. {@code null} and empty strings in the arguments are
* ignored.
*
* @param searchStrings to add to be looked for by the matcher.
* @return this
* @throws IllegalStateException if the {@link MultiStringMatcher} was already built.
*/
Builder add(String... searchStrings);
/**
* Returns the {@link MultiStringMatcher} built by this builder.
*
* Note that a {@link Builder} instance can build only one
* {@link MultiStringMatcher} instance. This is by design; otherwise the builder would have
* to store all the searchStrings somewhere, which may be rather memory intensive if a lot
* of search strings are added.
*
*
* @return the {@link MultiStringMatcher}
* @throws IllegalStateException if the {@link MultiStringMatcher} was already built.
*/
MultiStringMatcher build();
}
private static class BuilderImpl implements Builder {
private MultiStringMatcher m;
BuilderImpl() {
m= new MultiStringMatcher();
}
private void check() {
if (m == null) {
throw new IllegalStateException("Builder.build() was already called"); //$NON-NLS-1$
}
}
@Override
public Builder add(String... searchStrings) {
check();
m.add(searchStrings);
return this;
}
@Override
public MultiStringMatcher build() {
check();
MultiStringMatcher result= m;
m= null;
if (!result.root.hasChildren()) {
// no search strings were added; return a specialized "matches nothing" matcher
return new MultiStringMatcher() {
@Override
public void find(CharSequence text, int offset, Consumer matches) {
return;
}
@Override
public Match indexOf(CharSequence text, int offset) {
return null;
}
};
}
result.buildLinks();
return result;
}
}
/**
* Creates an initially empty {@link Builder}.
*
* @return the {@link Builder}
*/
public static Builder builder() {
return new BuilderImpl();
}
private static class MatchResult implements Match {
private final String match;
private final int offset;
public MatchResult(String match, int offset) {
this.match= match;
this.offset= offset;
}
@Override
public String getText() {
return match;
}
@Override
public int getOffset() {
return offset;
}
@Override
public int hashCode() {
return Objects.hashCode(match) * 31 + Integer.hashCode(offset);
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
MatchResult other= (MatchResult) obj;
return offset == other.offset && Objects.equals(match, other.match);
}
@Override
public String toString() {
return '[' + match + ", " + offset + ']'; //$NON-NLS-1$
}
}
/** A node in the trie built from the search strings. */
private static class Node {
HashMap children;
String match;
Node fail;
Node output;
final int depth;
Node(int depth) {
this.depth= depth;
}
Node next(Character c) {
return children == null ? null : children.get(c);
}
Node add(char c) {
if (children == null) {
children= new HashMap<>();
}
return children.computeIfAbsent(Character.valueOf(c), key -> new Node(depth + 1));
}
boolean hasChildren() {
return children != null;
}
@Override
public String toString() {
return "[depth=" + depth + ", match=" + match //$NON-NLS-1$ //$NON-NLS-2$
+ ", children=" + (children == null ? "" : children.keySet().stream().map(c -> c.toString()).collect(Collectors.joining(", "))) //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+ ']';
}
}
/** Root node of the trie. */
private final Node root= new Node(0) {
@Override
Node next(Character c) {
// Implements the sentinel loop on the root node for all non-matching characters.
Node child= super.next(c);
return child == null ? this : child;
}
};
private MultiStringMatcher() {
// Always use a Builder or the static helper methods to create a MultiStringMatcher
}
private void add(String... searchStrings) {
if (searchStrings != null) {
for (String searchString : searchStrings) {
if (searchString == null || searchString.isEmpty()) {
continue;
}
Node node= root;
for (char c : searchString.toCharArray()) {
node= node.add(c);
}
node.match= searchString;
}
}
}
private void buildLinks() {
// Build the fail and output links. See the paper referenced at the top; this
// is a one-to-one implementation of the original algorithm. Variable names
// s, r, and state are kept as in the paper.
List queue= new LinkedList<>();
for (Node s : root.children.values()) {
if (s.hasChildren()) {
// No need to queue nodes without children since we don't do anything
// with them anyway.
queue.add(s);
}
s.fail= root;
}
while (!queue.isEmpty()) {
Node r= queue.remove(0);
for (Map.Entry entry : r.children.entrySet()) {
Character c= entry.getKey();
Node s= entry.getValue();
if (s.hasChildren()) {
queue.add(s);
}
Node state= r.fail;
Node f;
while ((f= state.next(c)) == null) {
state= state.fail;
}
s.fail= f;
if (f.match != null) {
s.output= f;
} else if (f.output != null) {
s.output= f.output;
}
}
}
}
/**
* Finds all occurrences of any of the search strings of the {@link MultiStringMatcher} in the
* given {@code text} starting at the given {@code offset}, including overlapping occurrences.
*
* @param text to search (not {@code null})
* @param offset to start searching at
* @param matches {@link Consumer} all matches are fed to
*
* @since 3.10
*/
public void find(CharSequence text, int offset, Consumer matches) {
// Main search loop of the standard Aho-Corasick algorithm.
int textEnd= text.length();
Node node= root;
for (int i= offset; i < textEnd; i++) {
Character c= Character.valueOf(text.charAt(i));
Node next;
while ((next= node.next(c)) == null) {
node= node.fail;
}
node= next;
if (node.match != null) {
matches.accept(new MatchResult(node.match, i - node.depth + 1));
}
Node out= node.output;
while (out != null) {
matches.accept(new MatchResult(out.match, i - out.depth + 1));
out= out.output;
}
}
}
/**
* Finds all occurrences of any of the search strings of the {@link MultiStringMatcher} in the
* given {@code text} starting at the given {@code offset}, including overlapping occurrences.
*
* @param text to search (not {@code null})
* @param offset to start searching at
* @return a possibly empty list of matches
*/
public List find(CharSequence text, int offset) {
List matches= new LinkedList<>();
find(text, offset, matches::add);
return matches;
}
/**
* Find the next occurrence of any of the search strings of the {@link MultiStringMatcher} in
* the given {@code text} starting at the given {@code offset}.
*
* Performs a simultaneous search for all the strings, returning the leftmost match. If multiple
* search strings match at the same index, the longest match is returned.
*
*
* @param text to search (not {@code null})
* @param offset to start searching at
* @return the leftmost longest match found, or {@code null} if no match was found.
*/
public Match indexOf(CharSequence text, int offset) {
// Main search loop of the Aho-Corasick algorithm, modified to stop after
// the leftmost longest match.
//
// To find a match, we pursue a primary goal (lowest offset) and a secondary goal
// (longest match). We differentiate between primary and sub-matches. Matching starts
// by walking down one path of the trie. Any match we find on this path is a primary
// match and any new primary match is better than the one before. A sub-match is a
// matching prefix of a suffix of the text currently scanned along the path. These
// sub-matches occur on paths off the one we're currently following, and they are
// linked in the trie via the output links. Their offset is always greater than that
// of a primary match, and sub-matches further into the 'output' chain are shorter.
// Therefore we are interested only in the first such sub-match. While walking down
// a path, sub-matches off this path are not found in offset order, so we have to
// check whether a new sub-match is better (lower offset, or longer) than a previously
// found sub-match.
//
// When we can't continue matching on the current path, the algorithm uses the fail
// links to try to find an alternate path to match (which would match a suffix of
// what was traversed so far). Therefore, if we already had a primary match, it is
// returned, since any other match must have a higher offset. If there is no alternate
// path, we fall off the trie (the algorithm bring us back to root, and would start
// again from the top). If we have any match, we may stop and return it. If we _do_
// change to an alternate path but there's a sub-match with a lower offset, we also
// may return that. Otherwise we continue normally on the new path.
int textEnd= text.length();
Match primaryMatch= null;
Match subMatch= null;
Node node= root;
for (int i= offset; i < textEnd; i++) {
Character c= Character.valueOf(text.charAt(i));
Node next= node.next(c);
if (next == null) {
// Can't continue on this path.
if (primaryMatch != null) {
// Return primary match because any other match must have a higher offset.
return primaryMatch;
}
// Search for another path to continue matching.
do {
node= node.fail;
} while ((next= node.next(c)) == null);
if (subMatch != null) {
if (next == root) {
// We fell off the trie and could not switch to another. Return the best
// sub-match.
return subMatch;
} else if (subMatch.getOffset() < i - node.depth) {
// The new path starts at i - node.depth == i - next.depth + 1, so if a
// sub-match is earlier, we may return it. Any primary match on this path
// or on any other path we might switch to later on will have a higher
// offset, and so will any sub-matches we might discover on these paths.
return subMatch;
}
}
}
node= next;
if (node.match != null) {
// Any new primary match is better because all have the same offset but any new one
// must be longer. An existing sub-match from a previous path is checked above.
primaryMatch= new MatchResult(node.match, i - node.depth + 1);
if (!node.hasChildren()) {
// We will fall off the trie on the next character, so we can return right here.
return primaryMatch;
}
}
// Check for sub matches but only if there is no primary match because only another
// primary match can be better.
if (primaryMatch == null) {
Node out= node.output;
if (out != null) {
int newOffset= i - out.depth + 1;
if (subMatch == null
|| newOffset < subMatch.getOffset()
|| (newOffset == subMatch.getOffset() && out.depth > subMatch.getText().length())) {
subMatch= new MatchResult(out.match, newOffset);
}
}
}
}
return primaryMatch != null ? primaryMatch : subMatch;
}
/**
* Finds the leftmost longest occurrence of any of the given {@code searchStrings} in the
* {@code text} starting at the given {@code offset}.
*
* To match the same set of search strings repeatedly against texts it is more efficient to
* build and re-use a {@link MultiStringMatcher}.
*
*
* @param text to search (not {@code null})
* @param offset to start searching at
* @param searchStrings to look for; non-{@code null} and non-empty strings are ignored
* @return a {@link Match} describing the match found, or {@code null} if no match was found or
* there are no non-{@code null} non-empty {@code searchStrings}
*/
public static Match indexOf(CharSequence text, int offset, String... searchStrings) {
return create(searchStrings).indexOf(text, offset);
}
/**
* Creates a {@link MultiStringMatcher} for the given {@code searchStrings}.
*
* If there are no non-{@code null} non-empty {@code searchStrings}, the returned
* {@link MultiStringMatcher} will never match anything.
*
*
* @param searchStrings to look for; non-{@code null} and non-empty strings are ignored
* @return the {@link MultiStringMatcher}
*/
public static MultiStringMatcher create(String... searchStrings) {
return builder().add(searchStrings).build();
}
}
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